This Instructable will teach you how to build a tricopter with Rotor Bits. This Instructable also contains theoretical discussions, tips, tricks, and other information that I hope will get you well on your way to becoming a tricopter expert.

Craft Design

Let's begin by taking a moment to discuss the design to the multirotor aircraft we will be building in this Instructable. If you are at all interested in multirotor aircraft, you have certainly heard of quadcopters, the most popular type of multirotor. Quadcopters are multirotors with four propellers. There are many tutorials around the Internet for building various types of quadcopters (I even wrote one myself).

Tricopters are another type of multirotor that only have three propellers to provide lift for the craft.

For some reason, tricopters are not nearly as popular as quadcopters and as a result, there are not many high-quality tutorials online about how to build them. Tricopters are a really elegant type of multirotor though, and they have a number of advantages over other types of multirotor:

Because tricopters have only three propellers instead of four or more, they are the least expensive type of multirotor to build.
Because tricopters have only three motors they have a longer battery life that other types of multirotor.
Tricopters have a very wide space between the front two motors (120 to 180 degrees) making them excellent for aerial photography/videography.

Tricopters do have a couple important downsides though:

The rear motor on a tricopter is tilted by a servo for yaw control (more on that later), the servo assembly is a complex piece and is more fragile than other designs.
Tricopters have no redundancy in case of motor failure, if a motor fails during flight, your tricopter will inevitably crash.

Instructable Table of Contents

Steps:

Parts
Connect Arms to Tricopter Hub
Assemble the Rotor Bits Servo Mount Set
Attach the Landing Leg Mounts
Attach the Motor Mounts
Position and Attach the Landing Leg Mounts
Attach the Landing Legs
Mount the Motors
Attach the Propeller Mounts
Attach the KK2.1 Flight Controller
Attach the ESCs
Attach the Radio Receiver
Wire the Radio Receiver to the Flight Controller
Solder 3.5mm Connectors to UBEC
Attach the UBEC to the Tricopter Frame
Connect the Motors to the ESCs
Connect the Battery to the UBEC
Program the ESCs
Update the KK2.1 Firmware, Part 1: Setup
Update the KK2.1 Firmware, Part 2: Updating
Connect the UBEC to the Flight Controller
Load the Tricopter Motor Layout
Connect the ESCs and Sero to the Flight Controller
Bind Radio Receiver to Radio Transmitter
Perform a Receiver Test
Perform a Sensor Test
Calibrate Accelerometer
Mixer Editor
Verify Motor Spin Directions
Balance Propellers
Fasten Down Loose Wires
Attach the Propellers
Congratulations
Tuning your Tricopter
Appendix A: Charge the Battery

Step 1: Parts

In order to build your very own tricopter, you are going to need to order some parts, quite a few parts in fact. Before I list the parts used in this tutorial, I just wanted to make a note about the supplier I chose when purchasing components. I ordered all of the components used in this tutorial from HobbyKing. HobbyKing is an online retailer of a wide-range of hobby parts, including parts for building multirotor aircraft. The reason I chose to order components from HobbyKing is, quite simply, because their prices are very low. Now, I do not intend this page to be a review of HobbyKing, or of any of the products listed, but I just wanted to note that the trade-off for HobbyKing’s low prices is slow shipping speeds and non-existent customer service. This last point is probably the biggest drawback to using HobbyKing, their customer service is absolutely pathetic. If you don't want to use HobbyKing, you can usually find the parts you need from sellers on eBay.

Anyway, you will need the materials in the table below to construct your tricopter. I included some notes about each component below the table. The notes are numbered and correspond to the numbers in the left column of the table. One last detail and then I promise we will get to the parts list. HobbyKing has warehouses located in many countries, with their main warehouse located in Hong Kong. I found that ordering all of my tricopter parts from the Hong Kong (international) warehouse led to extremely high shipping costs (for me $114). So, after a lot of experimentation, I found that I could minimize shipping costs by ordering some components from the international warehouse, and some parts from the U.S.A. warehouse. I included a column in the table that tells from which warehouse I ordered each component.

Tricopter Parts

Part Number	Part	Quantity	Country	Link
1	RotorBits Tri-Copter Mounting Plate	1	U.S.A.	HobbyKing 171000339-0
2	RotorBits Servo Mount Set	1	U.S.A.	HobbyKing 171000393-0
3	RotorBits Motor Mount (Universal)	2	U.S.A.	HobbyKing 171000359-0
4	RotorBits T Connector	3	U.S.A.	HobbyKing 171000387-0
5	Carbon Fiber Square Tube 10 x 10 x 250mm	3	U.S.A.	HobbyKing 078000007-0
6	Carbon Fiber Square Tube 10 x 10 x 100mm	1	U.S.A.	HobbyKing 078000004-0
7	RotorBits M2.5 x 20mm Screw	1	U.S.A.	HobbyKing 171000416-0
8	RotorBits M2.5 NyLock Nuts	1	U.S.A.	HobbyKing 171000417-0
9	Turnigy 2200mAh 3S 20C Lipo Pack	1*	U.S.A.	HobbyKing T2200.3S.20
10	Turnigy Accucel-6 50W 6A	1	U.S.A.	HobbyKing ACC6
11	Hobbyking KK2.1.5 Flight Controller	1	U.S.A.	HobbyKing 9171000446-0
12	HKU5 5V/5A UBEC	1	U.S.A.	HobbyKing 5AUBEC
13	Corona 919MG Digital Metal Gear Servo	1	International	HobbyKing DS919MG
14	Turnigy Multistar 2213-980Kv 14Pole Multi-Rotor Outrunner	3	International	HobbyKing 9192000115-0
15	Turnigy Multistar 20 Amp Multi-rotor Brushless ESC	3	International	HobbyKing 9351000007
16	10x4.5 SF Props 2pc Standard Rotation/2 pc RH Rotation	3	International	HobbyKing 017000064
17	Turnigy 6X FHSS 2.4ghz Transmitter and Receiver*	1	International	HobbyKing 9255000014
18	Turnigy Multistar ESC Programming Card	1	International	HobbyKing 9351000006
19	10CM Male to Male Servo Lead	1	International	HobbyKing 258000011
20	Nylon Screw Phillips Head M3x8mm	1	International	HobbyKing OR009-00502
21	XT60 to 6 X 3.5mm bullet Multistar ESC Power Breakout Cable	1	International	HobbyKing 015000094
22	PolyMax 3.5mm Gold Connectors	1	International	HobbyKing AM1001A
23	Universal Propeller Balancer	1	International	HobbyKing 171000401-0
24	USBasp AVR Programming Device	1	International	HobbyKing 381000147
25	15CM Servo Lead Extension	1	International	HobbyKing 015000164-0
26	Male-Female Wire Jumper Cable	1	International	HobbyKing 438000072

* The Turnigy 6X is a six-channel transmitter, which means it has plenty of channels for controlling a basic tricopter, however, if, and this is a bit of a complex topic for this first step of the tutorial, you wish to put a camera gimbal on your tricopter, you might want to upgrade to the Turnigy 9X, which has three additional channels which can be used to control the gimbal motors.

Optional Parts

Part Number	Part	Quantity	Country	Link
27	Blue LED Strip	2	International	HobbyKing 6LED-BL
28	Green LED Strip	1	International	HobbyKing 6LED-GR
29	Turnigy Receiver Controlled Switch	1	International	HobbyKing 9107000266-0

Total Cost

The total cost of the parts, not including shipping, is about $245. Shipping obviously depends upon where you live, but it should be something around $50 total for the cheapest shipping option.

Part Notes

1-8 These parts are all in HobbyKing's Rotor Bits line of products. Rotor Bits is a modular multirotor construction system. The idea is like Legos for multirotors. Using different Rotor Bits parts, you can build just about any kind of multirotor.

9 The Turnigy 2200mAh lithium-polymer battery is the power source for the tricopter. You only need one battery for your tricopter, however, I recommend buying a second one so that in the field, you can quickly swap out the first battery after it goes flat and continue flying. Depending upon the payload I put on the my tricopter, and how aggressively I fly, I get anywhere from five to twelve minutes of flight time on a charge. This might not sound like a lot of time, but it actually feels like plenty of time when you are flying. Now you could buy a battery with more capacity, but batteries get rapidly more expensive with increasing capacity and they also get heavier so I like to just buy two smaller batteries.

10 The Accucel-6 is the charger for the battery. Note that you will need a 12V power source with a barrel jack connector to power the charger. Unfortunately, I don’t think HobbyKing sells one, but you can pick one up from any electronics retailer. You can actually also use your car battery as a power source for the charger using the included alligator clip connectors.

11 The HobbyKing KK2.1 flight controller is responsible for receiving commands from the pilot, monitoring data from its onboard sensors, doing calculations based on those commands and that sensor data, and then then issuing commands to the ESC to control the motors to move the tricopter. The HobbyKing KK2.1 is a fantastic flight controller but it does have a steep learning curve. The KK2.1 features an onboard LCD screen for its user-interface, meaning that programming the flight controller is extremely easy and does not require a laptop or specialized software. You will have to do a lot of research to understand the different settings, but once you do, it is trivially easy to change settings in the field if you have to. Plus the KK2.1 is extremely affordable. Later in this Instructable we will discuss programming and tuning your flight controller settings.

12 The UBEC is used to transform the 11.1V power supplied by the battery to 5V so it can be used to power the KK2.1 flight controller.

13 The servo is used for the rear motor of the tricopter. On tricopters the rear motor tilts in order to achieve yaw control (make the tircopter rotate around the z-axis).

14 The Turnigy Multistar 2213-980Kv 14Pole Multi-Rotor Outrunner are the motors we’ll use in this tutorial. Now when it comes to choosing motors for your tricopter, you have a near-infinite number of choices and I don’t want to make this step any longer than it already is. There is plenty of other information around the internet about choosing motors though.

15 The electronic speed controllers (ESCs) are the components that take commands from the flight controller (which in turn takes commands from you) and from those commands controls the tricopters’s three motors. We need one ESC per motor. Note that even though these are opto ESCs, we are not going to take advantage of the opto part because it is not really necessary in this craft.

16 These are the propellers for the tricopter (they come in packs of four). We only need three for our tricopter, but in a crash, the propellers almost always get broken, so you should definitely stock up.

17 The Turnigy 6X is a six-channel, Mode 2 radio transmitter. The transmitter features two control sticks that can move in two directions each, plus two toggle switches. The transmitter comes with a compatible receiver. You will need four AA batteries for the controller and you might want to get a lanyard so you can hang the transmitter around your neck, which makes it easier to control since your hands can concentrate on moving the sticks instead of supporting the weight of the transmitter.

18 This is a little card used to program and calibrate the ESCs (more on that later).

19 These three-wire servo connectors are used to connect the radio receiver to the KK2.1 flight controller.

20 These nylon screws are used to connect the flight controller to the Rotor Bits tricopter hubs. Nylon obviously does not conduct electricity, which is useful for mounting electronics, and it is also soft, helping to make certain you do not over-tighten the screws.

