What encoders to use for these motors?

[Cold Fusion]

I've decided to use a servo setup for my Bridgeport mill and I've got a couple questions regarding the motors and encoders. Here are the motors I just won today. They are made by Electrocraft, which is now Reliance.

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7519233701

0713-19-002 x2
0670-10-007 x2

I've been searching the forums for some data on these things and it seems that the larger 713 series motors have about 450oz continuous and 1500oz peak capability. Some more stats would be helpful on both motors, if anyone knows of any.

What type of encoders do I need to buy for these? Can anyone supply me with a link to where I can buy them?

For my power supply I am looking at a 48v 30amp. The motors are rated at 60v continuous, so hopefully 48v isn't taking too much performance out of them. I would rather buy a premade unit, instead of building my own with a toroid.

[lerman]

Originally Posted by Cold Fusion ... What type of encoders do I need to buy for these? Can anyone supply me with a link to where I can buy them?

Try http://www.usdigital.com

Ken

[Cold Fusion]

Thanks, what count encoder should I go with? I know a lot of people use 250, but isn't that kind of low? I would like a .0001 resolution with rapids close to 100ipm. My ballscrews are .2" and I have a 2:1 belt reduction.

[lerman]

Well, on my bridgeport clone, I'm using 500 cpr encoders (they came with the 1750 rpm servos). That gives 2000 counts per revolution. 5 pitch (.200 inch) leadscrews and a 2:1 reduction gives 2000 x 2 x 5 => 20,000 counts per inch. That's half a ten thousandth. Good enough for me.

At (2 x 5) 10 revolutions per inch, I get 1750/10 => 175 inches per minute. That also seems fine.

BTW: I just soldered the last wire tonight. Tomorrow, I move the computer to the shop and start configuring software (EMC) and (hopefully) spinning motors.

Ken

[Cold Fusion]

Congrats on your project! My mill isn't even here yet. Right now I'm just trying to kill time and get all of this little stuff ordered so it won't delay me when the BP gets here.

500 sounds good. I may have to get a faster computer because right now I'm only running a 400mhz with Mach2.

[DACMACHINE]

Cold Fusion

Are you planning to mount the encoders to the motor or ballscrew?

Using Lerman's numbers 1750 rpm .200 lead 500 cpr
= 29166 hrz ok if mounted to ballscrew
1750/2 = 875rpm / 60 = 14.58 rps (second) * 2000 = 29166 Hzs

= 58333 if mounted to motor (too high)
1750 rpm / 60 = 29 rps * 2000 = 58000

I included a nice little excel file to figure out numbers

Hope it helps

[Cold Fusion]

Thank Dac! I'm not sure right now. I've read that if you mount them to the ballscrew, it can cause excessive movement in the servo while it hunts for position. Also, since this is a bridgeport, my ballscrews are very large. 1.5" diameter would be my guess. Do they even make encoders for those size shafts?

I know the smaller motors pictured have a .375" rear shaft, but I don't know about the 713 models. I guess I'll have to wait until I get them to make a decision about where to put the encoder.

[DACMACHINE]

What size Bridgeport are you getting? 9X42

This is what I have, just guessing I would say ~1" max
the ends could be machine to accepts the encoder

I spoke to Mariss a week or so ago he said
mounting to ballscrew is ideal (more accurate)
as long as there's no play in the belts you should be OK

If it's possible to mount to the screw, it would be much more
accurate (in theory)

Dan

[Cold Fusion]

No, I like overkill. I'll be getting a hulking giant called a series 2. 6000lbs with 30x15x15 available travel.

That's good to hear. I'll have GT2 belts installed so there won't be any backlash to worry about. Maybe I could get someone with a lathe to turn down some reducing collars that would fit over the ends of the ballscrews?

[DACMACHINE]

Overkill = good

If I were in your shoes, I would see about having some
collars made.

In the long haul, you'll be glad the you did it.
rather than "wishing you would of"

AND x2 the resolution (in theory of course)

Dan