Need Help!- No speed?

[timbeaulieu]

I bought a kit from HobbyCNC a few years ago. I built it but never really tried to use it until now. I know it's their old design but it seems to work ok for the most. I'm using Zeus for the controls on a Pentium III. The problem I'm having is speed. When I try anythingabove 10ipm I start loosing steps. The motors came with the kit and are 7.4 v 1A 125in oz. For troubleshooting I have loosened the gibbs so there is no binding going on . The milling machine is small and I thought the 125in oz motors would be enough. At low speed they have plenty of power. I know that steppers basically loose power as their speed increases but 10ipm is hardly fast.

The power supply is 30v. I've read that steppers are usually run at 15 to 20 time the rated voltage. With the motors being 7.4 and the power supply at 30v that is only 4 times the rated voltage. Would lower voltage motors help?

[mettwoch]

Hi,

10ipm doesn't say anything about the speed of the steppers but only mean that the machine moves at that speed. You need to know the turns per inch of the leadscrew used on your machine in order to determine the stepping frequency required.

Example:

If it's 20 turns per inch then your stepper have to run at 20 x 10 = 200rpm which means 200 x (360 / 1,8) = 40000 steps / minute for a stepper with 1,8 degrees / step. At full step operation, that is 666 steps / s which should be OK. Multiply with the fraction of microstepping used. E.g. At quartert step = 4 x 666 = 2666 steps / s

Marc

[timbeaulieu]

Thanks for the reply and the information. My machine still has the stock leadscrews which are .050 per turn or 20 turns per inch. For some reason I had .200 per turn stuck in my head. I have an old bridgeport and I've turned the handles one to many times I guess. Makes complete sense to me now. Thanks again for the reply. I think it's time for some ballscrews.

[Monte]

Originally Posted by timbeaulieu ....I think it's time for some ballscrews.

Think about bigger motors and/or different drivers too. I was loosing steps for other reasons on my Taig, I went with a bigger power supply (from 26v to 37v) and "better" ($$$) drivers, I've jogged (keyboard) at 70-80 ipm (1400-1600 rpm). My problem was resonance in the motors at lower speeds. There are discussions on dampers on double shaft motors which can work. I went with some Gecko 203V drivers which have some electronic resonance damping in them, or at least the motors do run way smoother with them for whatever reason.

Monte