21 This cable harness is used to split the battery's power output into six pairs of 3.5mm bullet connectors. Three of the bullet connector pairs will be attached to the three ESCs. One will be used for attaching the UBEC. One will be used for connecting optional LEDs. And the last pair is extra, it can be used for a camera or something you add in the future.

22 We will solder these 3.5mm connectors to the input wires on the UBEC so that we can plug the UBEC into the battery wire harness.

23 The Universal Propeller Balancer is used to make sure both sides of the propellers weight exactly the same. Balancing the props will reduce the vibrations in our tricopter while in flight.

24 The wires from the servo are not long enough to reach to the flight controller so we will have to use this Servo Lead Extension to make the wires a bit longer.

25 We will use these Male-Female Wire Jumper Cables to fashion a wire harness for the power supply.

26 The jumper wires will be used to make some wiring harnesses and to connect the servo to the flight controller.

27-29 These optional components will be used to add LED lights to the tricopter in Step 36.

Step 2: Connect Arms to Tricopter Hub

In this step we will begin assembling the Rotor Bits tricopter frame. The first step is to attach the three arms to the central hub.

Now that you've ordered all your tricopter parts and endured the excruciating wait for your parts to arrive in the mail, it is time to begin building your tricopter. First we will assemble the Rotor Bits tricopter frame. The first step of this process is to attach the three tricopter arms (the 250mm carbon fiber tubes) to the tricopter hub.

If you take a look at the Rotor Bits tricopter hub, you should be easily able to identify the three square holes into which we will insert the tricopter arms. So simply take each arm and insert one into each hole as far as they will go.

While you are examining the tricopter hub, you should identify the top and bottom of the hub. One one side of the tricopter hub you will notice four conical mounting points. Later we will use these mounting points to attach the KK2.1 flight controller. So, the side with these conical hubs is the top.

Next we will permanently attach the arms to the hub using two screws/nuts for each. First though we will need to drill holes through the carbon fiber tubes. The easiest way to do this is to use the pre-drilled holes in the tricopter hub as drilling templates. Now, even though there are three holes in the tricopter hub for each arm, I think it is sufficient to use only two of them, the outer two. So, with a 3mm drill bit (or a 1/8in will be close enough) drill a hole all the way through each arm for the two outside holes in the tricopter hub.

Finally, insert one of the 2.5mm screws through each hole from the top of the tricopter hub to the bottom and stick a lock nut onto the other side.

Step 3: Assemble the Rotor Bits Servo Mount Set

In this step we will assemble the Rotor Bits servo mount set.

One of the things that is a bit frustrating about HobbyKing is that, even though most of their products are very nice, like the Rotor Bits servo mount set for the rear motor of the tricopter, they seem to forget that it's necessary to include instructions with their more complicated products. The Rotor Bits servo mounts set is a good example of this oversight. The kit is quite complex, there are a total of eighteen parts, and I have been unable to find any instructions, or even so much as some helpful tips, anywhere.

Anyway, that is enough for my little rant, I hope that this page fixes the problem of missing instructions for the Rotor Bits servo mount set.

Assembling the Servo Mount

Press the small metal gear onto the servo horn. Then, find the small brass bushing, and small screw. Insert the brass bushing into the metal gear. Finally, use the small screw to fasten the metal gear to the servo horn. Then set the servo with attached gear aside.
Find the largest plastic piece, the metal shaft, and one of the medium-length screws. Press the metal shaft into the plastic piece. You should see that the shape of the metal shaft matches the shape of the hole in the plastic piece. Then, insert the screw through the square opening in the plastic piece and thread it into the metal shaft.
Find the round motor mount, and small plastic cap. Simply insert the small plastic cap into the motor mount.
Now we will start putting everything together. Find the large plastic piece with attached metal shaft, the motor mount, the large gear shaft, and the long screw. Put the large gear shaft onto the smaller metal shaft, gear side first. Then put the motor mount onto the large gear shaft. Last, use the long screw to attach all the piece together; don't tighten the screw too tight or the motor mount will be unable to move. It is probably a good idea to use a bit of thread lock to hold the screw in place.
Now take the servo with attached gear and place it into the rectangular tray on the bottom of the large plastic piece. Make sure you insert the servo so that the gears mesh. Use the zip-tie to hold the servo in place.

Centering the Servo Horn

There is one last, slightly-tricky, step to getting the Rotor Bits servo mount working correctly. We need to make sure that the servo mount has the correct rate of motion. When the servo is centered, we want the propeller to the level to the ground, and we want the motor to tilt 90 degrees in each direction.

The easiest way to adjust the servo mount's range of motion is to:

lift the servo slightly so the gears disengage.
tilt the motor mount 90 degrees to one side
rotate the servo horn to one extreme of its range of motion to the same side
put the servo back down so the gears reengage

Test the range of motion by manually tilting the servo mount. You want the servo mount to tilt 90 degrees to each side.

Video Demo

Step 4: Attach the Landing Leg Mounts

In this step we will put the landing leg mounts onto the tricopter arms.

This step is a very simple one but it is important that we do it before moving on to the next step (attaching the motor mounts). The Rotor Bits 90-degree connectors will be used as landing leg mounts for our tricopter. So onto each arm, place one of the 90 degree connectors so that the short side faces downward.

We will not attach the mounts with screws just yet because in a little bit we will position the mounts relative to the motor mounts. So for now, we are done working with the landing leg mounts. On to the next step.

Step 5: Attach the Motor Mounts

In this step, we will attach the motor mounts, including the servo mount, to the tricopter arms.

Now that you have the tricopter arms attached to the hub, the landing leg mounts placed on the arms, and the Rotor Bits servo mount assembled, we can attach the three motor mounts (one of which is the servo mount) to the tricopter arms.

Attaching the Servo Mount

The first thing to do is identify the rear arm of the tricopter, where we will mount the servo-driven motor mount. To do this, take a look at the four mounting pegs on the top of the tricopter hub. These pegs form a square. The arm that is perpendicular to one side of the square is the rear arm. Take a look at the pictures for more clarification.

So, place the servo mount onto the end of the rear arm with the servo on the bottom side of the arm. You will notice two mounting holes on the servo mount. However, we will only be able to use one of these holes, the one closest to the tricopter hub, since the other hole is blocked by the servo.

Like you did when you attached the tricopter arms to the hub in Step 1, use the servo mount as a template for drilling a hole through the arm. Do not drill through the outer mounting hole or you will drill right through your servo. After you drill the hole, put a screw through and a lock nut into the screw.

Attach the Other Motor Mounts

The motor mounts on the other two arms are much easier. Simply place a motor mount onto each arm with the flat side of the mount facing upward.

Again using the motor mounts as drilling templates, drill holes through the arm for the two holes on each motor mount.

With the holes drilled, use machine screws and lock nuts to attach the mounts.

Step 6: Position and Attach the Landing Leg Mounts

In this step we will move the landing leg mounts into position and attach them to the tricopter arms.

In Step 4 we placed the landing leg mounts (the 90-degree T connectors) onto the arms but we did not attach them with machines screws. In this step, now that we have the motor mounts attached to the arms, we will position the landing leg mounts and use screws/nuts to hold them in place.

Later on, we will mount the electronic speed controllers (ESCs) to the landing leg mounts so the position of the landing leg mounts is based on the length of the wires on the ESCs. On each arm, measure 2.5 inches from the end of the motor mount towards the central hub. Use a pencil to put a mark at this location.

Slide each landing leg mount into position so that the end of the mount farthest from the hub is at the 2.5 inch mark.

Then, once again, use the landing leg mounts as drilling templates to drill holes through the tricopter arms. I chose to use only one mounting hole for each T connector because there is really no force being applied to the connection.

After drilling the holes, attach each landing leg mount with machines screws and lock nuts.

Step 7: Attach the Landing Legs

In this step, we will cut the landing legs to length and attach the to the landing leg mounts.

With the mounts for the landing legs in place and attached, we can now attach the landing legs themselves.

First though we need to cut the landing legs to length. We will cut the 100mm carbon fiber tube into three equal sections (33mm each, obviously). You will be able to cut the tube fairly easily with a hacksaw. Try to cut slowly though so the carbon fiber does not splinter too much.

With the landing legs cut, insert a leg into each landing leg mount. Insert the legs just far enough that they clear the mounding hole.

Then, just like we've been doing in every step, use the landing leg mount as a drilling template to drill and hole through the leg and then use a screw and nut to attach the leg.

Repeat this procedure for each landing leg.

Congratulations! The Rotor Bits tricopter frame is now fully assembled. We still have much work to do though before our tricopter is ready for its maiden flight.

Step 8: Mount the Motors

In this step we will attach the three motors to the three motor mounts.

The Rotor Bits tricopter frame is now fully assembled. So, for the next major part of our tricopter build we will be attaching the various electronic components to the frame, and then later on we will focus on programming the flight controller.

The first electronic components we will install are the motors. I think it is wise to install the motors first because we will need to drill some more holes in the Rotor Bits motor mounts and I think it is worth doing this first to protect the flight controller and ESCs from any damage that might occur from the drilling process.

Drill Mounting Holes

Like we have with all the drilling in this Instructable, we will use the parts themselves as templates for placing the drill holes. If you look in each of the boxes in which the motors were packaged, you will find a thin +-shaped metal mounting plate. The holes we want to use are the ones closest to the center of the mounting plate.

Choose one of the Rotor Bits motor mounts to go first and center the large hole in the middle of the metal mounting plate with the large hole in the middle of the Rotor Bits motor mount. Use a pencil to mark the locations of the mounting holes. Note that you will be unable to use the mounting hole directly over the arm.

Then, using a 3/16" bit, drill three holes in the spots you just marked.

Attach the Motors

With all our mounting holes drilled, we can now attach the motors. You will notice four small, tapped holes on the bottom of each motor. What you probably will not notice, because it is quite difficult to see with the naked eye is that the four mounting holes are not actually equally spaced around the central hole. Two of the diametrically opposed holes are spaced 19mm apart and the other two are spaced 16mm apart.

This means you will need to rotate the motors on the motor mounts until all three holes line up. So do this and while you're at it, try to make the wire face towards the central hub where it will be safer than if it faces outward.

Using the larger screws included with the motors, attach three three motors to the three motor mounts, including the servo mount. Use a bit of thread lock on the end of each screw to make sure the screws don't loosen under the tricopter's vibrations during flight.

Step 9: Attach the Propeller Mounts

In this step we will attach the propeller mounts to the top of the motors.

Now that the motors are attached to the tricopter frame, we will attach the propeller mounts to the tops of the motors. The propeller mounts are the metal threaded studs included with the motors.

First we will need to disassemble the propeller mounts by removing the nuts and then the metal plates.

You will find that the metal plates you just removed concealed three mounting holes in the base of the propeller mounts. Choose a motor to start with and place the propeller holder on top of the motor. Using the three thin screws included with the motor, attach the propeller mount to the motor. Then replace the metal plate, followed by the nut but do not attach the propellers yet.

If I may digress, this actually brings up the most important safety rule for working with tricopters or any other multirotor aircraft. Never, ever, ever work on your tricopter while the props are in place and the battery is attached. While the motors are at speed the props are just like blades and can cause horrific injuries when they hit flesh. I am not going to post any images here because they can be very graphic but if you have a strong stomach you can find plenty with a simple image search. Always remove your battery and/or props before doing any work on your tricopter.

