MC rate controller: add I term reduction factor #12296
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Reduce the I gain for high rate errors to reduce bounce-back effects after flips. Up to 200 degrees the gain is almost not reduced (<25%), so this will only take noticeable effects for large errors (setpoint changes), where we actually want to have an effect. This allows to increase the MC_*RATE_I parameters w/o negative effects when doing flips (i.e. bounce-back after flips). The 400 degrees limit and the x^2 are empirical. The better the rate tracking in general (high P gain), the less this is required (because of the lower tracking error). At the same time it also does not harm, as the i_factor will always be close to 1.
Previous commit allows to increase them again. Partially reverts commit 6c3e79f.
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tested on Pixhawk4 V5 f450 mission Mode: no issue |
Tested on Pixhawk 2 Cube V3:Modes Tested Position Mode: Good. Procedure Notes: Log: https://review.px4.io/plot_app?log=bfc710a5-e8af-4218-8e55-6549738a0864 Logs: Comparison to master Tested on PixRacer V4:Modes Tested Position Mode: Good. Procedure Notes: Log: |
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This pull request has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there: https://discuss.px4.io/t/pid-tuning-for-a-small-flying-wing-47-cm-wingspan/33705/5 |
As mentioned in #11560, as a result of keeping the integrators enabled, there is a bounce-back effect after a flip, due to integral build-up. This effect is non-linear, and therefore cannot be accounted for by the existing PID controller.
So this PR adds another factor to the I gain. It reduces the I gain in cases of very large rate tracking errors (in which case the P gain should reduce the error, not the I gain). The formula is visualized here: https://www.desmos.com/calculator/3o8tfaetan. Red is the existing behavior, and blue the adjusted I gain.
Up to 100 degrees tracking error, the behavior is nearly identical. And up to 200 degrees the gain is almost not reduced (<25%), so it really only takes effect where it should, without introducing steps. In the logs I checked, the tracking error is generally around or below 100 degrees for 'normal' flight.
The result is noticeably better, and it allows to considerably increase I gains in general w/o negative side-effects.
master:
this PR:
The better the rate tracking, the less this is required (because of the lower tracking error). At the same time it also does not harm, as the i_factor will always be close to 1.
I have flown this for several weeks/months and have not noticed any negative side-effects.
Here are some logs: