Recording thrust and torque setpoints ROS2

ROS / MAVROS / MicroDDS
1

I am currently working on doing some system identification for a custom UAV I have built and I need data to do so, specifically my inputs and outputs of the system. Inputs being the thrust and torque setpoints, outputs being position and attitude.

I am flying my UAV using offboard control with ROS2 foxy and the uXRCE_dds_client with an onboard companion computer and a Vicon system for GPS. This offboard control code is publishing to the vehicle_attitude_setpoint topic.

I can easily record the values for thrust setpoint since I am writing to them directly, as well as position and attitude thanks to the vicon. But recording what PX4’s generic attitude controller is setting the torque setpoint to is a mystery to me.

Is there any way for me to see and record the torque setpoint?
Thanks

2

Hi @R_mcc !

You have to record vehicle_torque_setpoint
This topic is not one of the defaul ones so you need to add it manually, see

for instructions.

Compile and then flash!

3

Hello!

Yes, I know I can enable the vehicle_torque_setpoint topic through the dds_topics.yaml file when building my px4 version, however it appears I can only enable them as topics px4 will subscribe to not publish to.

What I would like to do is this:

  1. Send my vehicle_attitude_setpoint command to my flight controller via publishing to the /fmu/in/vehicle_attitude_setpoint topic.

  2. Record the vehicle_thrust_setpoint and vehicle_torque_setpoint that the flight controller has turned my vehicle_attitude_setpoint command into.

Assuming I understand the way PX4 and its setpoints work? I am under the impression that at the end ALL setpoints become thrust and torque setpoints, which are then converted into PWM signals for the motors.

I am attempting to do some system identification on a vehicle I have built, and I think having the thrust and torque setpoints generated from my attitude setpoint will help me.

Thanks!

4

Or better yet, is it possible for me to record the PWM signal being sent to each motor? This would be the best way for me to do my analysis!

5

You have to add it to the list of publishers, i.e. under publications:.

That should be actuator_outputs (the output of the low lever mixer) or actuator_motors (the output of the control_allocator module)

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6

This worked, PX4 is publishing data now! I thought I had tried this before and it hadn’t worked, very strange!

actuator_outputs and actuator_motors are publishing as well! Thank you so much, this is very helpful!

I have encountered another problem however, the uXRCE-dds-client appears to be remaking all published/subscribed topics at irregular intervals? This is causing pauses in the data stream that will be problematic when I am doing offboard control. This did not happen before I had added the new topics to the build. Should I open a new thread for this issue?

7

That’s great!!

Are you using serial connection?
Try to increase the baudrate and to remove all the unused topics to the bridge.

8

I am connected over serial. I can’t seem to increase the baud rate any higher than 921600, I see there are more options above it in QGroundControl but when setting it higher the dds agent and client don’t seem to connect.

Regardless, after removing all the topics I wasn’t using from the bridge I have managed to get a stable connection, but only when using one of the actuator_outputs or actuator_motors topics. When using both I have the same issue as before, though luckily I think I only need one of them.

For reference here are all the topics I was having PX4 publish to:

/fmu/in/offboard_control_mode
/fmu/in/onboard_computer_status
/fmu/in/vehicle_attitude_setpoint
/fmu/in/vehicle_command
/fmu/in/vehicle_mocap_odometry
/fmu/in/vehicle_visual_odometry
/fmu/out/actuator_outputs
/fmu/out/failsafe_flags
/fmu/out/timesync_status
/fmu/out/vehicle_control_mode
/fmu/out/vehicle_odometry
/fmu/out/vehicle_status

In regards to hardware I am using a Holybro Kakuteh H7 connected to an Odroid XU4 via serial.

If anyone is reading this thread in the future I did find this alternative solution to the instability issue: Microdds_client disconnects with mRo Control Zero H7 · Issue #20843 · PX4/PX4-Autopilot · GitHub
I didn’t attempt it as I only needed the one topic, and felt this would lead to more problems for me in the future, but maybe it will help.

Thanks so much @Benja !

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