I need to specify a stepper motor to drive a system of gears that isn't yet produced. I have almost no information about the system except that it will involve a stack of planetary gear sets with a common 3/8" shaft, with a total weight of about 100lbs (mixed metal and plastic). It will need to rotate very slowly, about 1 rpm, and occasionally reverse.
I'll be able to get hold of one planetary gear set soon. What would anyone recommend to get a handle on the needed motor? I figured I'd wrap a wire around the shaft and pull it with a fish scale to see how many ounces it takes to move it, then multiply that by the number of sets. Given that value, how could I convert that to a motor spec? I'm assuming that most of the requirement will be in overcoming the initial inertia & friction.