Steppers vrs other

[rwskinner]

This is a little OT but I know most of you have played some in this area. I'm planning on building a wire feed unit to feed xx inches of wire and cut. I plan on using a pic and PBP to control the unit. The wire will be pulled directly from a wire box and it would range from 16-2, 18-2, and 22ga-6c so it's fairly small. Heck, I would like to feed heat shrink as well.

I planned on using a stepper to directly drive a wheel. There would be a spring loaded wheel running on the drive wheel. The wire would be feed between the wheels. There would be an inlet and outlet guide.

My delimma is, should I use a stepper motor, or would it be better to run a gearmotor with a indexed count wheel on it? It seems like the gear motor would have much more torque and I could start the motor and count the pulse from the wheel then stop it. On the stepper I could just increment the steps, but I'm not sure how large of a stepper I would need.

Any input would be appreciated.

[mackrackit]

I would go with the gear motor for the reasons you stated. Then you could have a matching index on the idler to test for slippage. I am thinking of a MIG feeder type of setup.

[aratti]

Use a stepper and a gearbox 1:6. Using a stepper nema 23 with 200 steps per turn, you will end up with a system with 1200 steps per turn or your gearbox shaft with a torque 6 times higher. You don't need special gearbox, since your system will pull always in the same direction so no problem with the possible backlash.
Using a stepper you have much more control on the system. If you will need a close loop system, then you can use an optical encoder driven directly by the wire, this will increase the precision of your feed, because in case of possible slip (your wheel driving the wire is acting on friction and slipping could occur) the close loop could easily compensate such an event.

Alberto