So I have 2.9.1 on an APM2.5+ and have been doing some bench testing without props.

A striking anomaly occurs at low rpm/throttle, it may also happen at high rpm but isn't as clear.

If I put the stick up just enough to start all the motors spinning. Motors 1 5 7 start to speed up as 8 4 2 slow down, for those not in the loop of the motor order those sets are all side by side motors, separated by 3 and 6, which appear to maintain constant RPM.

If the throttle is low enough 8 4 2 slow down so much they stop spinning, if I add throttle they do start spinning again but definitely less than  1 5 7.  it's not a constant increase i.e. it does stop, i would say that the amount of speed gained and lost is equal, with the sum of the speeds being the same as 3 and 6.

Is this just an oddity of a non flying copter? without any changes to sensors it's 'experimenting'?

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  • Developer

    So the issue here is that your THR_MIN is too low.  When armed in stabilize mode and throttle is above zero, the motors should never stop spinning.  The default is 130 so perhaps you should try increasing it to 140 or 150.  Alternatively if you haven't done the ESC calibration step as mentioned on this wiki page then you should definitely do that.

    3 motors running more slowly than the other three is just a sign that your copter is trying to control it's yaw.  At the moment it's sitting on the ground so friction stops it's heading from changing but it keeps trying harder and harder which means slowing down 3 motors and speeding up the other three...if you put it on a rotating plate you would see the problem goes away.

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