During the past few days we’ve conducted several test flights to assess ArduPilot’s ability to maintain level flight in the event of a motor loss.
Based on our experiments so far, the drone (hexacopter) will maintain level flight and control when losing any of the CW motors, but will lose yaw and enter a ‘swirl’ when losing any of the CCW motors.
A video showing CW motor loss:
(It’s a bit hard to notice in this video, but in this video we’re shutting down one of the CW motors, and the drone maintains flight very nicely. We’re also able to land and control it relatively well despite the motor loss).
A video showing CCW motor loss:
In this video, we’re shutting down motor #5, you can see that the drone will start losing yaw control, and gradually enters a swirl. We then power back motor #5 simply to avoid crashing the vehicle.
(We did a separate test without recovering the motor to make sure it’s not a matter of timing… the vehicle will indeed crash …).
Looking at these videos I’m somewhat puzzled why a CW motor loss is able to maintain flight so nicely, while CCW will fail. I would assume the motors have enough thrust since it still maintains flight with a CW loss, and therefore this is most likely either an algorithm issue, or, PIDs that needs further calibration?
Any input will be very much appreciated.
*I can also post the full flight logs for each of these flights if this can help.
Probably because of small mechanical alignment issues. Motor angles might be favoring yaw in one direction. What frame are you using?
Thank you Mallikarjun_SE.
This is a custom built frame, but we’re getting the same results with all CCW motors.
We can try it with another drone using the same frame structure, but I suspect we’ll get the same results
its hard to say with uploaded videos , please upload log file.
but in your second videos i can see a little bit oscillation before shutting down motor #5 , so maybe your PIDs are aggressive and as @Mallikarjun_SE said physically balance is very important in this situation.
also some CCW propellers generate less thrust than CW propellers , did you tested this ?
Thanks! I added below the relevant log files for each of the flights.
Log file for first video - CW motor loss, flight maintained:
Log file for second video, CCW motor loss, flight loss:
Regarding propellers thrust, I’m not familiar with this potential issue. What is the physical reason that CCW props would have less thrust?
check out RCout values , your copter is not physically balanced
poor design of propellers , i saw this issue with cheap and no brand propellers
I agree with Hosein. Your craft has a large yaw bias with all motors running and no Yaw command. This is usually from motors/props not level., twisted arms, twisted frame etc. Fix that and I suppose you will have equal authority whether a CW or CCW motor drops out.
CW and CCW motors shown in red and blue for effect but it’s essentially the same as Hosein is showing:
Thank you guys!
We’re starting to check this now and see if it helps. I’ll report back later this week, once we finish testing and see how it helps.
Hey! Really interested in this thread - wanted to see if there were any updates on the matter.
This is a really common issue for custom made frames and even other frames that come ready to assemble… It requires balancing the copter on X and Y axis and motor alignment… I have noticed this is a much lesser an issue on frames where the motor arms are angled towards center gravity (forgot the actual name for this, dyhedral?), like an s550