PixRacer with Ardupilot

This is a discussion to focus the feedback and support of ardupilot on the PixRacer board from

We believe that all teething problems encountered are now resolved and so we recommend people load Copter-3.3.4 which is available for all multicopters through the Mission Planner's (and other GCS's) Install Firmware screens.  Note that because regular Pixhawks are still on Copter-3.3.3 the install icon may show Copter-3.3.3 but rest assured, Copter-3.3.4 will be installed (you can check the version by looking at the very top of the Mission Planner).


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                • Alt hold does not work for me at all, trying to take off it just scoots on the ground.

                  If I take off in stab and change to alt hold i have to throttle all over the place.

                  I tried to use gps functions and was not working that I could see, but i am really not interested in gps on a racer so never really said much thinking it was because of how I had it mounted.

                  • Andrew,

                    Can I ask a couple things:

                    You said "You can avoid it by doing the takeoff in STABILIZE mode and then switching to ALT_HOLD in the air"

                    Well I'm not really so sure, when I switch the craft starts to sink, i have to move the throttle wildly for it to maintain, something seems odd even switching.  Can you test that and see, maybe on a 250 or smaller quad.

                    Andrew, please if you have time play around with Acro,  I have hours of exp. in acro mode on my vortex pro, but with the pixracer it seems "off" where it just wants to plow into the ground if i go forward instead of forward, then when i try to hover again its hard to get centered.  Granted, this ver well could be my lack of knowledge with ardupilot/acro pids and it just may be that I have not set it where I am used to it on the vortex.

                    And lastly does any GPS modes work right now on the pixracer?  A couple people here said no gps functions work, same with me, but i did not see where it was confirmed by a dev.

                    I'm gonna be flying today so I can try again a few things.

                    Like always, thanks for all the hard work, you guys rock!

                  • Developer

                    Sorry for the troubles and thanks very much to Tridge and Peter Barker for narrowing down where the issue is.  Hopefully a fix will be in master soon.

                    It's all a bit of a drag that the pixracer users are basically flying bleeding edge all the time.  Hopefully we can get the official beta testing started soon.

                  • Developer

                    we've tracked down the issue with ALT_HOLD and found it also affects LOITER.

                    The issue is the new code to detect if the vehicle is landed. It doesn't start to stabilise the vehicle until it thinks you have taken off. So if there is any roll or pitch discrepancy with the vehicle on the ground then the following happens:

                    • you switch to ALT_HOLD on the ground
                    • you start to raise the throttle a bit
                    • the motors start to spool up
                    • the vehicle is leaned over a bit, perhaps due to slightly uneven undercarriage
                    • the vehicle starts to get light, but ArduCopter thinks its still landed so doesn't try to stabilise
                    • the vehicle starts scooting over the ground

                    it is easy to reproduce once you know its there. It is not pixracer specific.

                    You can avoid it by doing the takeoff in STABILIZE mode and then switching to ALT_HOLD in the air, or you can instead wait for Randy and Leonard to fix it. I'm sure the fix will be in soon.

                    The bug seems to have come in as part of the recent re-work of the AP_Motors library.

                  • Developer

                    Hi Edgar,

                    Just letting you know that I have reproduced the ALT_HOLD problem on my pixracer and I am working on a fix. I'll get back to you soon!

                    Cheers, Tridge

                • Scott, what you are saying is true. I am using the 3.4 and when I go into AltHold the only control that will work for me is the throttle moving any of the other sticks has no effect at all. Stabilize mode works ok and so does Acro. Anything that used GPS is not working for me now like I said before the GPS unit I am using is one I don't put alot of trust in so I have got a CSG on the way. So for me for now I am not going to try any GPS assisted modes until I am 100% sure all is OK it's not worth risking my new Pixracer and 250 quad.

          • Hi, did you calibrated the throttle Mid ?


            Setting Hover Throttle — Copter documentation
            • Yes..  And even w/ it being too low.. Like, at mid throttle it doesn't lift off, it still has the issue.. 

  • EKF Compass error bug

    I think that I found a bug in 3.3.4 related to EKF compass error.
    No matter how well was the compass calibration , I always got the EKF windows that had compass that become orange or totally red even if in stabilize or loiter it flew well but always had a bad EKF compass.

    The weird thing was that when I powered up the system on the table under the shed that has a steel roof structure the EKF compass was green and remain green until I move the copter a little far (1 meter) from under the shed with steel roof structure.

    If I power up the system and take off in the same place in the grass, the EKF compass error did not shows.

    So it seems that the firmware recorded the compass values when powered up and if it sees a change in compass values start to show up the EKF compass error.
    I guess that any large steel structure, car, truck , bridge etc. will cause the EKF compass error if moving the copter after power up for take off, think that people should be aware of that, never read anything about it.

    Last word, the shed with steel roof structure cause a 4° error in compass , if I calibrated the compass far from it when I get close the 0° reading of compass becomes -4°, enough to cause the EKF compass error.

  • Hard crash (firmware error ? ) , Pixracer  destroyed !

    Short story , after having done successfully Autotune (all axis) of my large H quad  with Pixracer and 3.3.4 , I was testing the flightime and was in Loiter mode, some wind .
    Since I was just up a tree I gave a full Roll stick command to move it right , the radio was on the table and I made a mistake giving in fact a full stick Yaw command.

    The copter turned 90 ° on yaw and immediately 45° on roll axis loosing Loiter control and crashed  .

    There was a short in power cables , nothing important was broken a part the Pixracer hat is dead , green led, no USb connection and the ARM micro that after a while become hot .

    In attach the dataflash log , I'm not an expert , I have not seen anything wrong, so it is why I believe it is a firmware  error.
    Never happened in 7 years of multirotors a crash like that .
    Will rebuild the copter and make some tests with an old APM, I'm done with Pixracer...

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