@wolke Thanks for reporting back. I’m happy to hear that you were able to improve the flight performance of your vehicle by tuning.
Just some hints that might help you to improve further:
MC_ROLLRATE_K, and correspondingly for Pitch the same, from two to one.
I usually keep it on 1 if I don’t have a tuning that’s already very good and I know that just the output range changed a bit. That’s personal preference since it just scales all the gains at once.
MC_ROLLRATE_I has now been reduced from 0.6 to 0.3
Default is 0.2 and doubling can help especially with the drift you mentioned but higher values usually have to be handled with care.
MC_ROLLRATE_P has been reduced from 0.3 to 0.19
Default is 0.15. This often works well with the usual normalized ranges and ok ESC responses. A slight increase is desirable if there are no negative side effects. Sometimes those side effects can be dampened with RATE_D gain, sometimes not. 0.3 seems like a very high value to me. The output range or reaction times or something about the vehicle would need to be special. It could well be that this was the biggest impact leading to the experienced instability.
with our slower controllers (T-Motor Flame 60) seems to lead to uncontrollable mixer behavior
Very often slower reacting ESCs lead to such problems. If not in hover flight then with step inputs or other more extreme flight conditions. You might want to give these ESCs a try: 120F3[X] — Advanced Power Drives They should provide low latency reactions and might fit your requirements. They also support digital setpoint signal over Dshot and configuration via FTDI.
But we build tools that should fly safely and not race in acro.
I heard this argument a lot of times and while it’s not wrong in my practical experience the better any multirotor flies in acro the more robust flight performance you’ll get out of it independent of the size and use case. That said I’m not talking about flips but mostly quick, predictable accurate, non-oscillating, non-drifting flight with 100 deg/s back and forth steps in setpoint.
What definitely needs to change on a large platform is IMU filtering, often a notch filter based on high rate log analysis helps significantly. And attitude control gains. When giving unfiltered diagonal attitude step inputs the vehicle should not overshoot notably and fly very predictable. Usually on larger multicopters that have good rate control tuning it’s required to lower the attitude gains MC_ROLL/PITCH_P up to half the default value. This generally has less impact on disturbance rejection than any detuning of the rate controller.
It might be helpful to set a control time value as a parameter for tuning larger copters.
We discussed at least explicit documentation for larger vehicles and possibly configuration profiles for usual adjustments necessary with vehicle size that can be used as a starting point.
switched on Airmode
Be careful with airmode. While I’d enable it on a well-tested vehicle to increase flight performance in low total thrust command situations e.g. when an efficient vehicle with large propellers is braking or simply with low thrust descend in Stabilized/Manual mode. I’d disable the feature for bring-up, prototyping and tuning flights where risk of problems is higher because if e.g. some actuator, propeller, sensor orientation is wrong or the tuning is off the drone could flip or oscillate up very quickly even with zero commanded thrust.
UAVCAN:
Our wooden test copter twin has a Canbus GPS and compass combination. (Here 3)
