Re: Mariss' power supply circuit

John,

Actually that is pretty much it. Here are a few "rules to live by" if
you are designing from scratch.

1. Calulate power needed, "How fast do I want to go and what force do
I want at that speed?"

For linear motion use Watts = IPM times Lbs divided by 531
For rotary motion use Watts = RPM times in-oz divided bt 1351

2. Pick a motor that can deliver that Wattage (continuous rated
only!). It will be listed as rated Watts, or calculate the motor
power using its rated continuous torque and RPM spec with the "rotary
motion" equation.

3. If the answer is less than 150 to 200W, consider using a step
motor. It will do the job with a lot less complexity.

4. If "no" to #3, then calculate your reduction gearing ratio.
Calculate your output RPM (leadscrew, pinion or toothed belt pulley).
For a leadscrew RPM = TPI times IPM, for a pulley, RPM = IPM divided
by 6.28 times pulley radius.

Use 1/2 of your motor's no-load speed for the input RPM. This way,
peak power will be available if it is needed for short periods of
time. Your reduction ratio will be: input RPM / output RPM.

5. Reality-check the results. For a leadscrew, force in Lbs will be:
in-oz * ratio * .3927 * TPI * eff

Where:
"in-oz" is the motor's continuous rated torque
"ratio" is the reduction gearing ratio (input RPM / output RPM)
".3927" is 2 pi / 16
"TPI" is leadscrew turns per inch
"eff" is the leadscrew efficiency (0.3 for worst ACME to .95 for best
ball-screw)

6. If you have picked a motor whose output power is greatly in excess
of the application requires, you can trade in excess torque for speed
or visa versa. Use #5 and change "ratio" to see what fits best.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "jmkasunich" <jmkasunich@y...> wrote:
> --- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> >
> > This is a situation where both sides are right; the seeming
> > difference has to do with the size of the motor and the
application
> > it is optimized for.
>
> I expected there to be some difference due to size of the motors,
> but I didn't think it was that large. I failed to consider the
> fact that servo motors are optimized for peak torque, at the
> expense of continuous ratings (which aren't critical in CNC).
> Industrial motors are optimized for continuous ratings. Like
> the servo motor, the industrial motor has a stall torque much
> higher than the continous rating (1900amps makes a lot of torque).
> The big difference is that the shaft, frame, etc., and the magnets
> of the industrial motor aren't designed to handle that torque,
> because they don't need to in the industrial application.
>
> Thanks for clarifying this for me. I wonder how many other
> scaling effects I'll run into as I try to apply my industrial
> experience to CNC on a home shop scale?
>
> John