Re: Plasma table gear reduction

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

> Do a google for "Servo versus Stepper", there was a graph that

depicted the performance of each. It clearly shows that Servos perfom
best at near max RPM and steppers perform best at hold and very low
RPM. Servos need a transmission and Steppers do not. Operating a
Servo in this manner (without transmission of torque) will result in
very high current load and short life of the servo. It would be near
stall current at all times. This is ok for an automobile starter
however servos are not designed to tolerate continual spikes of
current. In other words, keep lots of fuses on hand. If it was
reliable at all, the heating alone would be an issue. One would need
to have a pinion on each side of the gantry to prevent "racking". And
these two pinions would need to be timed with one another via a long
shaft pillow blocked to the bridge of the gantry then timing belted
to each pinion on its ends. Belt the servo to this shaft with
reductions.

>
> Has anyone considered using one of the new 24 volt starters as a

largish Servo by adding an encoder? Could probably run one at 30
volts and not harm it. Would be a bullet proof servo. Higher voltages
at less amperage than its rating.

>
>
> Ron

I didn't find a visual graph, but did find some reading. Thanks.

As for the de-rating. As it appears to me, a 3/4hp dc motor at 90
volts would be something like a 1/4 hp at 30 volts ? That 3,000 rpm
would then be 1,000 rpm (still shakey on this after reading notes on
DC motors)

So, the motor range would be from zero to 1,000 RPM. and 0-30 volts.

It appears to me that the motors are available surplus in many
different sources so the cost will be pretty low. under $50.00
anyway.

Using the motor at low speeds also means low volts and I assume low
amps so the motor 'should' not be overheating.

I think I've got a few pieces together.

Waiting on delivery of the Gecko's from the Customer Appreciaton Sale.

I already have a couple 16 watt Pittman motors from old hp plotter
and a couple DC motors from a couple old-old-old printers. One has a
plastic film wheel with two seperate tracks of lines. I haven't
pulled the back off the other as yet, but would bet it is similar. I
did find one to be listed with 35v and 1.1 amps.

I do have a 2,000 encoder so it would seem that between the pittmans
this unit and the encoder, I should have enough to set up a couple
axies to try things out.

One thing I seem to remember is to put end switches pretty far in-
board to offer some protection from a run-away.

Anyone have an idea how long Gecko is taking for shipping ?
I was one of the guys who waited till the 15th.

I'm in no rush as with the holiday I seem to only have time to surf.

Dave