I have to design a robot, and for balancing purpose, I have to use a weight (200 gm) slides over a shaft of stepper motor, I want to simulate the movement of the weight in corresponding to the gravity (i.e when the weight goes right the whole model goes down from the right side , and when the weight goes left the model goes down at the left side. My problem is that the system keeps spinning and it looks like it does not respond to the weight movement(i.e. no effect of weight ).
Note(weight is heavier than the robot and initially its located at its COG)
Any ideas may be helped me