Re: [CAD_CAM_EDM_DRO] CNC Servo motor gear ratio: overheating. EMC step rate. Tablespeed

Kim Lux wrote:

>>So at 25 rpm for his 5 ipm which I am assuming is a speed he plans to
>>actually cut something at I think he will be risking getting very hot
>>motors and potentially frying them.
>>
>>
>
>We'll be cutting at this speed. 50 oz in per amp. Lets say we need 300
>lbs force, which is 200 ish oz in torque or 4 amps. 4 amps x 36 volts =
>144 watts. Is there some minimum speed that servo motors can run at or
>some sort of derating of torque at low speed ?
>
>

Well, 144 watts is not being dissipated in the motor. If these are the
Ametek
motors, they have a 4 Ohm resistance, so the windings are dissipating
4 * I^2 = 64 Watts. (Note that the IR drop is 16 Volts, so the motor will
have slowed to about half speed, unless you turn the voltage up.) If
you figure
how hot a 64 Watt light bulb would get, that's how hot the armature is
going to get in a couple of minutes. I'd guess these motors would last
about
10 minutes at this level before permanent failure. Obviously, you'd need to
limit the duration of even this load level to a minute or less.

Take the 600 Oz-In case, which looks like 12 A from the above numbers.
4 * 12^2 = 576 Watts, and the IR = 48 V (JUST to satisfy the resistance,
before you get any motion at all). The motor would not handle this over
one second, and probably should limit this to one or two seconds per
10 minutes, I'd guess.

I think the motors could handle about 2 A (16 W) continuous, at best.

>I obviously need more info if there is.
>
>

I don't know if this info is available. Some makers will not release
any info on OEM motors.

Jon