ArduPlane: Yaw drift when using /mavros/setpoint_raw/attitude with body rates ignored (MAVROS 1.20.1)

[ufktakimi]

When publishing to /mavros/setpoint_raw/attitude using mavros_msgs/AttitudeTarget in ArduPilot Plane (GUIDED mode), the vehicle performs an unintended yaw to the right, even when:

• Quaternion is identity (w=1, x=0, y=0, z=0)
• type_mask = 7 (IGNORE_ROLL_RATE | IGNORE_PITCH_RATE | IGNORE_YAW_RATE)
• Body rates are set to zero
• Thrust is constant
• Message is streamed at 20 Hz

The vehicle does not maintain heading and instead starts yawing to the right.

Expected Behavior

With identity quaternion (no rotation) and body rates ignored:

• The vehicle should maintain its current attitude
• No yaw change should occur
• No lateral drift should be observed

Actual Behavior

• The aircraft gradually yaws to the right.
• Heading changes even though quaternion corresponds to no rotation.
• Behavior differs from direct MAVLink SET_ATTITUDE_TARGET sent via pymavlink (which works correctly).

Test Details

MAVROS Version
1.20.1

Firmware

• ArduPilot Plane
• GUIDED mode

Topic Used

• /mavros/setpoint_raw/attitude

Message Published

type_mask: 7
orientation:
  w: 1.0
  x: 0.0
  y: 0.0
  z: 0.0
body_rate:
  x: 0.0
  y: 0.0
  z: 0.0
thrust: 0.6

Published at 20 Hz with valid header.stamp.

Additional Observations

• Sending the same SET_ATTITUDE_TARGET directly via pymavlink (bypassing MAVROS) produces correct behavior (no yaw drift).
• msgid 82 is confirmed to be sent when publishing via MAVROS.
• The issue only appears when using MAVROS /setpoint_raw/attitude.

This suggests a possible:

• ENU → NED frame conversion issue
• Quaternion frame interpretation mismatch
• Yaw axis handling difference between MAVROS and direct MAVLink

Questions

• Is there a known issue with ENU/NED conversion for ArduPlane in setpoint_raw/attitude?
• Should yaw be handled differently for fixed-wing vehicles?
• Is MAVROS applying an unintended frame transformation to quaternion?

[vooon]

mavros/mavros/src/plugins/setpoint_raw.cpp

Lines 262 to 265 in b1a6f84

	// Transform desired orientation to represent aircraft->NED,
	// MAVROS operates on orientation of base_link->ENU
	auto ned_desired_orientation = ftf::transform_orientation_enu_ned(
	ftf::transform_orientation_baselink_aircraft(desired_orientation));