Re: Plasma table gear reduction - motors

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Leslie Watts"
<leswatts@a...> wrote:

> 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
> http://www.lmwatts.com

Sorry for being so dense.

But, it seems one of your earlier posts mentioned flat and large
diameter motors are bad and long skinny ones are good. That makes
sense as the flywheel effect from the large motor would get in the
way of quick response. Ditto cast iron timing pullies vs. plastic
ones.

I do have the idea that a DC motor is rated on a somewhat linear
curve. and that generally speaking, a 100 volt, 10hp 4,000 RPM motor
is also a 50volt, 5hp 2,000 RPM or 25 volt, 2.5hp 1,000 RPM motor.

so, generally speaking, I can make a prototype axis a few feet long
and test the motors I have with different gear ratios to see the
acceleration.

Dave

Dave