Motor Balancing

This is a problem that is all too common in model train motors, especially mass produced, inexpensive ones: unbalanced armatures. An out of balance armature translates into vibration that in is transmitted directly to the frame and then the shell -- which becomes resonant -- especially when motors are rigidly mounted. Some manufacturers have actually taken steps to balance their motors at the factory, and surprisingly Mehano did it in the early 60's with the first of the 5 pole motors for the first C-Liners and BL-2's. They did it by drilling out the pole or poles on the heavier side of the armature to lighten them. I did the same thing here on a New One motor some years ago with mixed results. It was hard to find a sweet spot, balance-wise. The motor was a dog anyway, with worn bearings (the top one was soldered in, a definite no-no).

Another technique is to add material to the lighter side. Epoxy putty works great for this purpose, and I've seen it a lot in Roco motors, particularly those huge cans from the Model Power and Con-Cor era. When I first encountered it, I thought modelers were doing it to quiet their locos, but I've seen it too many times for it to be an aftermarket modification, and every time it was done with Green Stuff, the epoxy putty that used to be made by Duro and was available in every hardware store. The stuff has no equal and is used by modelers because it casts and carves beautifully.

I've had one of those big Roco can motors for about 4 years now that I bought at an Allentown show. I picked it out of a junk box for $1, and aside from a cursory cleaning and oiling I hadn't done anything with it. It vibrated horribly, which explains how it ended up in the white elephant box. A few weeks ago I finally ordered some Green Stuff while Amazon still had their January free shipping, so I decided to give it whirl (pun intended).

A Model Railroader article from years ago described how to balance Athearn armatures. They recommended resting the armature shaft across two upturned razor blades to determine the heavy side, which would obviously hang downward. With an armature this large I just placed it across the open jaws of my machine vise, and it didn't waste any time showing me which side was heaviest. Not surprisingly, it was the side with a heavy wrap of wire spanning two poles.

I mixed up some putty (as I'd been warned, this stuff sticks to everything), and pressed it into the pole gap I'd marked. It still favored the heavy side, so I added some more, covering the windings above and below the poles.

Dirty enough for you yet Sandy? 

Now it seemed to balance better, and a quick reassembly and test at low speed showed that it runs much more smoothly. No noticeable vibration. I just have to wait 24 hours for the epoxy to set up.

So that's all there is to it, aside from making sure you keep the epoxy within the armature profile. The waxed paper was a lifesaver when it came time to press it into the windings and give it a clean finish. Everything else stuck to it.

Btw, get a load of these brushes. Overkill much?