Inside Electric Motors

Motor Tuning Advice from a Pro

Words: Gary Katzer

Electric motor technology is one of those things that is constantly changing. Just when you feel like you have things figured out, someone goes and releases a new motor, brush compound, or endbell design. It can be difficult to understand your motor, how to maintain it, and how exactly to tune your motor. Troy Schroeder, owner of Fantom Racing, has provided the horsepower for many national champions in on-road, off-road, and oval classes. He recently provided his input on motor tuning, cleaning, and how to get the most out of your power plant.

Motor technology has changed quite a bit over just the last few years. As a motor builder and tuner, the challenge to stay on top of things and stay ahead of the curve must be a challenge. You have an advantage in being able to use Epic, TOP, or Yokomo-based motors. When you begin to tune a motor, what is the process you go through in deciding what brush and spring to use and, in the case of modified motors, what sort of timing to run?

Troy Schroeder
Before I go to an event, I already know which base motors have more rpm and which ones have more torque. Once I have my base platform chosen, I build armatures so that I have a wide range or performance, from high-torque armatures to high-rpm armatures. Once we get to an event, we start out with a base setting, then as the race progresses we fine-tune our motors to exactly what they need to be. By the end of practice, we tend to be in more of a fine-tuning mode, making minor tweaks to improve performance and drop the lap times versus broad changes. Whether it's altering the cut of a brush, running a specific amount of timing, spring increase or decrease, it all makes a difference and all gets squared away by testing and trying different things.

Brush size and shape has changed over the number of years. From left to right, here's an example of a TOP V2 Cylindrical brush, a laydown brush, and a standup brush. Below is an example of the new Octagon long-wear brush.

Motor brush technology has really gone in a number of different directions. The Slot Machine 2 introduced the world to "laydown" brushes for stock motors; the P-94 motor introduced oversized brushes; the TOP V2 motors introduced cylindrical and angled brushes; now the Shock motors have octagon-shaped brushes. How do you determine which variation of brush is best for a particular application?

For instance, the track layout here at this year's Snowbirds requires more punch than rpm, so we decided to use a larger brush. The P-94 brush is what we started with and we worked our way down from there. In my opinion, the way to go is the elliptical shaped brush because it creates the most surface area for current transfer while keeping the motor cogging to a minimum. That's the big key; you don't want any cogging whatsoever,but you want the largest surface area that you can get for improved current flow. The larger surface areas improve the torque of your motor as well.

Is the cogging issue the reason laydown brushes work so very well in a stock and 19T motor but Stand-Up brushes still dominate the modified classes?

Exactly. With a stock or 19-turn motor brush, you can get away with more brush overlap. The lower the turn (of the motor), the more specific you need to get with the timing and brush compound.

I go way back to some pretty old-school brushes. I remember things like the H-cut, diamond cut, timed brushes, and more. In more recent years, however, it seems like fewer people are actually playing with brush shapes, relying instead simply on the full face of the brush and the brush compound to create power. Is this perception true or are just as many people experimenting with brush cuts?

Yeah, don't be fooled; all the top guys are utilizing some sort of cut on their brushes. Some racers tend to be lazy and just run a full-face brush because with the batteries we utilize now it doesn't seem quite as critical. The top echelon guys are out there trying to fine-tune their motors and the brush cuts are very important, especially so when you're using a lot of timing in the motor. For example, a horizontal slot will reduce the amount of arching that will happen as the brush face rubs against the commutator. Also, on larger tracks we'll shave some material off the trailing edge of a brush and gear up. Don't be fooled into thinking that people aren't using angled or cut brushes.

If you've never taken a motor apart, here's what one looks like. The different parts are the endbell (top left), can (top right), brushes (soldered to the endbell), motor springs, and the armature.

Some were initially against "rebuildable" stock motors. Some feared that cheating would increase because of how much easier it would be to get inside the motor to tinker with things. As time has gone on though, that hasn't materialized and motors are lasting longer than ever now because maintenance is so much easier. Racers can now cut their commutator on a lathe whenever it's needed. On stock motors, you can often find greater excessive wear around the slots in the commutator than what a modified motor may have. It sounds like this is directly related to the arching and the overlap you've mentioned. Would using a timed brush or shaving material off the trailing edge help to prevent this issue? And just as important, what would that do to the performance of the motor?

