One Motor Intermittently Runs Slowly?

I am having a perplexing problem with my Quad. Often when I run up the motors from an armed but stopped state, one motor runs mush slower, perhaps 1/4 the speed, of the other three. It is always the same motor, the right side motor on APM 2.0 channel 1. If I shut off throttle and bring it back up, eventually they all start correctly. It might take one try, or 10. Once running correctly everything is fine until I shut the motors off. No reset or disarm/rearm is required to get it to work, just throttle off and then back up. The radios and BECs are located on the other side of the quad, away from the wiring and ESC. All of the other motors run fine, all the time.

If it starts up with the one (right side) motor running slow and I apply more power, all of the motors spin up, including the slow one. It just doesn't spin up as fast as the others and eventually instead of lifting off the quad simply flips over as you would expect. Otherwise it flies very well and is stable in flight and hover.

It's almost like the controller can't figure out how many poles the motor has. But why only that one motor? And since have already tried replacing the motor and the controller, why didn't the problem resolve, or at least move to another motor?? Like I said, I'm perplexed.

The only thing I haven't yet done is put a scope on the ESC control signals when it is misbehaving which would allow me to compare the APM signals between the good motors and the bad one, and isolate the problem to the APM side or the motor side. I don't have a stand to lock the quad down so I can debug under power with props on, nor do I really want to get that close to spinning props. Before I do that, I thought I'd ask if anyone else has ever seen a problem like this?

Any thoughts would be appreciated.

Thanks!

Mark

Specs:

- Turnigy 2.0 carbon fiber frame from HK

- 4 BP Hobbies Cheetah 2217-9 motors, 14 poles, Kv=950, 18A/200W max on 3S 2200mAH

- ESCs: Hobby Lobby eRC "ERC035RD" 35Amp controllers flashed with SimonK's high speed FW

- Single external linear BEC to drive the ESCs (onboard BECs are disabled)

- Spektrum DX8 with AR6255 6 channel 'carbon fiber compatible' receiver,

- 3DR Telemetry Transceiver, 915 MHz

- APM 2.0 running firmware 2.9.1b Quad in a "T" configuration

- Mission Planner 1.2.59 Mav 1.0

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Replies

  • Hi,

    You don't need the scope ... just swap the positions of the plug of the strange ESC with that of a normal one on the APM (of course it will not be flyable but that is not needed).

    Does the strange behavior migrate to the other ESC --> blame APM.

    If not, try swapping around motors instead. Does the strange behavior migrate to the other motor --> blame ESC. Else blame motor.

    Regards, Soren

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