I want to fit a cable drive system to an old pattern follower gas torch. The torch is on the end of an arm with two free joints. Directly above the torch is a motor driving a 1/4" diameter, knurled magnet. The magnet rolls around the edge of a steel pattern.

Drawbacks of this are that a pattern has to be made for every item to be cut. The patterns have to be 1/8" undersize all around. Sharp outside and inside corners aren't possible. the magnet can get stuck or come loose and when it does go around without a problem the corner is rounded.

The easiest way I can think of to add CNC to it is a square frame with a motor at each corner. The motors will pull on wire cables which at their other end will have a ring that slips over the drive magnet. It'd be like the systems used to fly cameras around race tracks, but much smaller and constrained to a 2D plane.

The motors won't have to be very powerful, the torch arm can be moved around easily using just one little finger.

Can Mach3 run this type of system? I'd like to use as much of the arm's operating envelope as possible, it's like a SCARA arm without motors.

Mach3 CAN do this in principle, but is definitely very poorly matched to the job. The problem is that the structure you are trying to control has considerable dynamics and inertia to cope with, and Mach3 has zero ability to handle the momentum calculations. Mach3 is for CNC; what you want is software for a robot.

It may work if you run slowly with very low acceleration.

Cheers

Look up IPAnema robot on YouTube. That sort of control, but with only 4 cables and working in a 2D plane.

The problem you face is that MACH3 is a GCODE type motion controller for CNC machines. It does NOT have the math channels to do anything but basic cartisian motions. XY as linear motion.

Mach3 does have a simple math channel for each axis but I dought seriously that you could manage to convert cartisian motion to the Motion required to position a cable system robot.

NOW Linux EMC does have the math channels needed to do such work(;-) Kenematics

Just a thought, (;-)TP

this link might give you a simple overview as to where you're thinking of going. As has been said, Mach is not fitted for this and LinuxCNC may be a way to go.

I think this would be great fun to do if you have the time and the money. However IMHO if you follow this route I think you're in for a journey that would make building a cartesian X,Y table look like a walk in the park (and cheaper).

Cheers

Ian