Introduction: Scratch Built Fireball Shooting Tricopter
"Whats this? A scratch built tricopter on Instructables? At a 250 racing size? With 10 inch props? A reliable, smooth and innovative YAW mech? AND A FIREBALL SHOOTER? How do I build one?"
Well, I'm glad you asked.
(For a shorter Instructable on just the fireball shooter click here)
Step 1: Video of the Tricopter in Action
Step 2: What Is a Tricopter?
First up, this tricopter is not really a drone. Nor are most quadcopters you can buy, or hexacopters or octocopters. A drone (or UAV) is an Unmanned Aerial Vehicle that can navigate autonomously. Most multicopters that you can go out and buy and most DIY multicopters are piloted via remote control and are therefore not autonomous. That being said, the definition of drone is, at this point, fairly loose and is beginning to refer also to remote control aerial vehicles. Multicopter is also not a standardised name for these vehicles with multirotors being a reasonably common name too. In any case, try not to call them drones to avoid being yelled at by nerds such as myself (and now you too =3).
So whats the difference between a tricopter and a quadcopter? As evidenced by their names, a quadcopter uses four motors while a tricopter uses only three. The other main difference is how YAW (turning) is taken care of; a tricopter turns by tilting the tail motor while a quadcopter turns by speeding up one pair of motors (spinning in one direction) while slowing down the other pair (that spin in the opposite direction), this allows the quadcopter to remain level while utilising the now misbalanced aerodynamic torques to turn (basically, motors spinning in one direction will speed up pushing the quadcopter around). The reason most multirotors you see are quadcopters is because four motors is the minimum you need for a fixed frame multicopter (no extra complex, moving or mechanical parts) .
Obviously the video above is not my video I just thought it helped explain what a tricopter is.
Step 3: Why a Tricopter?
So why build a tri? The tricopter or quadcopter debate is ongoing but I prefer tri's because; they are cheaper, easier to maintain and troubleshoot, are easier to make foldable and they have a wide angle between the front two motors (120° compared to a quadcopters 90°) and an even larger angle for our specific tricopter due to the way it was designed (150°). This normally means that your FPV camera can utilise a wider angle lens without being compromised by annoying propellers getting in the way of your view. In our case it mean that there is a bigger area to fire our fireball without it getting too interrupted by the propellers. We can also use bigger propellers as there is more space between the motors which I will explain in a later step. The movements of a tricopter are also a lot smoother as explained in the video in the previous step.
Once again this is Flite Tests video not mine.
Step 4: Why the Fireball Shooter and How Does It Work
I ended up deciding to add a fireball shooter to this to replace the FPV gear that I still cant afford. Of course you could always just make the fireball shooter or just make the tri (with or without FPV gear) but putting them together is a whole new level of awesome. The fireball shooter works off the exact same principles as the fireball shooter in my "Fireball shooting Harry Potter wand" so be sure to check that instructable out.
The fireball shooter works off a glow plug (and a 1.5v power source), a 8-12mm tube and flash paper (and/or flash cotton). When power is applied to the glow plug (inside the tube) the platinum wire glows red hot igniting either a flash paper "fuse" or the easier to light flash cotton. The fuse or flash cotton ignites a larger wad of flash paper inside the tube. The quick ignition and therefore expansion of gasses behind the ball of flash paper pushes the ball out of the tube where the flash paper is exposed to a large amount of oxygen. This large amount of oxygen allows the flash paper, once outside the tube, to burst into a spectacular ball of fire.
Step 5: So How Does Our YAW Mech Work?
I designed this YAW mech for a couple of reasons. First up, I was sick of 3D printed everything, I'm not saying 3D printed parts are bad, I just hated all my 3D printed YAW mech's and other parts failing on me after my first flight (I do use 3D printed parts in this project anyway just for ease of fabrication). The other problem I had with most YAW mechs is that they put the motor half an inch or so above the boom and as such the rest of the motors. For a larger tricopter this isn't such a big deal and even on a small tricopter like this one you can just drop the rear boom to put the tail motor at the correct height but that is always a hassle.
The way our tail boom works is actually pretty simple. I utilise the circular 8mm hole in our square 10mm carbon fibre booms to house two bearings. A small section of carbon fibre is allowed to spin freely on these bearings while a larger section is held secure and is attached to the frame. The smaller, freely spinning section (which the motor is attached to) is pulled left and right by a servo as demonstrated in the video. This gives us a solid, very smooth turning, YAW mech that doesn't require much from your servo to turn and puts our tail motor at the same height as the rest of our motors.
Step 6: Materials
This tricopter is made almost exclusively from parts purchased from hobbyking.com, most of the other parts can be bought at a local hardware or engineering/hobby shop.
Fibreglass (and resin and catalyst)
(optional) Vacuum forming plastic
25mm M3 bolts
M3 nuts and washers
M4 threaded rod
M4 Nuts and washers
Rubber grommets They come standard with most servos and even though the hole is 2.3mm, a M3 screw will fit snugly
Double sided foam tape
Normal double sided tape
1/4 x 28 (or whatever nut fits your glow plug)
And most importantly ZIP TIES!!!
3x 30a ESC for the motors I am currently using I only really need 15-20a ESC's but I'm saving up for Cobra 2206's which will draw a lot more power. Either way, the 30a is as big as the 20a and its always better to go with an ESC that can handle more current especially seeing as my 30a's get pretty hot anyway.
3x DT700 motors I've also hear great things about the DYS 1806's who's lower weight and need from smaller ESC's, props and batteries would bring your all up weight (AUW) to less than 500g. I am also saving up for cobra 2206's so I'll check back in when I've acquired those
10x4.5 slow fly propellers obviously you will want to check which propeller you want to use based on what motor you are using
Turnigy MG90S For the tail servo (though there are better options for a larger price)
The almighty HXT900 (or any other cheap, micro servo) for our servo switch
Batteries: I will explain what all the numbers mean later
Turnigy 2200mAh 20C 3S perfect battery for most applications including this build, high quality and gives you the "best bang for your buck"
Turnigy 2200mAh 25C 3S the battery I personally use incase I need a little more punch
Turnigy 2200mAh 20C 4S similar to the battery I built
Super clean male to male extension (100mm) to connect the receiver to the flight controller. Cannot recommend this product enough for a nice clean build
PolyMax 3.5mm gold "bullet" connectors for connecting wires that carry high amps such as the wires from the battery to the ESC's to the motors
40p 200mm male to female jumper cables I bought two packs of these thinking I'd never need to buy more and now I need to buy more =P
(Optional) external 5v/3A micro UBEC for cleaner power to your servo and/or flight controller and receiver. haven't used it, but I've gotta say, its pretty small
Glow plug no.3 (HOT) for lighting our flash paper
Turnigy pure silicone(Black/Red/Translucent black) I use translucent black as my hot colour (normally red) to keep everything looking black =3. In my eyes, Turnigy pure silicone is a killer product, it is easy to solder, can handle abuse, looks great and best of all, its is EXTREMELY flexible!!! If I had to pick the best item on this list, this would be it (though I may not know what I'm talking about having before this only ever worked with cheap quality wire from my local electronic store that I ended up soldering with a torch I kid you not).
Hobbyking T6a transmitter and receiver version 2 (Mode 2) or (Mode 1) sorry but I don't know much about high quality transmitters
USBasp AVR programming cable for programming our KK2 and our ESC's
(optional) Voltage checker and alarm I would definitely recommend picking up one or two of these
(optional) Quanum telemetry voltage checker and alarm
AAA battery and holder
Drill (and a 3mm or 1/8 inch bit)
Laser cutter (or coping saw, files, sand paper and a whole bunch of time)
Nutdriver or spanner
Hot glue gun
Loctite (high and medium strength/263 and 243)
Party sparklers (grind the ends into a fine powder)
Unnecessary pretty stuff
3mm wire mesh I ended up needing more mesh so I just bought it from a local electronics store. The one from the store was much thicker and harder to work with
Matte black spray paint (and a lot of it =3)
Step 7: How Do the Electronics Work
Transmitter and receiver
The transmitter and receiver work in tandem to take your inputs (you moving the sticks) and provide output wirelessly to your multicopter so that you have full control over it.
The flight controller (not to be confused the with Fat Controller) takes the outputs from the receiver and feeds new outputs to the ESC's based on readings taken from the FC's sensors (accelerometer, gyroscope and sometimes barometer etc.) and the outputs from the receiver.
