Tandem Helicopter PID Tuning

[frizensami (Sriram Sami)]

Thanks Rob and Bill, great points here.

@Rob_Lefebvre

This is normally due to the swashplate not being trimmed properly and/or not enough I_Leak_Min for the PID controller to be able to “auto-trim” it out.

Okay, that makes sense. Just to read that back - the I term is trying to correct the error it sees, but with ILMI not high enough, the error never closes because the I is leaking?

@Rob_Lefebvre

The problem is, DCP does not by itself give you yaw torque. It’s the thrust vectors becoming angled which gives you yaw torque. The magnitude of the yaw torque, will depend on the angle of the disks, multiplied by the collective pitch thrust.

Very good point - yaw control only works when there is thrust from collective. I haven’t seen any yaw-related issues yet, but that’s probably because I’m hovering at the same altitude using the same collective. Will keep this in mind to add.

@Rob_Lefebvre

First, the Attitude PID tuning is not nearly good enough. Particularly in pitch.

So I assume that this is because the constant offset between Pitch and Desired Pitch is quite large, >5 degrees generally? Strangely enough, while I see this effect in the logs, I’ve never seen any problems with pitch in Loiter or Alt-Hold.

@Rob_Lefebvre

Try to change the INS_ACCEL_FILT and INS_GYRO_FILT from 20 to 10.

Okay, will try this!

Generally:
I was trying to work out some of these tuning procedures with @TianChang_Yonah on SITL, and you can see Learning Arducopter Control Chain Tuning with Xplane 10 for some of what we’ve learnt. We hope to apply these lessons to tune the tandem as well.