Small, Simple, Budget Tricopter Build, V1 & V2

I got bored one night and started organizing my RC stuff, (an endless task indeed) I discovered I had just about all the parts I needed to build a small tricopter. The only issue was designing a frame... lone behold I had a quad frame with 3 good arms. No designing needed! Just had to figure out how to mount one arm off the back of it. Turns out that was super easy, just lined up the arm drilled a few holes and bolted it together.

The only other modification was the back motor had to tilt for yaw. I took 1/2 inch dowel rod and zip tied it to the top of the back arm. Mounted the motor on a small block of wood, drilled a hole through the block, and then tapped hole in the 1/2 inch dowel. Then used a long wood screw through the block, and into the dowel. The Hole in the block was larger than the screw allowing the block with motor to pivot. Then I rigged it with a servo rod and servo to get it to tilt. I do not have build pics, and only intended to fly it LOS. However once I had it built, I could not resist rigging it with FPV equipment. It was super fun to fly FPV, and the first and only flight video is posted in this article. All the lines in the video were caused by me flying on a 2.4ghz rc link with 2.4ghz video. So I decided to put a dragon link receiver on it, forgot to take the props off, and well the V1 mini-tricopter bit the bullet. The dragon link went into fail safe and copter flew across my apartment, smashing into my bicycle and breaking.

 
Since I was still not willing to buy a new frame for parts, I decided to start coming up with a new build for the mini-tricopter. I took pictures and notes of the build. It was super easy to build, its small and functions just as well if not better than the V1. Plus V2 has conventional parts that you can get at most hardware stores, making arms cheap and easily replaceable. 

So after thinking about it and figuring out what materials I had to work with, I got an idea in my mind and started turning it into a reality. I started with some 3x3inch metal erector set plates. I think I got them from Lowes, when I started building my most recent H-quad. They were in the nuts, bolts, screw, etc... section, mixed in with the drawers of bolts and odd parts. The drawer was labeled hobby parts, they got that right! They are not the lightest parts ever (34g for each plate), but they were cheap, durable and rigid.

I used the plates as a  diamond shape instead of a square, when it came to assembling the frame. I cut 3 pieces of 1/2 inch dowel to make the arms, I only needed 1 standard 36 inch dowel. 2 of the arms were cut at 25cm, and the other one at 30cm (sorry its in metrics, but I find it easier to work with). The 30cm dowel is the back arm and also used for support of the plates/frame.

Then I drew a line down the middle of all 3 dowels, from one end of the dowel to the other splitting it in half; this was a reference line, to help line up the dowel on the plates.

I started with the 30cm dowel, running it the entire length of the plate. Using the holes on the plate and the line I drew down the dowel, I was able to square it up with the holes in the plate. After lining it up on the plate, I used the holes in the plate to mark 2 spots out to dill holes in dowels. I Drilled out the holes and then used 3/4 inch number 6 machine screws with lock nuts to bolt the top and bottom plates to the dowel.

I did something very similar to the front arms.I lined them up directly with the second set of holes up from the outside corners on each side. You could use the first set, or the 3rd if you wanted, However I thought for my purposes and I wanted the CG to be on the back end of the plate; so the 2nd set of holes would be best. I lined up the dowels using my lines I made earlier, marked my holes again, drilled them out, and then bolted the on. The hardest part is drilling the holes straight through the rod. A drill press or a steady hand and a good eye helps.

147g for the main frame. Not too shabby!

The back motor needs to tilt to have yaw function.  This is where it gets tricky, but I tried to keep it as simple as possible. The back motor is mounted on a small block of wood (the block of wood is 3 short pieces of dowel. I cut them using the remaining portion of the dowel rod. Then glued and clamped them together) My plan is to run a screw through the block, and screw it into the end of the back dowel. Same setup that I used for the first version of the tricopter. I saw 2 issues with this: 1st I needed a screw that was long enough and big enough to take all the forces that would apply to it. A big screw meant great risk of cracking the back dowel. I used a simple 10x3inch wood screw, I pre-drilled or tapped a hole in the end of the dowel rod that was slightly smaller than the screw. The hole was big enough to prevent cracking the dowel, but would still keep the wood screw tight. I drilled the hole about 4-5cm into the dowel rod. 2nd issue: the back block had to pivot with little to no resistance, and also needed to be as slop free as possible. Easy solution: drill the hole through the block just slightly bigger than the screw. It allows the block to pivot on the screw, but prevents excessive slop. I also used a washer between the block and the dowel to help ease movement. Before I mounted the back block/motor I also drilled a small hole in the block, parallel with the other one, but on the outside edge of the block. I screwed in a servo ball joint ball, (cant remember the correct name right now) but that is the attachment point for the servo rod. It also will help save the servo in a crash.

