[Kevin Sevcik]

Loading depends on the center of mass of your arm, and how heavy an object you're trying to pick up. Gearing depends on the motor you're using, how fast you want it to go, and how often it will be moving.

If all 24 lbs of your arm is centered 40in off that pivot, you're talking about 960 in-lbs of torque. One CIM puts out about 25 in-lbs of torque at 40A. So you'd need at least 1:150 or so gear ratio, probably more, given the efficiencies you'd be getting at that ratio. Just for lifting the arm by itself. Four AndyMark StackerBoxes would get you to 1:160 or so, and you could reduce from there as necessary.

Also, this is for lifting the arm from dead flat, if it won't ever get there or you counter balance it, you could improve things.