FarrOut Slot Racing Club
Michael's Underwater Motor Break-in


1.                  PURPOSE

To Maximize electrical contact between rotating commutator and stationary brushes for optimum performance.

2.                  RESPONSIBILITIES

Racer’s Wife/Girlfriend

3.                  REFERENCE DOCUMENTS


4.                  DETAILED INSTRUCTIONS

4.1              Explanation

4.1.1          Motor brushes contact the commutator on the armature shaft inside the motor to deliver electrical current to the wire windings of the armature to create magnetic fields that interact with stationary magnets mounted inside the motor can which causes the armature assembly to rotate. Higher current creates more powerful fields and the resultant higher speeds as exemplified when a slot car is at full throttle voltage. The break-in process articulates the contact surface of the brushes to the curved commutator surface through frictional wear for maximum contact with minimal power loss due to resistance. Sealed-can motors such as the Ninco NC-1 are made non-serviceable with brushes of a relatively hard composition to extend motor life without brush replacement. This hard brush material wears the commutator surface during break-in creating diminishing returns, i.e. the commutator wears out as the brushes wear in. Wet break-in theoretically allows efficient break-in while protecting the commutator from excessive wear.

4.2              Immersing motors in distilled water during break-in

Distilled water cools and lubricates the commutator during break-in while floating away wear debris that would otherwise foul the contact surfaces and bearings.

4.2.1          Distilled water must be used to prevent fluid conductivity

4.2.2          Additional break-in duration required due to reduced frictional wear; (this is where wife/girlfriend comes in) as it takes as much as six hours.  I use disposable clear plastic cups from Costco so that water condition is visible and may be changed when noticeably contaminated.

4.3              Low voltage during break-in

Low voltage during break-in minimizes arcing that pits and damages the contact surfaces and helps control temperature.

4.3.1          Wet break-in may use higher voltage than dry break-in due to the cooling and lubricating effects of the liquid. I use 3.7 volts from a mobile phone charger because these low-voltage power supplies are so cheap and readily available.

4.4              Alcohol rinse

Isopropyl rubbing alcohol absorbs moisture inside the motor to aid drying, minimizes corrosion, and cleans effectively.

5.                  Final dry break-in

5.1.1          Relatively short duration dry break-in after wet break-in perfects contact surface by removing minor corrosion and is necessary for optimal performance.

6.                  Materials

6.1.1          High quality light viscosity lubricating oil such as Mobil 1

6.1.2          Clear plastic disposable cups/glasses or other suitable container

6.1.3          Distilled water

6.1.4          Articulating modeler’s vise/clamp

6.1.5          Low voltage power supply

6.1.6          Isopropyl Rubbing Alcohol

6.1.7          Compressed air

6.1.8          Wife/girlfriend/slave/friend/kind relative (optional)

7.                  Process steps

7.1.1          Lubricate motor bearings with quality oil such as light viscosity Mobil 1 and let the oil absorb into the bearings for about 24 hrs prior to break-in.

7.1.2          Immerse motor so that it is suspended vertically in distilled water with contact area up so that debris float out of the motor at the top.

7.1.3          Apply low voltage and let motor run for approximately six hours while monitoring carefully and replacing dirty water as necessary.

7.1.4          After completed duration, immediately immerse in clean isopropyl alcohol and continue running for three minutes.

7.1.5          Remove from alcohol and let run dry for not more than thirty seconds (remember that shaft bearings are un-lubricated out of the water until re-oiled), then immediately dry using compressed air blown into access holes.

7.1.6          Re-oil motor bearings with quality oil such as light viscosity Mobil 1.

7.1.7          Apply low voltage and let run dry for about twenty minutes.

7.1.8          Repeat with as many motors as you can afford and wife/girlfriend will do for you.

7.1.9          Install and test

7.1.10      Take wife/girlfriend to dinner


The test and tune was great fun and very helpful in providing valuable knowledge that would normally require several disappointing races to realize. For example, my Ninco Le Mans car was faster without weight added while testing alone, but very vulnerable to any side contact from another car causing it to de-slot. I added a bit of weight and it became much more stable in competition albeit a tad slower. I was also able to determine that I was giving up about one car length to average cars in each straight and that I need to work on that. Here are the rest of my thoughts after testing my cars and observing others:

Weight tuned classes

1. The thin weight sheets from Victory Station are the best. The adhesive is reliable even in hard crashes yet removable with some effort without ANY damage to the chassis whatsoever and the thinness prevents contact with the track.