The electronic speed controllers control the speed of our motors by (ESC's) taking the outputs from the flight controller (or in the case of a plane, straight from the receiver) and using an array of FETS or MOSFETS (which, as I understand it, are basically really reliable, fast, resilient transistors) outputs power directly from the battery to the motor windings sequentially via three heavy duty wires (or not heavy duty if your motors don't draw much power). All ESC's are rated for a maximum voltage and amp draw, In many ESC, even drawing half of the max amps will overheat the ESC(especially if the heatsink is not getting any air). In very few high quality ESC's the amp draw can be exceeded for short periods of time without damaging the ESC but please don't rely on that fact. It is always better to get ESC's that can cope with more that you think you will be drawing (all this info can be found on data sheets for both the motor and ESC and on RC forums). This information is specifically for brushless motors and ESC's as brushed motors and ESC's work differently.
The brushless motors such as the ones we will be using, use the alternating current from the ESC's to sequentially power its 12 windings. When one set of windings is powered, it will repel or attract (I don't know which sorry) magnets on either the shaft or bell of the motor. In both cases the windings (stator) remain stationary while the permanent magnets spin the shaft. An inrunner uses windings on the outside case of the motor to repel magnets on the rotor which turn the shaft and propeller. Inrunners are MORE suited to boats as they can be more readily made water tight. Outrunners use windings on the inside of the motor to spin magnets connected to the bell of the motor which is in turn connected to the shaft and propeller. Brushless outrunners are more suited to our needs as they are easier to work with and repair and can be more readily made "holey" to allow air to flow through them, cooling the windings.
The battery you will most likely be using to build a tricopter like this one is a lipo (lithium polymer) battery. Lipo batteries are ideal because they can discharge at extremely high rates to provide adequate power for your power hungry motors. This also makes them extrememly dangerous as shorting a lipo can cause a very quick discharge which can screw with the chemicals inside the battery (I'm sure you could find a better explanation with a quick google search, sorry) either rendering the battery useless or in a worst case scenario, shorting the lipo could lead to a chemical fire. Lipos are very dangerous so please be careful with them. Lipo batteries have three ratings; an mAh, C and S rating. mAh stands for milliamp hours and refers to the capacity of the battery (or how long you can fly). The C rating is the discharge rate and refers to how quickly the battery can discharge a 30C discharge means that the battery can discharge at 30 times the mAh rating so a 2000mAh battery rated for 30C could provide 60 amps (60000 milliamps) at any one point in time. This rating can usually be exceeded by a certain amount for short periods of time which will be specified in the batteries spec sheet. The S rating refers to how many cells the battery has. Each lipo cell is 3.7 volts (this changes based on the batteries charge but 3.7 is the standard voltage). This means that a 4S battery has 4 cells and therefore 14.8 volts (at an average charge). Very few batteries also have a P rating after the S rating and this shows how many cells are in parallel (more in parallel mean a higher mAh though you can get a higher mAh just by making the cells bigger) but we don't have to worry about that. More voltage means more power. Unfortunately your ESC's, motors and other equipment can only handle a certain voltage so make sure you check what those voltages are before you go plugging your tri into a 10S battery. As a general rule of thumb, a higher mAh means a bigger heavier battery as does a higher cell count.
I could write a whole instructable on proper care of your lipos (and I'm pretty sure there is one (found it)) but here are the basics:
Don't discharge too much (ruins the internal resistance)
Don't overcharge (makes the chemicals unstable and dangerous)
Don't charge while hot (heat speeds up the chemical reaction which will "puff" your batteries)
Don't store charged batteries (I have been led to believe that this lowers the batteries C rating)
Be carefully with puffy batteries (if your batteries are puffed it means something has gone wrong. Many people tend to chuck their puffed lipos but having never puffed a lipo myself I cant give any advice)
Keep in fireproof bag or inclosure when charging and/or keep a bucket of sand at the ready (lipos are most volatile when they are charging so always be prepared for a fire)
Never leave a charging lipo unattended (see above)
Avoid shorts at all costs
A servo takes an output from (in the case of a plane) the receiver or (in the case of a multicopter) the FC and turns a motor to a certain position based on this input. It does this through the use of a closed loop circuit and a motor connected to the shaft as well as a potentiometer via a gear train. The servo uses the potentiometer to read how far it is in its movement and allows it to stop when the resistance from the potentiometer matches the required resistance for the shaft to be in its required position. We will use two servos; one to control the YAW (turning) of our tricopter by moving the tail motor and another that will act as a switch for our fireball shooter.
A glow plug is commonly used in diesel engines which require heat to ignite the fuel (compared to a traditional engine ignition being based on the timing of a spark plug). In cold conditions, where diesel engines may have a hard time starting, the glow plug "pre-heats" the fuel to make it easer to start the car. "The glow plugs used in model engines are significantly different from those used in full-size diesel engines. In full-size engines, the glow plug is used only for starting. In model engines, the glow plug is an integral part of the ignition system because of the catalytic effect of the platinum wire." - Wikipedia
For our application, the glow plug only needs to light a small bit of flash paper (or flash cotton). It does this by heating up a thin length of coiled, platinum wire which glows red hot when current is applied due to its high resistance (similar to the more commonly available nichrome wire). By applying a current to the coil whilst its in is close proximity to the flash paper we can cause the flash paper (or cotton) to ignite.
All of the photos above are from Hobbyking.com
Step 8: Electronics Explanation
So how do all these electronic components fit together to make something that flies? I'm glad you asked. Lets start at the beginning: You have a receiver in your hand with two sticks and possibly some other switches, buttons and knobs. If you have a mode 2 transmitter then your throttle (speed of the motors) will be up and down on the left stick, yaw (turning) will be left and right on the left stick, pitch (your angle forward and backward as well as, with a multicopter, moving forward and backward) will be your right sticks up and down and roll (your angle left and right) will be left and right on your right stick. A mode 1 transmitter has the pitch and throttle on the opposite sticks. Note: throttle on a real multicopter is different from throttle on a dji or similar, on a dji, your throttle will control the altitude of your copter (e.g. throttling up will raise the copter until the throttle stick is released at which point the copter will level out) where as on a real multicopter, throttle will actually control the speed of your motors (a lot more useful for acrobatics and racing).
With the transmitter and receiver both powered on and bound to each other, your receiver will start outputting signals read by either your servos, speed controllers (ESC's) or in our case, our flight controller FC). All of these gadgets can be connected to the receiver with ordinary servo cables with come standard with servos or esc's. In our case, we will have to buy servo connectors to connect our receiver to our flight controller (superclean) because of the way that the receiver is powered, we only need one connection from the FC's power rails to the receivers power rails, we then only need to connect the signal wires from the FC to the rest of the receivers outputs.
The FC then has a set of outputs of its own. On a quadcopter, these outputs are connected to 4 ESC's which are in turn connected to the motors. In our case, the first three of our outputs will be connected to ESCs and another to our yaw servo. To check which ESC's connect to which outputs on the fc we can check the motor layout in the KK2 settings (the KK2 will aoutomatically be set to quadcopter mode so you should probably go ahead and set it to tricopter mode which is also already pre installed).
The ESC's are powered directly from the battery to supply voltage to the motors as directly as possible. To connect three ESC's to one battery we will need to buy or build a wiring harness (shown later). When connecting the ESC's to the battery, be sure not to wire the ESC backwards otherwise you will observe what the RC world likes to call "magic smoke" coming from your ESC's. Esc's have two inputs (one for the battery and one for signal as well as two outputs (most of the time) a BEC (battery eliminator circuit) regulated 5v output (connected to the same servo wire as the signal input) and an output to power the motor. If you buy an opto ESC (or other ones specially designed for multicopters) they may not have the 5v output to power your receiver and FC. To get around this you will need to purchase a 5v UBEC (universal BEC) which is an external BEC that will provide clean 5v for all of your 5v powered equipment (or any other voltage you require). The BEC in most ESC's is there to power your receiver and in our case, our FC as well. Note that the first output from the KK2 is connected to its own power rail which also powers the flight controller and receiver. The rest of the outputs are connected to their own separate power rail which is there to provide cleaner power to your FC as well as cleaner power to a tricopters or duocopters servos (if all outputs were connected to the same power rail then the FC, receiver and servos would all be pulling power from one BEC which could lead to a lot of interference). This power rail situation means that only two ESC's need their BEC's to power things (the first ESC to power the FC and receiver and the second to power the output rail) which in turn means that for a tricopter or anything with more than two ESC's (quad, hex, octo) you can cut off the power from the extra BEC's to the board (I just tucked the two wires up on themselves and used heatshrink to keep them from shorting and to hold them in place) we do this to stop interference caused by multiple BEC's connected to the same power rail. If your yaw servo is able to draw more than 5v or is too jumpy you can cut off the second ESC's BEC and provide power to the outputs power rail via a more powerful or more reliable UBEC (ESC BEC's are notorious for delivering unstable outputs due to the constant switching required to spin the motor) giving your yaw more punch and faster response and/or cleaner power. Unfortunately, although I do have a UBEC, I never got around to installing it on any of my tri's because I have never seen an apparent need for it.
