Setting joint velocity

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Hello, I have read the tutorial to set velocity on joints : https://gazebosim.org/tutorials?tut=s... but when I am trying to apply the velocity for a wheel with a joint motor, it seems that i can't manage to apply the Torque :

      this->model->GetJoint("orange_joint")->SetParam("fmax", 0, 100.0);
      this->model->GetJoint("orange_joint")->SetParam("vel", 0, 1.0);

I tried to return the torque but I only obtain 0. Do you know what would be the method to use to get the torque ? And can someone explain how can the join take into account the torque within one step (it is said in the tutorial that the velocity is reached in one step) ?

Anyway, my goal in the end is to set the velocity with a given torque, to have a realistic, continuous velocity function. I am using ros noetic and Gazebo 11 and ODE. Thank you in advance