This again is caused by the overlap of the brush or using excessive timing. Arching is never good; heat is never good. The idea is to have the most efficient motor possible with the most amount of torque. That's difficult to do without making some sort of hole or cut in the face of the brush.
I'm personally in favor of rebuildable stock motors, obviously; I'm also in favor of ball bearings in stock motors. Ball bearings would help make the motors more efficient and more user- friendly to the average person who may not understand how to maintain a bushing versus a bearing. It's tough, too, because there are so many motors out there right now that turn so many rpm's and draw so much current that it's hard for the end user to figure out what brush compound and spring to run. But I definitely think companies need to look at putting ball bearings into stock motors.

Some people believe that you should break in a motor with new brushes until the serrations are gone. Others believe that once the serrations are gone, the brushes should be replaced. What's a good rule of thumb to follow on this? How would you recommend someone prepare their motor before running it for the first time?

The reason why serrated brushes were even made was to speed up break-in. Serrations make it easier for the brush to become broken in properly on a particular motor. Serrated brushes are also more efficient and aid in cooling, which most people don't realize. I definitely recommend that if someone is going to re-run a particular set of brushes, that you re-serrate them each and every time they go back into the motor. As far as the time that it takes for the brushes to actually break in, I always use the rule of 2: 2-minutes at 2-volts. What I will do when breaking in a motor is to run it for two minutes with a fan on the output shaft of the motor, keep an eye on the amp-draw of the motor and decide from there what a particular motor may need in the way of tuning. If I'm not seeing the type of amp draw that I like to see, I inspect the motor to make sure the brush hoods are properly aligned or other things to try to bring the performance up. You should expect to see the amp draw increase as the brushes break in. For a stock motor, I generally look for the amp draw to be between 9-11 amps (at 2 volts). Then what I'll do is put a drop of Fantom Comm Drops in the motor, run the motor for about 24 seconds once the brushes are all broken in, and from that point on I don't touch the motor until after it's been run in the car.

Comm drops can enhance the performance of your motor. Applying just a little on each brush can improve amp draw, RPM, and torque.

How and why would you use Comm Drops on a motor?

Many companies use some sort of petroleum-base for their Comm Drops, and that will really create an increase to the motor's amp draw. But then again, amp draw alone is not always the best way to rate the performance of a particular motor. We use a synthetic blend in our comm drops instead because we believe it provides a better amp flow for the motor.

One of the most confusing concepts for newcomers to grasp is that when you install a "hotter" motor, you actually gear it with a smaller pinion. What are some of the other mistakes that you see people make?

There are two top mistakes I see people make. The first would be to increase the timing on a motor to increase the rpm's on a large track. The last thing you want to do is increase the rpm on a motor by cranking the timing. We actually tend to do the opposite on large tracks and turn the timing down to increase the torque of a motor and simply gear up. As a general rule of thumb, on a large track you'll be faster if you run less timing and more gear, and on a smaller track you will be faster if you run more timing and a smaller pinion gear. The second mistake I see would be people who clean the commutator and the brushes with a comm stick, instead of actually turning it on a lathe, because they believe they are extending the life of the motor and comm by not cutting so frequently. You're actually better off cutting a motor on a lathe after each run than to clean it with a comm stick and cut the motor every third run or so. The reason is that you will actually have to remove less material from the commutator to get a nice smooth surface if you cut it after every run versus when the commutator has really been run.

When replacing the brushes, it's well known that it is more efficient to solder the brush lead to the hoods than to use the screw-on terminals. Is it better to solder the lead onto the motor's tab where the ESC wires get soldered, or to solder it onto the hood itself?

You definitely want to have the most contact area and the most efficient current transfer possible. I'm not opposed to people soldering the brush shunt to the motor tab where the ESC leads get soldered, but you really need to be careful. The biggest problem now, and it's kind of a good problem, is that the brushes are lasting so long now that the brush shunt can get ruined before the brush does. You need to pay particular attention to your brush shunts because you'll find that solder can get wicked up on the brush shunts, and they can become brittle and basically ruined. That's where soldering to the side of the hood can be more beneficial, because the connection is still very efficient but you won't have to worry about the shunt bei

Some people believe that you should break in a motor with new brushes until the serrations are gone. Others believe that once the serrations are gone, the brushes should be replaced. What's a good rule of thumb to follow on this? How would you recommend someone prepare their motor before running it for the first time?