If none of this seems to make any sense, trust me, It makes a lot more sense when you have the parts in your hands. Just remember not to plug the ESC's into the battery the wrong way and you should be fine. A handy tip (that definitely does not always work) is that similar thickness wires will often connect to the same thing(s) for example, the wires coming from the battery and leading into the ESC are relatively thick as the carry a lot of current as are the wires from the ESC to the motor for the same reason. Similarly, the small pins comming from the FC and receiver can be connected to each other and via thin cables as well as to the ESC and servo via thin wires.
The image above is not mine, I stole it from this thread. As such it does have a problem. The positive and negative from the front two ESC's should be connected to the flight controller while the positive and negative from the rear ESC to the FC should not be connected to the FC.
Step 9: Planning
Lots and lots of planning
This tricopter was originally meant to carry first person view (FPV) gear, use a KKmini (still in the mail =/) and use five cobra 2206 motors but due to a limited budget I had to replace the FPV system with an even better fireball shooter =D and use my old DT700's off my previous dragonfly tricopter (plus stick with only 3 motors). This is why a lot of my drawings look very different to the final tri.
One of the big differences between my design and a standard tricopter (or T copter) is the angle between the front two booms. I made the angle between the front two booms much larger (150° compared to the usual 120°) so that I could bring the entire body forward, away from the tail motor giving me more room for the rear prop and yaw mech. It also gives me a lot more unobstructed room at the front of the tricopter for a wide angle fpv camera and/or our fireball shooter. Because of this fact we will need to do some simple trigonometry to figure out the lengths of each boom from the centre of the tricopter. Unfortunately the KK2 and the centre of gravity need to remain in the same place when bringing the rest of the tricopter body forward meaning both the battery and the KK2 will sit really far back on the body.
The rest of the plans are very standard and are somewhat based (as most tricopters are) off David Windeståls design so the sides are foldable and the rear boom is secured by friction. If you are designing your own tricopter the only things you really need to keep in mind are to keep all motors equal distance from the centre (when using standard tricopter angles) and keep the flight controller directly over the centre.
I then drew up all the plans on Adobe Illustrator thinking that I would later laser cut them at my school but ended up not doing so. I also made plans for use with a KKmini so once that arrives and I save up enough money for some nice 30a ESC's as well as the Cobra 2206's Ill post a photo of that. In any case, Here are the plans for both the KK2 and KKmini/Naze32
Step 10: The Donor Tri
Most of my electronics have been salvaged off my old tricopter (based on flite test's dragonfly design but foldable) hence the reason most of the electronics already have bullets soldered onto them. The dragonfly flew extremely steady and relatively fast (once I got the PID's dialled in) but my yaw mechanism was not the strongest and failed on multiple occasions which lead to me painfully rebuilding the yaw mech several times (which was harder than building it to begin with) so I decided to scrap it.
Step 11: How the Hell Are We Going to Fit 10 Inch Props on a 250 Frame?
If you fly racing quads you may be familiar with the struggles of fitting even just 6 inch propellers onto your 250 frame. So how in the world do I expect to get 10 inch props onto a 250 size frame. First up, because of the way multicopters are measured (farthest distance diagonally from one motor's centre to another) a 250 size tricopter actually seems a lot larger than a 250 quad. There are also less motors meaning more space between motors which means that our tricopter can accommodate much larger props whilst remaining in a 250 class. Above you can see images of a comparison between a 250 quad and tri and a comparison of a tricopter with 10 inch props and a quad with 6 inch props.
Step 12: Tips Before We Get Started
A few tips before we get started
How I solder bullet connectors:
The method that I have found to be most effective when soldering bullets is this; I first strip 5mm of insulation off my Turnigy pure silicone wire (ow whatever else I am connecting the bullets to) and tin the ends. Because the wire you are tinning is most likely very thick make sure you have adequate heat to allow the solder to flow throughout the entire cross section of the wire (try not to apply too much solder however otherwise the solder will run up the wire, under the insulation and make the wire very stiff). I then place the bullet in some helping hands (a hole in the table or a twisted piece of wire would work just as well if not better). Because of the amount of heat required to get solder flowing into the bullet connector your helping hands/hole/wire will quickly deteriorate so make sure you have spares. Once I am sure the bullet is secure I heat it up to a point where I can easily get solder flowing and apply solder to the interior of the bullet. Too much solder and it will flow out in our next step, too little solder and the connecting may be weak (the amount of solder required will vary depending on the size of your wire but you will quickly learn how much is best). Once I have a puddle of molten solder in the bullet I plunge the tinned end of the wire into the molten solder maintaining the heat by keeping my iron on the side of the bullet. The tinned part of the wire will now melt, fusing with the solder in the bullet. Allow to cool and you will have a very very strong connection. If we don't keep the heat on the side of the bullet to remelt the tinned wire a connection will still be made but only to the outside of the wire producing a very weak joint. There are plenty of other ways that you can find on youtube but this method hasn't failed me yet.
How to apply wire mesh:
Applying wire mesh is a difficult task. For the smaller 3mm wire mesh I first cut the length I need and singe both ends with a lighter (be sure to only get the ends because the mesh is pretty sensitive to heat and you can quickly burn a hole in it). Then I insert a matchstick inside the mesh to give me something to grab. I then remove any unnecessary parts of the wire I'm applying the mesh to such as the plastic housing on some connectors. I can then fairly easily slide the wire into the mesh and using the matchstick as something to grab, push the wire mesh over the wire, inching it along by expanding and collapsing it over the wire. You will then want to secure the ends of the wire mesh to the wire with a dab of hotglue or superglue. you can then slide the heat shink over then ends of the mesh to clean everything up. Again, when heating the heat shrink, be careful not to burn any part of the mesh as it is very sensitive to the flame. If you do however you will just be left with a small hole in your mesh that you can cover with a little extra heat shrink. The 6mm mesh is similar but I found that I do not normally need to put anything inside (the matchstick) to make it easier to work with due to it being a lot larger in diameter.
How to spray paint:
Spray painting for me is all about patience. The more coats and the thinner the coats the better looking and more resilient your final product will be. Sure its easy for me to day in a hot Australian summer where my coats dry in under 10 minutes but I would still suggest going for 3-4 coats minimum no matter how long it takes you. When spray painting, spray in short bursts, around 20cm from your job. When you are applying these short burst, move quickly from one side of the piece to the other, the spray should start off the piece, move onto the piece and finish off the piece to ensure that the entire surface is coated evenly. When moving the can, try not to use too much wrist as this will give your can a very arcy motion getting closer to the job in the middle and farther away at the ends of the spray resulting in an uneven coat. The closer you are to your piece the thinner the spray will be but the faster you will have to move to avoid dripping. The farther you are from your piece the wider the spray will be and you wont have to move quite as fast. Before you start painting your piece, make sure you have given it a light sand (I'm not saying its the best thing to use but I use 100 grit abrasive paper). Your first coat should be very very light and wont take long to dry, The second and third coats don't have to be too light but still light enough to avoid dripping, this is where you will want to cover most of your piece. Before the last coat I tend to give my entire piece a very light sand and then the fourth coat can go on fairly light (not as light as the first but not as heavy as the second and third).
How to use loctite:
The directions for applying loctite should be on your bottle but incase you bought an offbrand threadlockhere are a few guidelines. Shake the bottle beforehand and apply to the outside of the rod or bolt and inside of the nut (this is only really necessary with closed end nuts but does still help with normal nuts). Then tighten the nut down to where you want it and wipe off any excess (loctite will only cure between two metals so if its just in the air it will remain uncured for ever. Avoid getting the threadlocker on any non metal parts especially 3D printed ones as the glue may degrade them. It is suggested to allow 24 hours for a full cure but for our applications the threadlock should be cured enough in less than half an hour.
If there is anything I forgot just ask in the comments
Phew. That was almost an Instructable in itself. Anyhoo, now that thats over we can move onto making the actual tricopter.
Step 13: Preparing the Frame
To prepare the frame I took my plans, printed them on regular copy paper, roughly cut them out and using a generous amount of spray adhesive, glued them to the 3mm MDF. MDF does not have a grain so just place them wherever they fit (like a jigsaw puzzle).
I then cut out the pieces very roughly with a coping saw.
