Hello,
We had a recent crash of our Pixhawk quad in mid-air. It flew well for about 30 secs but then suddenly it looked like one of the ESCs or motors failed and the quad rolled over to the right. We are using Tiger Motor Air ESC 40A 600Hz No BEC 2-6s compatible with the Pixhawk and the T Motors 4006 380 kv motors.
The logs show NO brownout or software failure. CURRENT Vcc paramter shows a stable 5.1 volts in the log. Vibrations are also under the desired levels. Everything seems ok and then the sudden flip. These ESCs have a signal and a ground on the servo cable connector and we are plugging it directly into the motor outputs on the servo rail. Pixhawk has the latest stable firmware for the copter.
Could this be an ESC issue? Should we flash the BLHeli firmware on these stock ESCs.
We are attaching the dataflash log.
Replies
I would check motor/ESC #1 for damage and function. From the log the autopilot throttle up motor #1 and throttled down #2, motors #3 and #4 mirrored eachother. This is consistent with motor #1 failing.
If no physical damage is seen (scorched wires, broken wires, bad smell) then what might have happened is a motor/ESC sync problem. Reducing PID values to "detune" the quadcopter can help keep the motors from losing sync in some circumstances.
Hi Jimmy,
Thanks for your reply. The copper winding on motor 1 has broken but its hard to say whether it happened in mid air or after the crash. The motor 1 got yanked out of its socket perhaps because of its propeller and may have broken the copper winding.
We were completely in Auto mode and there was no manual control of the aircraft from the taranis.
The connections to the ESCs and motors other than that are confirmed all OK.
Can you explain a bit more about the motor/ESC sync problem? I have absolutely no knowledge about this issue and does this issue imply some kind of a compatibility issue of ESCs with Pixhawk or is it purely between the ESCs and motor since it seems to me from the log that the PWM pulses were being sent out ok from the Pixhawk? Is there a way to figure out the ESC/motor sync problem from the logs? And finally how does reducing the PIDs help is improving the sync?
After looking at the log again briefly I don't think it was a sync issue. Basically a sync problem occurs when the motor is at a low RPM and received a large throttle input. With a large motor and prop the acceleration can be too slow for what the ESC expects and they "lose sync." Sometimes the loss of sync results in a momentary stutter and things are back to normal, you can notice this sometimes with a large brushless motor on a fixed wing plane, when starting from 0 it will stutter a bit and then get going. Sometimes, however, the loss of sync results in the motor locking up in mid air, causing an unrecoverable spin and the copter falls to the ground. Even worse, sometimes the sync issue can cause a surge of current that will burn out the windings of the motor.
Based on your flight log, the inputs to the motor were rather sedated and not extreme at all. I would suspect physical failure or overheat. Some ESCs have overheat protection and will turn themselves off rather than exceed a certain temperature, so they continue to work after the crash.
Hmm. Only if we could confirm whether the copper winding on the Motor 1 came out in mid air or after landing. But I doubt if a motor of T motor quality could be damaged like that on its own in mid flight. But still it leads me to believe as well that this was not a sync issue. Funny thing we had 6 successful test flights before this one.