I just purchased 2 350oz/inch peak 50oz/inch continuous servos. I will be using them to replace some 25 year old electrocraft motors I got surplus. They are roughly equivalent to each other for specs.

The motors I have now are only 2 wire. One going to a terminal on each brush. The new motors also have a third ground wire. Do I have to use this ground wire or can it be capped in some way. The cables I'm using now are very nice 12awg shielded and I do not want to remove or replace them if I don't have to.

A few more questions. Does anyone know if I will get any better performance out of these new motors over the 25 year old ones I have now? They have pretty much identical ratings.

Last is if anyone can tell me how to know if I'm pushing my motors to hard. I can observe the current draw in my system in real time. The motors do not even get warm after 2-3 hours of continuous cutting. During rapids they draw 1 to 3 amps per motor. There continuous rating is 3.5 amps so this doesn't concern me. During cutting they can draw 7 amps or so of current on reversal with the acceleration limits I have now during complex 3d tool paths and tight cornering. This can happen quite frequently on one or all axis at any time. The higher current is only for a fraction of a second at a time.
I would like to increase the acceleration until worst case is up to twelve amps instead of 7. Is this a problem under my conditions? How will I know if I'm pushing to hard?

Any advice is appreciated and if I've left out any info needed let me know.

Thanks
Ben