Re: Treadmill motors as Servos

Thanks Les,

I was pretty sure that was you. Thank you for answering.

I put some pictures of the motors here...
http://www.flickr.com/photos/26361144@N00/

I didn't have a D cell put it turns smoothly on a single AA
Duracell, I guess thats a good sign.

No more lost steps??? I can't believe it!!!

Is that the same encoder you used?
How does it connect in all of this?

Is your mill still running with the treadmills or did you upgrade?
I think your old post is from a year or so ago on this topic.

I have nearly $1000. tied up in G202's and 600 oz Nema 34's
and it's not even as reliable as any of my 3 Hobbycnc boards.
It's likely something I'm doing wrong, but I just expected
better. When it goes off course on a $20.00 block of plastic, I just
shut it down and mill by handwheel. And it's done that 75% of the
time. I've changed the voltages, changed computers, adjusted the
trimpots, use Mach3 and CNCPro ,I need something that works.

I got the treadmills for making a spincaster later down the road
and was sifting thru old posts for refs on how to control them.
That's when I came upon some of your old posts.

So someone could have a working servo system where the motors &
encoders are a little more than $100.?

Naturally I've got to pay for more drives, but if it's reliable
enough to leave the room while it's running then it'd be worth it.

Which drives do you like?

Again, Thanks Les, for helping with this.

John



--- In CAD_CAM_EDM_DRO@yahoogroups.com, Leslie Newell <lesnewell@...>
wrote:

>
> Hi John,
>
> That was me. The encoder on those motors comes as two parts - a slotted
> metal disc and a plastic pickup. The disc is pressed onto the shaft and
> is fairly easy to remove. You must be a bit careful pulling the disc

off

> as I had one fly across the workshop. It took me ages to find it.
> afterwards. The encoders are only 200 line, giving 800 pulses/rev.

This

> is a bit low but it seems to be OK on my mill.
>
> I used a slightly different motor to the one you show. Mine had a
> convenient shaft sticking out the back that I ground down to fit the
> encoder. Also check that the brushes are at right angles to the
> commutator. Some are angled and this can cause problems. Surplus Center
> are very helpful and if you email them, they will have a look at the
> motor and check the brushes for you. If you already have motors, a good
> test is to connect them up to a 1.5V D cell. The motor should turn
> fairly smoothly. If it doesn't turn or if it seems to turn in a series
> of steps then it won't be brilliant as a servo. If I remember correctly
> I used 200V rated motors. The higher voltage motors have a higher

torque

> constant (more torque per amp) and turn slower on 80V. You don't really
> want a servo spinning at 6000RPM.
>
> You can't get nearly as much power out of them as you would think. The
> ratings are for full speed running and fan cooled. They are also only
> rated for intermittent use. On my Bridgeport I use about a 4:1

reduction

> ratio between the motors and the screws. This works well, giving me a
> top speed of about 100IPM with enough torque to snap a short 10mm
> carbide cutter without even noticing. Normally they run just slightly
> warm to the touch.
>
> Apart from the motors and encoders you need Gecko or Rutex drives. If
> you are already using steppers with Geckos then use Gecko servo drives
> as they are the same size and hole spacing. I would never go back to
> steppers. Lost steps? What are they? The only time you lose position is
> if a drive faults (overload or trying to move too fast) or you hit
> Emergency stop. Link the drive resets together so if one drive faults
> they all stop.
>
> Les
>
>
> kz1927 wrote:
> > Thanks Rich!
> >
> > That's a good starting point. I saw(think I saw) where someone
> > used this encoder
> >
> >

http://www.surpluscenter.com/item.asp?UID=2006110919282545&item=10-1834&catname=electric%3E

> >
> > and this motor
> >
> >

http://www.surpluscenter.com/item.asp?UID=2006110919282545&item=10-1783&catname=electric

> >
> > but I wasn't clear on how you make it work.
> > I think it was Les Newell on a bridgeport, so it MUST work well
> > if he says it does.
> >
> > Is that all one needs (besides some Gecko's)??
> >
> > Thank you for any help on this.
> >
> >
> > John
> >
>