Re: [CAD_CAM_EDM_DRO] Re: Treadmill motors as Servos

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