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Wobblyness and oscillations when trying to fly for the first time. [Solved]

Posted by Francisco D. on December 5, 2010 at 9:14pm

Here are two videos of us trying to get our baby to fly:

We have HK-SS20A ESCs and KDA-20-22L motors. We suspect pretty bad PID settings and we will continue to keep trying to fix the problem by tweaking the PID settings. But we wanted to know if any of you had any other ideas of what may be going wrong. Jani Hirvinen suggested that our ESCs might be of different kinds even though they are advertised as being the same or something may be wrong with them. But upon changing the connections of the control lines from the receiver to the APM the two motors that were running slower and causing the oscillations changed to another pair of motors. Also we have checked our ESC calibrations and that the motors are rotating in the correct direction. Any help would be greatly appreciated.

Edit: We FLEW!!! The problem was that we didn't have the APM + IMU properly placed on the ship!! Check here for details! :) See it fly here.

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Tags: configuration, esc, first, flight, motor, oscillation, pid, wobblyness
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Replies

  • emile December 8, 2010 at 8:29am
    It was wobbling like that for me when I had the direction of the APM wrong.
    Did you double check the direction of the electronics?!
    If you are using the RC1, it always have to point along the front arm with clockwise motors, if you are using trunk it should point in the middle of the arms for X setup and in front for + setup.

    I have a GAUI frame (much smaller than what you have) and default PID setting don't give that behaviour even though I had to lower them a little...

    Emile
  • Dean Lamborn December 6, 2010 at 6:12pm
    Double check to make sure you have the motors connected to the correct output.

    Lower the PID settings by 20%.

    It's easier to hold it in your hand when you are having problems. It isn't going to fly anyway, and you can lightly hold it and get a feel for which motor is trying to take over. Your hand can be a strong damper to a light damper as needed.

    If it looks pretty good with a light hand hold you can try a test flight.
  • Sebastian Gralla December 6, 2010 at 7:57am
    I had similar oscilations.. I switched my ESCs to I2C and the problem was gone.
  • Paul Thompson December 6, 2010 at 1:00am
    I would say you roll and pitch PID settings are way too high, drop them down a fair bit. It is safer to have a sluggish airframe to start with then to have it oscillating around violently. The two motors running at different speeds is probably APM trying to yaw the Quad in a particular direction. After the motors are armed, apply a little throttle (10-20%) and try yawing left then right until the RPM of all four motors even up. I find the motor arm sequence causes a little clockwise yaw if it is not corrected for.
  • Developer
    Randy December 5, 2010 at 9:32pm
    I guess I would first determine if it's a hardware problem or a software/config problem:
    - to determine if it's a hardware problem, swap the ESCs around - is it still the same two motors running slowly or has it changed. If it's still the same two motors then you know it's not a hardware problem. If the problem motors do change then it sounds like the ESCs (like Jani says) and I'd recalibrate them and if that doesn't work I'd get a new set.

    If the test above shows it's a software problem, then I suspect it's your PID values. The default PIDs are set-up for the default hardware so might not work perfectly for you. There's some description of the PID controls on the Flight Tips wiki:
    https://code.google.com/p/arducopter/wiki/Quad_FlightTips

    It's a bit of trial and error...I'd recommend reducing your P term down in stages (by 10%~20% each time perhaps) to see if it makes things better. If you end up with something that's sluggish but still wobbly then it starts sounding less like a PID problem and maybe it's excess vibration (but if you're using the standard ArduCopter frame this shouldn't be a problem).
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