2. Optimal weight for our cars is between 75 and 90 grams total and weight should be placed under the chassis in front of the rear axle and extend to approximately half way between the motor and the guide. Realizing that I fine tuned the weights on my cars during the test & tune day, I used a slipknot string to check them afterwards and discovered some things I find very interesting. Distance from guide pivot measured to rear axle divided by distance from horizontal CG (slipknot location when car is dangling perfectly balanced front to rear) measured to rear axle, multiplied by 100, equals the weight bias percentage. N :- N = A x 100 =% Vertical CG is determined by where the slipknot location when the car is dangling on its side with the chassis perfectly vertical from side to side. By day's end I had added weight to the Saleen, added more weight to the rear of the Cobra, and shifted some weight from front to rear on the RS200, all based solely on handling characteristics. Despite the fact that each car is very different, the horizontal weight balance is now very much the same for all three at approximately 35% front and 65% rear + - 1mm measuring tolerance from the rear axle to the guide pivot and the CG is also nearly identical at approximately 3mm above the rear axle for the Saleen and 2 mm for both the RS200and Cobra. Interesting isn't it? Of course, the optimal balance will vary depending on traction and track conditions.

3. All the tips that Stephen posted at last year’s test and tune and on the website (such as slightly loose screws, etc.) really work and cars should be properly tuned and adjusted BEFORE attempting to weight tune.

4. With everything set up properly such as tire truing and sizes, front axle movement, braids, and etc. then front to rear weight balance will affect whether the car's handling is loose (tail happy) or tight (front end rolls out of the slot in the turns).

All classes except 4W/D

1. Front axle movement: Rules dictate that front tires MUST touch the track and roll when the car moves but it is legal and advisable to true the front tires so that some of the car's front end weight rests on the guide. (with Ninco cars for example, you should be able to move the front tires up and down about 1/16th" with the car sitting in the slot).

All classes

2. It's much easier to eliminate drag than to find an especially good motor. Carefully oil the motor and axle bearings and use plastic-friendly light grease on the gears. Check cars carefully to be certain that everything moves smoothly and freely.

3. "Running-in" a car really works to make them smoother, quieter, and faster. If you have a "rolling road", great, but if not you can lay the car on its roof and use 2 to 4 volts for about an hour to gain noticeable improvements (I use a mobile phone charger rated at 3.7 volts and nowadays one can find low voltage transformers just laying around since they've become so common). Keep close watch on it, stop and check everything if anything seems wrong such as rubbing, binding, or excessive heat in the motor.

4. Braids can cause cars to run slower even when they may not hesitate or stop and they can also cause them to deslot more easily. Take the time to fray the ends slightly; make certain they are smooth and straight with enough pressure for good contact but not so much that they keep the guide from resting all the way into the slot. I'm amazed out how ignorant I was about this early on and further amazed by how many poorly adjusted braids I saw at the test & tune.

5. Plastic molded wheels and tires are seriously out of round so it pays to check them carefully and realize that they may need more than a little sanding on the truing block. The test & tune provided a rare opportunity for me to stalk other cars to see where I was faster and what might help the slower cars. Most are very loose and based on my personal experience I believe that proper truing and freeing up the chassis makes a huge difference. René taught me this when he fixed my Minardi from sloppy loose into one of the faster cars in the class.


I’m sharing something special that I’ve been doing that I believe helps my cars to be faster because they’re less tail happy but I must disclaim that it requires a more careful driving style as they can sometimes de-slot before sliding out. I true my rear tires to have a very slight taper from inside to outside so that when the rear axle tips ever so slightly in the turns (they all do this) the outside tire’s contact patch is flat on the track and the inside tire touches only on its inside edge. Moreover, I taper the front tires for the opposite effect so that the outside tire touches only on it’s outer most edge in the corners. Of course, I could be wrong so consider my thoughts with a grain of salt so to speak and be amused at least.

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