How do I build a fast car?
By Gary Woods
I have been asked to tell all on what I do to get my cars ready for racing. The first thing I do when I get a new car is put it on the track. I run a few laps to see how it runs. I’m looking for speed and handling. Then I hold the rear “tyres” (not tires) off the track and run the motor from low voltage to full throttle and listen to the motor. On the fast motors there is a point where the pitch will change from normal to high. My goal is to find this point closer to the middle then at the end of the voltage range. The main reason is because we normally run our club races at a lower voltage. If the higher pitch happens at a higher voltage then we run, then it is no good in a race. This is the first thing I look for in a fast motor. Also remember I normally don’t buy just one car, I buy at least 2 cars and most of the time I buy 4. The reason I buy 4 cars is two fold, first is so I have a car for each lane on my track so when my friends come over we can all race the same class of car. The second, it allows me to find the fastest of the 4 to use in the club races with a back-up car.
The second thing I do is motor burn in. (If the motor from the factory is not club legal, I have also purchased the NC-1’s when I got the cars). I now have my order of car, fastest to slowest. One by one I burn them in.
Step 1: Inspection I inspect the under carriage and change the motor if needed. I look at all moving parts inside and out. I check for the fit of each part, is it loose, tight or right. I take a mental note of each for later when it will be addressed. I go back and run more laps and see if my order of fastest to slowest has changed. At this point I have done nothing to the cars except open them swap the motor close them and run them. I have done nothing to the motors or the cars. I am looking for the fastest car out of the box, that’s it! I will move the motor around to see if that changes anything. Once I have my order, I move to the next step.
Step 2: Motor Burn-in I attach power leads from my transformer to the braids and then put the entire car (less the body) in a large bowl of distilled water. I run the car for about 20 minutes. During that time I am changing the voltage from the slowest speed to a mid way point to the highest speed my transformer will give. I hold the voltage at these points for about 5 minutes each. At the highest speed I have to cover the bowl because the tyres churn up the water so much that it splashes all over. I also have to be careful the wires don’t get wrapped around the tyres. Both made quite a mess. In the last 5 minutes I simulate the speed changes you have in a race. Side note: The reason I put the whole car (minus the body) in distilled water is so I have a load on the motor. I found it is the load on the motor that gives me a better burn in. It also helps with gear mashing and bushing and axle polishing. When I am all done with all the steps in this list I will go back to this step. I brake the motor out of the cars I am going to run in the club race and run it by itself in a blow of isopropyl alcohol for about 20 minutes to several hours depending on the motor. I do this to try and get better contact on the motor brushes. Dry, lube and glue.
WARNING: YOU MUST BE EXTREMELY CAREFUL WORKING WITH ISOPROPYL ALCOHOL. ONE SPARK FROM THE MOTOR AND YOU WILL HAVE A FIRE. I KEEP A FIRE EXTINGUISHER CLOSE BY JUST IN CASE. Do not try to blow it out. Smothering it works the best. I use a bowl with a cover. I have never had a fire. Knock on wood.
Step 3: Drying and Lubrication After the first burn-in is complete I start Step 2 all over on the next car while car #1 is dropping dry on a towel. When car #2 is doing its thing I use my air compressor to blow dry car #1. When all water is gone I submerge car #1 in a blow of Isopropyl Alcohol for a minute or two. The alcohol will displace any water the air compressor missed. I then drip dry and blow dry car #1 again. Now I am ready for lubrication. I found this spray-lube at Home Depot. It works real good in the motors. It is called CRC 2-26. I spray the crap out of the motor with it, then I blow dry the motor. Next I use Genie Garage door opener lube on the gears and a light lube like 3-in-1 Oil on the bushings and axles. After all 4 cars have gone through the first three steps I check my order of cars, fastest to slowest. Normally it stays the same.
