4 omni wheels rotating but the robot is not moving !!!!!!

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hello everyone i spent the last 10 days working an project ,which is an omni-directional 4 wheels ,octagonal robot,i added the controllers for my four wheels since i need to control each one of them , i can control each one but the movement of the wheels does not move the whole structure , i spend a lot of time modifying the inertia , the friction of the joints the friction of the ground plane also the gravity and some physics parameters of gazebo. i also verified the contact of my wheels with the ground , nothing works . i am clueless . all the Urdf files and gazebo plugins used are in this GitHub depository . Thank you in advance .