Next, I lay the fibreglass and resin on the side of the MDF without the plans so that I can keep the plans on while sanding to final dimensions and remove them later on. Make sure that every part of the piece is covered in the fibreglass sheet and make sure that all of the fibreglass is thoroughly "wetted out". (picture three shows what happens when you leave your fibreglass resin laying around for 4 years)
The fifth and sixth images show a lot of change; first up I covered the fibreglass in "builders bog" filler which is a filler that i have been led to believe is of similar chemical make up to our fibreglass resin (it certainly smells like it). The builders bog does not add any strength its just easier to sand than the fibreglass and wont make you itchy from all the fibreglass particles. I also cut, filed and sanded the pieces to their final dimensions as well as drilled the necessary holes (a 3mm hole will be a very snug fit for the M3 bolts while a 1/8th bit will make a nice, tight but easier to work with hole. I cant comment on 3.5mm as I never tried).
Next I gave each side 4 light coats of matte black spray paint sanding with 100 grit paper before the first and last coat (seems to help me get a more "solid" coat of paint). Make sure you use really light coats keeping the same distance from your piece (avoid "arcy" wrist movements which bring the can closer and furthe from the work). Use short sprays across the job from one side of the piece to the other to get smooth, even coverage.
I then put the frame together with temporary booms to get a rough weight and to look at how the holes were lining up.
I ended up not using the battery tray at the top due to the larger props required by the lower kv motor (explained later). When I get my cobra motors (which will require a smaller prop) I will be able to use the battery tray again.I also made a "vacuum formed" battery tray using a mould instead of a vacuum which I also ended up not using at this current point in time
Of course all of this could have been done in acrylic (or even fibreglassed MDF) on a laser cutter or CNC machine which was my original plan. My school would have allowed me to cut my own parts and I designed the parts in adobe illustrator for that reason but I ended up just wanting to do something one weekend instead of waiting around for the laser cutter so I just got to work cutting it by hand. In any case you can grab my plans for both a KK2 or KKmini/Naze32 in the plans step of this Instructable.
Step 14: Preparing the Vacuum Formed Battery Tray (Optional)
I also made a "vacuum formed" battery tray using a "mould" instead of a vacuum which I also ended up not using at this current point in time (for the same reason as the fibreglassed tray; my current props are too large).
To form the plastic I made an "inner mould" (a wooden rectangle the size I wanted the final tray to be) and an "outer mould" (a rectangular hole in a sheet of wood slightly larger than the rectangle). The gap between the rectangle and the hole when the rectangle is placed inside the hole should allow the plastic to slide a little without having too much spare space. We can then place the plastic on one side of the sheet of wood with the hole and tape it securely, temporarily in place with masking tape. We can then use a heat gun to heat the plastic until it is pliable and place the whole plastic and hole assembly (plastic side down) over the inner mould. This will push the sides of the plastic down and around the inner mould. a proper vacuum form will suck the sides down over the "inner mould" the same way that the "outer mould" would but they are expensive and cheap ones don't have enough suction to be feasible (especially for a simple shape like this).
Step 15: Preparing the Carbon Fibre Booms
To prepare the booms we will need to cut the booms to length as well as drill the required holes.
The problem with cutting any form of laminate is that the part will tend to delaminate when cut with a saw (not so much with an abrasive).
To get around this problem we mark where we want to cut our tube and lay masking tape on either side of the mark leaving a millimetre or so for the blade.
Next, using the finest hacksaw blade you can find (least teeth per inch; mine is 32 teeth per inch) "score" around the tube on every side around half a millimetre deep (for anyone who has access to a bunnings, I highly recommend this saw. The teeth last at least 10 times longer than the blades these sorts of saws come with). This scoring will ensure that the fibres will not delaminate when you reach the end of the cut.
We can then complete the cut of the tube in the usual fashion (taking care to watch out for any signs of delamination). Take it slow and don't press down too hard or try to force the saw, just let the saw do its thing.
I then carefully cleaned up the cut ends of the tube with a fine file (my needle files worked well) then some sand paper then finally coated them in superglue to avoid later delamination and sanded them again. I don't know if the super glue is necessary or even helps but it seems like a good idea.
It may seem like a lot of work just to cut a tube but the last thing you want is for your booms to start delaminating mid-air (quick side note, your YAW mechanism failing is also pretty bad).
Drilling can be approached in a similar fashion using an 8mm dowel inside the tube to stop delamination when the bit burst into the tube and masking tape on both sides to avoid delamination at the surface.
By marking and drilling from both sides rather than straight through we can ensure a straighter hole that will also require less clean up (though if you have a drill press that wont be an issue).
To finish the holes I also used a needle file and sand paper before and after coating the hole in superglue (the superglue did actually add a significant amount of thickness which i didn't expect but that was easily taken care of with the file).
I have also included a mount for the DT700's and 10mm square booms which I got my friend to model for me though I did not use it so I can not tell you how well it works (or if it even does work). I decided not to use it because (as mentioned before) I was sick of 3D printed parts failing on me and it would add many more points of failure, not just because the part would be 3D printed but also because I would have to cut the booms again and drill another hole.
Step 16: Preparing the Side Booms
The side booms are the booms that will fold in and out on a pivot and will be used to carry the two side motors
To prepare the side booms I took two 150mm lengths of 10mm square carbon fibre and drilled a hole 10mm from one end in each piece as per the plans. I then made a small mark where the centre of each motor would lay on the boom to make assembly a little smoother.
I could have cut the booms to a smaller length but I did not see a need.
Step 17: Preparing the Tail Boom
The tail boom is the essence of this tricopters YAW mech. As such I have put a lot of effort into making it as clean and smooth as possible. Likewise you will want to put in enough time when building it to ensure your YAW mech will work perfectly (and trust me, it does).
To prepare the tail boom is a little more complicated than the side booms. First I took my M4 threaded rod and cut a piece 160mm in length (150mm for the carbon fibre and a little extra for the nuts and washers on each end).
I then cut a 150mm length of carbon fibre into two pieces of lengths 100mm and 50mm
Next I placed two 8x4x3mm bearings on the rod (you will have to work out where to place them before loctiting them in place) with a little blue (medium strength/243) loctite on each of the bearings inner race being careful not to get any loctite anywhere else. (you don't need much as the bearing will be secured on either side by nuts anyway). You can then secure the bearings in place with four M4 nuts (one on either side of each bearing) and a little more blue loctite (place loctite on both the inside of the nut and the outside of the rod for maximum strength). The bearings outer race should stick out a little past the edges of the M4 nuts allowing the inside of the carbon fibre tube to run on the outer race of each bearing rather than the nuts. If the nuts are too large you can round off the corners with a file or rotary tool until they are smaller than the bearings. The nuts should also only tighten onto the sides of the inner race allowing the outer race to spin freely.
Once the bearing are in place you can place the 50mm carbon fibre tube over the bearings and secure it in place with a nut and washer on one side and a washer, 3D printed spacer and nut on the other side. The washers should tighten down on the nuts on the outer side of each bearing NOT onto the 50mm length of carbon fibre. This will allow the carbon fibre to spin freely on the bearings.
You can now place the last 3D printed spacer onto the other end of the M4 rod secured in place by one or two nuts (it doesn't need two nuts but may shake around inside the tube with only one nut). The 100mmm carbon fibre tube can then be slid over the spacers and secured at the end with another washer and nut combo. The 100mm tube should NOT be able to turn freely.
The 3D printed servo connector thingo can then be placed over the shorter, turning end of the tail boom (after being painted black obviously)
Remember to loctite all metal to metal connections. DO NOT loctite the 3D printed parts as loctite will eat away at ABS
Step 18: Preparing the Motors
DT700's are great little motors for their low price but they do have a couple of known problems. First up, the small grub screws that hold the base onto the motor are incredibly loose and no matter how much you tighten them they will quickly come loose with any vibrations from even the slightest of unbalanced props. To combat this problem I used a liberal amount of red loctite (high strength/263), blue loctite would probably work just as well (as long as your props aren't too out of balance) but I was just so fed up with loosing my grubscrews. The other problem is that the connection from the wires to the motors windings are loose and free to move around a lot. This makes them weaker overtime until they eventually snap. You can combat this problem with epoxy around the weak sections but I wanted my solution to be a little more flexible so as not to add another point of failure. I had two options here; use a flexible glue or use an all purpose silicone. I chose the silicone because it seemed like a more permanent solution. Again I used a liberal amount of silicone around where I thought the joints were weakest and left its for 48 hours to cure.