Step 10: Attach the KK2.1 Flight Controller

In this step we will attach the KK2.1 flight controller to the Rotor Bits tricopter hub.

Let's now attach the KK2.1 flight control board to the Rotor Bits central hub. We will attach the board to the four conical mounting points on the top of the hub. The direction you attach the flight controller is very important though. The side of the KK2.1 board with the row of four buttons should face the back of the tricopter. So orient the KK2.1 with the buttons facing the servo-driven motor mount and, using four nylon screws, attach it to the tricopter frame. Make sure the screws are snug, but don't tighten them so much that you risk cracking the board.

Step 11: Attach the ESCs

In this step we will attach the ESCs to the tricopter frame.

To continue populating our tricopter frame with electronic components, we will attach the ESCs to the frame. As mentioned in Step 4, we will mount the ESCs to the landing leg mounts.

If you take a look at the ESCs you will notice that on one side of ESCs there is a set of three colored wires and on the other side there are two colored wires and a three-pin connector. We will attach the ESCs so that the side with the three colored wires faces the motors because we will connect the motor leads to these three wires later on.

Attaching the ESCs is easy. Using two zip-ties attach one ESC to each landing leg mount. Tighten the zip-ties so that they are snug but do not crush the ESCs.

Step 12: Attach the Radio Receiver

In this step we will attach the radio receiver to the tricopter frame.

Next up in the list of electronic components we need to connect to the tricopter frame is the radio receiver. We will mount the radio receiver to the side of the tricopter hub using zip-ties. Choose one of the rear sides of the tricopter hub; you probably don't want to mount your radio receiver to the front of the craft because you might want to attach a camera to the front of the tricopter some time in the future.

Attaching the radio receiver is easy. First, loop a zip-tie through two of the triangular holes in the side of the Rotor Bits tricopter hub. The put the radio receiver through the loop so that the connectors on the receiver face outward and are accessible (see the picture). Then, tighten down the zip-tie as much as possible.

We will do something with the dangling antenna wire later when we take on the fun task of wire routing.

Step 13: Wire the Radio Receiver to the Flight Controller

In this step we will electrically connect the radio receiver and the flight controller.

With the flight controller and radio receiver both attached to the tricopter, we can now connect them together electrically.

Now, I am going to take a moment to explain the connections on the radio receiver, then, in the next section, I will explain the connections on the KK2.1, and finally I will explain how to attach the two.

About the Radio Receiver Connections

So, if you take a look at the radio receiver, you will notice that the connections come in sets of three pins. The label on the top of the receiver shows which rows belong to which channel. Unfortunately, we covered up this label when we mounted the radio receiver. Don't worry though, I took a picture of the label for reference.

Each channel on the receiver corresponds to a different action on the radio transmitter. For example, channel one receives commands when you move the right stick left and right, channel two receives commands when you move the right stick up and down, et cetera.

Each of the three pins for each channel carries a different electrical connection: the outside row of pins is ground, the middle row of pins is power, and the inner row of pins is signal.

About the KK2.1 Connections

Now that you understand the connections on the radio receiver, direct your attention to the flight control board. Looking at the board from the bottom (button side) you will find the connections for the radio receiver to the left of the screen. There are five rows of three pins. Just like on the radio receiver, each row of three pins corresponds to a different radio transmitter channel.

The channels on the KK2.1 board are a bit more difficult to understand than the ones on the radio receiver though because, if you take a look at the bottom of the board (I took a picture again so you don't have to do any disassemble), you will notice that the rows are labeled for airplanes, not for tricopters. Starting with the top row of pins, the order goes aileron, elevator, throttle, rudder, auxiliary. These labels correspond to the various control surfaces (flaps) used to control airplanes in flight. So we will need to form a mental map of the way these airplane controls correspond to tricopter controls.

Just like airplanes have four control channels, so too do tricopters, but the terminology used for tricopter control is a bit different. The four control channels are roll, pitch, yaw, and throttle. To translate the KK2.1 receiver connections from airplane terminology to tricopter terminology, we just need to substitute the airplane-related words for tricopter-related words:

aileron → roll
elevator → pitch
rudder → yaw
throttle → throttle (which basically means altitude for tricopters)

This terminology is actually really important. You should make sure to memorize the relationship between airplane controls and tricopter controls because throughout the rest of this tutorial I will often be using these terms interchangeably; and this is the same for many other sites. It will make your life much easier if you do not have to come back here to look at the above chart every time you encounter one of these words.

The auxiliary connection is the same for airplanes and tricopters since it is just used to control other accessories like lights or the auto-leveling feature. Our radio transmitter actually has two auxiliary switches.

Connecting the Radio Receiver to the Flight Controller

Armed with your new knowledge of the radio receiver and flight controller pin layouts, we can now connect the two parts together. Before we begin, there is just one more piece of information to consider: on the radio receiver, all of the ground and power pins (the outside and middle pins) are connected together. Therefore, we only need to connect one ground pin and one power pin to the KK2.1 flight control board. The practical upshot of this is that we will only need three servo leads to complete all the electrical connections instead of five.

First, plug one of the servo leads across the three pins on the radio receiver that correspond to channel one. Orient the plug so that the brown wire is on the outside. Then, plug the other end of the servo lead into the aileron plug on the KK2.1 board, which is the top one. This plug should be oriented with the brown wire on the outside pin. On my tricopter I tucked the wire underneath the flight controller so that it isn't hanging around in midair.

Now for the next wire. Since we’ve already connected a ground and power wire from the KK2.1 board to the radio receiver, we will only need a signal connection for the remaining four signals. So, connect the second servo lead going down the row of inside pins (signal pins) with the yellow wire plugged into channel two, the red wire plugged into channel three, and the brown wire plugged into channel four. Then, plug the other end of the wire into the pins closest to the screen on the KK2.1. The yellow wire should be closest to the aileron plug.

There is one last connection to make, the connection for the auxiliary channel, which we will use to turn on and off the self-leveling feature of the KK2.1 via the left switch on the radio transmitter. More on that later, for now connect another servo wire, this time across the entire fifth row of columns on the radio receiver. Connect the other end across the fifth row of pins on the KK2.1.

Step 14: Solder 3.5mm Connectors to UBEC

In this step we will solder 3.5mm connectors to the input wires of the UBEC.

The input wires on the UBEC come unterminated, in other words, they do not have any kind of connectors on them. So, in order to plug the UBEC input wires into the wiring harness for the battery (which we will get to later) we will need to solder male 3.5mm connectors onto the two input wires of the UBEC.

There is a good video on soldering bullet connectors on YouTube: https://www.youtube.com/watch?v=B9yY9Kk4bEA. The technique illustrated in that video is the one I used and it works quite well.

Before you solder on your 3.5mm bullet connectors though, remember to put a little (about 1 inch) piece of shrink tubing onto the wires. After you solder on the bullet connectors, slip the shrink tubing so that it covers the base of the connector, but does not prevent the top part from rotating. Use a heat gun or lighter to shrink the tubes.

Step 15: Attach the UBEC to the Tricopter Frame

In this step, we will attach the UBEC to the tricopter frame.

What is a UBEC?

Before we attach the UBEC to the tricopter frame, let's take a moment to understand what the UBEC is and what purpose it serves on our tricopter.

UBEC stands for "universal battery elimination circuit." The UBEC is basically a beefy voltage regulator. Its purpose is to transform the high voltage (11.1V using the battery in this Instructable) from the battery to a lower voltage (in this case 5V) needed to power the flight controller and servo. If we were to simply plug our battery directly into the KK2.1 board, we would just fry the KK2.1. So, we put the UBEC between the battery and flight controller to lower the battery's voltage to an appropriate level.

The UBEC has one more purpose. It also smooths out the power source being fed to the flight controller which helps to reduce problems that can occur with excessive noise and interference in the power supply.

Connect the UBEC to the Tricopter Frame

Attaching the UBEC to the tricopter frame is easy. In fact, we will attach it just like we did with the radio receiver. So, on the side of the Rotor Bits tricopter hub opposite the radio receiver, the one on the back of the hub, thread a zip-tie through two of the triangular holes to form a loop. Then, stick the UBEC through the loop and tighten down the zip-tie. Make sure the zip-tie is snug, but this is not the time to demonstrate your finger strength, be careful not to squish the UBEC.

Step 16: Connect the Motors to the ESCs

In this step we will electrically connect the motors and ESCs.

The next electrical connection we need to make is between the motors and ESCs. This step is very simple. There are three wires coming from each motor, all three are black. There are also three wires coming from the ESCs on the side closest to the motors, a red one, a yellow one, and a black one.

For now, just connect the three wires together in any order. The order in which you connect the wires is important, it determines in which direction the motor will spin, but for now, since we have not attached the propellers, we don't know what direction we want the motors to spin. Later on, after we connect the propellers, we will test the spin direction of the motors and fix it if necessary. So again, for now, just connect the wires in any order.

Step 17: Connect the Battery to the UBEC

In this step we will attach the wiring harness to the battery and the UBEC to the wiring harness.

The next several steps will require us to supply various components with electricity. Plus we will obviously need battery power for the tricopter to fly.

We will get started on our electrical system by attaching the wiring harness to the battery plug. The wiring harness serves two purposes. First, it splits the battery output into six parts so we can connect all our components. Second, it adapts the battery's XT60 plug to 3.5mm bullet connectors, which are the connectors on the ESCs and the connectors we put on the UBEC a couple steps ago. So simply plug the male XT60 connector on the battery to the female XT60 connector on the wiring harness.

The KK2.1 flight controller and the ESC programming card (which we will use in the next step) are powered through the UBEC. As discussed in Step 15, the UBEC transforms the 11.1V from the battery to 5V. So the next step in hooking up the tricopter's electrical system is attaching the UBEC to the battery through the wiring harness. Pick any red wire on the wiring harness and attach it to the red wire on the UBEC. Then pick any black wire on the wiring harness and attach it to the black wire on the UBEC.

Step 18: Program the ESCs

There are a number of ESC settings we will need to configure before the tricopter fill fly properly. In this step we will use the ESC programming card to program each ESC.

Before we connect the ESCs to the flight controller, we will need to program the ESCs. Programming the ESCs involves adjusting a number of settings related to the electrical system and flight performance. To program the ESCs, we will use the ESC programming card.

ESC Settings

Before we get to the ESC programming process, let's take a moment to go over the different settings we will use the ESC Programming Card to configure. The underlined options are the ones we will be using. We will discuss how to select these settings in a moment. For now, the ESC Programming Card allows us to adjust six different ESC parameters:

Batt Type (Battery Chemistry): NiXX, LiXX, Life

The battery chemistry parameter tells the ESC what kind of battery is being used to power it.

Cut Off Voltage: High, Medium, Low

The cut off voltage setting specifies at which point, as the battery drains and starts outputting less voltage, the tricopter will cut power to prevent damage from a low-voltage condition. There is a chart on the back side of the ESC Programming Card that shows what the actual cut off voltage is for each Cut Off Voltage setting for each Battery Chemistry.

