I am new to ArduCopter APM 2.5 and I am struggling to get it stable enough to fly. I have issues with spontaneous flipping and losing ESC calibration.  What I discuss below may (or may NOT) be an issue, but at least I can reproduce the issue and measure it with some certainty.

Setup:  + config, no props, quad and board leveled , ESCs calibrated, 11.4 VDC input from regulated power supply, throttle up one click above off, no hands on Tx.

Observed: Front and Rear motors run 9200 (+/- 400) RPM.  Right and Left motors run 6300 (+/- 100) RPM.  There is some small drift over a few seconds.  The +/- drift occurs over tens of seconds.  Randomly about every 30 to 50 seconds the RPM will blip ( I cannot tell if it blips up or down) and return to previous state.  This has been observed several times over periods of ten to twenty minutes.  There is no overheating.  There are no loose connections.  Voltage and current are stable.  I used both a laser strobe and a strobotach for RPM measurements and they agree within about 100 RPM, depending on the severity of the drift.

Here is a screen shot of the pulses going into the ESCs.  The pulses are steady and show no noticeable difference in length over time.

3690993301?profile=original

Here is a shot using the strobotach.  Neither silver lines should not be blurred.  I did not have enough flash strength to capture all discs at once and get a decent photo.

3690993308?profile=original

Question: Is this an issue or not?  I would expect all motors to run at the same RPM.

Any and all comments are welcome.

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Replies

  • Update:  My issue was resolved by programming each ESC individually without going through the APM board and then set the throttle range per ESC instructions.

    Now I have consistent start up and arming.  All motor RPMs are the same (when level) but I still get random, small RPM blips.

    IMHO trying to program four or more ESCs in parallel is unpredictable due to timing and OEM manufacturing tolerances.  In my case, while programming four ESCs, there was a noticeable difference in the start of beeping in each ESC.  This procedure needs to be simplified or clarified.

    My thanks to all who commented.  Together we learn!!

  • You can log and graph the output to the ESC in the log with the motors  log.  This would tell you if  the  esc calibration was off.    The  system  controls Yaw by varying the CW and counter Cw  motor  speed , setting the yaw pid to zero removes  this. 

     With the copter level calibrated the speed  should be  roughly equal  when level.  The logging is a good tool to see what is going on.

  • MR60
    Hello,
    What motors do you use? Because for slow flyers such as quadcopters, a normal rpm would be around 800 per minute per volt. By definition the APM is modifying dynamically the motor RPMs to stabilize for example or follow a direction.
    Instead of leasuring on a bench,did you try an actual flight to see if it flies in a stable state ?
    Are your props not sliding around the axle ?
    Maybe these questions will help,
    Cheers
    Hugues
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