Ted sent me these questions by e-mail. As he suggested doing and as I prefer to do, I am posting them here so that others may discuss and benefit:
Dear Bob,
I have been reading some of your posts on the CTT forum and find them very informative! Although I am not a regular there, perhaps you can answer some questions that have been bugging me for a long time about Lionel “Pullmor” AC motors.
[Please forgive my an aversion to calling them by that name, since it was originally American Flyer’s name for what we now call “traction tires”, and was applied by Lionel to their motors only in recent times after they bought American Flyer. I would also not call them “AC” motors, since they also run just fine on DC and in fact used DC pretty much exclusively in the very early days. What they are is “universal” motors, that is, series-wound motors with laminated magnetic circuits designed to run on either AC or DC.]
Some trains run better than others. In my experience, the best running Lionels are the ones built from about 1950-1957. Early postwar (1940s) locos tend to be clumsy for switching and run very fast. Most agree that the company cut a lot of corners as demand shifted away from trains in the late 1950s. MPC is inferior, or at best equal to the original Postwar. Like the '40s locos, MPC motors tend to run FASTER at a given voltage than their Postwar counterparts. I always imagined this was because no 20-volt transformers were produced during the MPC era, so to get the same speed, Lionel retuned the Pullmor motor for more RPM at a lower voltage. I presume that faster operation was obtained through differences in the wire gauge, number of turns, etc., and also the number of laminations, thickness, metallurgy, etc.
[It is obviously possible to design motors for any particular voltage range, simply by changing the wire size and number of turns. The magnetic circuit&nbs
I can’t resist a motor question. I think Ted actually needs to take a class on motors. I mean no disrespect. You covered a lot of characteristics about motors. You know what you want to do but don’t know how to do it. It seems TMCC does the trick but you want to find another way. I never took the class but I will try to make some points.
From my experience the armature has 3 windings (poles)these are connected to a commutator plate, the other ends are soldered together and isolated from the armature ground. The Lionel armature I wound had 97 turns of 26 gage wire( at each pole). Yep I counted them. I settled on 50 turns. because any more would not fit in the housing. Winding is an art and by hand it will try your patience. I did start with 97 turns but my work was bulky so the the brush plate was raised for the bench test the motor ran but the fields rubbed against the body and shorted. I didn’t notice any speed difference between the 97 and 50 turn tests. The motor will run which is what I want but I’m predicting a power loss. I will notice this in climbing and pulling, but the motor will still run fast.
More windings (turns)will give you more speed. The motor is really too small to alter by winding, in the end only so much wire will fit. However in the smaller scales they went to DC and pulse control and those motors have 5 windings (poles).
Gearing is everything, My Army switcher runs slow because it is geared that way. To run slow you need a large gear and that is where the wheel size limits the gear. Larger wheels and you go off the scale. Belts would be an option but you have to be a machinist to manufacture the parts.
I hope I’m not leading you astray, I found the letter very interesting and this should be a good thread.
All else being equal, Dub, the more turns, the higher the voltage for the same speed, or the lower the speed for the same voltage. Each turn sees the same amount of magnetic flux change each revolution and the same induced voltage per turn; so twice the number of turns means twice the total induced voltage. With twice as many turns, you need only half the current to get the same torque, which is good because you need wire with half the cross-sectional area to be able to squeeze all those turns into the armature. Similar arguments apply to the field coil. The result is that the rewound motor will behave the same mechanically as the original, but electrically will have twice the voltage across it and half the current through it. It’s just like putting a 1:2 transformer in front of the motor.
Of course, there is the insulation on the wire to consider. It probably makes up a greater fraction of the wire thickness when the wire is small. So it might not be completely practical to make this kind of change. And, as you discovered, motor rewinding is quite an art, even if you stick to the same wire size.
One simple alternative to rewinding, for two-motor locomotives, is simply to wire the motors in series. This will accomplish the same voltage-speed scaling as rewinding, without the hassle. One minor complication is that the two fields have to be put in series separately from the two armatures, so that the e-unit can reverse the armatures’ polarity without disturbing the fields.
By the way, if anyone has noticed that armatures always seem to have an odd number of windings and commutator segments, I can tell you that there’s a reason. The armature windings are in series in a complete ring, with a commutator segment connected at each junction in the ring. With 3 windings, you have at any one time two windings in parallel with one winding. As the armature rotates, one brush at a time moves to the next junction
EDIT: I GOT INTERRUPTED A MILLION TIMES AND WOUND UP POSTING THIS AFTER BOB’S POST. SO MY IGNORANCE IS THERE FOR ALL TO READ.