Cut Off Type: hard, slow down

When the battery drains to the point that it reaches the Cut Off Voltage, this setting determines the behavior of the motors. The "hard" setting just stops the motors dead. The "slow down" setting gradually slows the motors, allowing the tricopter to slow its descent.

Brake: off, medium, hard

The brake setting determines how the motors behave when the throttle is set to zero. With the "off" setting, the motos coast to a stop naturally. This action requires no additional power and so it increases battery life, but in an emergency situation the props may still be spinning after the throttle is zeroed out. With the "hard" setting, the motors stop immediately when the throttle is set to zero. This setting allows the tricopter to lose altitude more quickly, and can also be very useful in preventing damage in an impending crash, but additional power is required to stop the motors, which reduces battery life. The "medium" setting strikes a balance between "off" and "hard."

Timing:auto, high, low

The timing mode setting is complex, but it roughly adjusts the speed with which the ESC communicates with the motors. In general, motors with a higher number of poles should use higher timing modes, and motors with fewer poles should use lower timing modes.

Start Up: high, medium, low

The Start Up setting determines how quickly the motors accelerate from stationary during takeoff. A setting of "high" means the tricopter will get off the ground very quickly. A setting of "medium" or "low" means the tricopter will get off the ground more slowly.

Adjusting Settings on the ESC Programming Card

If you look at the sides of the ESC Programming Card you will notice a bunch of pins and six 2-pin jumpers. The ESC Programming Card has a label on each side, on one side is information about cut off voltages for different battery chemistries and recommended settings for different types of motor. The other side is where the important information is found.

The label shows which pins correspond to the six different settings described above. There are six 2-pin jumpers that correspond to the six settings. By moving the jumpers so that they bridge different sets of pins, you can change the settings on the ESC Programming Card. Move the jumpers around so that the settings are configured as follows (also check out the picture):

Batt Type = LiXX
Cut off Voltage = medium
Cut off type = slow down
Brake = medium
Timing = auto
Start Up = medium

Programming the ESCs

Alright, let's actually program the ESCs. We will need to program each ESC individually so just repeat the procedure below for each ESC.

On the side of the ESC Programming Card with all the settings listed, in the upper-right corner you will find a set of three connection pins labeled, "Controller." This is were you will plug in the ESC with the yellow wire on the input in and the brown wire on the - pin.
The only connections remaining on the ESC is the power connection, the red and black wires. Connect the red wire to one of the red connectors on the wiring harness. Then connect the black wire to one of the black connectors on the wiring harness.
In the upper-left corner of the ESC Programming Card, opposite the ESC connection, plug in the red/black output from the UBEC as shown on the label. Note that the top pin will be empty.
When you plug in the power, you should hear two beeps which indicates that the ESC has been successfully programmed. If you hear only one beep and then the ESC keeps beeping (technically it is the motors that make the beeping noise by the way), disconnect the power, switch any two of the motor leads, reconnect the power, and try the programming procedure again.

Repeat for the other two ESCs.

Step 19: Update the KK2.1 Firmware, Part 1: Setup

This is the first part in a two-step process of updating the KK2.1 firmware. In this step we will do the preliminary hardware and software setup for updating the firmware on the KK2.1 flight controller board.

Introduction

When you place an order for a KK2.1 flight control board somebody goes into a HobbyKing warehouse somewhere, finds a KK2.1 on a shelf, puts it in a box, and sends it to you. The problem is, like most electronic devices, the software installed on the KK2.1 evolves over time - bugs get fixed, features get added, algorithms get optimized, ect. - and depending on how long the particular KK2.1 board you get has been sitting in the warehouse, its software is probably out of date.

By upgrading the software (called firmware) on your KK2.1 board, you can improve the performance of your multirotor, as updated firmware has more advanced control code. For example, the auto-leveling algorithms on the newest KK2.1 firmware are far superior to the ones that come with firmware version 1.5, which is the firmware installed on most KK2.1 boards when you order them. So by updating the firmware, your multirotor will fly much better in auto-level mode for example. So, let's get to the firmware update setup.

Determining Current Firmware Version

As mentioned above, the firmware installed on your KK2.1 board when it arrives in the mail may or may not be out of date. This is especially true if you purchase your KK2.1 secondhand on eBay or somewhere; the previous owner might have already updated the firmware. Fortunately, discovering what firmware version is installed on your KK2.1 is really easy. When you first apply power to your KK2.1 board, either with a battery or with a USBasp programmer (more on that in a second) a screen will flash across the screen that displays the current hardware and firmware versions. You might have to unplug and replug your KK2.1 a few times to read the firmware version as it only displays on the screen for part of a second, but you are going to look at the second line in the splash screen, which says "FW: ###". That number is the firmware version currently running on your KK2.1.

Hardware Needed

You will only need two pieces of hardware to update the firmware on your KK2.1 board:

A USBasp programmer: a USB in-circuit programmer for Atmel AVR controllers, of which the KK2.1 flight control board is one (the popular Arduino microcontroller is another).
A 10-pin to 6-pin AVR programming cable: this cable is an adapter that goes between the 10-pin interface on the USBasp programmer and the 6-pin interface on the KK2.1 board.

You can order both of these parts in a single package from HobbyKing, as described on Step 1, although there are many other places you can buy them, including Amazon, eBay, or SparkFun.

Software Needed

On the software side, we are very fortunate to have fabulous and generous programmers in the multirotor community who donate their time an energy to create easy-to-use software tools for updating the KK2.1 firmware. The software I like best was created by "Kapteinkuk" and "Lazyzero." The "KKmulticoper Flashtool" they created provides a graphical interface for updating the firmware on the KK2.1 board, along with a host of other boards. To download the software:

Go to http://lazyzero.de/en/modellbau/kkmulticopterflas...
Scroll down to the download section.
Download the "Latest stable software versions" for your OS.

Now, if you are on Mac OS X, you are ready to start updating your firmware, just skip to the next step.

If you are on Windows (like me), you will also need to download the driver software for the USBasp programmer:

Head over to http://www.fischl.de/usbasp/ and scroll down to the "Drivers" section.
Download the .zip file containing the latest USBasp driver.
Go to wherever you just downloaded the .zip file and extract it.
Remember the location of this file because we will use it at the beginning of the next step. See you there.

Step 20: Update the KK2.1 Firmware, Part 2: Updating

In this step we will update the firmware on the KK2.1 flight controller board.

Plug in your KK2.1

We will start by plugging the KK2.1 board into our computer via the USBasp programmer.

First, plug the 10-pin end of the programming cable into the USBasp programmer board. Second, plug the USB end of the USBasp programmer into an available USB port on your computer.

Now, the third and last step is to plug the 6-pin side of the ASP programming cable into the KK2.1 board. However, the direction of the cable does matter. Fortunately, it is easy to figure out if you have the cable the wrong way, and if you accidentally do plug in the cable the wrong direction, don't worry, no harm will befall your KK2.1 board. So, when you plug the 6-pin side of the ASP programming cable into the KK2.1 board, you should see the KK2.1's screen light up and display the "SAFE" screen. If your KK2.1 does not light up, you have the cable on backwards, so just turn it 180o and everything will be fine.

For Windows users, there is one last thing to do. When you plug in your KK2.1, you will probably notice a message appear on your computer informing you that Windows is attempting to install the driver for your new device. Despite its best efforts, Windows will fail at this task and we will have to give it some help by locating the USBasp driver we downloaded in the previous step:

Go to your start menu and type "device manager." Then open the Device Manager, which should be the first item in the list of programs.
In the Device Manager, you should see section called "Other Devices" and if you expand this section, you should find an entry called "USBasp."
The little yellow exclamation mark means something has gone wrong, namely the driver failed to load, so right-click on the USBasp entry and from the menu, choose "Update driver software..."
From the dialog box that appears, choose "Browse my computer for driver software."
On the next screen, click the "Browser..." button.
Locate the USBasp driver folder we downloaded in the previous step, select it, and click "Ok"
Finally, click next, and Windows will install the USBasp driver software and now we are ready to move on.

Update your Firmware

At long last it is finally time to do the actual firmware updating. So start by running the KKmulticopter Flashtool we downloaded in the previous step (it usually takes ten seconds or so to start). There are a total of five fields in the KKmulticopter Flashtool software we will need to set for the firmware update to work.

In the "programmer" field, choose "USBasp"
In the "port" field, choose "usb"
In the "controller" field choose "HobbyKing 22.1 and KK2.1."
In the "Flashing firmware" box, under the "Repository" tab, choose "KK2.1" from the first dropdown menu. Just a bit of explanation here: there are two ways to update the firmware on your KK2.1, you can either choose a firmware file from your computer, or you can let the software retrieve the best firmware from the repository managed by Lazyzero. This second option is much easier. At the time of this writing, the best firmware available is the "KK2.1 V1.9S1 by Steveis" but when you update your firmware an even better version may be available.

Finally, with all the fields set, click the green button on the right side of the Flashing firmware area. The firmware update process can take 20 to 30 seconds or so but eventually you should see a message in the KKmulticopter flashtool indicating that the firmware flashing process was successful.

Congratulations, you have successfully updated your KK2.1 firmware.

Step 21: Connect the UBEC to the Flight Controller

In this step we will connect the UBEC to the flight controller.

Now that we are done using the UBEC to power the ESC Programming Card we can switch the UBEC's output lead to the flight controller. Now one of the weaker parts of the KK2.1 flight controller's design, in my opinion, is the way it is supplied with power. Power to the KK2.1 can only be connected to the Motor 1 input pins or through the radio receiver, however, power to the servo must be connected to one of the motor inputs other than Motor 1. So, we will need to split the power output from the UBEC so we can connect power to both the radio receiver and Motor 8 connection.

Create Power Cable

Unfortunately, I could not find a product for splitting the power output from the UBEC, so we will have to create our own. The good news is that this part is quite easy to make.

We are going to do some surgery on four of our jumper wires. So, take out two red jumper wires and two black jumper wires. Cut all the wires in half and grab two red female connections, two black female connections, one red male connection, and one black male connection.

So strip about 1/2" of insulation from the end of all the wires. First of all, place a little, about 1 inch long, piece of shrink tubing over the red and black male wires. Twist together all the red wires. Then twist together all the black wires. You should now have a red "Y" connector and a black "Y" connector.

Use a bit of solder to fasten together the twisted wires. Finally, slip the shrink tubing over the joint and use a heat gun or lighter to shrink it down.

Connect Power to Radio Receiver

Now, recall from when we connected the radio receiver to the flight controller, we said all the ground pins and all the power pins on the radio receiver are connected together. Therefore, it does not matter to which channel we connect the UBEC power output wire. Also recall that the outside pin on the radio receiver is ground (black/brown), the middle pin is power (red), and the inside pin is signal (yellow). So, on the unused channel 8 pins, plug in the power output wire harness we made a second ago with the black wire on the outside and the red wire in the middle.

When you make the connection, the screen on the KK2.1 should light up. You should also see a red light on the radio receiver, which indicates that the receiver is powered as well. We are not quite done yet though.

