I get a number of emails asking if I can service someone's motors. Sorry I am not in the motor rewinding business. Most cities have motor repair shops that could probably do a much better job than I plus I only work on very small motors that cost less than 10 bucks each.
Now, back to the motors. If you want to try this yourself be prepared to buy more than one motor. I get them bulk from a All Electronics Corp. They are about $2 each.
I usually rewind motors in order to give it fewer windings of a heavier gauge of wire. This decreases the resistance and increases the RPMs per volt. However, the no-load current goes up. I also rewind motors as part of my ongoing process of getting to understand motor physics and their limitations. These motors are so cheap I have no problem running one or two to destruction.
Depending on the motor, disassembly usually consists of carefully bending back the metal tabs that hold the plastic end on and gently sliding it off. WARNING: some of the Mabuchi motors (for example the ones that look like cylinders that have been flattened on two sides) have brush holders that come off easily. Most of the brushes consist of two small copper alloy leafs in the shape of a U that lie against the cummutator. They bend very easily and are a real pain to get back into shape. Also, these types of brushes usually have some kind of goo on them that I guess is designed to reduce arcing. Anyone out there know what this stuff is? I've learned not to clean it off when taking apart motors. Unfortunately, These brushes are cheap and don't seem to last very long under higher current. Some of the better motors have copper alloy springs that hold down little blocks of what appear to be graphite. Occasionally, I have been able to mix and match bits and pieces of motors to get a good final arrangement.
The cummutator is usually a three pole arrangement and the armature windings are three pole as well. A "130 sized" motor uses 70 turns of a wire that looks about a #32 single wire gauge. The windings are usually a single long piece of wire that is soldered to a tab on the cummutator, is wound around the armature poles, makes a stop at the other poles and comes around full circle. When unwinding, I keep the wire on a spool (you never know when it might come in handy) and I very carefully illustrate how the windings come off and how they are connected on a piece of paper. Then, working in the opposite direction, I put on the windings of the larger wire. Of the motors that I have (un)wound, they were wired in this fashion:
Look at the armature from the end with the cummutator. All of the motors I have done have had three laminated silicon steel poles that are wrapped with the windings. These we will label 1, 2 and 3. You will see that between each pole is a lug that is attached to the commutator. We'll call these A, B and C with A being between pole 1 and pole 2. Both are labeled clockwise. To wind, the wire goes from lug A, around pole 3, to lug B, around pole 1, to lug C, around pole 2 and back to lug A. If you view the armature from the side with the cummutator to the left the windings go around in a counter-clockwise direction. I use one long piece of wire and as I pass over a lug I *VERY* carefully scrape off the insulation, wrap it once around the lug and give it a dab of solder when I am done. Easy as pie.
I've found the easiest way to wind was the rotate the armature around while feeding the wire out between my fingers instead of trying to hold the armature steady, especially the smaller ones. Also, I always try to keep a good tension and not have the windings criss-cross. Both allow the maximum number of windings. I also count out loud and try not to daydream while I am doing it. Having a motor with a different number of windings on the poles would be bad.
I did a mabuchi like the one I talked about above and it took 40 turns of #28 or #29 wire that got from the coils of TV. The motor that resulted has a very similar RPM/volt that one of Dick Miller's MM1s has and will fly an airplane on one cell or use 2 cells and a geared arrangement. I just have to make sure that the current stays below 3 amps or it will fry. Its also not as efficient as the MM1 (I did some head-to-head tests) but will probably make an excellent one cell motor for my Peck One Night-28 (which is where its going). Fortunately, I prescribe to Dick Miller's point of view that a motor running for a minute with enough power for a decent climb is quite sufficient for free flight aircraft. As long as the power is ok and I am not putting excessive wear on the motor, I'm happy. Once my equipment is set up I will be publishing the motor constants for these on this web page.
The main reason I rewind motors is to try and perhaps get a motor that will fit a particular situation. For example, I have a 35cm wingspan bipe that is almost ready. I was planning on using a motor like the flat-sided mabuchi 130 but with it the airplane is so nose heavy that I would have to install the batteries past the tail of the airplane (the full-sized airplane used an inline engine and it had quite a long nose for a bipe). I could extend the motor shaft but then I would have to rip out all of this structure I put in to allow me to make thrust adjustments. Looking through my 50+ motors I came across a Mabuchi motor made for a disk camera that looks like it will be light (10 grams) and still be large enough to handle the 4-5 watts to fly my airplane. It looks very much like the photos I've seen of the Hiline micro-4. However, its wound for a much higher voltage (170 turns of this very fine wire) and I want to stay to 2 cells to keep the airplane's weight down. Using some wire out of an old transformer I rewound it with 62 turns (I don't know the gauge since its too small for me to measure accurately). Here is a picture of what I am talking about.
Last modified: March 20, 1997