I also soldered a male bullet to each wire and covered each joint with heatshrink. I then gave the motor my standard black heatshrink and wire mesh treatment with 10mm heatshrink and 6mm wire mesh.
Make sure you take your props off before adding the motors to the frame or testing the electronics.
It was an incredibly stupid idea to use DT700's, a motor designed for a larger frame, slower flight and larger props on a tricopter designed with a smaller frame and for more acrobatic flight. Any motor commonly used on a 250 racing quad would be much more suitable requiring smaller props and giving you faster flight characteristics.
Step 19: Preparing the Props
Any set of propellers, no matter how expensive, have a high chance to be sold out of balance which is a significant PROPblem (get it =3). To balance the prop you could use a proper prop balancer which suspends your props on a rod suspended in the air by two magnets for the lowest friction. You can then use the steps below to check if or where your prop is out of balance and balance it accordingly.
Good prop balancers are hard to find and ones that a guaranteed to work well are often expensive so instead I use another method that I discovered and will now share with you. You will need a length of threaded rod the size as your motors shaft. You will then need to insert a prop adapter inside your prop so that it will fit both your motors shaft and your homemade balancer. It is always a good idea to balance with your prop adapters on because they can be out of balance as well. For our method, we secure our prop to the length of (in my case) M4 rod with a couple of nuts and washers. We then take two glasses of the same size and place them on a level surface. The two ends of the M4 rod can then be placed on the edges of the glasses (using the lips of the glasses will give you less friction then using the base).
We first need to balance the actual propellers. To balance the props, place the prop horizontally and see which side falls (this step is normally a lot easier to see and fix than the next step). You can then place a small strip of tape on the leading side of the heavier prop (the side that is in front when the prop spins in the correct direction). You can also spray a light coat of clear or black spray paint on the lighter side or lightly sand the heavier side (when balancing you can either add weight to the lighter side or take weight from the heavier side, I always add weight rather than remove it because adding is usually faster). Next we can balance the hub. To do this we place the prop straight up and down and allow the prop to fall into a horizontal state. After doing this a couple of times you should see that the prop tends to fall to a certain side. This is the heavier side of the hub. you can then add weight to the opposite side with a blob of hotglue until when the prop is placed up and down it doesn't fall to a horizontal. Ive found that in many cases, the hub doesn't need to be balanced(and I'm told this is a lot more common with higher end props) but I have also found that when the hub does need to be balanced a lot of hotglue needs to be used (I guess the hotglue just isn't heavy enough to make a significant difference with only a small amount). When you are finished you should be able to place the prop at any position (straight up and down, horizontal or diagonal) and it should stay where it is placed.
Step 20: Preparing the ESC's
To prepare and pretty up the ESC's many things were done. (sorry I didn't document the process because most of the modifications had already been done before I started this instructable
First I soldered bullet connectors to the input wires from the battery and output to the motors (as a rule of thumb, male is for any inputs while female is for any outputs) I then put heatshrink tubing around all of the bullets to avoid them shorting (shorting a lipo battery can have disastrous effects on both your battery and anything you love that is flammable).
Then I stripped the original ugly, blue heatshrink from the ESC to gain access to the pads for flashing the ESC. I then flashed the ESC with SimonK firmware. Im not going to go into too much detail about how to do this but I will say that I used the KKmulticopter flashing tool to make flashing a breeze and I pretty much followed this video the first time I did it. Note: to flash an ESC in this manner you will require a USBasp and a way to connect the USBasp to the pads (check out the last two photos of this step). Also note that flashing the ESC is not entirely necessary but will help your tricopter respond more quickly to inputs (be it corrections from the flight controller or your transmitter)
Next I re-covered the ESC's in clear heatshrink and cut away a small window infront of the heat sink. The heat sink is very important as it draws away a lot of heat from the FET's that are constantly switching to spin the motor. A hot ESC is not as efficient as a cool one so we want to draw as much heat away from the heat sink and the ESC. By cutting a small window and exposing the heat sinks to the cool blowing air from the props we can cool the ESC's quicker and more efficiently without the need for a larger heat sink or fan.
Once I was happy the ESC's were working correctly I braided the three wires that go to the motors and covered all the wires in 3mm and 6mm wire mesh using 10mm and 5mm heatshrink to secure the mesh in place. This step is completely unnecessary but hey, black looks pretty damn sexy. As you can see in the third picture you can still manage to get enough turns around the ferrite ring with the mesh on (it is quite a fair bit harder than without it) as long as you remove the bulky plastic housing from the connectors first. I also coloured the ferrite ring black with sharpie because, as mentioned before, black is pretty sexy.
On the inputs from the batteries I coloured the hot (red) side of the heatshrink with silver sharpie to help avoid plugging in the battery (or batter harness) backwards because this would lead to the aforementioned, infamous "magic smoke"
I also coloured the signal side of the servo connectors with the silver sharpie to help me orient them while assembling (its hard to see the wire colour under the wire mesh).
The last picture shows the difference between the thinner, easier to work with mesh from hobbyking and the thicker, harder to work with mesh from my local electronics store. The thicker 6mm mesh is nice for the big wires where I dont want to see the ugliness underneath but especially for the nice flat servo wires I prefer the stuff from hobbyking.
There are plenty of other. more suitable ESC choices for this tri. If you are using DT700's, then you only really need 20 amp ESC's (I am using 30 amps because I want to use Cobras in the near future and because when it comes to ESC the more amps it can handle the better). You can also get opto ESC's such as the little bee ESC's or Kiss ESC's and use and external UBEC. In any case, you will want to do a lot of research before you go out and buy your motors or ESC's.
Step 21: Preparing the KK2
The KK2 1.5 is the brains of the entire tricopter. To prepare it I cut a square of black foam to the size of the kk2, punched holes in it and stuck it to the back of the KK2 using double sided tape. This step is not necessary but due to the fact that we will be hiding a bunch of stuff underneath it I wanted it to be safe from shorts. The foam also provides a nice vibration dampening when mounted directly to a frame (stuck on with more tape or simmilar) and does add a little vibration dampening when connect how we are going to (on raised platforms).
The rubber grommets come standard with most servos but can be purchased separately. We can use them here as vibration dampening for our flight controller. When we mount the KK2 in its final position more spacers will be added below the grommet for added height.
Just to be a little different I salvaged a chirping bird circuit from a small kids toy and soldered that up to use instead of the standard buzzer (unfortunately due to the higher voltage the chirps no longer sound like chirps but they do still sound pretty cool). Once again, I coloured the hot wire silver so that i could orient it properly in final assembly.
Step 22: Updating the KK2 Firmware
Now you are going to want to update your KK2 to the latest firmware using the same USBasp that you used to flash your ESC's but with the supplied connector. We are also going to use the same program we used to flash the ESC's to flash the KK2. You can just follow this guys tutorial. I didn't flash my KK2 for my first two tricopters and I had weird problems every now and again with my tail motor dropping out for a second or two then picking back up again. To the best of my knowledge that problem is gone now that I updated the KK2 but if anyone knows any other possible causes id be more than happy to listen.
EDIT: The motor cutting out problem still exists with my new tricopter. I have narrowed it down to a bad battery as the problem only occurs when I'm using that battery. Fortunately, after around a minute of hovering an inch from the floor (so as to avoid breaking my tri when the motor cuts out) the battery seems to warm up enough to provide power to all of my motors efficiently.
Step 23: KK2 Vs Naze32
As you can clearly see, I am a KK2 guy, I have used the same KK2 on all of my builds with no troubles (except for a fading LCD screen). The build quality of the board is superb as are the components used and at the price its a complete steal. I have since purchased another KK2 1.5 as well as a KKmini. The primary advantage of the KK boards are their ease to setup, with the LCD screen and buttons they are easy to setup and tune on the fly without the need for a computer.
The Naze32 and other cleanflight/baseflight based FC's are harder to setup requiring a computer and a means to connect the FC to the computer. This also makes the boards impossibly hard to tune on the fly. The advantage of the Naze32 is that it is more customisable, CAN give higher performance (with the right setup) and is more compatible with other software and hardware (such as FPV, GPS, and OSD systems as well as software like Oneshot) which for me is the only real advantage of a cleanflight system.
The way I think of KK2 vs Naze32 is like apple vs android. The KK (like apple) is user friendly, sturdy, well built, reliable and very powerful (unlike apple however it is also very cheap). The Naze32 can be more powerful when used and setup correctly but is a lot more complicated to setup, It also has a bunch of optional add ons to better suit your needs.
Of course there are other boards, a lot of them similar to the Naze32 (please don't hurt me =3) in the fact that they use the same software and similar hardware. I just chose the KK2 and Naze32 to compare because they are, in my opinion, the most common boards.