Connect Power to KK2.1 Motor Outputs

So we've connected the UBEC power output to the radio receiver which provides power to the KK2.1 board, but, we need to also connect power to the KK2.1 motor outputs to provide power to the servo, which we will connect, along with the ESCs, in a little bit.

So if you look at the KK2.1 board from the bottom (the button side) the motor output connections are located on the right side of the screen. The KK2.1 has a total of eight motor connections, but we will be using only four. Just like with the radio receiver, the connections come in sets of three pins. The signal pin is the one closest to the screen, the power pin is in the middle, and the ground pin is farthest from the screen.

So, using the other two connections from our UBEC wiring harness, connect the ground (black) wire to the outside pin of the bottom motor connection, and connect the power (red) wire to the middle pin.

Step 22: Load the Tricopter Motor Layout

In this step we will load the firmware for tricopters on the KK2.1 flight controller.

Alright, now that our KK2.1 flight controller is running the latest and greatest firmware available, we can continue with hooking up our various electrical components, specifically the ESCs and servo. Before we can do that though, we will need to load the tricopter motor layout in the KK2.1. Motor layouts tell the flight controller what kind of multirotor it's attached to. It also loads all of the algorithms and settings used to control the specific kind of multirotor.

Since we just attached our UBEC power output to the KK2.1 through the radio receiver, your KK2.1 should already be turned on. On the screen, you should see a large "SAFE" label, followed by information about various sensors. In the lower right corner of the screen you should see a MENU item.

Controlling the KK2.1

Controlling the KK2.1 is fairly easy. Along the bottom side of the board you have doubtless noticed the row of four buttons. While navigating the KK2.1 user interface, menu items and interaction options always appear along the bottom side of the screen. These interaction options appear in four different "slots" on the screen. To select an item, just press the button below the desired action.

Loading the Tricopter Motor Layout

So, now that we understand how to navigate the KK2.1, we will load the motor layout. First, press the far-right button to enter they menu.

Once in the menu, you will see many items, many of which we will use soon, but the one you are looking for at present is the "Load Motor Layout" item, which is somewhere in the middle of the list. Use the middle two buttons to scroll up and down in the list of menu items. When you have the "Load Motor Layout" item highlighted, press the far-left button to select it.

There are a whole bunch of motor layouts included with the KK2.1 firmware, this is one of the coolest things about the KK2.1, that it can control so many types of multirotor. For now, scroll down to "Tricopter" and press the far-left Enter button.

You will be asked "Are you sure?" to confirm that you do wish to load the motor layout. When you load a motor layout, all of the KK2.1 settings will be reverted to their default values for the motor layout selected, so the KK2.1 just wants to make sure you do not accidentally clear any important work. Press the far-right button to confirm.

Finally, you will be presented with a little graphic of the motor layout you selected. This is going to be very important for the next step.

Step 23: Connect the ESCs and Servo to the Flight Controller

In this step we will connect the three ESCs and the servo to the flight controller.

If you just finished the last step and you didn't press any more buttons, you should be looking at the KK2.1 tricopter motor layout. If this is the case, skip over the procedure for viewing the motor layout below. Otherwise, if you navigated away from the motor layout graphic, you will need to bring it back up so we know how to connect the motors:

From the KK2.1 home screen, the one with "SAFE" written on it, enter the Menu by pressing the far-right button.
Scroll down to "Show Motor Layout" and press the far-right Enter button.

Identifying the Motors

Let's start by making sure we understand where we will be connecting our ESCs on the KK2.1 flight control board. If you are looking at the board from the bottom (the side with the buttons) the motor outputs are located on the right side of the screen, opposite the radio receiver connections we made earlier. There are eight motor connections on the KK2.1. The Motor 1 connection is the one on top, and the Motor 8 connection is on the bottom, with the other motor outputs numbered in order.

Like with the radio receiver output and input pins, motor connections come in sets of three pins. The column closest to the screen is signal (yellow wires), the one in the middle is power (red wires), and the column on the outside is ground (block/brown wires).

So now we understand where the motor connections are located and which pins correspond to which ESC inputs; the only piece of information we still need is which motor the KK2.1 identifies as Motor 1, Motor 2, and Motor 3. Also we need to know where to plug in the servo.

This is where the motor layout graphic we just loaded comes into play. If you look closely at the graphic, you will see that each motor in the layout is numbered. So, from the graphic:

The front-left motor is Motor 1
The front-right motor is Motor 2
The rear motor is Motor 3

Let's make those connections now.

Connecting the ESCs

Starting with Motor 1, the front-left motor, plug the three-wire bundle into the top row of motor outputs on the KK2.1 with the yellow wire closest to the screen and the brown wire on the outside.

Then connect Motor 2, the front-right motor, the same way.

Finally, connect Motor 3, the rear motor.

Connecting the Servo

With all three ESCs connected to the KK2.1 in the correct spots, the very last connection we need to make is the servo connection. Again, the KK2.1 motor layout will tell us where to connect the servo. With the motor layout on the screen, press the "Next" button. This gives us some additional information about Motor 1, specifically the spin direction. Press "Next" two more times and you will discover that Motor 4 is for the servo connection. If you continue pressing Next, you will also find that the remaining four motor outputs are unused.

You will need to use a servo extension cable because the wire lead on the servo is not long enough to reach to the flight controller. So, plug the male end of the servo extension cable into the servo lead until the little clip snaps into place.

Then, plug the other end of the servo extension cable into the Motor 4 output on the KK2.1 with the white wire closest to the screen, and the black wire farthest away.

Step 24: Bind Radio Receiver to Radio Transmitter

In order for the radio receiver to process signals from the radio transmitter, the two devices need to be paired in a process called binding. In this step, we will bind the radio receiver and transmitter.

The radio receiver is now electrically connected to the flight controller, however, in order for the radio receiver to process signals from the radio transmitter we must virtually connect the two in a process called binding. Binding pairs the radio receiver and radio transmitter so that the devices recognize each other and are able to communicate.

With both the radio receiver and radio transmitter turned on, locate the bind button on the radio receiver. The bind button is located in the corner of the radio receiver in the upper-left corner of the label.

Press the radio receiver bind button and keep an eye on the color of the light on the radio receiver. When the light turns green, release the bind button. The light should now stay green to indicate that the radio receiver and transmitter have been successfully paired. If the light on the radio receiver flashes alternately green and red, the binding process failed, so just try again and it should work fine.

Conveniently, binding the radio transmitter and radio receiver is a one-time process. From now on, unless you bind the receiver to a different transmitter, the two devices will be able to communicate.

Step 25: Perform a Receiver Test

With the radio transmitter and receiver bound together, we will now perform a test to make sure signals from the transmitter are being received correctly.

So now we have the radio receiver bound to the radio transmitter but we still need to make certain that the flight controller is actually receiving signals from the transmitter and is interpreting those signals in the right way. Welcome to the longest step of this entire Instructable. In this step, we will calibrate our radio transmitter and the flight controller’s receiver settings.

Let’s get started with a tiny bit of theory. There are four different directional controls on our radio transmitter, which you should be familiar with already: throttle, roll, pitch, and yaw. Each of these directional controls has a range of values that depend on the positions of the two sticks on the radio transmitter. This is how we communicate with the tricopter.

Our goal here is to make sure that when we move the transmitter sticks, the KK2.1 receives commands in the correct directions. In other words, to use an example, when we move the pitch stick up, we want the KK2.1 to detect an upward pitch control, not downward. Chances are though that without setting up the transmitter, at least one of the control inputs will be inverted. To correct this, we will use the Receiver Test tool in the KK2.1 menu.

Alright, let's get started. First, turn on your transmitter and, in the KK2.1 menu, select Receiver Test. Try moving the sticks on your transmitter. You should see the values in the Receiver Test screen change as you move the sticks. In the sections below, we will observe these values as we move the sticks and make changes to the transmitter settings as necessary to achieve the correct directions for the controls.

One last thing before we get started. There are two sets of buttons on the transmitter that we will use to adjust the transmitter’s settings. First, if you take a look at your transmitter, you will notice a row of six switches below the sticks. These switches are used to reverse the direction of each channel. When we move our sticks, there is a chance that the KK2.1 will read some of our inputs as going in the opposite direction. For example, we might move the rudder stick left, but the KK2.1 will read a right rudder input. In this case we would flip the rudder switch to the opposite position. The second set of switches, of which there are four total, are located below and to the sides of the sticks. We will use these switches to trim the values output by the transmitter so that the minimum values are reached when the sticks are in their minimal positions.

Adjusting Throttle Trim and Direction

So, start by moving the throttle stick to the bottom position, in other words, move the left stick to the bottom. When you do this, the throttle value in the KK2.1 Receiver Test will change. We will adjust the throttle stick direction and trim value based on the throttle values displayed in the Receiver Test tool.

First, if the number goes to some high value around or greater than one-hundred, and displays the word Full, flip the throttle channel switch (thro), which should should change the input to a small number. Otherwise, if, when you move the throttle stick down, the value is already small or zero, leave the switch in its original position.

Second, if the throttle value in KK2.1 is greater than zero with the stick at the bottom, click the small switch to the right of the throttle stick down to decrease the value to zero. Otherwise, if the value is zero, click the switch to the right of the throttle stick up until you see a value of one, and then click the switch down once to set the value to zero. The point here is to make sure that, when the throttle stick is at the bottom, the KK2.1 reads a value of exactly zero. You will also see the word Idle displayed next to the value.

Adjusting the Yaw (Rudder) Trim and Direction

We will use the same procedure for setting the trim value and direction of the yaw stick that we used for the throttle stick. So, move the yaw stick (left stick) to the far left and observe the readings in the Receiver Test tool.

First, if you see a negative number, or the word Right, flip the rudder (rudd) switch to change the direction of the output. This should cause the value in the Receiver Test change to some positive number. Keep in mind that for yaw controls, moving the stick left should yield a positive value in the Receiver Test tool, and moving the stick right should yield a negative reading. This is a little counterintuitive and can be confusing. The reason for this convention is because a right yaw input causes the tricopter to rotate clockwise, and clockwise rotation is usually denoted by a positive value.

Second we will adjust the trim value of the yaw input. If you take your thumb completely off the left stick, it should snap to the middle, where we want a rudder value of zero. If, in the Receiver Test screen, you see a positive value, click the yaw trim button, located below the left stick, to the right until you achieve a reading of zero. Otherwise, if the reading displayed is negative, click the trim button to the left until the reading reaches zero.

Adjusting the Pitch (Elevator) Trim and Direction

Now that you are getting the hang of adjusting trim and direction settings, let’s move on to the elevator stick, which adjusts the pitch of the tricopter. Before we begin, like with the yaw values, the pitch values can be a bit confusing. Pushing the stick forward gives a negative reading and pulling the stick back gives a positive value.

So start by moving the elevator stick all the way down. In the Receiver Test tool, you should see a positive value and the word Back. If you see a negative value, flip the elevator (elev) switch.

