SetLinearVel() is not constant ?

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Hello !

I am using GAZEBO 7 and ROS to make a simulation on pioneer3-AT for my internship.

I am facing a problem that is just blocking me for days, I have my plugin that at a specific moment is using the fonction SetLinearVel(), however, I can see that the model got an accéleration and then stop and just slide.

I wanted to know if there is a way to solve this issue ? I do need a constant velocity and I don't know how to do, here are my 2 functions :

    void definirVitesseLineaire(const double x, const double y){

        this->model->SetLinearVel(math::Vector3(x, y, 0));
    }

    void definirVitesseAngulaire(const double z){

        this->model->SetAngularVel(math::Vector3(0, 0, z));
    }

Even if my robot are going the same speed, they wont actually follow each other as they're supposed to do ( with my code ) because the ammount of time both of the functions above are being called is different from a robot to another. This is why I need a constant velocity.

Thank you in advance !