Uncommanded throttle peak / copter jumps 10-20cm / only once


Hi all,

I experience this behavior regularly, however not in each flight.
But it is always the same: after take off in Stabilize I switch to PosHold. A few seconds later the copter jumps about 10 to 20 cm. But only once. As you can see from the logs it seems to be exactly the same time after take off in each flight. Any idea what might be the cause?
I am not sure if this is related to http://ardupilot.com/forum/viewtopic.php?f=80&t=10155. But it seems to be different problem.

Any help is greatly appreciated!

PS: I am currently flying AC 3.2 with Jonathans fixes #1466 and #1457. However, this happens since the very fist AC3.2RCs. I haven’t tested it with 3.1.5.

That’d be the EKF kicking on in-flight, causing a step-change in altitude.

The branch I personally fly has an EKF pre-arm check and a buzzer tone to alert the user that the copter is ready to arm. Feel free to cherry-pick any changes you like out of it (I can help with that if you like): github.com/jschall/ardupilot/tree/alphatest

There’s also my devbuild branch, a subset of my alphatest branch, which has automatically-built binaries available (it should be building a version that has been rebased on master as we speak, maybe wait for the modification dates on the files to change to at least November 9th)
Source: github.com/jschall/ardupilot/tr … jon-copter
Binaries: firmware.diydrones.com/devbuild/ … on-copter/

Hi Jonathan,
this makes sense!
It is pretty scary :slight_smile: But since it only happens sometimes and only in the beginning I got used to it. Which is maybe not the best thing to do… This is why I am really happy to hear about your pre-arm check!
I saw that the 3Hz filter is also included in your dev-build branch. I’ll give it a try later today. So no need to cherry pick for now :slight_smile: Thanks a lot for offering your help!

Hi Jonathan,
I just installed the binaries from your branch.
One short note: PosHold mode seems to re renamed to Position. This was also the case with some AC3.2RC. This makes it a little complicated when using a GCS or when using the log analyzer. I’ll make some tests…

Hi again,
Unfortunately, I had no luck with your firmware:
I get a permanent RC Failsafe. On the calibration screen there are some random spikes but basically all is black. I am using a Spectrum AR8000 with a PPM encoder.
After switching back to 3.2 everything is fine again.
Any idea?
Best regards,

Hi Jonathan and all,

the problem still persists and it seems some others observe a similar behavior:
However, there are not that many reports.
Since EKF is now on by default (in master; https://groups.google.com/forum/#!topic/drones-discuss/gKjLtkItVus) it would be great if there would be a solution.
Jonathan, do you know if your pre-arm check is already in master?
I just checked and it seem there have been no further updates on you alpha and dev-build branches. Any idea what went wrong with the RC input?

Thanks and best regards,

Jonathan, I just downloaded and installed your dev build again. Now everything looks fine so far. Strange! But good :slight_smile: I’ll make a flight test tomorrow.

In several flight with Jonathan’s dev-build and alphatest branches there were no jumps. So anyone with similar problems should give it a try.

Thanks again to Jonathan!