Re: [CAD_CAM_EDM_DRO] Re: More on servo motor selection

Drew,

I think the reaction to the power thing was probably just because these
things need to be so carefully set out it needs that kind of careful
wording. A decimal in the wrong place and you have something costing
hundreds of thousands more. Imagine the torque and speed is electricity.
Say, voltage is your speed and current is your torque. If I put 100W of the
electricity into a step up transformer I get 100W out the end, but I get it
at a higher voltage and LOWER torque so the result is the same but just with
different components. With your mill it's just the same. If I connect up
some 100oz/in motors I will only ever be able to make a maximum of 100oz/in
from what I get out. So you hook up your motors normally with no belts or
anything and you get 100oz/in at such and such inches per minute of speed.
But say you want to move a heavy machine with big parts and big cuts, the
100oz/in isn't going to be enough anymore. So you could put it through a
belt to give you 200oz/in at HALF the speed. You see now you have more
torque but less speed, the power is the same but you're exploiting one
particular aspect of it, the torque. Of coarse now you think, I want this
thing moving quicker. But if you make it move quicker with the same motors
you reduce your torque like you did the speed in the first place. So bigger
motors are needed. In theory I could run a monster mill off tiny tiny motors
with huge belt ratios, it'd just move incredibly slowly. Remember that old
saying "Give me a leaver long enough and I will move the moon!" I think it
was? It's just the same. You can NEVER increase power without adding it.
Power is lost everywhere in a machine, like it's bearings, the friction in
the air as it's spindle turns. A jet engine only whistles because the
machine is not perfect and is vibrating itself at high frequencies. If you
can hear it, it's loosing energy because the noise is created by friction.
If you could make power by changing ratios you'd have some very weird mills
knocking about. I hope this helped anyway.

John H.

> Thanks Mariss. I guess I need to be sure and keep my terminalogy
> correct. Once I learn what what that is. I always think in terms
> of how much work the motor can do at the table. Am I correct in
> thinking that if a "gear down" the motor either through belt reduction
> or increasing the leadscrew pitch I have more "push" available
> at the table?
>
> Drew
>
> mariss92705@... wrote:
> >
> > Drew,
> >
> > I think you are confusing something here. Gearing cannot change
> > power, only the mix of torque and speed.
> >
> > Your motor is 60 in-oz at 2600 RPM, or 115 Watts. If you used 10:1
> > reduction you would have 600 in-oz at 260 RPM, which is still 115
> > Watts.
> >
> > Mariss
> >
>
> --
> Drew Rogge
> drew@...
>
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