Inverted pendulum with counterweights - equations of motion

Could someone help me to derive the equations of motions for the system shown in the attach file. Basically it's a 2-dimensional "box" which should be stabiized on its rotating(pin) joint by adjusting counterweights m1 and m2 with linear motors. Counterweights m1 and m2 can move of speed v1 and v2 respectively. We can assume the box and the linear motors themselves doesnt weight anything here. Angle alfa can have values from 0 to 90 degrees. Any help would be much appreciated.

The loaded trainer has a mass of 900 kg with a center of mass at G and is attached at

Please see the attached file and please include FBD.