Tinycopter Returns… Again!

It’s back!

Once again!

Part of the full-documentation project logging process is that everyone sees the painful and some times expensive vacillations between working and not working that a project goes through during its lifetime. This has happened with pretty much everything I’ve built and which is on this site. Usually it’s some kind of motor controller. But the most learning opportunities arise from the drift of a project about the boundary of dysfunctionality, so that’s why I still like this format over a finished and polished portfolio site.

Anyways, back to Tinycopter.

The first step of reconstruction was making the frame again – this was a relatively easy process since I still had square carbon fiber tube material remaining. The center joint was once again CA glued together. This time, I also left a little more material beyond the motors so the tube didn’t tend to split when the mounting screws were tightened.

While rummaging for hardware in a stockroom, I discovered a bin of glassware corks that I decided to turn into landing gear. I think this will work quite well – cork is pretty elastic but also very light, and not just squishy like something I’d find out of foam rubber in a similar size.

I obtained this big brick of memory foam from a disused mechanical engineering class (2.75) project. I’m going to just slap the entire electronics deck on top of a little brick of the stuff this time around. My experience with silicone tubing standoffs was less than satisfying since the tubing just tended to crack and shear with impact. Not trying to build Battlecopters here, but I’m definitely going to crash this thing infinity times, so a big surface of foam was still more advantageous.

To extract a small 2″ square memory foam block from it, I finally got a chance to legitimately use my hot-wire cutter that I built last year when I thought I was manly enough to work with pink styrofoam to build Chuckranoplan (sorry Ryan, I’m still afraid of making foamy things). The side effect of this is that now I have an asston of filet de mousse à mémoire, so if anyone else at MITERS feels like building an n-copter, it is available.

I bought a few 10A controllers from Hobbyking a few weeks ago in anticipation of eventually using them on a fresh build of Tinycopter. These things are pretty small and functional (having practically no settable parameters, not even throttle range calibration). Having flown Tinycopter using them, I also can’t recommend them too highly because their throttle appears to be nonlinear.  However, 6 dollars.

One thing I didn’t like, and which would have interfered with my mounting plans, was the big electrolytic cap that hangs off them and makes neither side very flat. This was a small ESC, and I had 1206 package 16v, 22uF ceramic capacitors left from Tinytroller work (remember that?). The electrolytic was only 100uf, so I elected to replace it with 3 SMT capacitors, making the end result very flat and clean. Maybe I could have used more, but I didn’t think the ripple currents of such tiny motors was enough to warrant it – and what I lose in capacitance I probably gained back in lower ESR since ceramic caps tend to be inherently low resistance.

So this is the plan. Superglue board to foam brick, then superglue foam brick to frame.

That’s seriously it.

I repacked the ESCs in heat shrink tubing, then superglued them to the foam brick. Ryan, is this how you build foamy planes?!!?

The tangentially located ESCs on this version allowed the wiring to be very clean and simple. It’s not nearly as big of a tangled ball as previous version, and the battery is now slung underneath the frame for easy access. Yeah yeah, pendulum effect, etc…. but on this scale, I have a feeling it doesn’t matter much at all.

And that’s it.

I ended up borrowing 2-56 standoffs from Shane again and impaled the corks upon them. The corks themselves weren’t structurally sound enough to just glue to the CF frame, so the standoffs provide a metal substrate which is directly mounted to the spare motor ears.

The Hobbyking 10A ESCs required alot of additional tuning of the controller before I got it to fly reliably. Their throttle seems to be quite nonlinear, and they are “punchier” at the beginning than the previous Turnigy Plush 18A controllers. This necessitated dropping the P and D gains down to 1.2 and 0.2 respectively, from their former values of 2.2 and 0.6! The difference between ‘slowly sinking’ and ‘slowly rising’ altitude is pretty much two left-stick ratchet clicks, which means it’s much harder to hold altitude.

All said, after some more loop tuning and poking, Tinycopter flies once more.

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