Did any of you ever notice that a drummer (flesh/blood kind) does not hold his sticks at the very end? He holds them somewhere between halfway and one tenth of the length. I am guessing (not being a drummerboy myself) that this improves the rebounce of the stick from the drumskin. Because the bottom end of the stick balances (both weight and inertia) the business end. Try it out with a pencil on the tabletop. (nb: will destroy pencil)
Did you ever consider placing the motor higher up the drum stick?