Re: [CAD_CAM_EDM_DRO] Re: Treadmill motors as Servos

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
>