[quote user=“Dub”]
I can’t resist a motor question. I think Ted actually needs to take a class on motors. I mean no disrespect. You covered a lot of characteristics about motors. You know what you want to do but don’t know how to do it. It seems TMCC does the trick but you want to find another way. I never took the class but I will try to make some points.
From my experience the armature has 3 windings these are connected to a commutator plate, the other ends are soldered together and isolated from the armature ground. The Lionel armature I wound had 97 turns of 26 gage wire. Yep I counted them. I settled on 50 turns. because any more would not fit in the housing. Winding is an art and by hand it will try your patience. I did start with 97 turns but my work was bulky so the the brush plate was raised for the bench test the motor ran but the fields rubbed against the body and shorted. I didn’t notice any speed difference between the 97 and 50 turn tests. The motor will run which is what I want but I’m predicting a power loss. I will notice this in climbing and pulling, but the motor will still run fast.
More windings will give you more speed. The motor is really to small to alter by winding, inthe end only so much wire will fit. However in the smaller scales they went to DC and pulse control and those motors have 5 windings.
Gearing is everything, My Army switcher runs slow because it is geared that way. To run slow you need a large gear and that is where the wheel size limits the gear. Larger wheels and you go off the scale. Belts would be an option but you have to be a machinist to manufacture the parts.
I hope I’m not leading you astray, I found the letter very interesting and this should be a good thread.
Thanks for the response Bob and Jack! Any information about motors is appreciated. Jack I did enjoy the slot car info. I was into Aurora HO in my youth but I never altered the number of windings.
My rewinding experiment is not at end . I may not settle on 50 turns. When I get another bad armature I will try the 30 gage wire and try to perfect my technique.
For general information the enamel coated wire is available at Radio shack. For 5 bucks you get 3 rolls, 22,26,and 30 gage wire. The 26 gage roll had enough wire to do five poles. The 30 gage wire is the size on the decoupler electromagnet and the 24 gage looks like the size used on the coil field for the motor.
Rewinding motors by hand while keeping the windings uniform, straight, tight, and contained (no clearance issues beyond the exterior pole surfaces) can be done well. But it requires practice. I rewound about a half dozen engines before I got it right, fuctionally and aesthetically. The motor on the sixth try was a keeper, won a lot of races.
The good news is that toy train motors don’t operate at insanely high rpm, so balancing the armatures after rewinding doesn’t become an issue. For the same reason (low rpm), you don’t have to epoxy the windings after rewinding to avoid wire movement (outward). You just need to know two things.
If we could answer roughly (1) the correct wire gauge and (2) the # of windings for the application we require…trial and error can be discouraging. Bob gave us a start. I would be looking for lower rpm at a given voltage in exchange for the torque gain. The consist would operate slower at a given voltage but the additional torque would be there for added cars.
You said so well that the train engines don’t give you gearing options because of their positioning and clearance. Replacement of an existing ratio is easy, the available replacement gears may be of a different material but their dimension is the same. Changing gear ratios, not much choice in the matter. A lower (higher numerically) gear ratio would mask some of the issues some have with uneven track voltage around the layout. So many great posts and threads on how to provide uniform power over the entire track and switches.
But many like me simply look at their engines’ modest pulling power, see those spinning wheels, and would love to tap that wasted power. On upgrades it only gets worse and downgrades require throttle adjustment. As you said, some would like to gear the engines for smoother sta
The speed of an ideal series motor actually has no upper limit. When there is no mechanical load, the speed is theoretically infinite at any finite voltage. Of course, there is always some friction and wind resistance; but this fact explains why a light (unloaded) locomotive can run so fast.
I doubt that any rewinding is going to get more torque out of the motor. The iron in the magnetic circuit is probably saturated or close to it at full transformer voltage. Otherwise, Lionel would have exploited that to make a smaller motor that was saturated. The only changes that rewinding is likely to make are electrical and approximately equivalent to putting a second transformer upstream of the motor. Like wiring two motors in series, they just get the same performance at a different place on the existing transformer’s control range. This can make it easier to control a locomotive by expanding its low-speed range to use more of the transformer’s range, at the expense of losing high-speed performance.
In any case, once the wheels slip, increasing the motor torque won’t help.