Step 24: Preparing the Receiver
To prepare the receiver to connect it to the KK2 I got my receiver and super clean wire and started modifying them.
I removed the plastic housing from the transmitter to reduce bulk and weight. I then had to cover the now exposed receiver in clear heatshrink to stop anything shorting and to make everything a little more robust. I also filled the antenna end of the heatshrink with hotglue to make it even more robust and because I was afraid that the solder joint on the base of the antenna would fail.
Next I took the super clean wire and ripped off three of the wires (we only need 5 signal wires, one of which will be in connected to a ground a positive as well). I ripped off the black, white and grey so that I was left with a very bright rainbow of colours. I then proceeded to cover all of these colours in black wire mesh and black heatsink as I did with everything else. You can then use the super clean to connect the KK2 to the receiver by joining all the signal pins of the KK2 to all the signal pins of the receiver (just match the aileron to aileron, elevator to elevator, throttle to throttle etc.). The last signal wire (with the ground and positive wires as well) can be connected across the power rails for both the KK2 and the receiver to provide power to the receiver.
Step 25: Preparing the Transmitter
The transmitter can be used straight out of the box (after installing 8 AA cells and binding the transmitter to the receiver) but I did a quick modification to better suit the transmitter to my needs. The problem I had with the T6a transmitter is that it ate up my AA's so quickly (especially if you forget to turn your transmitter off). To combat this problem I took a XT60 connector and soldered two wires to it (they don't have to be too thick because they don't carry much current, they only need to be as thick as the original wires from the batteries to the circuit board). I then soldered the exposed ends of the wires to the first and last contacts of the battery array where the original wires to the board are soldered. I then cut and filed a hole in the back of the transmitter where the batteries should go in such a way that I could still place the AA's in if I decided not to use the lipo. The XT60 can then be placed inside this hole and epoxied in place.
With this lipo mod in place I can forget to turn the transmitter off, leave it on overnight and it will still be on (with very low battery) the next morning. Don't do this on purpose though because leaving the battery on overnight could over-discharge the battery, raising its internal resistance to an unusable point as explained in step 4.
Step 26: Preparing the Tail Servo
The tail servo is one of the most important parts of a tricopter as it will passively keep the tri from pirouetting (like the tail motor on a helicopter) and it will control your YAW (again like the tail motor on a heli). For this reason we want the tail servo to be strong (metal geared) so that the gears don't strip in a crash and you want the servo to react quickly to inputs (digital servo). It controls the YAW by turning the 50mm section of the tail boom that we kept loose on the bearing on which we will also mount the tail motor (refer to the "What is a tricopter" step for more details)
Preparing the tail servo is a simple operation, I cut off the mounting point on the side of the servo farthest from the horn and the wires and sanded the side flat. This will allow you to more easily mount the servo flush with the booms. You can then take any horn that is long on two sides and secure it on the output spline with the supplied screw (make sure your servo is centred first, you can do this with a servo centring tool, connecting it to the KK2 when its powered on or like me, manually by testing the range of motion on each side). I then gave the servo my black heatshrink and black wire mesh treatment with 5mm heatshrink and 3mm mesh.
There are plenty of other tail servo choices but if you want to use one not mentioned here try find one that is digital and metal geared. In my experience, I doubt the tri will not benefit from either a high torque or high speed servo. Some other choices include; Probably the most common, reliable tail servo, the BMS-385DMAX, and my old tail servo the Corona 919MG. While the Corona may look like the ideal choice, it had a single, sacrificial, nylon gear (that I cant find where to buy) that stripped on one of my first few crashes, other than that it is an incredibly reliable, fast, strong and cheap servo which makes the fact that it has a nylon gear even more disappointing. My current tail servo, the Turnigy MG90S is extremely cheap for a digital, metal gear but because of this fact it does have a lot slop. Other than that, it has lasted many crashes in my old direct drive system around three of which broke the rest of the YAW mech while the servo remained pretty much intact.
Step 27: Preparing Y Harness
The Y harness is used to give power from our battery to all three ESC's. To start with I took a small length of copper pipe, cut it down the side and opened it up into a flat strip (you could just buy copper sheet but I didn't have any on hand). I then roughly drew up the shapes I wanted and cut them out with a hacksaw, finishing up the edges with a file.
Three female bullet connectors were then soldered directly to each copper piece (for a larger tri, wire can be used between the copper and the bullets but we don't need to) as well as two small lengths of turnigy pure silicone wire (as explained before I use translucent black instead of red for my hot wire to keep everything nice and black) which you can then solder to an XT60 connector (or whatever connector will plug straight into your battery). Make sure you solder the connector the right way. At this point you can also solder two female jumpers to the copper pieces to later connect to the KK2 so that it can read the batteries voltage further on down the track. Place heatshirink over all bullets as well as a liberal amount on each copper piece (you really don't want anything here shorting because you will be directly shorting the battery). I used electrical wire to prevent the copper shorting as I found it difficult to apply the heat shrink correctly with all the protrusions .
Step 28: Preparing the Battery (optional)
For my first two tricopters I used a 3 cell 2200mAh battery (25C). These batteries gave me plenty of flight time but not as much punch as I would have prefered. When I accidentally left one of my batteries connected to the quanum telemetry voltmeter and two of the three cells depleted to less than one volt each I saw this as an opportunity to make myself a four cell battery with more voltage for bigger punch by adding the good cell to one of my other three cells. The other thing I ended up needing to do is add a female jumper and strip the hook from one side of the original balance connection. This allows me to plug all the necessary wires into a balance charger for balance charging. This step is completely optional but If any of you want to do a similar thing to your batteries I would be happy to help. Otherwise you could just buy a four cell battery.
If you do decide to open up your lipo make sure know exactly what you are doing. Also make sure to cover any exposed contacts whilst soldering because the last thing you want is for your soldering iron to short with another contact, igniting the battery while you are holding it and a very hot soldering iron.
Step 29: Preparing the Switch Servo
The switch servo will be used to operate our fireball shooter (one side for one fireball the other side for the other).
To make the switch servo I started out with the famous HXT900, took some double sided tape (preferably foam tape as you want a little bit of foaminess) and stuck it on one side of the servo as close to the top of the servo as possible. I then lay a layer of aluminium (or aloominim for all you Americans =3) over the exposed side of the foam tape and cut it to size. Repeat on the other side.
You have now made the pads that the next part of the switch will contact to turn the device we connect on and off.
Step 30: Preparing the Switch Servo Part 2
Using a lighter I bent the servo horn into the shape shown (a sort of C shape). This step is not necessary but will provide extra support for the paper clip later on.
To make the second half of the switch I took a paperclip and bent it as shown to fit "inside" servo horn we bent earlier. I then superglued it in place and attached the whole horn assembly to the top of the servo
Because (as i mentioned before) I really like black, I coloured the whole servo black and added black heatshrink and wire mesh (once again colouring the signal side of the servo connector silver for ease of installation). In hindsight it probably would have been easier to spray paint the servo before modding it and use a black horn but everything worked out in the end.
Step 31: Preparing the Switch Servo Part 3
We can now solder the black wire from the AAA battery holder to the paperclip. After the next step we will also need to connect the two wires from the ends of the glow plugs to the pads with tape (make sure that the tape doesn't get in the way of where the paperclip will make contact with the pads).
You can also use a proper receiver operated switch such as this one which will fit easier into your frame and would make your tricopter a little lighter (but wheres the fun in that =P)
Step 32: Preparing the Fireball Shooter
To prepare the fireball shooter we first take two 50-100mm (mine are 65mm) lengths of 12mm aluminium tube. I then sanded them with 100 to 600 grit abrasive paper in preparation for polishing. One end of each tube was rounded inside and out with needle files to avoid cuts when loading (and to make it look a little nicer). I then took two 1/4x28 locknuts and filed the tops off them in order to get to and remove the nylon ring because (as you can see in the photo) it will melt from the heat (If you find normal 1/4x28 nuts you can epoxy them right onto the tube but the only normal ones I could find were 10x as expensive as the locknuts). I then epoxied the nuts to the ends of the tube as well as epoxying the two tubes to themselves. I mixed some metal shavings with the epoxy to help it blend with the aluminium (aluminium shavings would have blended better than rusty steel shavings). The shavings do make it a little harder to work with the epoxy so i recommend mixing it in AFTER you have thoroughly mixed parts A and B.
