Tricopter V1
This project was the result of a series of failures with planes. After repeated designing, I couldn’t figure out why my planes favored the ground instead of the air- I eventually discovered that most of my designs ended up being underpowered or tail heavy, and I couldn’t fix them before repeated crashing. In frustration, I turned to different aircraft; multirotors. To keep costs as low as possible, I built a tricopter. I don’t have the resources to take apart the tricopter and rebuild it, so the pictures are of the finished tricopter rather than each step. However, I will give you all the details you need to build your own. If you want to build a quadcopter, this will probably offer you some help as well.
Materials:
The Frame-There are nearly unlimited options for the frame. Each has a specific advantage over another, but if you’re new to rc, I’d suggest going with wood. Here are the advantages of various frame materials:
Wood– probably what you want to go with for your first tricopter. The best size for booms is 1/2” or 10mm square dowel, which you can get at your local hardware store. Wood is cheap, strong, and light. It’s easily replaced and easy to set up for the tricopter. Also, wood tends to absorb some of the vibrations that come from your motors and propellers. However, if you do crash from higher than 10 feet or so, a boom does tend to break.
Aluminum– If you can find 1/16” tube stock at your local hardware store, then you might consider using it for booms- it is probably the strongest for its weight. While you’re at your local hardware store, you might also want to see if towel rods are cheaper or lighter. They’ve been used with great results as well. However, aluminum tends to carry vibrations right back to the control board, so finer tuning of motors and propellers is necessary. They likely won’t bend or break in the event of a crash.
Carbon Fiber– Although very expensive, carbon fiber does have its benefits; it is very strong for its weight. It does have fibers, however, that in time could separate or fray, ruining the frame. I’d suggest gaining some experience flying 4 channel planes for a while before investing in a carbon fiber tricopter frame. An advantage of a carbon frame is the extremely low weight and vibration dampening.
3d printed/ CNC cut/ store- bought frames– can’t really argue with them. If you have the resources, go for it.
Frame plates– Light plastics and plywood that is rigid works best for the frame plates. I can vouch for the durability of 1/8” polycarbonate and 1/8” inch plywood. After working with these plates, I’d suggest going with 2 or 3 Light ply. 1/8” might be overkill. I’ve crashed far too many times- without anything happening to the plates.
Now to the electronics- you’ll spend most of your time fiddling around with electronics. Here’s what you’ll need;
Motors: Choose a motor that has about 700g of thrust, and draws about 10 to 15 amps. The lower the better-you’ll be lucky to find powerful enough motors that draw around 10 amps. As long as they’re easy to work with, and you can find propeller adapters for them, they’ll work. You’ll need 3 of them.
Speed Controllers: You’ll need 3 high-refresh rate speed controllers. Most commonly used are Turnigy Plush, but most speed controllers work. Make sure you get connectors for the motors. You won’t need connectors for power unless you want to use them for other applications- you can just solder them together.
Propellers: While getting the highest quality Carbon Fiber propellers, may enhance performance, their benefits are not worth the cost when starting out. You will crash at first, and the first things that break are propellers. Get cheap nylon ones at first, and if you really want carbon fiber ones, wait until you’re comfortable flying.
Propeller adapters: these allow you to attach your prop to your motor. You’ll need three. Make sure they’re the right size for your motor shafts.
Battery: 2200mah 3s or higher, based on your motor’s requirements. My tricopter gets around 14 minutes or higher. Make sure you know how to take care of your battery and charge it correctly.
Tail Servo: Unlike quadcopters, which use the torque of same-rotation propellers to yaw, tricopters require a mechanical function to do this as they have 3 rotors. You can use same rotation props on a tricopter for this reason, but not on a quad.
The servo on the back boom pivots the platform that holds the motor, thereby vectoring the thrust to yaw. Metal gears are a must. I started out with a plastic-gear servo, and I stripped about 4 before I realized it would be much easier to have just started with metal gears.
Control Boards: I used a cheap one, but you can use any one that supports a tricopter. There’s no reason to buy a super high-quality board if you’re just building a tricopter for flying around in the backyard. However, if you want a gps enabled multi-function board with multiple sensor inputs, go for it.
The Build:
Start with the frame. If you buy a frame, this skip this step; you’ll likely just need to put it together. Whether you’re using wood, aluminum, or something else, you’ll need to cut down your booms to the appropriate size.
Front two arms: The front two arm lengths I used were 11.5”. A little longer would be better;the farther apart the rotors are, the more stable the tricopter will be-just don’t get too crazy, as the longer your booms are, the heavier the copter will be. Around 15 inches is about the biggest I would use. 13” booms should be perfect for most applications. Don”t go too small, either- the shorter, the less stable it’ll be.
Back arm: The defining facet of the tricopter is the back boom, which has the servo pivot for yaw control. This arm should be about half an inch longer than your other two. This is because the front arms aren’t 120 degrees apart. They’re closer to 140 degrees, which means the back arm needs a little more leverage on the tricopter.
