[How do I?] Wiring Up A Treadmill Motor (i Know, I Know)

Guess I'm late to the party, but here are a few things I've stumbled onto (or into) while working with several treadmill conversions. Others have mentioned some of them. Three sets of motors and controls are in use on my lathe, mill, and drill press; and there's one slated for the vertical bandsaw and possibly another for the horizontal. I love these things.
  1. Almost all the motors have flywheels with 1/2-13 LH threads. Nuts and taps are readily available.
  2. The easy way to get the flywheel off is to run the motor forward and then stop the shaft suddenly. The easy way to do that is to set up a SPDT switch in one side of the line, wired so in one position it feeds the motor, and in the other, it opens the line and shorts the motor. (See below for more on this.) I do have a couple of 3 HP motors that use a keyed shaft.
  3. The flywheel will add momentum to the tool, for better or worse. It's kind of like using a sledgehammer instead of an engineer's hammer. It's harder to stop, which I wouldn't like if I were tapping a hole because it could break your tap if it bogged down. In fact, I'd rather have a slip clutch for tapping.
  4. The flywheel usually has fan blades that provide cooling in proportion to the speed. But the main point of using a DC motor with PWM is that you can create a lot of torque at low RPM, and that takes a lot of current that produces a lot of heat. Better to use a PC fan that runs full speed all the time, with the bonus of continuing to cool the motor down after it stops. This is another reason to lose the flywheel.
  5. These motors have incredibly strong permanent magnets. They're great for cleaning up your chips and filings around the shop - they'll pick up every last little shard. Problem is, they weren't designed for machine shops. I put duct tape over the openings as soon as I can get to them, and don't take it off until you have to. Part of the retrofit requires making some sort of shield and screen to keep stuff from getting drawn in by the combination of magnetism, cooling airflow, and Murphy's Law.
  6. The pot is usually 5K and always linear. The value isn't critical, but I wouldn't go below 1K or above 10K without some electronics investigation. It's important that it be linear, not audio or log, to keep the speed proportional to how far you turn the dial. (If you're into that stuff, the reason the resistance isn't critical is that the pot is a voltage divider feeding a high impedance, carrying little current, so value is not a big deal. And with the other nonlinear pots, the speed changes pretty fast at one end, and pretty slow at the other.)
  7. Treadmills can be shut down by the feedback loop that tells the controller how fast the motor is going. The controller compares this with the speed control setting (pot) and cranks up or down the juice as needed to maintain the target speed, even as the load varies. That can be helpful for things like avoiding chipping carbide tips. Say you're milling an irregular piece of stock that isn't uniformly hardened (think case-hardened, or unseasoned cast iron, for example), and the speed is bogging down so you crank the pot and the speed comes back up. Then if you hit a hollow or soft spot, the mill speeds way up almost instantly, and you slide right through the hollow only to have the tips hit the case-hardened surface on the other side, and bang! Carbide doesn't like shocks like that - though it's really hard and takes hi temp beautifully, it just can't handle impact.
  8. Some controllers will shut the motor down if they don't get a signal back indicating that it's moving. Most treadmills use a magnet or stripes on the flywheel and a coil or phototransistor nearby on the frame to create the signal. Problem comes after you remove the flywheel and lost the signal generator. You can fabricate a substitute, too complicated to go into here, but I would be glad to explain offline.
  9. About stopping the motor with a switch: Actually, this is pretty effective. Here's how it works: a motor and a generator and one and the same, though optimized differently. A spinning motor generates a voltage proportional to its speed. If you disconnect the power and then put a low resistance across the motor terminals, current flows with the effect of slowing the motor down rapidly. I’ve got a kill switch on my lathe that does just this, and it stops the chuck in less than 1 second.
  10. Most switches and relays can't handle nearly as much current when it's DC as when it's AC. Look for switches rated at least 10 amps at 110 VDC. They can be hard to find, and you may have to settle for something less. Just be aware that they can overheat, open the circuit (cutting power to the motor), short the power (could fry the controller, although you can minimize the risk by putting a fuse between the controller and the reversing or shorting switch going to the motor; or - perhaps worst of all, it could flake out and suddenly turn on when you have it in the off position.
  11. Because unintended start-up could be disastrous to the operator, as well as the tooling, the machine, and the work, I would ALWAYS PUT A RELIABLE, ADEQUATELY RATED DPDT SWITCH IN THE AC LINE BEFORE THE CONTROLLER, IN A VERY HANDY LOCATION, AND ALWAYS SWITCH IT OFF WHEN NOT USING THE MOTOR. This is the only way to be sure the motor won't start up without warning.
  12. About opening the pot's center lead to turn the motor off: I would use the same AC line switch as above to kill the power absolutely for sure before assuming the motor will never start up on its own. I don't pretend to know a lot about machining, or everything about electronics, but I do have a lot of years worth of surprises and scars because I assumed circuitry was dead when it wasn't. Components fail, solder joints break - both aggravated by the vibration that machines inevitably create.
 