As you can see, the glowplugs can now be screwed into the nuts. A glow plug receivers power from its little tail thing and from the threads. The red wire (or black, they are interchangeable for this purpose due to the construction of the glow plug) has to make contact with both glow plugs threads so to do this we make an electrical connection between both 1/4 nuts (I just did this with half of another nut soldered to both 1/4 nuts) and then we can solder the red wire from the battery holder to any part of the nut assembly (I just soldered it to my connection to keep everything symmetrical). I ended up replacing the solid connection from the battery to the nuts with a male and female jumper connection to make the whole barrel assembly removable for easier loading. As you can see, the battery should now connect to both the paperclip on the servo and the nuts on the barrel.
The last connection we need to make is from the pads on the switch servo to their respective glow plugs tail things. To make the glow plugs replaceable (they wear out pretty quick because of what we are putting them through) I did not solder the wires directly to the glow plugs tails. Instead I made a loop of exposed wire and soldered that together. Then I placed the loop over the tail of the glow plug and gave it a couple more twists to get everything nice and tight. I then covered the connections in black heatshrink.
Step 33: Assembling the Frame
To assemble the frame I took the two main plates, the side booms and tail boom as well as eight 25mm M3 bolts, eight M3 nuts and 12 M3 washers (I didn't use washers where the bolts would eventually end under the KK2 so that I could fit more of the junk I wanted to hide underneath the KK2). I then assembled the frame as shown using blue loctite on any metal to metal connections. Make sure not to make the stopping bolts for the folding arms too tight otherwise you wont be able to fold the arms out fully. I also strung four pairs of zip ties around the bolts that hold the tail boom in place (this is easier to do before sliding in the tail boom and tightening everything down). I also placed the four bolts to hold the KK2 in place (also M3 25mm) through the frame because they are incredibly hard to add after the ESC's have been tightened down.
Step 34: Attaching the Side ESC's
The ESC's can then be passed through the zip ties. As long as you crisscross the zip ties first the ESC's are actually really really secure in this setup. The ends of the ESC's that connect to the motors face toward the side booms and can at this point be bent slightly outward. The ends that connect to the battery can be passed around the back of the frame to prepare for connection to our custom Y harness
Step 35: Attaching the Rear ESC
The two side ESC's can now be plugged into our Y harness (making sure that the ESC's are not plugged in backwards). The signal wires of each side ESC can now also be passed around the back of the frame and between the four posts that the KK2 will rest on. The ferrite rings should sit out the back side of the KK2 while the ends of the wire should stick out the front end of the tri, this will keep everything clean and tight in a crash or just through normal use. The rear ESC is then placed in the centre of the KK2 posts with the outputs sticking out the back and the battery wires wrapped around to point toward the the rear so that you can connect them to the Y harness as well. The signal wire of the rear ESC is then placed in such a way that the ferrite ring is also held secure out the side of the KK2 board with the ends sticking out the front along side the ends of the two side servo wires.
Step 36: Attaching the KK2
Because our build is pretty small, everything needs to fit tight. Because I did not want to chop everything to an exact length so that I could use everything on later projects we need somewhere to hide all of our loose wires. Because we still want our tricopter to fold, the area between the two plates is not as viable an option as with a standard quadcopter. To get around these problems I simply stuffed everything I could under the KK2
The posts for the KK2 to be mounted are set up with spacers to keep the KK2 as elevated as possible (so that we can fit our junk underneath it). I personally used a thick washer, M3 nut, meccano spacer and a rubber grommet to get the board to the correct height. In any case, a rubber grommet is a must to help avoid vibrations screwing with the KK2. The KK2 should be mounted with the buttons at the back and the big white arrow facing the front of the tricopter. Be careful not to put your KK2 too high otherwise we wont clear the propellers
The KK2 is then placed over everything we did in the last step. The Y harness and all the ferrite rings as well as the ends of the signal wires should stick out the the sides of the KK2 otherwise you make not be able to get the KK2 resting on the grommets. This is where the foam we placed on the back of the KK2 in one of the previous step comes into play to avoid shorting the KK2 on anything underneath it such as the large heatsink from the ESC.
The signal wires can then be connected to the KK2 as per the motor layout (output one is for the left motor, two for the right and three for the rear. Output four will later be connected to our servo). Remember that the power from the ESC's BEC's only has to be carried to the first and second outputs which is why the third output only has a signal wire. (the servo will still needs all three wires as it is TAKING power from the rails rather than supplying it).
In the last photo you can see where I have plugged in the jumpers from the Y harness to the KK2. This will allow us to read our batteries voltage directly off the KK2's safe screen and will also let us use the KK2's buzzer (or in my case chirping thing) as a low voltage alarm so we know when to land.
Step 37: Securing the Tail Servo
(all photos of this step are as seen from the bottom of the tri). Because the carbon fibre is hard and slippery it is very hard to secure things to it with zip ties (compared to wood where the zip ties really bite into the booms). If we want to we can just use double sided foam tape as something for the zipties to grip but that will leave a tacky surface on the outside which will collect dust and other gunk we don't want on our tri (and its not black). Instead I took normal double sided tape, lay it around three sides of the end of the 100mm length of carbon fibre closest to the end and lay a strip of foam around that (this is essentially single sided foam tape). The tail servo was then secured to the end of 100mm length of carbon fibre with two pairs of zip ties (in opposite directions for maximum strength). The wire from the servo can then be fed up to the KK2, I passed the wire under the KK2 a couple of times to keep the build clean and the wires out of the way of the props.
Step 38: Connecting the Servo Horn to the Tail Boom
The servo horn can be connected to the tail boom with proper linkages but because we have two points of connection (one on each side) only one side need to pulled at any one point in time depending on which way the servo is turning, the horn never actually needs to push the boom. This means that we really don't need our linkages to have any compressive strength. Because of this, in reality we could actually connect the servo to the boom with two lengths of fishing wire (which I tried but I could not get the fishing wire tight enough). Instead of fishing wire I ended up using two lengths of thin metal wire (nichrome in my case but anything strong and thin will do). The metal wire was ideal because after it was installed it could be tightened to the desired point by further twisting the wire.
Step 39: Attaching the Motors to the Booms
The motors were attached to the booms in a similar fashion to the servo (again, I did get a friend to model a mount that I did not end up using so if you do use it please show us). This time, instead of laying a large strip of foam around the boom I used little pieces of foam with double sided tape on the back (single sided foam tape if you will). Im sure you could buy this stuff but it works just as well if you make it. These pieces were then secured to the boom where they were needed and the motor mounted on top with two zip ties again facing in opposite directions. The reason I did the foam tape slightly differently to the servo mounting is not because one is better than the other but because I just wanted to try both methods and so far they seem about the same.
The tail motor was done in exactly the same fashion as the other motors.
You can now connect each motor to its respective ESC.
Make sure you remove your props before adding your motors to the boom for safety reasons.
Step 40: Attaching the Receiver
To attach the receiver I first connected the receiver to the KK2 with our modified super clean wiring. I then twisted the wiring around for aesthetic reasons as well as to keep the wire out of the way of the props. The receiver was then mounted to the front of the tri with regular double sided foam tape.
The antenna was then attached to one of the side booms with a rubber band.
Step 41: Securing the Battery to the Frame
The battery is secured to the frame using a single small length of double sided velcro strung between the two plates of our frame.
Adjusting the centre of gravity. Because the battery is most likely the heaviest mass in your tricopter it is essential in the correct balance of your tri. The tricopters centre of gravity is correct when if loosely held at the middle of the KK2 (where the centre of all three motors would be) it does not tip forward or backward (it should be balanced left and right due to its construction). To adjust the centre of gravity we can simply slide the battery slightly forward or back. This is very helpful later on when we want to add heavy equipment such as FPV gear, gopros or fireball shooters which would otherwise throw the whole tri out of balance .
Step 42: Preflight Adjustments
Always turn on your receiver before plugging in the tri. To turn on the tri simply plug the battery into the XT60 connector from the Y harness. The power should run from the battery, through the Y harness to the ESC's whose built in BEC's will take our 11.1 volts and turn it into 5v for the KK2 and receiver. The power from the left ESC (connected to the KK2's first output) will provide power to the KK2 and receiver rail which will then give power to the receiver (through our super clean wiring). The BEC from the second ESC will power the rest of the output rail including the servo. If everything is right, your KK2's LCD screen should light up and all three motors should beep when the tri is turned on. The servo should also snap to the middle and hold there until you go into the menu.
Before you try throttling up there are a few settings that you can fix already. First, go into the KK2's menu and choose "Receiver Test". Then adjust your transmitters trims until all of the variables read "0" (the auxiliary channel can read anything). Also make sure that when you bump your aileron left, the channel reads "left" and when you bump it right it reads "right". Do the same for your elevator and rudder channels. If they don't read the right ways you will have to reverse whatever channels are wrong on your transmitter. Then bump your throttle stick fully up and the throttle channel should say "Full". If not you will have to adjust your transmitters end points. When bumped fully up/down or left/right, your aileron, elevator and rudder channels should read between 90 and 100. If not you will have to adjust the end points for those.