The front 2 motors are screwed on the dowels just using 2 screws that are about 1/4inch long. I pulled on each motor and it held really well.


Next I set up the landing gear. I used 1 inch J-hooks. They are light PVC plastic parts, that you can get from lowes, home depot or probably any hardware store that carries PVC piping. They are super light durable, cost less than a dollar each and I zip tie them on. In a crash they absorb force, and the zip ties seem to break before the hooks or the arms. Increased durability. I can also drop the tricopter from 1-1.5 feet and it just bounces off my floor. I like them, they are cheap, light (9g each before cutting them down) and they come in different sizes (I use bigger ones on my RCexplorer v2.5 tricopter). They are pretty long to start so I cut them down to the size I desire, then mount them using the zip ties.


Next I mounted all my ESCs. I just used zip ties to hold them on. Then I mounted the KK board. The KK board needs to be lined up with the back edge of the metal base plates. If you used the second set of holes on the plate, this will line the KK board up directly over the CG. Using the plate makes it super easy to line up the board. I just used double sided foam tape, layered 4 times, and cut into small cubes to mount the board.

For the back servo I had to trim off the mounting hole/tab on one side just like RCexplorer full size copter. I used zip ties to mount it, I am currently using a simple analog 9g servo on it. It is a bit twitchy, but it is all I had and seems to work well. I have a servo rod with the ball joint hooked to the ball end on the wood block. The servo rod needs to be short enough to not hit your prop on the back motor. It is a simple easy setup that works really well. The ball joint part can pop apart in a crash, and potentially save your servo. (especially if you are using a cheap 9g servo like I have...lol)

I may have to replace the servo in the near future with a digital metal geared one. I also am considering getting  a KK2 board for it. I love the way V1 flew, and this one should fly better. Adding more appropriate advanced parts would greatly increase performance.

Then I soldered on my battery connector, with a wire harness to hook up my FPV gear, I zip tied on my camera mount, (same one I used on my quad build, check that out if you want more information on it Quad build) it was super easy to mount with all the holes in the base plates. I added the rest of my electronics, and set it up to fly. It is a great little copter, flies LOS very well, you might even be able to fly it indoors, although it is pretty quick. I had to turn the rates down to 65% to fly FPV.  I do not believe it has enough power to fly FPV with a standard GoPro. The key to keeping it agile is keeping it light.

I have it completely rigged for FPV, but I have not had a chance to actually fly it FPV. It felt more stable than V1 and seemed to have more precise handling characteristics than the V1 during test flights. So I am guessing it will fly better than the first version. The biggest issue I have found during test flights is the back servo is a bit twitchy. I think a better servo or a digital servo would stop the issue. 

V2 Parts list:

 Turnigy 2826-10, 1400kv motor (x3) $9.48ea

HK multirotor control board v2.1 (x1) $12.99ea

Turnigy AE-20 amp ESC(x3) $8.99ea These are prob not the best ESC, but they are really cheep. I am using APC 8x3.8 props, they pull 18.5amps at full throttle.I have the ESCs programmed for low voltage cutoff, which is 2.8volts per cell. I have a low voltage buzzer for my battery, it beeps when I get to 3v per cell. So I can land before the ESC cuts out 3s battery buzzer($3.99)

J-hooks (x3) $0.89ea

2: 3x3inch erector plates $2.98

1/2inc square dowel rod $1.44

I do not know what brand or type the servo is...if you want to use a cheap metal gear analog servo I would try this one Turnigy TGY-50090M($4.99)

If you want to spend a little more this is the digital metal gear servo I was considering placing an order for BMS-376DMG($15.24)

Also some miscellaneous hardware, screws, zip ties, velcro, mostly random stuff I had laying around I do not know the prices of.

Base price: about $84.50. With digital servo about 94.75. Still less than $100 for a multicopter.