Get the Most from Your Stock RC Elect Motor

So you wanna get the most out of your stock motor? Sean Cochran, top motor builder for Reedy Modifieds, knows more about tuning stock motors than anyone else we know, combining his professional knowledge with 12 years of racing expertise. We interviewed Sean for the latest scoop on stock motor tuning.

Tork: What's the first thing you do to a brand new stock motor?

Sean: The first thing that you want to do with a brand new motor is to determine if the brushes are useable. How? You need to see how much current the motor is drawing. The biggest problem with most stock brushes is that they don't allow enough current draw. You need to test the motor to make sure that it's drawing at least 8 amps at 3 volts with a motor fan installed. Chargers like the CEI Turbo 35 have this function built in. If you're not getting 8 amps or more, it's a good idea to change the brushes. Reedy stock motors are supplied with good brushes. With other types of motors, you have to do the current test to see if the brushes will give acceptable performance.

Tork: What's next?

Sean: Next, you'll want to remove the brushes and springs, disassemble the motor, and then cut the commutator to be absolutely sure it's true and has a perfect surface finish. Next, you'll want to check to see if your shimming is correct. Move the motor shaft shims from one side to the other until the armature is in the middle of the magnetic field. You can tell this by moving the motor shaft in and out in an assembled motor, and, when the shims are properly spaced, the magnets will naturally try to center the armature with equal endplay on each side.

Next, you'll want to break in your bushings. There are many ways to do this. I use a Dremel chucked up on the motor shaft at high RPM for several minutes, although recently I've acquired a precision reamer that I pull back through the motor to precisely ream the bushings. Lastly, you'll need to solder the selected brushes in place and reassemble the motor.

As far as springs in a stock motor go, the type of racing determines how stiff your springs should be. Off-road racing requires a firmer spring, while sedan and 1:12 scale racers will want to use a medium-firmness spring. Generally, you want to have the same spring tension on both sides, although some racers prefer a slightly stiffer spring on the positive side to reduce arching.

Tork: How do you choose the right brush?

Sean: There are many compounds and cuts of brushes. Selecting the right motor brush depends on many elements: the track, gearing, driving style, etc. Here are a few hints to help you make the best brush selection to meet your racing needs.

First, let's talk plain-face brushes. Plain-face brushes are good for larger tracks where you can carry momentum, especially where there are long straightaways where top speed is crucial. It is important to know that plain-face brushes get better with time. Your first run is not going to be your best run. Reedy brush #766 is made of our exclusive Quasar compound. Most people don't realize that plain-face brushes will usually be good for the life of the motor. You know that you need new brushes when the tips get burnt or discolored. Be sure to try to wipe the discoloring away. If it rubs off, you're still OK. If you can't rub away the discoloring, your brushes have been burnt, and it's time to change.

Serrated brushes are quite different from plain-faces. This type of brush offers more "punch" than the plain-face with less top end. If you're running off-road or on a tight track and you need quick acceleration to make the jumps, serrated brushes are the way to go. They need to be replaced, however, after the first few runs. Reedy brush #767 is our Quasar serrated brush version. Normally, we use full-face brushes, but, if runtime is a problem, I will occasionally use the #768 slotted serrated brush or the #769 cavity serrated brush to get added battery life. You should know that all three serrated Reedy brushes are the same compound.

The number of competitive runs you get out of a serrated brush will depend on gearing, the track, and other racing elements. Typically, the first and second runs are the best, while the third run falls off slightly. Then, it's usually time to rebuild the motor with new brushes and a commutator cut to bring back the original performance.

Lately, I've been experimenting with narrowing the brush slightly, reducing the overlap. This allows the car to roll more freely through the turns when you're off power, and is advantageous on some tracks.

Tork: How about break-in?

Sean: Once you've reassembled your stock motor, it's time to break it in. How long you break in your motor depends on what type of brushes you're using. For plain-face brushes, you'll want to break them in for 200 seconds at 3 volts, free-running the motor with a fan and then by running the motor on the track. For the serrated brushes, free-run the motor with a fan for only 30 seconds at 3 volts. Install it in the car, and go race. Don't run the motor on the track to further break in the brushes, because the first and second runs will be the best.

Tork: How often do you true the commutator?

Sean: How often you re-true is largely dependent upon what type of brushes you've selected. If serrated brushes are being used, I recommend truing the commutator every time you change your brushes—about every third to fourth run. Plain-face brushes are a little different. With plain-face brushes, you'll want to wait until "motor falls off," giving reduced performance. This will require you to pay close attention to how your motor is running. Typically, you should be able to run six or seven times before you will need to re-true with plain-face brushes. I normally true the comm before each race. The second and third runs, the motor will be at peak performance. Be sure that you don't cut your commutator too small. I like to keep mine as big as possible to maintain higher RPM's. Each comm will vary with how much you need to trim it, but remember—in the case of commutators, bigger is better. The smallest diameter I'd recommend using is .270". If your comm gets down to this size, it's time to replace the armature.

Tork: Do you use motor drops?

Sean: In my experience, motor drops are not something I would recommend. Motor drops don't offer any additional performance, and, in fact, can cause the motor to burn up. Motor drops are petroleum-based, and promote arcing between your comm and brushes. To help you understand a common misconception, motor drops may offer a short-term gain because you will see your RPM spike. However, in the long run, they cause burning and will result in performance deterioration. Whether or not to use drops is up to you, but our experts wouldn't recommend it.

My last bit of advice is that stock motors will only put out so much power and go so fast. For most drivers, spending more time working on driving skills and strategies can have the greatest gains. While there are a lot of things that can be done to improve the performance of a stock motor, there aren't major differences among stock motors, but keeping everyone on an even playing field is the idea anyway. The key to winning is the ability to make minor adjustments, good driving skills and a little bit of luck! And don't forget—always have fun while you race!

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Copyright 2008 Horizon Hobby, Inc. All Rights Reserved. Used With Permission.