Re: Treadmill motors as Servos

Hi Les,

Yes, they run smooth in both directions on a AA camera battery
that's about half dead (it won't work in the camera).
I hooked them up to an 18V. Dewalt battery, look to be running
around 800 rpm (wild guess), and hard to stop by hand.
Fine in both directions.

I'm not after high speed or super power as much as reliability.
All I want to do is cut out the same shapes in MDF or plastics
as exact as is possible from one to the next.

I don't generally leave it unattended, except to run and get
a cold drink in the next room. But with the way it is now, I
have to watch it like a hawk.

I have 2 desktop routers for engraving pictures that use Dave's
Hobbycnc board. Those things are so reliable (I can't recall even
a concern about missing steps) that I'd probably take my wife
shopping while it runs unattended. Wonder how long That could take??

I think I have to at least try this.
I'll use the Gecko's like you suggest.
If I had to get better motors at least I'd be that far along.

It'll be Monday before I can order the stuff, but what I'll
do is keep a running file of how and what for the next guy who wants
to try this.

Do you think a step-multiplier in the G340 would be to any
advantage(as opposed to the G320)..(Gecko)?

I'm very grateful to you for your time and very clear answers.

Thanks again Les,

John



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

>
> Hi John,
>
> > I didn't have a D cell put it turns smoothly on a single AA
> > Duracell, I guess thats a good sign.
> >
>
> If they run smoothly on a 1.5V AA cell they should be fine. Do they run
> the same in both directions? I used the encoders from those little

servo

> motors. I still have the motors kicking about somewhere. You will
> probably have to reduce the diameter of the shaft on the back of your
> motors. I strapped my motors onto my tool and cutter grinder, ran them
> slowly and ground the rear shaft down. You could also take the rotors
> out and turn them down.
>
> > No more lost steps??? I can't believe it!!!
> >
>
> I never even think about lost steps. The motors are either working or
> stopped due to a fault. As long as you use good quality screened cable
> for the encoder signals you should never get silently missed steps like
> steppers do.
>
> > Is that the same encoder you used?
> > How does it connect in all of this?
> >
>
> Yes. The encoder had 4 wires. This is from memory but I am fairly sure
> it is correct:
> Black - Encoder ground
> Red - Encoder 5V
> Green - A
> White - B
>
> If the drive keeps faulting out, swap over A and B on the Gecko.
>
> > 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.
> >
>
> The motors are still going strong. I have had zero problems with them.
>
> > 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 know what you mean. I wasted money on steppers myself. On steppers

the

> mill had a tendency to lose steps and occasionally destroy drives.

With

> servos it just works. Suddenly stopping the machine (e.g hitting

stop in

> Mach) while it is moving fast will sometimes fault out the drives

but at

> least you know instantly that there is a problem.
>
> > So someone could have a working servo system where the motors &
> > encoders are a little more than $100.?
> >
>
> All I can say is it worked for me and I would do it again. In my case
> the motors were more expensive because I had to import them into the

UK.

> Carriage for heavy items from the US is expensive!
>
> > 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.
> >
> I tend not to leave the machine on it's own but that is more a case of
> general paranoia than anything else.
> > Which drives do you like?
> >
>
> I use Geckos on the mill and Rutex on the lathe. Rutex drives are more
> work to wire up but they can be tuned to give slightly better response
> than Geckos. There isn't a huge amount in it though. Geckos will fault
> if the motors lag more than 128 counts behind the desired position.
> Rutex drives will allow huge errors which means they quite probably
> won't fault if the machine has a crash (BTDT). One nice feature about
> the Rutex drives is the separate power for the logic. This means that
> the drives can keep track of the machine position even in emergency
> stop. With Geckos you have to re-reference after estop. As you have
> already got Gecko stepper drives I would suggest using Gecko servo
> drives as they are virtually a drop in replacement.
>
> Les
>