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PX4 / PX4-Autopilot

PX4 Autopilot Software
https://px4.io
BSD 3-Clause "New" or "Revised" License
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[Bug] Brake twitching on huge multicopter( wheelbase >800mm) for new V1.7.2 code #8527

Closed whyscience closed 6 years ago

whyscience commented 6 years ago

Log is here: https://logs.px4.io/plot_app?log=e9e92a61-7db0-487c-99cc-ad68b171e0d7

image

image

Using the default params, the wheelbase is 800mm and 1200mm, when the drone brakes, it brakes twice or triple, as shown in the log. On DJI F450, it's OK.

whyscience commented 6 years ago
LorenzMeier commented 6 years ago

The controller goes into saturation on the outputs: https://logs.px4.io/plot_app?log=6d4f4e0d-7707-44b9-a673-057fbb2a4a15#Nav-Actuator-Outputs-Main

This is not a Firmware issue, but a tuning issue on your airframe. We have improved the control performance in V1.7 and you might need to adjust your attitude / rate control gains.

whyscience commented 6 years ago

OK, thanks.

whyscience commented 6 years ago

@LorenzMeier I still have a doubt, there is only saturation in one brake in the log. But in the video, it twitched in more than one brakes, the corresponded log didn't go to saturation. PS: only in V1.7, it has this problem, there is no problem in V1.6.5.

bokeh_plot

LorenzMeier commented 6 years ago

Your system is in marginal stability and you need to tune it. The parameter reference has some explanations, but in general familiarity with PID controllers is required.

I can see that you have not tuned the PID gains at all for your airframe and used the default gains. This will not work (it never works for any flight controller). If you fly a big drone you absolutely need to tune the control loops. The defaults only work for default-sized drones.

Tuning gain reference is here: https://dev.px4.io/en/advanced/parameter_reference.html#multicopter-attitude-control

If you do not know how to tune you can drop me an email to lorenz@px4.io and I can put you in touch with people in the community that offer commercial support. You can alternatively post to http://discuss.px4.io for help from the community.

This is not a software issue but an issue with your airframe setup, so we will not continue to analyse it here. Thanks!

whyscience commented 6 years ago

Thanks again.