RE: [CAD_CAM_EDM_DRO] Re: Plasma table gear reduction

Dave,
Power is just torque times rpm. The motioneering software selected motors
and displayed a torque curve showing the operating point was in the
safe region.

Although I did not list it, the optimum motors were in the range of
600W or so rated cont power. This occurs at max cont torque and max
rpm.

At the 3 to 5 reduction the motor will only be going a few hundred rpm
for the gantry speed I used. The power actually delivered will be
only perhaps a tenth of what the selected motor is capable of. The
voltage will similarly be much lower than rated.

I know this may seem really sub optimal to use the motor this way, but
we are trying to optimise cost- not motor power utilization or efficiency.

The only mechanical load that really consumes real power is friction. That
is
very low in your proposed machine. What we need is FORCE to accelerate the
moving
mass... and in a regenrative servo system you actually get that back when
you
deccelerate....it pumps up the supply cap voltage.

So it turns out that the software selected motors capable of the torque
required
can generate much more power if they were run at a high rpm.

The smaller motors at the high ratios run at higher rpm, but they have to
use
more torque to fight their own rotor inertia. As you can see the software
found
NO practical motor that would give the selected machine performance above
20:1.

Let's say you had a car that you wanted to be fast off the line. You can use
smaller and smaller motors with more and more gearing to get the same
torque.
At some point the time to wind up the smaller motors to high rpm would
actually
be the limiting factor rather than the car's mass.


Les
Leslie M.Watts
L M Watts Furniture
Tiger Georgia
(706) 212-0242

Main page:
http://www.lmwatts.com
Engineering:
http://www.lmwatts.com/shop.html
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http://www.lmwatts.com/forsale.html
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-----Original Message-----
From: turbulatordude [mailto:dave_mucha@...]
Sent: Tuesday, December 28, 2004 2:19 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Plasma table gear reduction




<snip>

> 3) 3:1 reduction drive with 1" diam timing pulley
> 250 in oz torque 0.1 oz in sec^2 rotor inertia

<snip>

> So with the numbers I used you can see that there is a sweet spot

at about

> 3:1 to 5:1 where the peak torque required is minimum and a

reasonable and

> typical
> rotor inertia gives a good impedance match.
>
> This is not anywhere near the point where the motor delivers best

power or

> is
> most efficient. It is simply the point of best economy for your

design.

>
>
>
>
> Leslie M.Watts
> L M Watts Furniture
> http://www.lmwatts.com

Thanks Les,

dumb question, but is that power into the drive ? or do you also
divide the power by the ratio to get the motor power needed ?

I see is that a 1,000 RPM motor is the place to start. that would
offer something between 200 and 300 inch per minute rapids.

Thanks for your efforts to guide me straight.

Dave







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