Like we did with the rudder stick, now let the elevator stick go and it will snap to the middle. If you see a positive value in the Receiver Test tool, click the elevator trim button, located to the left of the stick, to the down until you get a value of zero. Otherwise, if you see a negative value, click the trim button up to get a value of zero.

Adjust the Roll (Aileron) Trim and Direction

Now for the last control direction. The roll stick should yield a positive value to the right, and display the word Right, and a negative value to the left, along with the word Left. If you get the opposite values when you move the aileron stick, flip the aileron (aile) direction switch.

Then, release the stick and adjust the trim button, located below the stick, to achieve a value of zero in the Receiver Test tool when the stick is centered.

Step 26: Perform a Sensor Test

In this step we will perform a test to make sure all the sensors on-board the KK2.1 are functioning correctly.

I think it is time for a nice easy step. Before we fly our tricopter for the first time, it is a good precaution to make sure that all of the sensors on-board the KK2.1 are functioning correctly. This will hopefully help prevent the tricopter from going crazy on takeoff and damaging itself or something else.

So, in the KK2.1 menu, navigate to the Sensor Test tool and press the Enter button. The KK2.1 has two types of sensors onboard: a 3-axis gyroscope, which senses the rotation of the craft around the roll, pitch, and yaw axes, and a 3-axis accelerometer, which senses acceleration of the craft in all three directions. The Sensor Test tool should list the three axes for these two sensors. You should, hopefully, see that the status for all six lines is listed as “OK.”

It is probably a good idea to run this sensor test from time to time, especially after a crash. Unfortunately, if, for whatever reason, one or more of your sensors fails the test, you don’t really have any options other than replacing the KK2.1 board. If your board is brand new, you should return it. I have never had a sensor fail though, even after some fairly serious crashes, so hopefully neither will you.

Step 27: Calibrate Accelerometer

In this step we will calibrate the accelerometer on-board the KK2.1 flight controller.

Now that we've performed a sensor test to confirm that all the sensors on-board the KK2.1 are functioning as expected, we can now calibrate the accelerometer.

Ready for one more bit of theory before we are done programming the KK2.1? I think it is worth knowing a bit about how accelerometers work before we calibrate the one on the flight control board. First of all, accelerometers are devices that sense acceleration forces. They can detect two different types of acceleration: static acceleration forces caused by the Earth’s gravity, and dynamic acceleration forces caused by movement. So when we calibrate our accelerometer, we are giving it a zero reference so that the sensor knows what direction is down (the direction of gravity).

The KK2.1 can then talk to the accelerometer to figure out which direction is down and it can combine this information with data from the gyroscope, and data about the tricopter’s movement-related acceleration to determine exactly how the tricopter is oriented in three-dimensional space.

Calibrate the Accelerometer

Let’s calibrate the accelerometer. The most critical part of this process is setting up our calibration environment correctly. In order to calibrate our accelerometer, we need the tricopter to be completely level and on a solid surface. So, using a bubble level, find some solid surface in your work area that is completely level. It is worth the extra effort to make sure the surface is level because if you calibrate your accelerometers while the tricopter is in a non-level position, your tricopter will probably drift around in the air, making it more difficult to fly. Avoid using a wiggly table or a swiveling stool or something because if you tricopter moves during the accelerometer calibration process it will throw off the accuracy of the calibration.

So, place the tricopter on your chosen level surface. Then, in the KK2.1 menu, scroll down to the ACC Calibration tool, and click the Enter button. The KK2.1 will tell you to place the tricopter on a level surface, which we’ve done already, so press the Enter button again. The KK2.1 will then go through the calibration process, which takes eight seconds or so. Make sure you do not bump the tricopter or the table during this process. And finally, the calibrated accelerometer readings will be displayed.

Step 28: Mixer Editor

The Mixer Editor is used to input information to the the KK2.1 flight controller about the design of the tricopter. In this step, we will program the KK2.1 to fix a specific problem in the default settings.

We are obviously not finished building our tricopter, like, for example, we still don't have propellers, but if you were to fly your tricopter right now, it would spin around uncontrollably in the air and it would crash. The reason this would happen is that the KK2.1 thinks the servo on the rear motor is oriented on the opposite direction than it actually is.

When your fly your tricopter, the rear motor will always be tilted slightly to counteract the induced yaw of the propellers. Only the KK2.1 thinks the servo is pointed in the opposite direction so it will actually tilt into the direction of yaw, making the tricopter spin around like a top. Let's fix this problem.

Introducing the Mixer Editor

Actually though let's start with an introduction to the KK2.1 Mixer Editor because it is an extremely important part of getting the best performance out of your tricopter.

Let’s start by talking about how the KK2.1 controls your tricopter. In order to control the movement of the tricopter, the KK2.1 adjusts the lift produced by each of the three rotors, and adjusts the tilt of the rear motor. By adjusting the amount of lift produced in just the right way, the KK2.1 can make the craft ascend, descend, or tilt to move in any direction.

In order to determine exactly how to control each motor, the KK2.1 uses, as you might expect, quite a lot of math. I am not going to explain how all this math works - frankly I don’t understand it all myself - but I will explain the mathematical foundation upon which all of the flight calculations rely. In order to calculate the lift required by each motor correctly, the KK2.1 must know the exact position of each of the three motors relative to itself. By knowing these positions, the KK2.1 can calculate the leverage each arm has over the orientation of the tricopter. Using this information, the KK2.1 can calculate how to adjust the lift produced by each motor and move the craft.

Fortunately for us, the design of our tricopter actually matches the default configuration in the KK2.1 (except for the backwards servo issue we will address in a moment), so we will not need to do any math right now to adjust the motor layout. I think it is worth knowing how the KK2.1 controls the tricopter though.

Fixing the Servo Settings

First of all, accessing the Mixer Editor is very easy, just enter the KK2.1 menu as we have done before, scroll down to "Mixer Editor" and press Enter.

You will then see a whole bunch of words and numbers on the screen. We will cover more information about all this stuff in a later step, but for now, look in the upper-right corner of the screen. You will see CH:1. This indicates that the settings displayed are for Motor 1 (the front-left motor). We want to get to the settings for the servo, which is Motor 4.

So with the CH:1 highlighted, press the far-right button to change to CH:2. Press the button twice more to get to CH:4, which is our servo. Again there are a bunch of settings here, but the one we are interested in is the Rudder setting. By default, the Rudder setting will have a value of 100.

Scroll down to the Rudder setting by pressing the "Next" button. Then press the "Change" button to adjust the setting. We want to change the Rudder setting to -100. Do to so, just hold down the "Down" button until you get to -100.

Changing this setting from 100 to -100 will just switch the direction of the servo, which is what we need to do.

Again, the Mixer Editor is extremely important for tuning your tricopter, so you will definitely see it again. For more information, see Step 34.

Step 29: Verify Motor Spin Directions

In this step we will make certain the motors spin in the correct directions, and make corrections if necessary.

Are you ready? Because your tricopter is about to come to life for the first time.

Way back in Step 16 we connected the motors to the ESCs. We said that we would just connect the three wires randomly and correct it later if need be. In this step we will check to see if we got lucky and connected our motors the correct way, and if we got unlucky, we will fix the problem.

First though we need to determine in which direction the KK2.1 expects each motor to turn. To get this information we will once again use the motor layout we loaded in Step 22:

From the KK2.1 home screen, the one with "SAFE" written on it, enter the Menu by pressing the far-right button.
Scroll down to "Show Motor Layout" and press the far-right Enter button.

If you look really closely at the diagram, you will notice that each motor has a little arrow next to it indicating the direction of spin. If you press the "Next" button, you can get a more explicit description for the spin direction of each motor.

Test Motor Spin Directions

First connect the battery to the tricopter if it is not connected already and turn on your radio transmitter. You should see a green light on the radio receiver.

We will now arm the tricopter. Arming the tricopter let's the motors turn. You've already seen the message displayed on the KK2.1 to indicate that the tricopter is disarmed. The word "SAFE" on the home screen of the KK2.1 means the tricopter is disarmed and the motors will not turn.

To arm the tricopter, simply move your left stick on the transmitter to the lower-right corner of the input area. Later, to disarm your tricopter again, move the left stick to the lower-left of the input area. Always make sure your tricopter is disarmed before approaching it.

Alright, so let's start with Motor 1 which, by inspecting the motor layout, we know should rotate clockwise as seen from above. So arm the tricopter and give it just a tiny bit of throttle. You might need to pulse the throttle up and down until you can discern the direction that the motor is spinning. If your Motor 1 is spinning clockwise, congratulations, you can move on to the next motor. Otherwise, if you find that the motor is spinning in the wrong direction, first disarm your tricopter. And then, after your tricopter is disarmed, disconnect the battery. Then, finally, just switch any two of the wires connecting the motor to the ESC, this will switch the direction that the motor spins.

Repeat that procedure for each of the three motors. Remember to disarm your tricopter and disconnect the battery before you do any work on the motor-ESC connections.

Just to note, the servo is controlled differently than the brushless motors, so we know automatically that it will rotate in the correct direction.

Step 30: Balance Propellers

Balancing the tricopter propellers is an extremely important step in minimizing the vibrations produced by the spinning motors. Minimizing vibration improves battery life, the life of the craft itself, and video quality.

Now the only components left to attach to the tricopter are the props. Before we attach the props to the motors though, we need to balance the props. By balance the props, I mean we need to make sure that each blade weighs exactly the same. Unbalanced props cause three main issues during flight. First, unbalanced props can cause intense vibration since the props spin extremely fast. This vibration can interfere with the accelerometer as well as loosen screws or damage components. Second, if you are doing aerial videography with your tricopter, the vibrations caused by unbalanced props will cause the infamous jello effect in your video (or, to use the correct terminology, the rolling shutter effect). Third and last, since some of the energy put into the motors is wasted on vibration when your tricopter has unbalanced props, balancing the props can increase battery life slightly.

To balance our props, we will use a special tool called, unsurprisingly, a prop balancer. A prop balancer consists of a metal shaft suspended by two magnets. By using magnetic suspension, there is practically zero friction, which means, when we test our props, even the slightest difference in the weight of the two sides of the prop will be noticeable.

Let’s balance our props. First, select one of the props and mount it in the prop balancer by slipping the metal shaft through the hole in the prop and sliding the rubber pieces to the middle so that the prop will be held in the center of the shaft. Then, hold the prop in a horizontal position and, taking care that your fingers do not bump the the prop one way or the other, carefully let the prop go. Unless your prop is already balanced, which, unless you opted to buy very high quality props, is unlikely, one side of the prop should fall. Repeat this test several times to make sure the result is reliable. The side of the prop that falls is, obviously, the heavier side. So, cut a very small piece of electrical tape and apply it to the light side (the side that went up) of the prop. Then re-test the balance of your prop. If the original heavy side still falls, move the piece of tape further from the center of the prop. Otherwise, if the side to which you applied tape now falls, move the tape closer to the hub, or cut it smaller.

It will probably take some fiddling, perhaps quite a lot of fiddling, but you will know your prop is balanced when, after positioning the prop horizontally and letting it go, it does not move at all. Then, repeat this process for the other two props, and, if you are not terribly bored with prop balancing already, balance some spare props so that if one of your props breaks in the field, you can immediately replace it and keep flying.