With the new high-silver content brushes, you can get multiple runs out of a set before you even need to think about them. Like I mentioned before though, it's key to maintain your motor even though you're not replacing brushes. Skim the comm after every run, clean the brush base, take care of your brush shunts, and re-serrate them. If you follow that maintenance pattern, you're going to get a lot of runs out of a set of brushes; upwards of 30 runs! With the standard brushes that we've seen in the past, normally speaking with any serrations left on the brush, I'll simply clean it and re-run it again. If the serrations are completely worn off, the only way that I'll reuse that brush is if the corners of the brush don't show any signs of being burnt. Once the corners have been burnt, the brush has lost its lubricating properties which will reduce performance and increase wear and tear on the comm.
As far as replacing the springs, that's something that is overlooked way too frequently. The springs will lose their tension from heat and, while they may feel fine at room temperature, once they heat up under race conditions, the spring actually becomes softer. It's something you may not realize in the pits but it's noticeable on the track. You should replace your springs once every ten runs or so.

Some manufacturers have come out with motor zappers to increase the strength of the magnetic field. Does this actually make a difference on the track or is it a gimmick?

We at Fantom have a high-quality magnet zapper that we use on every motor that leaves our shop. Does it make a big difference to the average racer that makes up 95% of the racing community? Yes and no. There is an increase in performance, but if you make one mistake on the track, the advantage that you've gained by zapping your magnets is neutralized. But at the highest level of competition it can make a real difference to the outcome of a race. Generally speaking, the average racer shouldn't worry about their magnets “going flat” on them. The magnets will lose a little bit of strength after being run a few times, but after that you can run a motor 100 times and the field won't drop any more after that.

The Stock and 19-Turn classes are still extremely popular around the USA. In some parts of Japan and Asia, they have gone to a 23-turn Spec motor and 8-minute long races for sedans. Do you foresee this as a viable option that could eventually takeoff here in the USA?

Not really; longer races takes away from the amount of racers that can participate in an event and how large an event can really be. Race weekends can only be so long and you can only fit so many heats into a day, so to accommodate the longer race format you'd have to restrict the amount of entrants to be able to fit the race program into the available time. Plus, just the amount of concentration that it takes the average driver to drive one of these cars for five minutes is incredible. It's definitely underestimated how much concentration people need to focus on their car during a race. I'm personally a fan of the 5-minute formats.

The JMRCA (the governing body in Japan, similar to ROAR here in the USA) recently announced a rule change for their upcoming 2006 racing season. All sedan classes will now have the number of cells allowed in the car reduced from 6 to 4. This seemed to help out the 1/12 scale division along with oval racing here in the USA. Do you see this coming to the USA and what are your feelings on it?

I don't think it's quite time for that…and I don't think the technology has quite gotten up to that level where I would say it's a viable option. I think we're honestly having too much fun right now with the voltage and the rip that we have available to us to take away 2-cells and 2.4-volts. I think eventually it might be the right move, because it definitely helps people budget for their hobby easier, and maybe in a couple years it might work here as an option in the U.S.

What advice would you offer the person who is just starting to tinker with their motors in an effort to improve performance and extend the life of their motors?

My biggest rule is that after each run check your motor, keep it clean, and skim the comm regularly instead of putting it off or letting it go. Make sure you armature is centered in the motor's magnetic field and not over-shimmed, which would cause excessive drag, binding the motor up, causing the motor to overheat and slow down. You need to ensure that the brush hoods are always properly aligned for the best performance and wear on the comm and brushes. One of the biggest things that people overlook is the possibility that your lathe's bit is cutting on a taper; you need to ensure that your lathe is always cutting square. Make sure, when you install a brush into the hood, that the spring isn't skewed on the back of the brush. If it is, the spring will not provide the proper tension on the brush, potentially causing a brush to hang up during a run.

The motor on the right has been run a number of times, while the motor on the left is brand new. The brush on the right is slightly discolored, which indicates possible over-gearing.

Maintain your motor's performance by cutting the commutator on a motor lathe. A motor lathe uses a carbide or diamond bit to skim the surface of the commutator, providing a clean and smooth surface for the brushes to ride on.

Keeping ahead of the learning curve can be challenging, but taking some time and not being afraid to experiment can pay huge dividends. Keeping your motor properly cleaned and maintained can make the difference between winning and not making the A-Main. We'd like to thank Troy Schroeder from Fantom Racing for taking time to answer our questions.






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