How to publish reference speeds for each motor

[Robotkhan]

Hi! I am a freshman in Ros2 and Gazebo, currently working on control of Crazyflie. So, once I defined the u1, u2, u3, and u4, how would it be correct to publish the thrust (u1) and the corresponding torques (u2, u3, and u4) to control Crazyflie? I appeciate your comprehensive answer :).

[gemenerik]

Hi! I need to understand better what you’re working on to give you a comprehensive answer.
Are you using a specific ROS 2 package for Crazyflie, like crazyswarm2?
Are you working in simulation with Gazebo, or are you controlling a real Crazyflie?

[Robotkhan]

Hi! I do not use any ros2 package for crazyflie. What I have is: model.sdf of the crazyflie, my sliding mode control node, and ros_bridge node. I use ROS2/Jazzy and Gazebo modern (Harmonic). I implemented the traditional smc for attitude control. The smc outputs are thrust (u1), and three motor torques (u2, u3, u4) for roll, pitch, and yaw control. So, as far as I know I cannot directly publish these control outputs to the cmd_vel topic as msg.linear.z = u1, msg.angular.x = u2, etc, since the control outputs are force and torques, but cmd_vel topic accepts linear and angular velocities. So, how can I correctly publish the u1, u2, u3, and u4 in my case? Thanks!

[gemenerik]

Just to clarify, it looks like you’re using Bitcraze’s .sdf model, though you didn’t explicitly say so—please correct me if I’m wrong! If that’s the case, this model uses the MulticopterVelocityControl plugin, which expects velocity commands rather than direct force/torque inputs.

If you’re trying to apply thrust and torques, you’d need to figure out how to either convert them into the velocity commands this model expects or modify the .sdf file to support force-based control instead.

I’d recommend asking in the Gazebo community or the ROS 2 forum for advice on how to approach this—someone there might have experience with a similar setup.