Although this flight doesn't show it, I added 3-axis stabilisation using OpenAero and a redundant KK Multicopter control board. After some messing around with the KK flash tool software, I gave up and flashed the board from a command line using AVRdude
So the last outing the 'Headcrab' had showed I had some vibration issues that may have been affecting the gyro performance... On reflection I think that the ESCs were not properly calibrated to the new motors I'd paired them with.
I wasn't very satisfied with the double sided foam attachment method for the flight controller board, so I made up a stand-off board with some scrap laser-cut plywood and used vibration damping foam to isolate it from the bolts holding the board up. Hopefully this will reduce the gyro interference to a manageable level using low-pass filtering in software. I also calibrated each ESC, just in case.
Vibration testing didn't look that much better, but I strung the quad' up to test its stability in acro mode and level mode:
This time the quad' looks rock solid at all power settings... the new Turnigy motors may be a tad overpowered :) I hope the ESCs and batteries can cope with the amps!
Batteries are on charge now. If I'm feeling brave tomorrow there may be a free-fright test :]
The 'Headcrab' quadcopter design now has an underslung battery carrier and vibration-damped camera mounting, thanks to some more laser-cut plywood from RazorLab. It's ready to fly! Almost!
But first, I needed to spend some quality time with the PID controller built into the MultiWii code. Basically, if this bit isn't right then the 'copter will be an un-flyable, rogue manhack that will not stop until it has lacerated its maker into mincemeat... or it crashes, or whatever...
PID tuning is a bit hit and miss (for me) but a nice safe way is to pop the 'copter on strings that hold it in one place and let it rotate about either the pitch or roll axis. This was working great, but I noticed that the quadcopter needed a constant pitch down input to stay level. As the throttle went up, more pitch down was needed to hold the drift in check. At this point I did the only sensible thing: put the quad away and thought about the problem for a few weeks (don't rush me!).
[Video of the gyro noise at different power settings - sad face]
I concluded that the likely cause was vibration (despite using foam tape and a big mass on the flight controller to try and damp things down). This is not a good sign. I already had concerns that the lovely body shape I'd created in Sketchup might act like a multi-modal resonator (kinda like how a guitar or violin amplifies vibrations).
Next stop is some serious damping efforts before I give up and try a different body plate design. I really wish sometimes that I could remember my lectures from university, especially the ones with control laws...
I've recently been busy building the new 'headcrab' quadcopter rather than fixing up the ol' X600 frame... The deployed frame is starting to take shape, with motors and ESCs (four yellow bits with all the wires coming out) mounted and connected up.
Here's the quad folded
The flight controller board will have a separate mounting plate that will be vibration-isolated from the main board. In addition, I've ordered another laser-cutting run to make a battery/camera mounting plate to hang underneath the quad, again using an anti-vibration mounting.
If this thing flies well and if anyone is interested, I'll put up the build steps and links to the laser cutting plans... but only if I see some comments from all three of you! :D
