Re: [CAD_CAM_EDM_DRO] pulley ratios for timing belts

Christopher Prosser wrote:

> Hi Folks,
> I'm sitting here, stuck in my house reclining with a bad back. So I
> thought I'd run some numbers trying to decide if I wanted to do a 2:1 or 3:1
> reduction from the motor to the leadscrew (or ballscrew when I get around to
> upgrading).
>
> I'm using G320 drivers with EMC. I picked up a servo motor with a 250cpr
> encoder on it from Dan Mauch.
>
> I'd make a nice table, but this is ascii after all.
>
> Assumptions:
> EMC can only do 5KHz for driving the steppers. Does anyone know if freqmod
> will do faster?

Steppermod is a little faster, but gives rough steps. Freqmod is much
smoother, but takes more CPU resources. I don't think 5 KHz is a limit
unless you insist on Pentium I (classic) processors. If you can get a
333 - 450 MHz pentium II, I think you can go well above 5 KHz without
trouble. These CPUs are cheap now, where they were expensive top of the
line systems 2 years ago.

> The gecko drives will take up to 25KHz for step input. They will fault out
> at +/- 128 counts.
>
> The motor therefore can run at 1200 rpm with a 5KHz input, giving 600rpm, or
> 400rpm at the lead screw.
>
> My lead screws are 10tpi (RF-31).
>
> 2:1 drive ratio
> Max err before fault: +/- 0.0254
> Max table speed at 5KHz pulse rate: 60ipm
>
> 3:1 drive
> max err: +/- 0.0169
> Max table speed at 5KHz pulse rate: 40ipm
>
> I'm probably going with the 3:1 drive.

This all depends on the high speed capabilities of your motor/driver
combination, the max cutting forces expected at the machine table,
and the CPU.

Jon