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450 Quad APM 2.8 Throttle Issue

Posted by Neil Gates on September 13, 2015 at 9:16pm

I'm building a 450 class quad using APM 2.8 and an 8 channel PPM Spektrum compatible receiver. I've completed all the first flight calibration and pre-flight checks, including all-at-once throttle calibration. Now for the first test flight - every time I attempt to take off the quad wants to tip over to the right (starboard) side. I'm using stock Gforce Multirotor 30amp ESC's with SimonK firmware. No power distribution board - all ESC's are wired into a custom harness and JR connectors run straight to APM with center 5v wires disconnected.  

With the props off and the quad on the bench, and reviewing stats in the bottom left window of Mission Planner, RC OUT 1 and 4 show around 1100 but RC OUT 2 and 3 are around 1500 at motor start. Then as I advance the throttle, the pairs advance maintaining the same gap of roughly 400 between them. 

I thought this was an ESC calibration issue, so I swapped out the PPM receiver for a standard PWM receiver. Connected all four ESC's at once using Y cables and repeated throttle calibration independent of the APM. Then I reconnected the ESC's to APM and repeated the bench throttle test. The results were exactly the same, with about a 400 gap between sets. 

This is leading me to believe that APM is telling the port side motors to run faster than the starboard pair. I don't know why it would do this unless some other aspect of my calibration process went awry. Perhaps APM thinks it's listing to port and is trying to correct? But the roll and pitch numbers are pretty much zero out to four or five places. 

I've spent hours messing with this over the last few days, repeating calibration steps and reviewing forum discussions, and am finally at the point where I need to ask for help. 

Thank you,

Neil

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Replies

  • Richard criss January 6, 2016 at 6:52am

    Hey Mr gates has this issue ever come back with the fix you did the first time.

    Cause on my APM 2.8 I barely have enough throttle to get off the ground. And I also have spent HOURS

    looking through threads.

    • Neil Gates > Richard criss January 10, 2016 at 6:20am
      Glad you figured it out and that it was simple. You may want to go through the radio calibration process to ensure that 1500 is really the max output from your xmiter. Your other channels may not be optimized either, and doing the calibration again will help ensure they are.

      My issue ended up being the DJI knockoff props I chose to use. When I switched back to simple slow fly props my problems went away.
      GWP
    • Neil Gates > Richard criss January 6, 2016 at 10:58am
      No, after that initial problem and recalibration of the ESC's it never came back. I did have a similar problem that you are experiencing later though. But to understand your situation I would need some more info. Specifically what does your quad weigh, what size motors/ESCs are you using, and what brand/size props. Oh, and flight battery size/voltage/mAh rating would help too.
      • Richard criss > Neil Gates January 10, 2016 at 4:01am

        I  figured out my issue I had to go in the parameters and set the THR_MAX higher. Yes it was that simple.

         Well for me at least, it was at 1000 and I raised it to 1500 and it worked great!!!!!

        Thanks for your quick response on this though.

  • Neil Gates September 14, 2015 at 7:37pm
    After hours of goofing around with this and searching other threads I went in and reset all the RC1-4 trims to 1500 and recalibrated the ESC's a few dozen more times. Then finally it started working well enough to get into a hover. Hopefully it stays that way for the next flight. I've read that a few people have had trouble with throttle calibration "saving".
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