Accelerations and IMU data - MAVROS

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?

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

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?

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 -

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?

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