I'm trying to figure out the right stepper motor to buy for a computer controlled slider. So, it's basically the same as a CNC machine, except that I don't care about position accuracy and my load is about 8 pounds on a linear guide rail that I'm planning to move using a v-belt.

So, I'm considering a 640 oz-in NEMA 34 stepper motor. It has about 32 lbs of force at 1.5 inches. And I was thinking to connect it directly to the sheave to drive the v-belt.

Speed is important. I calculated that 1 rotation per second would be about 9 inches in linear motion. If I could do about that much with this motor, that would be great. But, the load inertia to the rotor inertia is between 10 and 35, depending on whether I pretend the load is lighter or use a sheave with a smaller radius.

I could really use some help in this design! I have more details if needed. I chose a v-belt for simplicity, durability and cost. But, if it's the wrong choice, I'll consider changing.

Am I doing this right? S
hould I use a different motor or different belt or maybe no belt?

The belt will drive the slider about 6 feet. I could possibly drop the load to 3 pounds, but I was thinking that I would double it so that there is a counter balance that moves in the opposite direction of the first load. The reason is that this is actually a jib arm... like the ones used to film soccer games from the side lines. Like a camera on the end of a long pole. So, the slider goes up and down the arm, making it a telescoping arm. If I use a balancing load, then when the arm is up in the air, it is balanced, and requires less power to move up and down. But, maybe its better to use a linear actuator to move it up and down and forget the balancing.

Thanks!
Dave