New to servo's, will these fit the bill?

[yukonho]

I am planning to CNC a large benchtop mill. (the thing weigh's about 700 Lbs.)
I will be using Gecko drives, but have not purchased them, or the power supply yet.
I have foung these servo's and would like to know if they will work in my application, can you guys help me out?
By the way I will be using 5 TPI ball screws. My plan is to use these on the X and Y and will have to find another servo for the Z.
here is a link to the spec's, it is model number C-33 400E
http://www.satcon.com/products/pdf/motors_c33.pdf

Oh yeah, is $100 a good price for two of these? They come with 1000 line encoders.
Cheers and thanks,
Colin

[ger21]

Be careful using 1000 count encoders. Geckos see those as 4000 steps per rev (quadrature), So with no gearing, you'll be at 20,000 steps per inch. Since most likely you'll be gearing the servos for more torque, that will limit your top speed.

[pstockley]

Unless you go with Rutex which has an internal multiplyer to avoid the speed reduction problem with high encoder counts. I don't think it improves the resolution or accuracy however.

Just out of curiosity, where are you getting these motors from? I am looking for some servos myself.

[ger21]

You can also get the Gecko's with the step multiplier as well. Forgot about that.

[yukonho]

Thanks for the input guys.
I was curious about the 1000 line encoders, and now I understand what a step multiplier does, too.
My intention is to go with the Gecko's and the Rex controller, would I still need multipliers in this case?
So, I am guessing that $100 is a good price then for two, is this so?
PStockley, these are on Ebay.
Colin

[ger21]

If you use the G100 (Grex), you won't need the step multiplier. It might be a couple months or more before Mach4 is ready to run it, though.

[pstockley]

I had a look at the specs and the only problem is the maximum amperage is 48amps. This is above the 40amps supported by Rutex and way above the 20amp supported by gecko. The 48 volt version would have been perfect for Rutex.

[yukonho]

Is this a big issue? I know that I wouldn't be running them at their max, but does that really matter?
Colin

[pstockley]

I don't really know. I would guess you might get away with a 40 amp controller like the rutex. The problem is how much current they take when accelerating the table or head, especially from a standstill. I wouldn't be too comfortable running them on a 20amp controller.