Notes on making a tricopter

Making a Quad- or Tri-copter is a project I’ve been tempted by for a long time. Ever since I got an RC heli, which I’ve since abandoned. The Heli was too hard to fly, and there wasn’t much motivation to persevere — having learned, all you can really do is aerobatics, which I’m not very interested in. A quad, on the other hand, is easier to fly and much more flexible: I could add cameras, sensors, telemetry, code it to do interesting things, etc. And lots of people have done this so it’s an easy thing to Google about.

The tricopter seems the most appealing so far – interesting build, nice balance of stability and maneuverability.

Interesting things so far:

I’ll update this post with more stuff.

Design notes

Frame

I thought there would be maths (shuddder) about frame size vs prop size vs motor power and all that sort of thing, but this FAQ says the main considerations are maneuverability and stability. A smaller frame is more nimble but less stable, and vice versa.

Since I’m a beginner, a larger, more stable frame seems like a good idea. It also seems plausible that it’s a better platform to develop from: I could perhaps add bigger motors/props to increase lift, for example, without having to change the frame. (Guess).

The RCExplorer v2.6 arms are 480mm, which seems a good place to start. I think I’ll also use the frame design from RCExplorer as it’s well proven and designs are available.

Some tips from this thread:

  • Prop wash over the arms causes vibration. Try to mount the props at least as far above the arms as the prop radius.
  • ESCs (unsurprisingly) work better if kept cool. Perhaps worth mounting them in the prop wash?

Props

Not much headway on this yet. RCExplorer (again!) recommends the smallest props you can as smaller props are lighter and have less air resistance, making them more stable.

Trial and error seems a sensible approach here, as long as the prop doesn’t overwork the motor.

Control board

From this table, Arducopter seems both very functional and reasonably priced. Lots of resources for it too.

Beyond (advanced) features (that I won’t need for ages, if ever), I still don’t have a clear idea what the pros and cons of the various boards are, though. For example, noob-friendliness, ease of repairs. The KK board does have a screen to guide you through the process, which might make it preferable to start with. And it’s cheap, so easy enough to replace with something more feature-rich later.

ESCs

There are so many important bits of information in the big tips thread that it’s not really worth reproducing them here. Just go read it.

Use NiMH mode even for a LiPo battery, because the low-voltage mode engaging (to protect the LiPo) causes flips (eek).

Motors

RCExplorer uses these for the v2.5. Mentioned elsewhere too. Is 750kV enough? What are the considerations?

Batteries

TBC

Video

Not planning to do this immediately, but from reading so far, there is stuff worth noting.

Apparently, the only legal frequencies for airborne video tx in the UK are 2.4 and 5.8GHz. These are very short wavelengths with poor penetration and are limited to 10mw and 25mw respectively. This sounds totally dreadful, but people do claim that they can get decent range (up to a mile) with a high-gain antenna. A significant number of other people are (unsurprisingly) completely flouting the law. It does seem a bit OTT.

Obtaining an amateur radio licence makes no difference as they do not include airborne transmissions (out of date but probably still accurate: Amateur Radio (Foundation) Licence Terms, Provisions and Limitations Booklet BR68/F, para 2(6)). Possible exception: higher power 5.8GHz transmitters at 250mw rather than 25mw.

It seems that to stay legal you can only use 2.4GHz or 5.8GHz. My transmitter is 2.4GHz and I don’t want to replace that with an (obsolete) 35MHz transmitter. So it seems it’s 5.8GHz or bust.

Telemetry, sensors

I’ll think about these later.

Transmission of telemetry data is permitted on 433.05 to 434.79MHz up to 10mw.