Step 31: Fasten Down Loose Wires

In this step we will do some wire routing and fasten down loose wires.

While we've been attaching various components and making electrical connections we have not bothered much with wire routing. However, we obviously don't want a whole bunch of loose wires hanging around when we fly because the wires could find their way into the propellers. That would be bad.

So we need to fasten down loose wires to make sure they are not flopping about. This process is a bit subjective, but it is also not very difficult. Just use a bunch of zip-ties to fasten wires down to the arms and hub. You can also, if you want, try to wrap wires around the arms or stick them through holes. Just do some experimenting and fiddling around until all your wires are fastened down nicely.

There are only two wires you really need to worry about. The first is the antenna from the radio receiver. The antenna is the thin wire sticking out of the radio receiver with a bare end. You don't want the antenna too close to the ESCs, or the motors, or the flight controller because these devices could, theoretically, cause some electromagnetic interference with the radio signals. I just fastened my antenna to the underside of the Rotor Bits tricopter hub and it works just fine.

The second set of wires you need to be careful with are the ones coming from the rear motor and servo. You need to make sure these wires have enough slack so that they do not impede the motion of the tail servo, but are not so slack that they can get into the propeller or the servo gears. Just find a good tension empirically by holding the wires and turning the servo with your hands (make sure the battery is disconnected for this).

Step 32: Attach the Propellers

In this, the final step of this Instructable, we will attach the propellers to the motors.

For safety reasons, we've waited until the very end of our tricopter build to attach the propellers to the motors, but the time has finally come to complete this last step before our Rotor Bits tricopter can take to the air.

Mounting the propellers is quite simple. First of all, remove the nuts from the propeller mounts on all three motors.

If you try to put a propeller onto one of the motors, you will notice that the hole in the center of the propeller is too large for the threaded shaft on the propeller mount. We will need to use a thread adapter to make the propeller fit properly. Included with the propellers are a set of thread adapters that look like a selection of different sized plastic rings. Find the correct thread adapter by simply testing each adapter until you find the one that fits.

So, having identified the correct thread adapters, first place a thread adapter onto each motor. Then, put a propeller onto each motor with the wider part of the hole facing downward, it should fit over the prop adapter. Then, finally, replace the nuts on the prop adapters and tighten them down until they are very snug.

Step 33: Congratulations

Congratulations

Yay! It has been a long process but your tricopter is finally ready to take to the skies. I just wanted to take a moment not only to congratulate you on completing your tricopter but also to thank you for reading through this Instructable.

When you are in a wide open space (like outside) where there is nothing too valuable or alive to accidentally crash into with your Rotor Bits tricopter, remember that to arm the KK2.1 for flight, move the left stick down and to the far right. Arming the KK2.1 allows the motors to turn according to the throttle input you give. In other words, arming the KK2.1 allows the tricopter to fly. Remember to always disarm your tricopter when you land by moving the left stick down and to the far left.

Now go fly!

Step 34: Tuning Your Tricopter

Every tricopter flies just a little bit differently so you will need to tune your tricopter's settings. This page goes over the basics of tricopter tuning.

I might have deceived you a bit in the last step because you are not completely done with your tricopter. Actually building your tricopter only gets you part of the way towards successfully flying. You will need to tune your tricopter's settings in order to optimize its flight characteristics. Specifically, you will need to tune your "PI Roll and Pitch" settings. The default settings should get your tricopter flying fairly well, but again, every tricopter flies a bit differently and every pilot controls their tricopter a bit differently. The key to successfully tuning your tricopter, and I doubt this will be surprising to you, is knowing what each of the flight controller's settings do.

Now, I don't want to go into tons of math or electrical engineering to explain the actual inner workings of a flight controller's PID loop in this step. If you want to learn how PID loops work, there is plenty of information out there that you can access with a quick Google search. In this step I just want to cover how each parameter in your flight controller's PID loop settings affects the tricopter's performance.

All of these settings are accessible from the PI Roll and Pitch section of the KK2.1 main menu.

P Gain

The P Gain (which stands for Proportional Gain) parameter basically controls how your tricopter prioritizes pilot input versus input from the flight controller's on-board sensors.

A high value of the P Gain parameter means that the readings from the sensors will be very important. A low value of the P Gain means that pilot input will be very important.

If the P Gain is set too high, you might notice the tricopter oscillating or kind of twitching in the air. This effect is caused by the flight controller's frantic attempts to correct even the tiniest sensor discrepancies. If the P Gain is set too low, the craft will seem sluggish and slow to react to changes in orientation on control input. It will probably be difficult to keep the tricopter airborne if the P Gain is too low since the tricopter will be expecting you, the pilot, to do most of the work needed to keep and craft stable, and unfortunately, our brains and our thumbs are just not quick enough to make the rapid adjustments needed to keep the craft in the air.

I Gain

The I Gain (which stands for Integral Gain) controls how quickly the tricopter will respond to changes in angular orientation.

In other words, let's say you are flying your tricopter and you want it to move forward. To do this, we tilt the tricopter forward. This forward tilt directs some of the tricopter's lift backwards instead of all the lift being directed downwards, which makes the tricopter move forward. When we release the stick, the tricopter will return to a level position.

Neither the tilting forward nor the returning to a level position happen instantly though. It obviously takes a little time for the tricopter to actually move. The I Gain basically controls how aggressively the tricopter attempts to achieve the designated tilt.

If the I Gain value is too low, the tricopter will seem sluggish and slow to respond to control input. If the I Gain is too high, the tricopter will again oscillate in the air as it fights to keep a perfect position.

Tuning P Gain

Starting with the default values, if you feel like your tricopter is a bit too sluggish, turn up the P Gain in intervals of five until you get the responsiveness you want. If you notice your tricopter shuttering in the air, back the P Gain off a bit.

Tuning I Gain

Starting with the default values, if you notice your tricopter does not stop and stabilize after moving the sticks and returning them to center, increase the I Gain increments of five until you get a quicker response time. You want to get to a point where the tricopter returns to a level position quickly and does not wander around in the air.

The I Gain value is also useful if you are flying in windy conditions where it is more important for the tricopter to correct its angular position and not get moved around by the wind as much.

Step 35: Appendix A: Charge the Battery

This supplementary step will show you how to charge the tricopter's LiPo batteries.

Connect Battery to Charger

Battery technology is great, as it allows us to bring a portable power source anywhere we go, including high into the sky. The unfortunate downside to battery technology is that batteries go flat after being used for a while; you already know this. Never fear though, this appendix to the Rotor Bits tricopter build tutorial Instructable will show you how to safely charge your batteries using the Accucel-6 charger.

The first step is to connect your battery to the charger. So, take a look at your battery and you will notice that there are two sets of wires coming out one end: the thick red/black set that we use to connect the battery to the quadcopter, and a set of four thinner colored wires with a thin plug at the end. We will plug both sets of wires into the Accucel-6 charger.

First, included with the charger were several wire adapters with red and black plugs on one end, and a variety of connectors on the other end. Locate the adapter with an XT60 plug on the end, this is the plug that matches the red/black plug on the battery. Next, on the right side of the Accucel-6, you will notice a red port and a black port. Connect the red and black plugs on the battery adapter into the matching colored ports on the Accucel-6. Now plug the XT60 plugs on the battery and on the battery adapter together.

Now let’s plug in the set of colored wires from the battery.Take a look at the right side of the Accucel-6 again and you will notice a bank of white female connectors with pins in them. Notice that each connector has a different number of pins. Now shift your attention to the group of four colored wires from the battery, notice that the connector at the end has four male pins. You can probably guess what we’ll do next. Connect the white battery plug to the slot on the Accucel-6 that has four pins.

Program Charger

With the battery connected to the Accucel-6 charger, we now need to set up the charger to use the correct settings for charging our battery. Before we begin this process, I want to make a very important safety note: it is absolutely imperative that you use the correct settings for charging your battery. Failure to charge the battery with the correct settings could result in damage to the battery, the charger, or even catastrophic failure of the battery which could result in a fire/explosion. Also, during charging, always put your battery in a LiPo bag, which is a fire-proof bag designed to contain any battery failure. You should also never leave a battery unattended while it is charging.

I certainly do not wish to scare you with this information, but lithium polymer batteries are capable of high discharge rates and are made with some pretty volatile ingredients, like lithium, and it is important to be safe. In reality, if you handle, charge, and discharge the batteries with some care, you will be just fine. LiPo batteries almost never fail the way you see in some videos on YouTube.So with the safety information out of the way, lets get started setting up the Accucel-6 to charge our battery. First, we will need to gather some information about the battery, which should be printed on the battery’s label, otherwise you can obtain information from the manufacturer’s documentation. The information we will need is: the number of cells in the battery, the voltage of the battery, and the maximum charge current of the battery. For the Turnigy 2200mAh 3S 20C Lipo Pack used in the SK450 Dead Cat quadcopter tutorial, the information we will need is as follows:

Number of cells: 3
Voltage: 11.1V
Maximum charge current: 2.2 Amps

The first two pieces of information here, the number of cells and the voltage of the battery are easy to find, they are written right on the battery label. The third bit of information, the maximum charge rate, requires a little bit of math to figure out though, which I will take a moment to explain.

First of all, calculating the maximum charging current requires two other pieces of information: the battery’s capacity, and the maximum charging rate of the battery. The battery’s capacity is written right on the battery label. The battery’s capacity is expressed in units of milliamp hours (mAh), which basically describes how much power a battery can supply for how long. The capacity of the battery used in the SK450 Dead Cat quadcopter tutorial is 2200mAh. As for the maximum charge rate for the battery, the maximum safe charge rate for our LiPo battery is 1C. Here, the C stands for coulombs, which is basically a unit of electrical charge. This is probably a slower rate that you could technically pump into the battery, but we want to make absolutely certain that the battery does not start on fire, so we will go with the safe rate of 1C.

From the battery’s capacity, and the maximum charge rate of 1C, we can calculate the maximum charging current of our battery. First of all though, charging current is expressed in units of Amps. To find the maximum charging current for our battery, we will multiply the battery’s capacity in amp-hours by the maximum charging rate in coulombs. First, move the decimal point in the 2200mAh capacity listed on the battery label three spots to the left to convert from milliamp hours to amp hours. We end up with 2.2Ah. So, multiplying this figure by the maximum charging capacity of 1C, we end up with a maximum charging current of 2.2A.

So now that we did all that work and all that math, I am going to tell you that, unless you are in a big hurry, you should probably not charge the battery at the full 2.2A charging current. It will prolong the life of the battery if you charge at a lower rate. So in this tutorial we will use a charging current of 1A.

Now let’s finally get to programming the Accucel-6. First of all, plug in your 12V power adapter to the plug on the left side of the Accucel-6. As soon as you connect the power, the Accucel-6 will emit a loud beep. You should get used to these extremely loud beeps as the charger will be deeping a lot in the next few minutes. After the Turnigy splash screen goes away, you will be presented with a screen with “PROGRAM SELECT” in the first line and a battery type in the second line. If the battery type listed in the second line is anything but “LiPo BATT,” press the leftmost “Type” button to change the battery type. Once you have “LiPo BATT” in the second line, press the right-most “Enter” button.

