Disable Roll-Yaw Coupling in Offboard-Mode

PX4 Autopilot Fixed Wing 🛩️
1

Hello,

I’m looking for ways to disable roll-yaw coupling in offboard flight mode to disable compensation for adverse yaw/dutch roll effects. I know that in acro flight mode, the parameter FW_ACRO_YAW_EN can be used, but I’m struggling to find an equivalent for offboard mode.

One approach could be setting FW_Y_RMAX to zero, but I’m not convinced this is the right solution. Additionally, commanding a 0 value for yaw_body in the VehicleAttitudeSetpoint message doesn’t seem to be effective based on my flight analysis.

Any ideas or suggestions would be greatly appreciated. Thanks!

2

I don’t think that by default there’s any sort of coupling in the control algorithm. Roll and yaw rates are stabilized independently from each other.

Only if you set FW_RLL_TO_YAW_FF to something non-zero will there be a true coupling.

What makes you think there is roll-yaw coupling compensation in your current setup?

3

Thanks for your response, @Georacer!

Unfortunately, I’m unable to find the parameter FW_RLL_TO_YAW_FF in the parameter reference.

Based on the flight test video footage, the rudder appears to move synchronously with my ailerons, suggesting there might be a mixer working in the background. Additionally, the log data shows some coupling of the roll and yaw torque values:

Plot
Plot2225Ă—1212 35.8 KB

This coupling seems to occur in level flight, so I don’t believe it’s due to the coordinate conversion from the NED to the FRD frame.

Could there possibly be some other form of automatic damping at play here? Thanks for your insights!

4

I think at this point you’d better share a log of the flight, so we can take a better look and make more educated guesses.

5

@spin the turn coordination is done here: PX4-Autopilot/src/modules/fw_att_control/fw_yaw_controller.cpp at 05672f343dab78a381d67631fb006ec352ef2c12 · PX4/PX4-Autopilot · GitHub
Unfortunately, I don’t think you can disable it with a parameter. However, you can comment out this line and re-compile the code if you want.

6

@bresch Thanks a lot! This is super helpful to know where it is coming from!