I thought i'd post this link. I know many of you have likely already considered and/or are using a treadmill motor for their potential for infinite speed adjustment. I've attached a video and a schematic that summarizes a bunch of reading I've been doing on treadmill motors. Many of them typically use a PWM (pulse width modulation ?) speed controller. In particular, the MC60 speed controller board is very easy to use on DC motors. These controller boards can be bought seperately on ebay (search for "mc60 speed controller") and treadmill motors can sometimes be found at the curb. Just kidding, but many people sell them cheaply. Some treadmills will have a usable mc60 already. It seems to be a fairly easy wiring job to get a powerful DC motor working with nearly infinite speed control on the cheap if you can find an old treadmill. Here's a wiring diagram that I found and there's a great youtube video at . I've got dibs on a treadmill sitting at the inlaws house and plan to use it this year on my grinder version 2.0. I'll let you know how it goes but, I'm super slow with things so it may be this time next year. In the meantime, thought you guys may find this interesting and useful.