Step 4: Wheel and Tyre Tuning I remove the rear tyres and run the bare rims on a piece of 220 grit sandpaper. This will true the rim and removes any burrs left from the mold. I sand them down just until I see they are uniform. I then take the club approved tyre for that class of car I am working on and turn the tyres inside out and inspect them for imperfections. Next I install the tyres and run some more laps, rechecking my order. (I do not have a tyre tuner yet so I use the car to tune my tyres. If I am going to remove a lot of tyre, I will remove the rear axle and install it on a car with an NC-6 motor for more torque). I connect power leads to the brushes and run the power high enough the give me a good grind on an 80 or 100 grit sand paper, it depends on the tyre. What I am looking for is a true tyre on each side of the car. I use my clear plastic jig and turn the car upside down and move the car back and forth watching the contact point of the tyre on the glass. When the tyre is true there is a straight line across the tyre on the glass. Once I’m satisfied with the size and shape, I polish the tyre by sanding on 220 then 600 then 800 grit sandpaper. On the 600 and 800, I use water on the sandpaper. When they shine they are ready.
(Note: of all the things you do to your car this next step is the most important thing you can do. Remember your car runs on electricity, nothing else. If your contact point is weak then your car will run bad).
Step 5: Guide and Braid Tuning. I start by removing the guide, leads and braids from the car. I inspect the wire going through the small silver barrel. Next I fan out the wire on the side that will make contact with the braid. I check the braids length to make sure it is the same size as its twin. I inspect the guide for freedom of movement and defect. If it is tight I use 600 or 800 sand paper to loosen it a little and/or remove any defects. Next I install the braid into the guide from the top down. I leave a ¼ of an inch of the braid above the braid shoe and align the fanned out lead wire on the silver barrel so the wire is directly touching the braid. I then press the silver barrel into the guide shoe. (Note: I found this method gives me the greatest amount of current flow. If soldering was legal it would be the only thing better). After the braids are installed I reinstall the guide into the car and press the braids flat against the guide. I check that they are the same length and bend the last 1/8” down at about 45 degrees. This creates a racking effect at the end of my braid and puts a spring like wave on the braid. Next I move the power lead from the motor to the guide so they act as springs to keep the guide centered when the car comes off the track. On some cars there are places where you can wedge them in place and on others I hot glue them in place. Next I use my solder iron and remove the lead going to the motor and re solder it back in place. I do this to make sure it is a good solder joint. If in manufacturing of the car the joint was done in haste and there was a cold solder joint I have eliminated it. This also allows me to remove any overly excessive wire.
Step 6: Gear Meshing and Axle Polishing At this point I glue the motor in place with hot glue. Using my Goodwood Portable Pit with break-in/warm-up stand with rheostat controlled voltage. (Found at Mr. Model Car currently on back order until I build some more). I then set the car on my warm up stand and adjust the voltage to low. With the body set aside and gears exposed, I use a small amount of valve grinding compound (found at auto parts stores) and apply it to the gears and continue applying it along with the Genie garage door opener grease until they run quite and smooth. When this is complete I use Goof Off 2 to clean up. Next comes the axle polishing. I remove the wheels from the rear axle and the axle from the car. Using my Dremel with a polishing wheel and polishing compound, I polish the axle at the point where it comes in contact with the axle bushings. When it shines and there is neither paint nor defect it’s ready. I reassemble the axle and bushings back on the car and put one small, small drop of Krazy Glue on the outside of the bushing to keep it from moving. Next I put a small drop of glue on the end of the axle and assemble the wheel on the axle. I then put a small amount of glue on the rim and tyre. I then lubricate and assemble the car for racing.
Step 7: Race, Race, Race, Race I recheck my order of fastest to slowest car. I then check to see which car handles the best. I have found that the fastest car is normally not the one I use in a race. No, it is the car that I can drive the fastest without crashing that makes it in to my winner's circle. It is this car that I will use to race and the fastest is used as a backup. The fastest car can’t help you if you can’t control it.
How do I build a fast car and why do my cars go faster then yours? These are good questions. I hope I have answered them for you.
Here is the answer in a nutshell: I get more current to my motor. I have less drag. And I have better traction then you do. It is simple physics.
Ah, these three (3) categories are where the magic happens. Remember; Current, Drag and Traction can be your best friends, or worst enemies. If your car is not up to speed, then check these 3 to see why. I’ll bet it’s your braids; 8 out of 10 times.
Embrace the juice and let it loose.