Controlling actuator velocities using simulink blocks

[HusseinHazem]

I launched the mav_hovering_example.launch file and commented out lines 32 till line 36 (the part where the lee_position_controller node launches) to be able to control the speeds of the motors using the message publisher in rqt.
Is it possible to control each motor speed from the simulink ros blocks? and if so how can i do it?
My attempt leads to gazebo freezing and even then i don't how to access each motor speed separately.

[gsilano]

I suggest you to read something about the MathWorks Robotics System Toolbox

[HusseinHazem]

![screenshot from 2018-05-02 15 58 33](https://user-images.githubusercontent.com/36478570/39527571-0b638eb2-4e22-11e8-88fd-4ec5c4b672b5.png
that was my attempt.
but i also followed https://it.mathworks.com/help/robotics/examples/work-with-ros-messages-in-simulink.html but i couldn't get it to work.

[gsilano]

I suggest you to read these tutorials: Connect to a ROS-enabled Robot from Simulink, Install robotics system toolbox support packages and Create custom messagges from ROS package.

You have to take in mind that mav_msgs/Actuators is not a standard ROS message. It is not present in the default MATLAB installation (with the Robotics System Toolbox) and you have to import it by using the tutorials I linked you.

[HusseinHazem]

thanks but i already went through all of these and installed ROS custom message interface. and as you can see from the screenshot the message type mav_msgs/Actuators in available for use. My problem is how to publish the message to the motor speeds.

[gsilano]

You right!! It is not allowed to publish a message via Simulink, at least I did not succeed. You should use MATLAB, in particular the commands as reported below:

[pub, msg] = rospublisher('/command/motor_speed','mav_msgs/Actuators');
msg.AngularVelocities = [Omega_1_SIMULINK.signals.values(end), Omega_2_SIMULINK.signals.values(end), Omega_3_SIMULINK.signals.values(end), Omega_4_SIMULINK.signals.values(end)];
send(pub,msg);

where Omega_1, Omega_2, and so on, are the propellers angular velocities you would publish.

I hope I have made it clear.

[HusseinHazem]

Thanks a lot , i changed it a bit to the above and it worked. My goal is to use my controller from simulink to control the motor velocities, any idea how i could do that?

[gsilano]

Great!! You have to combine SIMULINK with MATLAB. The MATLAB script handles the communication, receiving data from ROS and passing such data to Simulink. The control scheme in Simulink computes the control actions and saves such actions in a toWorkspace block. Later MATLAB, thanks to the command I showed (and you corrected a little bit), sends the motor command to GAZEBO.

To do that you have to synchronize the enviroment by using the GAZEBO services pause and unpase physics.

[HusseinHazem]

Do you know how i can remove this error? the u here is a vector of length 4 coming from a mux and for some reason the function can't recognize the ros function.

[gsilano]

You cannot use this kind of Matlab function in Simulink. I mean, you cannot publish a ROS message via Simulink by using it.
In attached two files: a MATLAB script that handles the communication between MATLAB and GAZEBO, and a Simulink that allows you to implement your control law. I mean, the Simulink scheme is able to use the Gazebo data (MATLAB makes them available) and to compute the propellers angular velocities. Such velocities every simulation step (Ts seconds) are sent to MATLAB (a simple toWorkspace block) that has the aim to publish them.
Furthermore, the MATLAB script makes the two environments synchronized: when MATLAB is running, Gazebo is in pause and vice-versa.

I don't know if I got it across. I hope so.

The 2018a version of MATLAB you need to run these files

Issue_GitHub.zip

[HusseinHazem]

thanks i will try it out and get back to you, but will 2017a version not work?

[gsilano]

I made the Simulink scheme by using 2018a version of MATLAB. I don't know if you can open it with a previous version of the software. You should try.

[HusseinHazem]

it is possible but you have to change the file from a simulink 2018a as shown in the pic

Can you export to version 2017a and send it again?

[gsilano]

Yes, of course. You find it in attach.

GitHub_issue_RotorS_MALTAB2017a.zip

[HusseinHazem]

Thanks a lot, but i am having a bit of trouble understanding how i am supposed to run it using my control method from simulink. Am i supposed to send my omegas generated from my control to the omega blocks instead of the constants and run the simulink model first then the matlab script?

[gsilano]

As I told you before, the MATLAB script has the aim of handling the communication. It is enough to run the MATLAB script to execute the entire simulation.
Thus, you have to think in your mind an event triggered system. Such system brings data from the environment, computes the next action to do (the propeller angular velocities) and acts it in order to reach the goal. Every step, each Ts seconds (1e-3 in my example) the cycle is run. How many time? The number of the simulation steps.

In other words, the code works like an automata. In each state, some actions are done and later the results used by the next node, and so on.