Re: [CAD_CAM_EDM_DRO] Re: Newbie question: Motor sizing

Here is another of Mariss' papers:

Alan KM6VV

mariss92705 wrote:

>
> Hi,
>
> A good place to start is to ask "how fast do I want it to go and how
> much "push" do I need at that speed?" Use IPM (inches / min) and lbs
> for "push".
>
> (1) Watts = IPM times Lbs / 531
>
> Use your answer (Watts) to size your motor.
>
> 0 to 100W, use a size 23 step motor.
> 100 to 200W, use a size 34 step motor.
> 200W or more, think about servos instead of steppers.
> -------------------------------------------------
>
> (2) Steppers have lots of torque at low speeds and very little torque
> at high speeds. This is a good thing. Work is done at low speeds
> where you need a lot of torque; high speeds are usually "rapids"
> where little torque is needed.
>
> As a rule of thumb, steppers are pretty much out of torque (rapids)
> at:
>
> Size 42, 300 to 600 RPM, 800 in-oz or more low-speed torque
> Size 34, 600 to 1,200 RPM, 150 to 450 in-oz low-speed torque
> Size 23, 1,200 to 2,400 RPM, 50 to 150 in-oz low-speed torque
> Size 17, 2,400 to 4,800 RPM, less than 50 in-oz torque
> -------------------------------------------------
>
> Now figure the torque you need from the motor.
>
> (3) in-oz = 2.55 times Lbs of "push" / TPI times "eff"
>
> If you know your leadscrew efficiency (as low as 30% for an ACME
> thread to as high as 95% for a ball-screw), make "eff" that value
> (0.30 to 0.95). That will be what you need from the motor.
> -------------------------------------------------
>
> (4) Now figure the speed you will get for a "rapid"
>
> IPM = RPM / TPI
>
> Use the guidelines from (2) for your estimate. You will probably have
> more speed than calculated because the values in (2) are conservative.
> -------------------------------------------------
>
> (5) Let's go thru an example of the above using what you have (and
> many guesses on my part).
>
> Assume the following:
>
> TPI = 5 turns per inch
> Lbs = 500 lbs of push needed
> IPM = 60 inches per minute max for your "work" speed
> eff = 75% (0.75) for your leadscrew.
>
> >From (1), W = 60 times 500 / 531 = 57 Watts, so consider a size 23 or
> 34 motor.
>
> >From (3), in-oz = 2.55 times 500 / 5 times 0.75 = 340 in-oz, so a
> size 23 is out of the competition. Use a size 34 double or triple
> stack (in-oz > 300).
>
> Finally, from (2) and (4), your "rapid" will be IPM = 1,200 / 5 or
> 240 IPM or better. That will take you from end to end on your major
> axis (32") in 8 seconds or less.
>
> Hope that helps, hope I did the math right.
>
> Mariss