Coincidentally most Treadmills use a 80-260 VDC motor with a suitable HP rating and a PWM motor speed controller to allow the user to change the belt speed and keep a good constant speed and torque while running on it.
There are Commercial DC Motor/PWM controllers available or you can build the PWM circuit from scratch and buy all the components seperately but you will spend a lot of time and money either way. All the parts you need are on the treadmill.
Tear your own apart or get one on Ebay.
(shameless self-promotion below)
Motor/controller combos on Ebay
Safety and Disclaimers- You should have some knowledge of electricity and the dangers of household current and know your abilities/inabilities. Serious injury may occur to you or others from use/misuse of these motor set-up. If you are in doubt DO NOT ATTEMPT. IT CAN KILL YOU. Any Crazy Ideas found here REQUIRE your testing. Your appliction and use of any ideas here are all on you and you agree I cannot be held liable. You equipment should have On/Off safety switches, Fuse protection, ground wires on your machine as required and your power source should have ground fault interupters, circuit breakers,properly grounded sockets and cords and always unplug equipment before tinkering and any other safety practise I am forgetting to mention.
Step 2: The PWM circuit board
You can visit wikipedia for a better definition of PWM.
But basically (as best I can understand) it's an efficient speed controlling circuit that pulses the Voltage and the width of the signal to the motor off and on thousands of times per second. This transfers more power to the load and wastes less power to heat than a resistive type speed controller.
PWM style controller Trim Pots- located near one of the edges of the board.Each Set for specific motor
MIN (Minimum speed-Touch if you dare) adjusting MIN Trimpot may affect MAX, may be necessary to adjust both until desired levels are achieved
MAX (Maximum speed-Touch if you dare) Note that MAX adjustment may affect MIN
IR COMP (Inrush compensation-Don't touch)Improves load regulation by providing minimal speed fluctuation due to changing loads. If the load presented to the motor does not vary substantially,the IR adjustment set at a minimum level. Excessive IR comp will cause control to become
unstable causing motor cogging.
CL (Current Limiting-Don't touch)The CL Trimpot sets the current which limits the maximum current to the motor. Also limits the AC line inrush current to a safe level during startup.
ACCEL (Acceleration Time Period, 0-full speed in seconds)I've never seen one on a treadmill circuit card, only on commercial PWM DC motor controllers. There must be something on the treadmill board that sets the time value..resistor perhaps?
Step 3: The speed Pot
The Pot talks to the circuit board through 3 terminals usually marked High,Wiper and Low (or H,W,L).
Some controllers use a digital console to change the motor speed. You dont want to scroll through programmable selections, excercise routines and heart beat monitors just to change the motor speed on your lathe.
Solution: Throw it away and replace it with an appropriate Pot(usually 5 or 10K Ohm Pot). The digital console interfaces the PWM Circuit board the same way that The speed Pot does. through those 3 terminals (on some marked G O H or L W H and colored black, white and red or S1,S2,S3, colored Blue, Grey, Orange.
You should also use a switch for ON and OFF. The Pot is for speed control once the machine is running.
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
Step 5: Drive Pulleys and Belts
Taking the flywheel off can be a pain. The flywheel are left-hand 4m thread and can really be cinched down or corroded onto the shaft. Chuck the flywheel end in a vise and turn the shaft on the opposing end Clock-wise and the flywheel may come off.
Some Motors don't have 2 shafts. The shaft on the brush side is usually hidden under the bearing housing. For the stubborn or single shaft motors I use a hacksaw and run the motor on low speed and use it like a metal lathe and saw the pulley through once or twice. It always comes off easily when you turn the nut into 3 thinner nuts rather than one wide nut. Just make sure you don't cut into the motor shaft. Eyeball it close and then test it by turning it with a pair of vise grips until you are through the threaded portion.
Or.... If you don't mind the flywheel...
You can use the motor(at a very low speed) as a metal lathe and carve a suitable groove to fit the belt of your choice. It can be a bit tricky (dangerous) as your cutting tool is not fixed. ** USE eye protection, gloves, faceshield etc.**
A rat tail file will work for a round belt or a small bastard file can carve a v shaped groove for the common automotive style belt.
Remember again- 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 it.
Step 6: More Idiosyncrasies
problem 1) Treadmill motors have a 3-4 pound fywheel. Engineers calculate the energy stored by spinning this heavy flywheel to obtain Horsepower ratings referred to as "Treadmill Duty Horsepower". Any quick changes in speed aren't noticed because of the kinetic energy still stored in the flywheel. Sometimes you can hear the motor totally turn off till the flywheel spools down and balances the motors RPM with the respective setting on the rheostat. If the load is restored or the speed setting raised above the motor's present speed, the motor turns right back on. Solution: remove the flywheel. Some of that kinetic energy will be stored in the piece of equipment you are powering but if not then some horsepower could be lost.
problem 2) When starting up a treadmill you wouldn't want it to start up at full speed while you are on it. If the rheostat is not set to the lower end of the resistance value the circuit will not start. Now you have the Motor/controller combo on your drill press or mill and it won't start because the rheostat is not set in the start position.
Solution: Turn the rheostat to the start position before turning on.
Step 7: My Treadmill Powered Tools
[http://www.faireandfoundry.com//robs%20hobbies/treadmill_tools.html My Treadmill powered Mill/Drill]
(Future pics of Sewing machine mod will be here)
The machine is the 1940 style heavy duty leather machine and had its own 4 ft bench and a 50 LB friction clutch motor hooked up to a treadle. The machine and bench just would not fit in my garage. am fitting it with one of these set-ups and have tested it enough to know it will work. The foot control is off of a newer sewing machine that used an AC motor speed control circuit also utilizing a Pot. I tore out the rest of the circuit and replaced the Pot with the 10K Ohm Pot my treadmill motor speed control needed. Now I can operate the sewing machine in my living room like a normal portable machine. It has as much torque as the original clutch motor and will sew right up your arm.