I am an aerospace engineering student, so industrial servo's aren't really my strongest area. I am currently working on a gravity simulator project that requires a servo to apply a constant torque on a cable attached to a rover below the gantry while it slides along an x-axis. The rover will be about 40 or 50 lbs (could be scaled down if necessary), and for simplicity sake I would attach a 2 inch diameter rotor so that the maximum continuous torque I would need would be 40-50 lb-in. Ultimately, the goal is to maximize the torque resolution to within 0.01 lb-in but we aren't sure if thats feasible yet.

We are probably going to be getting some servo drives from Advanced Motion Controls through their University Outreach Program. The list of available drives is attached.

I found several servos on Ebay that meet the torque requirements for the project listed below, but I'm not sure which would be the best for maintaining constant torque. I think all of these can be driven with one of the drives listed at the bottom for most of these I think I would end up using the B30A40.

So the AMC drives are just dumb drives from what I have read here on the forum. I just want to run these drives in constant torque mode, so what is the easiest/cheapest way to do that. I have read that I can use EMC2 but need 2 serial ports (one for pwm and another for the +-10 vdc signal), I'm not sure how difficult this is to implement, any experience out there? I saw a post on here where the encoder output was translated back to the drive as hall sensor output, would that be possible here to use servo's without hall sensors? Alternatively, is there is a simple plug and play controller available to do what we need instead of using EMC2? Any help would be greatly appreciated.

ALLEN-BRADLEY 1326AB-B420H-21 AC Brushless
-Max cont output power: 2.08 KW
-Max cont rms amperes: 5.46 amps
-Max cont torque: 42 lb-in
-Resistance: 3.150 Ohms
*Not sure what the voltage is on this motor or if it has Hall sensors

Pacific R46GENA-TS-NS-VS-00 DC Brushless
-RL 3.7 OHMS
-Ke 128 V/KRPM
-Ics 6.7 Amps
-Tcs 64 LB-IN
-360VDC
*The TS seems to indicate that it doesn't have Hall sensors, I'm not sure what Tachsyn is though.

Allen-Bradley BulletTN 8500 AC Servo
-Rated Output - 0.85 KW
-Rated Torque - 55 kg-cm / 47.7 lb-in.
-Rated Current - 6.2 A (RMS)
-Rated Speed - 1500 RPM
*Don't know voltage or if it has Hall sensors

AEG Modicon brushless servo motor cgp31-tb
-feedback: resolver 1/1
-rated current ic stall: 19.0
-motor torque: 225lb-in/25.4nm
-poles: 8
*Dont even know if this is AC or DC