Step 4: Types of Treadmill Motors
DC Permanent Magnet with PWM controller (Great for torque at all speeds).2 wires to the motor (Usually).
DC motor with Armature-voltage DC Motor Control. (Great for torque at all speeds).4 wires to the motor. 2 run to the shunt-field current , 2 run to the armature. Vary the voltage applied to the armature, vary the speed. Not all 4 wire motors are Armature Voltage controlled. Some have 2 wires that are part of a thermal protective circuit. The ones I have seen are usually both blue.
AC motors. (Probably not any better than the AC motor your'e thinking of replacing).Motors are running at a constant. Incorporates a special sliding pulley.Changing the belt speed is done manually-controlled with a cable that changes the size of the pulley's diameter. Larger motor pulley diameter faster belt speed, smaller pulley slower belt speed (I think).
The DC motors vary in size but most are Permanent Magnet,have brushes, a flywheel,and have either tapped holes or a bracket or flange welded to the case for mouting. They typically can range from 80-120VDC but as high as 260VDC. The HP's 1/2 to 3.5HP (treadmill duty rating), Upper end RPM 2500-6000, 5-20 Amps.
The Max RPM isn't as critical when you can adjust to any RPM within the range and keep a near constant torque.
You can reverse the direction on the DC motors by reversing the polarity. Simply swap the 2 motor wires (usually Black & White or Black & Red)at the terminals on the PWM circuit card. Remember if you reverse the direction of the motor you can't use the flywheel as it is. Because of left hand threads it could come off. Drill tap and set-screw the flywheel to the shaft