On the next screen, the first line lists what action the Accucel-6 is taking. The device is capable of charging the battery, balancing the battery, fast-charging the battery, storing the battery, and discharging the battery. These functions are all useful and some are covered in other tutorials on this site, but for now, use the middle two arrow buttons to select “LiPo CHARGE” since we are interested in charging the battery right now.

The second line lists settings for the charging process, from left to right the settings are:

charging current
battery voltage
(battery cell count)

To change these settings, press the Enter button. The charging current setting should now be flashing. Use the arrow buttons to set the charging current to 1.0A. Now press the Enter button again to select the battery voltage/cell count setting. Use the arrow buttons again until “11.1V(3S)” is selected.

With the correct settings applied, we are finally ready to charge the battery.

Charge the Battery

To start the charging process, hold the Enter button for three seconds. The Accucel-6 will beep a few times and then it will check the battery. After a couple seconds, a you will be presented with a new screen. The first line lists the settings you entered on the right, and the settings detected by the Accucel-6 on the left. If these settings do not match, press the leftmost “Back” button to return to the previous screen and double-check your settings. Otherwise, if the settings on the top line to match, press the Enter button to start charging.

The Accucel-6 will display the status of the charging progress. It lists the battery type and cell count, the current charging current, the current battery voltage, the charging time, and the battery capacity. Now you just need to wait for the battery to finish charging. Remember never to leave the battery unattended while charging. If you have to leave before the charging process is complete, stop the process by pressing the left-most “Stop” button. Lithium polymer batteries do not have a “memory effect” so you can always finish charging the battery at a later time.

When the battery is done charging, the Accucel-6 will start beeping. First press the Stop button, and then disconnect the battery from the charger. Now you are ready to fly some more.

Step 36: Appendix B: Add LEDs

This supplementary step will show you how to put LEDs on your tricopter that are controlled by a switch on your transmitter.

Theory

Before beginning the actual process of attaching LEDs to the Rotor Bits tricopter and wiring them up to work, I just want to take a moment to cover a bit background information so the process will make the most sense.

The LEDs we will be using on the tricopter are strips of six LEDs available from HobbyKing. We are going to use two different colors. This will allow us to put two strips of one color on the front two arms, and a third strip in a different color on the rear arm. This way, when flying, especially when flying at dusk, it will be easier for us to tell which side of the tricopter is front. So, for example, in this Instructable, I am using two blue LED strips on the front arms and a green LED strip on the rear arm. You can choose any color you want though, many different colors are available:

The LED strips run off 12V, which, as it happens, is the power supplied by the battery. So, we could just connect the LEDs straight to the battery, but the question is, should they be wired in series or parallel?

The answer is, we want to wire the LED strips in parallel. Here’s why:
Our battery supplies 12V and, as far as LEDs are concerned, unlimited current (part of the reason we use LiPo batteries for multirotors is because they can discharge a very high current, far higher than we would need for any number of LEDs we could cram on our tricopter). If we were to wire the LED strips in series, that 12V would be distributed among the three LED strips. So, each LED strip would get 4V, not enough to run the LEDs.

With the LEDs wired in parallel, however, each LED strip gets 12V. In parallel, the current required for the system is sum of the current required by each LED strip. But, as I just mentioned, current is no issue for our battery. The 12V for each strip is enough to make them nice and bright. So, we will be wiring the LED strips in parallel, with all the negative leads wired together and all the positive leads wired together.

If you want some more information about wiring LEDs, there is a nice, simple tutorial at http://www.quickar.com/ledbasics.htm.

There is, however, one more issue to address here. I think it is nice to be able to turn the LEDs on and off. If you are flying in the daylight, you might wish to turn off your LEDs, or maybe you just don’t want them on all the time. We will be adding a switch to the LED circuit. The nice thing is that the switch we will use is turned on and off by the receiver, so we can turn on and off the LEDs remotely with the radio transmitter. Specifically, we will use the CH6 toggle switch to control the LEDs.

Let’s get to the build.

Create Wiring Harnesses

The first thing we need to do is make ourselves some wiring harnesses to connect the jumper pins on the LED strips to the bullet connectors on the battery. You will need two wiring harnesses: the first goes from three jumper pins to a male bullet connector, and the second goes from three jumper pins to a female bullet connector.

So take two red male-to-male jumper wires and two black male-to-male jumper wires and cut each in half. Strip the ends of all the wires by about ½ inch. Take the three red wires and twist the ends together. Then, loosely double the twisted ends. Repeat this twisting procedure for the three black wires.

Then, break out your soldering iron, and, using the same procedure as you used to solder bullet connectors to the UBEC (check https://www.youtube.com/watch?v=B9yY9Kk4bEA for a quick tutorial) solder a female bullet connector to the black wires and a male bullet connector to the red wires.

Solder Bullet Connectors to the Receiver-Controlled Switch

We will also need to solder bullet connectors to the leads of the receiver-controlled switch since the switch comes with these leads unterminated. Use the same procedure we used when soldering bullet connectors to the UBEC.

Attach the LEDs to the Tricopter

Alright, it is finally time to attach the LEDs to the tricopter frame and connect them electrically to the rest of the system. As before, we will do all the wiring and verify that everything functions as expected, before actually attaching everything to the frame.

Connect one of the bullet connectors you just soldered onto the receiver-controlled switch, it does not matter which, to the black (negative) lead of the battery’s wiring harness.
Connect the red wiring harness you made to the positive (red) lead of the battery’s wiring harness.
Connect the other wiring harness, the black one, to the free lead of the receiver-controlled switch.
Finally, connect the three wires from the black wiring harness to the outside pins of the three LED strips. Then connect the three wires from the red wiring harness to the middle pins of the three LED strips.

Now that we have the whole LED system wired, we will test the LEDs just to make sure everything is working before we start zip-tieing everything to the frame (it will be annoying to undo this if we find the LEDs don’t work after we do it). Connect the battery to the wiring harness and turn on the radio transmitter. Then, if the LED’s have not turned on already, which would happen if your CH6 switch happens to be on already, flip the switch. You should be able to turn the LEDs on and off. The LEDs should also be quite bright, we want to see them clearly from far away after all.

Fasten Everything to the Frame

The last thing to do is attach everything to the tricopter frame. As we've done with all the rest of the tricopter components, I like to use zip-ties for this task. There is a very important piece of information to keep in mind while you are mounting your LED strips. Carbon fiber is electrically conductive, its kinda like pencil lead which you might have used in grade school science class. The carbon fiber tubes we used to build the tricopter have a coating that is supposed to prevent the tubes from conducting electrical current, but the coating is very thin. The little metal spikes on the bottom of the LED strips, the leads from the LEDs themselves, are more than capable of penetrating this layer. This situation will result in an electrical short, which will damage your tricopter. I actually learned this the hard way and an electrical short fried one of my LED strips (specifically it fried the resistors). Also it smells really bad. Anyway, to avoid this issue, put a few layers of electrical tape onto the tricopter arms. This will make a nice nonconductive mounting pad for the LED strips.

Then, after mounting the LED strips to the tricopter frame using zip-ties on top of the electrical tape pads, mount the receiver-controlled switch to the Rotor Bits tricopter hub. Finally, fasten down all the wires so you don’t end up with loose wiring finding its way into the propellers.

And you are done! By this point your tricopter probably looks really crazy, like some kind of mad scientist contraption with wires and LEDs everywhere. I actually think it looks pretty cool, especially with the LEDs. Enjoy your much more glowing tricopter!

Grand Prize in the
Formlabs Contest

Participated in the
3D Design Contest

Build a Tricopter With Rotor Bits

Step 1: Parts

Step 2: Connect Arms to Tricopter Hub

Step 3: Assemble the Rotor Bits Servo Mount Set

Step 4: Attach the Landing Leg Mounts

Step 5: Attach the Motor Mounts

Step 6: Position and Attach the Landing Leg Mounts

Step 7: Attach the Landing Legs

Step 8: Mount the Motors

Step 9: Attach the Propeller Mounts

Step 10: Attach the KK2.1 Flight Controller

Step 11: Attach the ESCs

Step 12: Attach the Radio Receiver

Step 13: Wire the Radio Receiver to the Flight Controller

Step 14: Solder 3.5mm Connectors to UBEC

Step 15: Attach the UBEC to the Tricopter Frame

Step 16: Connect the Motors to the ESCs

Step 17: Connect the Battery to the UBEC

Step 18: Program the ESCs

Step 19: Update the KK2.1 Firmware, Part 1: Setup

Step 20: Update the KK2.1 Firmware, Part 2: Updating

Step 21: Connect the UBEC to the Flight Controller

Step 22: Load the Tricopter Motor Layout

Step 23: Connect the ESCs and Servo to the Flight Controller

Step 24: Bind Radio Receiver to Radio Transmitter

Step 25: Perform a Receiver Test

Step 26: Perform a Sensor Test

Step 27: Calibrate Accelerometer

Step 28: Mixer Editor

Step 29: Verify Motor Spin Directions

Step 30: Balance Propellers

Step 31: Fasten Down Loose Wires

Step 32: Attach the Propellers

Step 33: Congratulations

Step 34: Tuning Your Tricopter

Step 35: Appendix A: Charge the Battery

Step 36: Appendix B: Add LEDs

Recommendations

Introduction: Build a Tricopter With Rotor Bits

Step 1: Parts

Step 2: Connect Arms to Tricopter Hub

Step 3: Assemble the Rotor Bits Servo Mount Set

Step 4: Attach the Landing Leg Mounts

Step 5: Attach the Motor Mounts

Step 6: Position and Attach the Landing Leg Mounts

Step 7: Attach the Landing Legs

Step 8: Mount the Motors

Step 9: Attach the Propeller Mounts

Step 10: Attach the KK2.1 Flight Controller

Step 11: Attach the ESCs

Step 12: Attach the Radio Receiver

Step 13: Wire the Radio Receiver to the Flight Controller

Step 14: Solder 3.5mm Connectors to UBEC

Step 15: Attach the UBEC to the Tricopter Frame

Step 16: Connect the Motors to the ESCs

Step 17: Connect the Battery to the UBEC

Step 18: Program the ESCs

Step 19: Update the KK2.1 Firmware, Part 1: Setup

Step 20: Update the KK2.1 Firmware, Part 2: Updating

Step 21: Connect the UBEC to the Flight Controller

Step 22: Load the Tricopter Motor Layout

Step 23: Connect the ESCs and Servo to the Flight Controller

Step 24: Bind Radio Receiver to Radio Transmitter

Step 25: Perform a Receiver Test

Step 26: Perform a Sensor Test

Step 27: Calibrate Accelerometer

Step 28: Mixer Editor

Step 29: Verify Motor Spin Directions

Step 30: Balance Propellers

Step 31: Fasten Down Loose Wires

Step 32: Attach the Propellers

Step 33: Congratulations

Step 34: Tuning Your Tricopter

Step 35: Appendix A: Charge the Battery

Step 36: Appendix B: Add LEDs

Recommendations

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