I would really suggest testing different approaches to make the fp with gearbox work, what is the weight being held on the end of the arm? You could use counter-weights, springs, surgical tubing, etc... to help offset the weight of the arm. Since the tubes do not weigh very much most of your weight is the mechanism. Play around with different systems, this way you won't overheat your motor.
You have it built already so make some modifications on it and actually test the performance.