Re: [CAD_CAM_EDM_DRO] Re: What makes a motor a servo? calculating power

replies inline...

>en it is rapiding. That is not the case. At slow cutting speeds,
>the servo is actually using less power than the stepper, yet this was
>not pointed out. Where do you spend your time, cutting material or
>doing rapids?
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depends, on my router, I run a 30,000 rpm spindle, feeds are usually
around 45-90 ipm, cutting .063 al. my machine spends as much time
traversing as cutting (8'x12' table) so, once again, it depends on your
machine and particular needs. I can tell you that I've retro'd servos
onto an identical, only smaller version of my machine,and were it not
for the customer insisting servos are better, would have steppers.
AAMOF, I recently did a machine in Kentucky that was r&p drive, with 4:1
reduction (1" per rev) and had the same situation, steppers would have
flat out beat the pants off of any servo, on that machine, in that
situation (routing mdf all day long), but alas, the customer wanted
servos, and I had to reduce the motors significantly to get them into
the sweet spot while actually doing work.

>>Is my NEMA42 800oz in motor just as good as a NEM34 800oz-in motor? I
>>thought there were reasons the NEMA42 were not as good.
>>
>>
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>NEMA is just a frame size and has no bearing on the motors performance.
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Oh, were it so, in fact, as you increase frame size, you also increase
winding size, with a conmensurate increase in inductance, and the corner
speed drops. Some of the nicest stepper driven tables I've seen use nema
23 triple stack motors and achieve some exceptional performance.

>
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>>As for servo's. how do you calculate for a 230 volt motor that is
>>rated for 1-1/2 hp and 5,600 rpm when you are going to use a Gecko on
>>it with a 66 volt power supply ?
>>
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>Sounds like trial and error to me.
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well, since power (oversimplified, negating losses) is torque x speed,
pretty easily, we know that the speed will be approximately 1/4th, so
roughly your 1 1/2 hp 230v motor will max out about 3/8 hp.

While it would be nice to think that all of this is black magic, in
reality designing any machine (cnc or otherwise) is an exercise in
compromise. Compromise between cost/performance being the pertinant one
here, I for one prefer steppers, you can say what you want, and are
welcome to come over and try to stop my 800 lb gantry moving at 200 ipm,
using any or all of your body mass. I've sheared 3/8" straight router
bits with it, and I'm assuming that there's enough headroom in the
available forces to do any work I need done.


erie