Original 5-phase 2.7A steppers
The axes were originally controlled by 5-phase steppers at 2.7A per phase. There are three basic choices for retrofits here:
Use the existing steppers and stepper cards[]
It is possible to use the existing stepper cards inside the machine if you still have the control. The cards require 50-0-50VAC (probably around 6A -- that's a guess) and a separate 20VAC as input. These power supply requirements may be harder to meet than some of the other solutions....
Use the existing steppers with other 5-phase drivers[]
It is possible to get used 5-phase drivers with step and direction inputs (Vexta UDX5128NA is one). Get a pentagon driver (not star) and wire the 10 stepper connections into a pentagon, connecting them to the 5 outputs on the drivers. Also be sure to get drivers that can supply 2.7A/phase; The last two digits in the Vexta part number signify the phase current. See connection diagram for Berger-Lahr motors to Vexta 5-phase drivers.
Retrofit more common 2-phase steppers and drivers[]
This allows you to use more commonly available CNC stepper drivers (Geckodrive, etc.). Used 5-phase drivers are about the same price as new 2-phase drivers though. Make sure your motors will physically fit. You may need to bore/replace your pulleys and make a new mounting plate.
Retrofit servos and servo drives[]
There are a few models of brushless servo that will fit in place of the original axis motors. Sanyo Denki P50B07030VXKS7 is one that will physically fit and has sufficient torque (new mounting plates would be needed; pulleys would need to be bored/replaced). The Ametek 38 VDC brushed motor with a U.S. Digital E2 series encoder will also fit and work with Gecko servo drives and Mach3.
Pulleys/belts/mounting[]
Stock stepper belt and pulleys[]
Belt: 80132 x 3/4" (type MXL, 0.080" pitch, 132 teeth, .750" belt width)
Pulleys: ballscrew: 100 teeth; stepper: 50 teeth; flanged MXL pulleys of .750" width.
Making replacement pulleys (other reduction ratios/wacky motor shaft size)[]
As best I can tell, standard MXL belts and pulleys seem to only go up to .375" width. Lengths of MXL timing pulley stock of various tooth counts is available at sdp-si.com. It would be possible to machine new pulleys from stock of a different tooth count and use two 0.375" MXL belts stacked. If anyone finds a source for .750" pulleys or belts, please mention it on here!