I. Make sure that the control box and the motion box are connected by a wire or a metal rod.
II. Search the animatronic (at the control box end, head end, or arm end) to make sure that the costume is not caught in the motion mechanism.
III. Some motion boxes use a rubber drive belt that connects the motor to the gears. Sometimes, this is hidden under a small plastic cover. Locate this piece (if your motion box has it) and make sure that the belt is installed properly and is not broken or worn.