The Pivot:
Apart from setting up your control board, this is probably the most onerous task of the build. Start by cutting a 2.25” piece of your wood. This is the pivoting plate that will hold your motor. Find the center by drawing two lines from corner to corner.
Then, drill out a .25” hole through the center. You can drill smaller if you have appropriately sized screws. The screw will be the axle on which the wood pivots. Clean it up with sand paper, or at least pick off splinters and tearout from drilling.
Slowly drill out a .25” hole lengthwise in the back boom. Measure how much your bolt extend through the pivot, and drill out an appropriately deep hole. Be careful not to split your wood.
Now your booms are done. Glue them to the plates.
Frame Plates:
You’ll need to cut out your frame plates. Since I didn’t care to make this aesthetically pleasing, I just cut out two rectangles. The top plate is a 2”x5” rectangle from Masonite. the bottom is a 3”x6.5” rectangle. The extra length is for a camera. Once everything’s glued together, you’ll need to drill out a slot for the strap that holds on the camera. If you’re using a camera with a case, you can just attach the case to the frame.
Attaching the booms to frame plates:
I did some trigonometry to spread the front arms out 120 degrees, because I didn’t have a protractor laying around. Draw midlines for the booms, and then draw lines .25” from either side, to have a reference for where the booms will line up. I used Gorilla glue to glue them down. I did one plate first, then after drying I glued on the second. After this step, the frame is nearly done. Now onto the electronics:
Preparing the ESC’s
I’d suggest picking up some soldering skills before you work with the speed controllers. I started by making a power harness with the pre-tinned esc power leads. I wrapped a strand of copper wire around the red and black bundles, which made it really easy to solder them together. remember to put the heat shrink on each bundle first. I soldered them to a short length of 12 AWG wire, which was crimped with my battery connector. One thing to keep in mind is how much wire is left to stretch out along each boom. The three motor leads on each wire should be soldered to bullet connectors. Use female for the esc wires, and male for the motors.
Preparing Motors:
Not much work involved here-all you need to do is solder on the bullet connectors and attach motor mounts. Loctite the screws which hold the mounts to the motor- they like to come loose after they’re in the air.
ESC’s and the Frame:
Zip ties are your friend. I started by zip-tying the pcb board of each esc to the booms, keeping in mind the lengths of the motor leads- I attached them a little closer than necessary, so there would be slack for the wires in case of a crash. If the copter takes a hard enough hit, the zip-tied motors will break loose, unplugging the bullet connectors from the esc’s- for this reason, I didn’t zip tie the motor wires to the frame.
Hugging the esc’s with zip ties helps to relieve some of the strain on the solder joints as well. The pwm cables from each cable should be wrapped around the frame until they are just long enough to reach the control board. I tucked the wires around some of the zip ties that I already used to hold the esc’s in place to save a few zip ties. The servo pwm cable should also be zip tied down- On my 2nd flight of the tricopter, the excessively long servo cable caught the back prop and the tricopter did a back flip. Zip ties are cheap-use a lot of them.
I zip-tied the bundles from power and ground to each other, making a neat bundle under the frame. I separated them an inch on either side to make room for the velcro on the underside of the frame that the battery attaches to. I also use a velcro strap around the front part of the frame to be sure it doesn’t go anywhere during flight.
Receiver and Control Board:
Vibration is a huge problem with multicopters- when sufficient vibration is carried to the control board from the motors, performance suffers greatly. I didn’t think it would be a big problem at first, as I did attach the board with some sealing putty I found in my garage. It worked well, but if I were to build the copter again, I would mount the board with a layer of velcro and some foam rubber in between.
The receiver’s location is not critical and it can be attached with velcro as well. As long as the receiver wires can reach the control board, it’ll be fine.
Attaching motors:
More zip ties! They break loose in crashes and save the motors. I used a small strip of gasket rubber under each motor before zip tying them down. The elasticity dampens vibrations to the booms. It also helps to have well-balanced propellers.
Landing gear:
I zip-tied 4” sections of a pool noodle to the frame, halfway between the plates and the motors. Pool noodles are great because they’re very light but they absorb a crash exceptionally well. They’re resilient and don’t wear out. The only thing to watch out for is tilting them when they’re attached to the frame. They must be even and lie flat on the ground. The most important part of any landing struts for multirotors is that they’re even- the control board calibrates gyros when it’s turned on, and if the copter is tilted one way or another, the board will bring the copter back to that position in flight.
To attach the pool noodle sections, I poked two holes through a side and zip tied through them to the frame. They shouldn’t be able to move.
That’s really all there is to the build; the next step is to trim it out in flight and set up your radio for optimal flying inputs with dual rates/expos. It took me a while to figure out, but I got great results from experimenting with control settings for a while.
I’m working on getting quality video from the tricopter, but I have recorded only a few flights with decent results. I have to straighten out some vibration issues, and then I should be ready to use it as an FPV platform.
DIY Robotics 