[dberndt]

I have a project I'm in the planning stages of, that involves using a largish threaded rod, ballscrew, etc. The axis runs in the vertical, and it carries a grabber, that all told probably will weigh something like 5-10lbs. The distance between the limits on this axis will be somewhere in the 4 to 6 foot range and I'm looking for a solution to traverse the area quickly.

I've never worked with stepper motors before so I don't really know how I should judge my needs, what realistic stepping speeds (rotations per second), etc are. But my rough calculations are as follows:

rod has 10 turns per inch
1.8 degree stepper motor=200 steps per rotation
something like the salemcontrols single axis controller will do about 1000 steps/second (limit impossed by their programming interface)
assuming I can get a full 1000 steps/second thats 5 turns per second, or in other words, .5" per second.

In this scenario it seems like the stepping motor is going relatively fast in terms of rpm and steps per second, so some sort of a gear system to increase the ratio of rod rotation to motor rotation would seem like a good idea. But then there is the question of how much I can get away with, how do I calculate my requirements?

For example, my initial thinking goes something like this, friction will be small, so we will leave that out for now, and look simply at the weights involved and the gear ratios. So a 10tooth per inch thread acts like a 10:1 ramp or 1:10 depending on how you want to look at it. Throw in a gear box at the motor that is 1:10 putting the motor turns per inch at 1 to 5. So 48 inches in ~10 seconds which is much more to my liking. But the question of how much torque will the motor actually need to move that 5lb-10lb object straight up still remains.

It's 2:30 in the morning so thats about as far as I will carry this for now. I will encourage anyone to come in here and give me ballpark figures for what I want or if anyone has any equations to show the actual requirements that would be nice. Please point out any errors in my plan, I'm new to this and might have some wrong ideas.

Edit, forgot to mention, My goal is something like repeatable positioning along the axis to something like +/- 1/20th of an inch. I dont really need any more precision then that.