Two of my 14 electric locomotive motors run much more erratically than the others at low speeds (below 60 rpm). (All my motors are Athearn #84040 from “blue box” kits. They are little used, but not recently manufactured. They may not be the best motors, but they are what I have to work with.)
I have tested the problem motors with nothing attached except the flywheels. They rotate smoothly through 180°, struggle with several stops and starts through 45°, advance easily 90°, and then struggle through another 45°. (Degrees approximate.) They spend more than half the time in the two problem sectors. Above about 60 rpm, the flywheels take over and the motors run fairly smoothly. The problem motors also seem to growl louder than the others at low speeds.
I suspected a bent shaft. But I can detect no displacement of the flywheels as the motor turns.
I read somewhere that the Athearn motor runs smoother if you cut 1/3 off the brush springs to lessen the pressure on the commutator. However, I am reluctant to take this drastic step.
The commutator is darkened, but not really black. Would cleaning it help? What is the best mothod?
Or I am just very lucky that my other motors run so well?
Maybe one of the poles is open or shorted. I beleive the Athearn motor is a five pole motor. Look for broken wires where the coils are connected to the commutator. Clean the commutator with fine emery paper (400 grit or finer). Check for arcing of the brushes to see if the brushes are seated OK. An open coil will be more likly to show up at low speeds.
Athearn did use 5 pole in the older BB units. Sounds like you are losing contact to the motor. So here are some questions to look at first.
1.Are you using the little metal strap on the top of the motor that goes to each truck to make contact?
When is the last time you oiled the bearings on the motor itself?
3.Have you checked the brush length to see if its got a bad brush or broken brush spring?
Are the wheels in need of a good cleaning and polishing?
Is there an oil build up on the bottom of the ground contact on the power trucks where it comes into contact with frame?
These are just some basic questions to check for before you have to do surgery. Sounds more like your loco has a contact problem to me, since the motor is making allot of noise. Test the motor at the bench first by hotwiring it. If it seems ok check the upper contact strip for rust or other problems. If need hardwire the trucks in instead of using the strip. Pull the motor and check for brush and spring problems. Let us know what you find.
Because you disconnected the motor and ran it, without anything connected to it that pretty much eliminates everything but the motor itself. Can you detect any binding if you turn it by hand? If all is smooth, bent shafts are not the issue. You would also have a severe vibration if your shafts were bent. Try cleaning the commutator with some fine sandpaper then polish with an ink eraser. Clean the groves with a Xacto knife. Inspect the brushes then oil the bearings and retest. If the problem is still present you probably have shorted pole windings, which are causing the magnetic field being generated by one or more of the poles to be weaker than the others. An open winding will result in a dead spot so that does not sound like your problem. I have not personally tried trimming the brush springs as I have replaced mine with the PPW motors. I have heard it does help a little. The theory is the motor does not have to work as hard due to the tension on the brushes being less. Supposedly the noise level will also decrease.
try some electric contact cleaner from your local auto parts store…but one WARNING, some of these products will melt plastics into a big stickey gooball…so try it on some plastic befor you spray it on the unit…
I had a Con-Cor diesel several years ago that started giving me problems a couple of weeks after I bought it. Upon opening it up, I didn’t see anything wrong at first, but later found that one of the wires running from a contact to the motor was broken inside the insulation where it couldn’t be see. Once I replaced the wire, I was back in business.
Clipping the springs will generally provide smoother low speed operation, however, if there’s not enough brush pressure at higher RPM you could start to get arcing and added carbon build up on the commutator. I never had great success by doing this. All this fiddleing with a low quality motor could be better spent in just repowering the units with A-line or Proto Power West- the difference a good can motor makes for performance is worth the cost.
Bob K.
I take a little issue with your description of Athearn motors being of low quality. They are a different type of motor, being open-frame type as oposed to a can type. There are hi and low quality motors of both types. Motors that can run for 20 years or more can hardly be considered low quality. The Athearn motors are of an older design philosophy when reliability and torque were the priority. Large brushes,large comutators with large gaps and large diameter armature wire all lend themselves to the louder heavy-duty performance with a heavier current draw but not so well to the quiet, low draw, low speed performance todays can motors. The Athearn motor is just old technology.
My recommendations regarding crawfordc’s problem: Clean the commutator and polish with a pencil eraser (be sure to blow out the eraser waste), check the brushes, they should be 3/16 to 1/4 inch long. If they haven’t been run in a while, run the motor at medium to high (12v) speed for a good minute or two to re-seat the brushes.
If you are turning the motor by hand and feel some resiistance eevery few degrees, that is normal and is called cogging and happens when the armature is “caught” between the poles of the motor and makes for less than ideal low speed running, which is why we now have “scew” wound motors.