My 450 heli just made its maiden autonomous flight yesterday. Unfortunately, it became intimate with a tree when I apparently lost control of the aircraft. It was in Position Hold/Simple Mode for the whole flight, which initially went just fine. At a certain point, however, the aircraft started traveling in a direction other than where I was telling it. After fixing the damage, I was performing a pre-flight and I noticed that the swash-plate movement was about 60 degrees off from my cyclic control movements. The stabilize movements were correct when I moved the aircraft around, but the cyclic controls were off by a lot. I looked through the parameters looking for some sort of setting that might have gone nuts, but I didn't see anything obvious.
What's causing this to happen, and how can I prevent it from occurring again? I am using ArduCopter 2.7.1.
Replies
Thanks Randy. This crash wasn't too bad; the rotor struck a branch and the heli fell about 60 feet to land flat on the skids. New main shaft and rotors and it was good as new :) It didn't even bend the torque tube!
I have a new theory about what might have happened: Somehow Simple mode got "stuck" in one orientation, in my case about 60 degrees off from "simple forward". This happened mid-flight and persisted even after resetting the APM2 and disabling Simple mode, until I performed another compass calibration. Since the calibration, everything has been working fine.
I'm trying to find the log for this flight; I have about 20 from that day. Hopefully this was just a one-time glitch...
No, this happened last week.
I have examined the parameter files and the only differences are in the sensor calibrations:
Crash Params: Good Params:
COMPASS_OFS_X,-88.252 COMPASS_OFS_X,-93.063
COMPASS_OFS_Y,123.38 COMPASS_OFS_Y,168.221
COMPASS_OFS_Z,120.977 COMPASS_OFS_Z,136.92
INS_XH,8630 INS_XH,32072
INS_XL,-17185 INS_XL,-17160
INS_YH,5230 INS_YH,15340
INS_YL,15388 INS_YL,15295
INS_ZH,23706 INS_ZH,-4879
INS_ZL,-17380 INS_ZL,-17380
Thanks for the replies! I appreciate the credit Robert. I do have a background in engineering and programming, but I have very little r/c flight experience.
I'd like to think that I have a good understanding of how Simple mode works; I was actually having some fun flying in Stabilize/Simple before I had the rudder trimmed properly. The helicopter was spinning wildly and, despite my novice piloting skills, I could still fly just fine.
I'm using Robert's governor code on channel 8, so the APM2 was definitely armed before takeoff. Since I currently only have a 4 channel transmitter, I mapped the flight modes to the collective. With the stick at minimum the flight mode is Stabilize/Simple and it changes to Position Hold/Simple as soon as it's raised. I waited for GPS lock, armed the APM2 in Stabilize/Simple, raised the collective which activates the governor and changes the mode to Position Hold/Simple, and I proceeded to hover for about 5 minutes. The crash occurred as I was bringing the aircraft in for a landing. I told it to fly past the tree, and it flew into it :)
Troubleshooting found that disabling Simple mode did not correct the problem of the swashplate being off, but a compass calibration did. I hypothesize that GPS "jumping" combined with an extended hover and compass auto-declination caused the compass to acquire an odd calibration. I will attach the before and after parameters in case anyone wants to look at them.
crash parameters.param
good parameters.param
Yes, Rob's right of course.
Remember on a helicopter you should still "arm" the motors (throttle down, rudder full right) because this resets the barometer and also sets the heading used by simple mode.
Are you sure you know how simple mode works? I sounds like you were in simple mode when you thought you weren't, or not in simple mode when you thought you were.
Or, could be a gross magnetometer mis-calibration.