Step 1: What Shall It Do?
Rule 1: Brushless Motors are twice as efficient than brushed on lower power levels(under 65%)
Rule 2: More Motors means more power and more lift!
Tricopter: The little baby brother of the multi-rotor family. Its one of the easiest to build and the cheapest to build, however when it comes down to performance its motors take the most strain because they are running on a higher throttle than any of its other siblings leaving it with low flight time and low lift capabilities.
Quadcopter: One of the most popular craft in the multi-rotor family. Its a little more challenging to build and a little more expensive. The quad is only a couple grams heavier with the extra rotor but that extra rotor gives the quad a huge boost in lifting capabilities and flight time. If a motor fails though the whole vehicle will go down.
Hexacopter: In-between a quad and an octacopter. It can be difficult to build and more expensive to make and it also takes more ground prep time then the quad or the tricopter because it tends to have multiple batteries. It can carry a much heavier load than the quad can but it may require 2 batteries to achieve the desired flight time you want from a multi-rotor. Even if one of the motors fails you will just lose yaw control of the aircraft but manage to stay flying.
Octacopter: The big brother of multi rotors. It is the most challenging and the most expensive to build. It can take the heaviest load for the largest payload you want on it and can have up to a 40 minute flight time. Before flight it can require a lot of prep work as some octacopter a can take up to 4 LiPo batteries.
Step 2: Materials!
When you begin construction one of your first and main concerns is weight and most of the weight can be reduced or added by just the frame itself. With that being said depending on how powerful your motors are you can't go and grab any material because the motors can rip the material apart.
If you do go lightweight you may want to consider the box method where you build the arm out of a box shape instead of just a flat piece of material. (Round pipes is in the box family). Another benefit of the box is you can run your wires back inside the pipe leaving less exposed wires for something to go wrong.
For materials you'll also need to decide what kind of motor and prop system to use. This can often take a lot of little tweaking as you don't want props that are too big and take to much energy to spin but also not too small where you don't get enough thrust and you have to run them on a higher setting then you should.
Along with the motors you need something to control them. For that you look to electronic speed controls (ESC). They depend on how much current your motors draw (find that in the data sheet). The ESC is then connected to the battery and motor which can be controlled from your R/C transmitter.
After the motors you have to power them. For most hobby aircraft nowadays they are powers by LiPo batteries. These batteries can come in various sizes and can last from 10-30 minutes depending on the size you use for the battery. The battery I choose was a 5000mAh 11.1 volt 3 cell battery. This is one of the larger batteries that you can buy and gives me about a 30 minute flight time.
For the motors to power all of them you'll have to make a PDB. A PDB is a power distribution board that allows one battery to power all 4 motors at once.
The next step would be to select your transmitter and receiver. For any multi-rotor you need AT LEAST 4 channels. These four are for all the basic commands like throttle, yaw, pitch, and roll. Now if you want to add autonomous functionality or control LED lights on your quad then you need 5 channels or more depending on what you want to do.
The final part you'll need is the brains, the microprocessing board that controls every function in the quadcoptor from moving to staying stable while hovering. They're are many different choices for board but the one I chose was 3DRobotics arduino based micro controller with RC plane shield. This board is based off of Arduino which means that (if you want) you can modify it or tweak it to suit your needs.
If you just read all that you're welcome to go and try and mix and match parts on you're own. If not and would like some help you're more then welcome to copy my build below.
1x ArduPilot Mega from 3DRobotics ($75-200)
1x PDB power distribution board (you'll make this) ($10)
4x 10x4.7 slo-flyer propellers. (You may want get spares if you hit or break one) ($5-$15)
4x 850 KV brushless motors. From HobbyKing (many other places sell these they just tend to be in different colors, logos, and quality) ($5-$15)
4x 20C electronic speed controls ($5-$15)
1x 9ch turnigy RC transmitter and receiver ($50-$300)
1x LiPo battery 5000mAh, 11.1 volts ($10-$20) (remember this is a HUGE battery if you want you can go smaller to add more payload then flight time)
4 sheets of 1/2in acrylic (it also depends how wide you're arms are) (free - $5)
2 sheets of 1/4in acrylic (for the center tower) (free - $5)
Red and black wires ($5)
Also for this project you'll require miscellaneous screws and connectors
Because many of these parts are on the same website ill post just the link to the main website. Its for your benefit you'll be forced to read and learn more stuff about this and its less work for me ;)
The total price for what i put into this quad was about $300 for every part brand new. You can find these parts in more then one place but if you want to you can get them from where i got them. You can order most the parts online or go to a hobby store (most are overpriced!) but some things you'll have to go out and explore to find who sells them in your neighborhood like the wires and acrylic.
Step 3: Frame Design
The first thing in your design that you should do is figure out how much space you'll need in the center. Some of the things in the center can range from the ESC, RC reciever, control board, and the battery. It all depends on how you want to space out and arrange your aircraft.
For my design I used velcrow on the bottom to hold the battery attached to the tower. Next I added the autopilot and have that area around an 1/8 of clearance. Next level was where the PDB went. And finally at the top was the RC reciever. Myhe center of mine was cut out useing 1/4 inch black acrylic.
When drawing your flat arm there's three main things you need to find out when you cut your arms to make assembly easy and give yourself the best performance.
First: add the motor mount and figure out where you need to put the screws. This is one of the major things to do because even if one of the screws is a little off it can rattle the motor out completely.
Second: for the arm length give your self the propeller size from the middle of the quadcopter. Example. From the center of the tower I measure tip to tip on the propeller and that's where the motor will go.
Third: Be sure to give yourself some space when you attach the center of the quad to the arms.
For any of these parts if your doing it on the laser cutter feel free to engrave it and name it! And you can borrow some of my files that I used for my cutting.
For the drawings the "Final Arm" is for just one arm if you want to make a tricopter or an octacopter. "Final Center Tower" is the two plates that are in-between the arms and autopilot. "Top Plate" is where the PDB is help and has some decals and an easy spot to carry it from.
The files are also for a very strong arm material. I have a very rough box arm file where it just prints a box, but it has been unsuccessful with these motors because the motors are bit to powerful for it.
Step 4: Electronics
After they're soldered the next step is to make the PDB. Remember this is what powers all 4 motors. For the connections copy the connector pattern below. It's easy to follow. The one plug is for the battery while the other 4 are for each ESC. Again don't forget the shrink wrap!
Step 5: Assembly
Step 6: Add-ons
For add-on weight you have a TOTAL quad weight of about 2kg that will carry a lot of stuff and still be easy to maneuver