can anyone provide me with a formula I can use to either machine a flywheel, capstan, pulley or use motors, flywheel, capstan from various donar decks to produce a linear tape speed of 3.75 ips? various makers use different dimensions/rpms to produce standard ips speeds. would it be better to get motor,flywheel, pulley, capstan, bushing from a specific model as a matched set? I would prefer to machine my own. if I could know the capstans rpm as it relates to ips speed for a given diameter that would be a good starting point. all advice welcome.