Now we will want to go into "Load motor layout" and load the tricopter configuration. You can now also check that all of your motors and your ESC are plugged in the right way.
We also want to go into the "Mixer editor" menu in the KK2 setting, go to channel four and change the rate from low to high. A low rate is only used if you want to use an analogue servo but we have a digital servo so we can bump the rates up to high for faster response. If you do this with an analogue servo you will most likely fry it which is why it is set to low as a default.
You will also want to calibrate your KK2's sensors so that it knows when it is level. To do this, place your tri on a level surface and choose "ACC calibration" in the KK2 menu. The KK2 will then calibrate for 5 seconds and you will be ready to go.
Step 43: Testing and Correcting (without Props)
Before you attach your props there are a few things you should test by throttling up without your props on.
First up, make sure your motors spin the correct ways. The front two motors should spin inwards (left=clockwise, right=anticlockwise). If they don't spin the right way you can just switch two of the wires from the ESC to the motor (they can also both spin out but I have always been told to make them spin inwards, if anyone knows the reason why I would be happy to learn). The rear motor can spin in any direction just make sure to use the correct prop (I usually make it spin in the direction I have the most props for so that if I crash a bunch I can keep quickly replacing the props).
Next we need to make sure the motors react correctly to the sticks, (make sure your sticks are working properly in the "Receiver Test" menu first otherwise things could get confusing). First bump your aileron stick left and make sure the right motor throttles up and the left throttles down (with the props this would make the tri roll left). The opposite should happen when the stick is bumped right. When the elevator stick is bumped up the back motor should throttle up and the front two should throttle down and when the elevator stick is bumped backwards the front two motors should throttle up while the back should throttle down. If any of these are backwards you have probably plugged your ESC's into the KK2 wrong. Check that your motor layout matches the motor layout in the KK2's "motor layout" menu option.
The rudder is a bit harder to see. Looking from the back of the tri, when the rudder stick is bumped right, the servo should pull down on the left side pulling the tail motor to the left. With the props on this would pull the whole back of the tri to the left ultimately spinning the rest of the tri right. Its hard to imagine now but easy to see once the tri is off the ground.
The last thing you want to check is how the tricopter reacts to being pushed around. Turn your auxiliary knob until the KK2 is in self level mode (you can check this on the home screen). Throttle up again and try tilting the tricopter. The motor that you push down should throttle up (when the prop is on this would push the tri back to level.). You also want to try turning the tricopter. The tail servo should tilt the tail motor the opposite direction to the way you are turning it, it will look like the tip of the tail motor is trying to stay in the same place (when the prop is on this will pull the tri back the way its original position). If Your tail servo moves the wrong way you will have to go into the KK2's "Mixer Editor", go to channel 4 and change the rudder value from 100 to -100 (or vice versa).
For any other problems refer to the KK2 user manual (or google)
Step 44: Attaching Props
The props are normally secured to the motor exactly how you would expect, with a couple of washers and nuts/locknuts. In our case however, our props will pass right above our entire tri including a bunch of wires. For this reason I have placed the prop higher on the shaft through the use of a couple of spacers. Because at least one of our motors will be spinning in such a way that a nut would fly right off it we really need to tighten down our nuts. Unfortunately, tightening your nuts down too much will push the bell of your motor down to a point where it will start rubbing on things, making it inefficient and even completely stoping it in some cases. If you want you can cut all of your shafts down to your preferred height and use a locknut to secure the props tightly. If I had done this however, I never would have been able to use the spacers I am using for this tri because my old tri's didn't need them meaning I would have cut my shaft a lot smaller. The way I secure my props and nuts is by using two nuts. The first nut tightens down onto the prop reasonably tight (not too tight) and the second nut can be tightened down onto the first nut as tightly as you want. Remember to threadlock all metal to metal threads. Just using one nut and some threadlock would probably work too but using two nuts is only a little extra effort for a lot of added security.
Step 45: Testing With Props
You can now test with your props on. Power up your tri and receiver then place the tricopter down on a hard flat surface (tall grass and dirt will get in the way of props so try avoid those ground types). Arm your tricopter by pushing your left stick to the lower right corner for a second or two should arm your tricopter. You can now attempt to take off. I suggest turning your tricopter off self level mode when you first take off because otherwise the tricopter will constantly be trying to go a way you may not want it to making it extremely difficult to take off whilst remaining level. Many people (including myself) suggest to just never use self level mode... ever. All it is is a pain in the arse, constantly fighting everything you try to do. Yes it limits the amount of corrections you need to make and its a little easier to learn but to be honest it will only take you an extra 3 batteries to learn to hover with self level off and you will end up having a lot more control over your tri. Once you are up you can follow flite tests tutorial on learning to fly a multicopter. If you are having trouble you can look up a bunch of other beginner exercises or leave a comment here and I'll try to help.
It doesn't matter if you have already flown multicopters before or if this is your first take off a couple of things can still go wrong. If your tricopter flips, you probably have the ESC's plugged into your KK2 wrong or a motor is spinning backwards. If your tricopter pirouettes on take off you will have to go into the KK2's "Mixer Editor", go to channel 4 and change the rudder value from 100 to -100 (or vice versa). If something else goes wrong, comment here and/or try a quick google search.
Step 46: Adjusting PID's
Just follow this helpful video
Step 47: Attaching the Fireball Shooter
I'm really sorry I couldn't find a clear way to explain this step but I will give it my best try. If anything here is confusing just leave a comment and I'll try clear things up.
The AAA battery holder is secured to the frame near the KK2 with double sided tape. The servo has been mounted upright on the receiver making sure there is enough room on either side for the horn to turn. The wire from the servo can also be plugged into the second auxiliary port from your receiver. If all goes well, when powered up, you should be able to control the switch servo with your left auxiliary knob
Basically, the positive lead from the AAA goes to a male jumper which will later attach to the female jumper connected to the nuts on our barrel. The nuts will then make an electrical connection with the glow plugs connecting our positive to the walls of the glow plug.
The negative lead from the AAA goes to the paperclip of our switch servo, The two wires from the glow plugs will go to the pads on either side of the switch servo. When the servo is turned one way the paperclip will touch one of the pads making an electrical connection from the negative of our AAA to the tails of our glow plugs.
Step 48: Loading the Fireball Shooter
First up we will want to dry our flash paper. It is shipped wet to avoid spontaneous combustion so we have to dry it in the sun before we can use it (it seems obvious but please don't try and dry it over a fire =P). To load the fireball shooter we will first need to prepare the ammunition. To do this I take my ground sparkler powder and place some in the middle of a small section of flash paper. The flash paper is then rolled into a tight ball, the tighter you can get it, the harder it will be for air to get in, the further the fireball will fly.
The ball is then pushed into one of our barrels with the end of a scalpel, pencil etc.. We can then roll two small fuse out of thin strips of flash paper and place them inside each glow plug making sure they make contact with the platinum wire. I explained a little more about the hot part of the wire as well as loading in my "Fireball shooting harry potter wand" Instructable.
The glow plugs and fuses can then be screwed into the ends of the barrels making sure that the fuse touches the main ammunition. The fireball shooter is the secured to the frame with velcro. The glow plugs fit snuggly between the two plates giving the fireball shooter a nice angle and securing it further.
When you are ready to shoot (ie. tricopter on, transmitter on and ready to take off) you can plug the jumper wires together from the AAA battery to the barrel to "arm" the fireball shooter.
Step 49: FIRE!!!
With the tricopter turned on, the fireball shooter connected and your receiver in hand you can arm your tricopter and take off. To shoot your first fireball you will have to turn your left auxiliary knob fully counter clockwise and to fire the other fireball you will want to turn the knob fully clockwise.
Step 50: Final Thoughts
Some things to think about if you make one of these yourself (or when I get around to building another
1. Try find flash cotton to use instead of a flash paper fuse as pushing the fuse into the glow plug every time significantly reduces the life of the glow plug.
2. Consider fibreglassing the bottom of each plate as well as the top as folding the arms in and out is slowly eating away at the exposed MDF
3. Adding a switch where I have a male and female jumper to connect the barrel to the positive end of the AAA battery would act as a very effective safety switch.
4. Using a proper receiver operated switch instead of a home made servo switch would reduce bulk and weight and would make your build a lot cleaner
Second Prize in the