I will second what Al said on the 5645's. They have a 3 pole motor and nowhere near the torque needed for the elevators. You should use nothing less than a 5955 on everything. The gears on the 5955's will last forever and you will have much better precision and torque with them. You should be able to sell the 5645's and the extra money for the 5955's is well worth the gain.