Thanks for the amazingly thorough reply Monty, that's a great source of information. I think it would be worth sticking all this in a "how to" sticky post once I'm done as it would be a waste for all the info to be stuck somewhere in my thread.

I think I've addressed most of your points, especially the extra switch to isolate the whole caboodle - that's the first one on the AC line in my sketch on the first page. I'll be using an illuminated switch so it should be easy to see if the controller is energised or not. All the switches I've bought are 110V 15A rated, so that should be enough - the fuse (which I'll be reusing if I can) off the treadmill I scavenged is 15A rated too.

I'm replacing the flywheels with fans mounted to the motor shaft, but if I have trouble with cooling at low speeds I can always add a PC fan and wire it to the 12V supply for the tach.

Almost finished making the adapter hub to mount a 120mm PC fan to Jake's motor. Screwed up the first one because I was tired, but this one fits perfectly. Need to tap a hole and make a set screw then that part is done. After that I need to bore out the pulley to fit and figure out a mount then the lathe motor will be ready for wiring up. I'm not sure how I'll stop chips getting inside other than the chip shield I plan on making for the lathe, but I'll ruminate on that.
 
Got the hub done, which was a comedy of errors. Started with a perfect piece of scrap alu then turned it too small. Started again with some mystery steel round, hacksawed it off, faced off both sides, drilled hole for arbor then turned the OD down to an interference fit with the fan hub. Changed to outside jaws, drilled then bored the ID to a sliding fit on the motor shaft. Then drilled and tried to tap a set screw hole for a 10-24 screw, tap wasn't having any of it, so I had to drill oversize (after sharpening that drill!) and even then I was worried about breaking the tap. Lots of cutting fluid helped but it was still a b!tch. Then I couldn't screw the set screw it (made by cutting the head off a screw and then cutting a slit for a screwdriver), turns out I picked out the only M4 screw that I'd mistakenly put in the 10-24 drawer. Doh! Anyway, got it finished and pressed in to the fan hub. Slips on and works just fine, although I'll be attaching the fan frame to the motor too as most of the air currently comes off the side of the fan.

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thanks Mike! thought I'd finished the pulley but when i put it on it had a ton of wobble, despite me boring and recutting the V in one set up. I'll add a couple more set screws so i can try and dial in the pulley better. i doubt I'd be able to make one from scratch any better - there's just not enough shaft to properly locate the pulley
 
Got the motor torn down, cleaned and mounted up:
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The treadmill rubber underneath helps a little, but I'll be bolting it to the bench on rubber grommets to cut down on a bit of electrical whine from the motor. I also realised that with a CW rotation the fan is pushing in both directions as it's rotating backwards and flipping the fan around makes it 100% pull, which is pretty ineffective for such a poor flowing object (moves a lot of air at 4000rpm though!), so I'll try running the motor CCW. The brushes are at right angles to the stator (commutator?) and there was no "set" to them that I could see when I took them out so it should be fine.

Once I get the pulley done I'll get started on the one for the drill press.

Any suggestions for control boxes? I was going to make them out of thin plywood with alu plate at the back (to bolt the drive to) and lexan at the front so I could see the lights on the controller board, but I'm not sure if I have any scraps around. Could always buy some I guess but, you know..

edit: Jake may get a kick out of this, but the frame mount for the fan and the base for the motor were both from the bits of wood he used to pack the motor he sent me :)
 
Nice job Matt.:encourage: I would either buy or build a metal box, just for fire safety.
 
thanks Jim! Good point about the box, hadn't thought of the downsides of wood and electrics :) I'll wander down to HD and see what they have and to get some ideas.
 
Im glad the packing worked in your favor! The pot should be in on or before Thursday .
When I initially found it I " put it where I would remember it" after scouring the shop twice I remembered it was in the house. :confused:
You might consider a tin bread loaf pan for an enclosure.
Sent from somewhere in East Texas Jake Parker
 
awesome, thanks Jake! Good idea on the bread pan too, there are loads of those in the kitchen :)

got the pulley wobble mystery figured out - it was run out in my 3 jaw of about 3 thou. Took a while with the DTI to figure out what was going on, but ended up with the 4 jaw on instead. I have to re-cut the V of the pulley to true it, but I'll get to that tonight and I'll do the other pulley too which has a fair bit of wobble in it.
 
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