Ok, new question...

I am looking at getting my motors and dont know how to spec them.

i have been offered a couple of free mclennan M500 servo motors (without gearboxes) http://www.mclennan.co.uk/datasheets...reddcmotor.pdf

They need repair (positional optics parts) but are free

are they suitable?

what spec do i need for medium duty >400mm travel?