Jason, Gigio and I just got back from a day of test flying four ArduCopters, which is the most we've ever had out at one time. These were of different designs, with different props, motors, ESCs, batteries, frames etc. The point was to try to see why some people have great-performing ArduCopters and others have issues. We assumed it was due to hardware differences, but we needed to test to know more.
Unfortunately, the wind was around 20Mph, gusting to 30, so it was a pretty tough environment for flying. Serious stress testing! We had our share of "hard landings", but all quads lived to fly another day.
Here's what we learned (and are doing):
- Quads with the gyro filters enabled do seem to fly better, but this seems to be most obvious only if they've got vibration issues to begin with.
- Balance your props! Out-of-balance props lead to vibrations that can cause IMU errors to accumulate, leading to the "I have to hold the stick all the way over to stay in place" problem. Jason is going to put a better software filter on the accelerometers to try to compensate for that, but the main difference between good-flying quads and bad-flying ones seems to be vibration.
- While you're at it, double check that your motors and props screws are tightened down. Check them often. We had one motor fall off in flight (d'oh! It wrapped itself around the one arm on way down and pulled out a wire. need a new motor now) and one prop fly off. One of those (the former) was mine, so I feel pretty dumb about not checking.
- We've fixed that bug where the quad gains altitude quickly in alt hold at the transition between using the sonar and the baro sensor. That will be in the next code pushed in a day or two.
- Position hold ("loiter") in 25 mph winds is hard ;-). Jason is going to tweak the algorythm for that situation, where the quad has to tilt by 20 degrees just to fight the wind. That's near the max angle of tilt in the code, so if it gets blown downwind, it can't tilt further to come back. For these kind of steady-state tilts, he's going to allow it to tilt further to return to position.
- Something I learned: if you want to reset "forward" in Simple mode, just disarm the motors, point the quad in the direction you want forward to be and rearm. That will reset the direction.
Jason is going to be releasing 2.0.24 in day or so. If that solves most of these issues and passes beta testing, we'll take AC 2.0 out of beta!