Accelerations and IMU data - MAVROS

ROS / MAVROS / MicroDDS
1

Hi,
my setup is ubuntu 18.04 + mavros + px4 + gazebo v9 + matlab 2019b.

I have few questions:

  1. For accelerations commands, I publish to /mavros/setpoint_accel/accel and it seems to be working, but I couldn’t understand the units. When I sends 0.565 [units] in the z direction, the drone starts to hover, but what are the units of the commad? I can multiply by 0.565/9.81 to get it with m/s^2 is that correct?

  2. I also tried to get feedback from the imu, with the /data/imu topic. I notice that there is a mismatch between my setpoint_accel/accel and the imu data after reaching steady-state. Is it just unit conversion problem?

Can someone help me with those issues?
Thanks!

2

I think you need to subscribe to /mavros/local_position/accel to compare feedback, IMU values are raw values.

3

Thanks so much for the answer.
I don’t know why, but it seems that this topic is not publishing, when I try to subscribe it with:

$ rostopic echo -c /mavros/local_position/accel
I get :
WARNING: no messages received and simulated time is active.
Is /clock being published?

Is it possible?

4

it seems mavros/local_position/accel is not being published,
PX4 has dropped support for LOCAL_POSITION_NED_COV in these PR conversations as I understand - https://github.com/mavlink/mavlink/pull/1138
https://github.com/PX4/Firmware/pull/11081
https://github.com/PX4/Firmware/pull/11084

5

So if I get it correctly, at this moment there is no topic that can give a feedback of the acceleration?
Do you think it possible to create an algorithm that extract the IMU measurements and gives the acceleration in body frame?

6

Just get the IMU values.That should be the way to go as I think.