Tricopter

This is the tricopter “drone” I built starting in June of 2014. I had outgrown the quadcopter I built previously, and I was enamored by David Windestal’s tricopter videos, and thought a tricopter would be a really interesting next step to explore aerial cinematography and first person view (FPV) flying. When I designed this, my goal was to design a very stable aerial-cinematography platform, and to fit the APM 2.6 flight CPU plus a GPS and gimbal. I designed the frame in Autodesk Inventor and most of the frame was laser cut out of hobby plywood at my high school. Other notable achievements with this tricopter included designing my own 3D printed 2-axis gimbal (the red components below) and dabbling in FPV flight for a time. Check out some of my videos below, and read on for some more details and photos!

I choose a tricopter instead of an improved quadcopter mostly for personal choice. I wanted to do something different than a quadcopter, and as I mentioned above, David Windestal had me convinced of the benefits of a tricopter platform. Let me explain; since tricopters have an odd number of blades, just like a regular helicopter they would spin out of control because there is an uneven amount of torque acting on the body of the helicopter. On regular helicopters this problem is generally solved by adding a rear tail rotor; tricopters solve the spinning problem by having a servo motor that tilts the whole rear motor. The tilting tail motor offsets the uneven torque experienced by the body of the tricopter and allows it to fly in a stable fashion. The tricopter’s tilting tail motor assembly gives the tricopter a unique “swooshiness” to them that is not replicated by quadcopters or other even-bladed multirotors. Essentially, tricopters have a nice “analog” motion that not only makes them fun to fly, but it gives their aerial shots a unique look.

The second reason I went with a tricopter was because there is a larger angle between the individual arms. Since a tricopter has only three arms, versus four for a quadcopter, there is 120 degrees of separation between each individual arm, compared to 90 degrees of separation for a quadcopter. This means it is easier to mount a wide-angle GoPro without getting propellers in the shot. I had trouble with propellers getting in my shot with my quadcopter, and always had some sketchy method of mounting my GoPro on the quadcopter I didn’t want to replicate going forward. I could have just mounted the GoPro beneath the quadcopter, and long landing legs, but stylistically I didn’t like that. Plus, since I wanted to have an immersive “flying” FPV experience, I wanted to have my camera mounted near the center line of the tricopter.

Finally, I chose to go with a tricopter because in theory tricopters are generally more efficient and should have longer-lasting batteries than quadcopters. The tricopter has less motors, of which spin much slower with larger propellers compared to my quadcopter, so I was hoping to see much improved battery life but I was a little disappointed by what I saw. I only averaged about 15 minutes a flight which was a bit short compared to the twenty I was hoping to see.

At the heart of this multirotor was an APM 2.6 flight CPU. I was really hoping to continue to use APM’s awesome autonomous flight features like I did with my quadcopter but unfortunately the tricopter’s tilting tail mechanism didn’t work well with APM’s software in general. I never got the GPS return to home feature to work reliably which came back to bite me when I was flying FPV in Cajon Pass and lost signal to my video feed. As a result my tricopter crashed HARD into a rock as my next photos show. I was actually lucky to find the tricopter at all, it took an hour of gut-wrenching searching between my Dad, me, and my two brothers to find the wreckage. It was getting dark and if we hadn’t found it in the couple hours of daylight we had, my tricopter would probably still be sitting out there in the desert somewhere.

In my quest to get a more capable aerial cinematography platform, I tried for the second or third time to design a 3D printed, 2-axis gimbal to stabilize the GoPro footage produced from my tricopter. As opposed to my half-hearted effort to design a gimbal initially with my quadcopter, this time around I bought a dedicated gimbal control board, the RCTimer V1.0, and I tried to design the gimbal as more than just an afterthought. The main challenge turned out to be making sure the gimbal was balanced perfectly on both the pitch and roll axes, which in retrospect I don’t think I ever did properly. I did design the gimbal so that the center of gravity of the GoPro lined up with the respective pitch and roll axes, but I didn’t account for the mechanical parts of the gimbal itself. In any case, I never got any version of my 2-axis gimbal to work reliably. I got the gimbal to work at times, but it wasn’t super reliable. At the time I had a lot of problems tuning the PID values for the brushless gimbal as well, probably because the design was unbalanced, and no amount of PID tuning could make up for an unbalanced design. In conclusion, while it was fun experimenting with a brushless gimbal for a GoPro, and I got a couple of cool aerial shots with it, in the end I never got a super successful gimbal design working.

And that is about it for my tricopter project! If you made it this far thanks so much for reading! To conclude, while I had a lot of fun with my tricopter, and while the tricopter was a super cool project, ultimately my tricopter proved too finicky and unreliable for my liking. The unique tilting tail has its strengths, but in my experience, the downsides to having an extra mechanism tilting a motor outweighed the few benefits, at least when using the APM software. I had numerous mechanical issues with the tail, and it was never an aspect of the tricopter I had a lot of faith in. Every time I took off with the tricopter there was the anxiety that the tail mechanism would fail, melt, or crack in the case of my 3D printed designs, which happened numerous times, causing a crash. Furthermore, either because of my poor tuning or because of the APM software being poorly setup for tricopters, I was never able to get a reliable GPS return-to-home capability working for the tricopter. This caused me a lot of worry and at least one crash out in the field, when I was unable to just flip a switch and have the tricopter return to me like I could do on my quadcopter. If I had to do it all again, I think I would have built a larger, more capable quadcopter or maybe scaled up to a hexacopter, or even used a dedicated tricopter control board. Still, there’s no denying I had a lot of fun with my tricopter, and I learned a lot!