The motor controller is a device that converts the input AC voltage to variable output DC voltage. There
    are many motor controller manufactors and many different types of controllers. All the information given here
    is on the Cycletrol 150 Controller only. And please note that I know just enough about controllers to be dangerous.
        The motor I used is a 2hp permanent–magnet 120 vdc motor ( surplus treadmill motor )
    Even though the Cycletrol is rated 0-100 vdc 1/8 to 1 hp. it works fine with the surplus treadmill motor. One thing
    to remember on treadmill motors is that the hp rating is no where close to actual hp. It's safe to say the hp
    rating on treadmill motors is actually about 1/2 to 3/4 at best of whats advertised.
        This motor controller does not offer a motor reversing feature so I added a 3 position toggle switch to accomplish
    this. The toggle switch is wired to the DC output leads and simply reverses the + and - dc voltage.
    The motor must be switched off before reversing or the motor will run full speed for a split second.
 
 

 If you are using the KB Electronics Controller  from www.plccenter.com  Here's an email  from Mike Christensen that will help:

I ended up doing the change to a DC treadmill motor on my HF 9x20.  I bought the 2.25 hp motor from American Science & Surplus similar to the one you describe, although I think mine is a different manufacturer.  However, one thing I did a little different was that I bought a KB Electronics KB240D controller from www.plccenter.com (9370 controller, 9860 reversing switch, and 9861 heat sink).   I bought the maximum horsepower resistor to go in it from a local source (1 hp at 110, or 2 hp at 220).

I initially hooked up the rig as a 110VAC system, which gave me a max of 1 hp and a max armature voltage of 90 VDC.  To hook it up to 220VAC would give 2hp, but it would also increase the max voltage to 180VDC, which was way over the max for the motor (120VDC max).  At 110VAC, the lathe just wasn't performing well.  It would slow down substantially with anything more than a light cut, it would cause flexing of the toolpost (because of the changing speeds), and just generally didn't seem to be operating right.  Well, I finally decided to call KB and talk to tech support.  After some time, I managed to get it out of them that I could actually run the unit at 220VAC and achieve the 2 hp, but I would have to adjust the "MAX SPEED" trimpot to limit the voltage to around 120 at the highest speed.  Low and behold, after switching to 220VAC and readjusting the trimpot, it works great!  It provides much smoother cuts, it doesn't slow down under heavier cuts, and is not causing any chatter.

This may be something for you to consider as a part of your description on doing this mod.  The use of a KB Electronics controller at 220 VAC with adjustment of the max speed trimpot is a good way to get more horsepower out of the 9x20, which in turn improves the performance dramatically.

Thanks,
Mike Christensen