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HOME BODY DESIGN Weight Placement Friction Reduction Axel Modification Wheel Prep - Tuning

Remember : Some Axel Modifications are not legal under Pinewood Racing rules. You will need to check your RULE sheet to find out. You would not want to be disqualified after winning should they inspect your car.

The best way to reduce the influence of friction on your Pinewood Car is to ELIMINATE IT! Unfortunately since Friction is a powerful foe, it cannot be completely eliminated but we can however change the coefficient of friction in each specific area as well as reduce the probability of inconsistent surfaces altering our coefficient of friction randomly. Confused? hold on a second. let me explain a little. .

AXEL modification Tips- When working on your Axels The Phrase "Less is More".. is what you need - (More or Less) you really need Less surface area AND more !

In case you just joined us, Once your pinewood racer hits the flat track, it can no longer gain any speed. It can only Lose speed. This Loss is due to Friction. A close look at the wheels, axels and body will allow you to understand there are several areas in which friction can influence your pinewood racer. I know, I just said that in the Friction Reduction Section, but it's worth repeating because Each area of friction is unique and in each area, our objective is to reduce the coefficient of friction. You will remember that The classic law of friction states that friction is the product of a coefficient and a force. Fr = u x W

The classic law of friction states that friction is the product of a coefficient and a force.
Fr = u x W

Fr = the resistive force of friction, u = the coefficient of friction, and W = the weight of the object in this case the body weight of your pinewood car..

You would think that there is more friction when the surfaces are larger. But the friction law states otherwise.

Reduce the probability of inconsistent surfaces You must think 'small' for a second. Very small. super small Let say for example that you needed to sand down the top of your pinewood car before painting it. Ok You sand it down with progressively finer sheets of sandpaper until it is really smooth.

NOW, if you look at the the sanded area with a magnifying glass, WHOA! it would still have all sorts of ridges, low spots, high spots, mountiains, craters and other 'not so smooth' areas. While this is ok for PAINT, it's coefficient of friction would be very high.

How could you reduce the coefficient of friction withough sanding it further? Well since we know that The amount of Friction is Independent of the amount of surface areas being 'rubbed together' What would happen if we were to find the BEST looking area (the smoothest area) and cut the rest of it away. There would be LESS surface area now, which does not matter anyway, frictionally speaking, BUT the QUALITY of the remaining surface will have more consistency to it. Less variables. Less mountains, valleys, ridges and craters. SO, without further sanding, we have reduced the coefficient of friction to it's lowest possible value. ---->>>

 

OK, I see, but what does that have to do with the axels ?? and why is my car cut in half now?? First off - it's just an example to show you that no matter how much you polish your axels, there will still be scratches, bumps and ridges that will interfere with the tire and that simply by eliminating the majority of the axel surface, you can increase the QUALITY of your axel surface that actually contacts the wheel.

 

If you simply polish your axels - you may have 50 imperfections which will influence the coefficient of friction in a negative manner. By eliminating 80% of the axel from the equation, you could ultimately reduce that to only 10 imperfections, which would give you a much more consistent coefficient of friction value because now you only have to worry about 10 little bumps or scratches, instead of 50. LESS area - LESS problems to deal with. Of Course we are looking at each axel under a magnifying glass in order to acheive desired results.

Axel modification techniques are fully explained in the DVD for you to see

 

Just a Side Note : since we are trying to REDUCE the Coefficient of friction The coefficient of friction also varies with temperature. Looking at this graph (detail provided by Nanoscale sliding friction versus commensuration ratio )

 

The relation between c and temperature we can see that for a fixed a/b ratio the c coefficient increases linearly with temperature (of course this is at the atomic level). As we have discussed before after your car has broken free from static friction, SLIDING friction is your next element to deal with. The aformentioned document provides Observations regarding sliding friction and temperature of the surfaces at the particle level. Too small to mess with? possibly, but nonetheless, if as stated, the coefficient of friction INCREASES with temperature and the obverse is true, the coefficient of friction DECREASES as the surface temperature decreases, why not look into this? . ------------------------>>

For clairity, I present to you this theory. IF one could cool (ie. reduce temperature of) the axels of your pinewood derby car, would it not DECREASE the coefficient of friction presently factored into your friction equation? My thinking is that YES, it would. And, since a lower coefficient of friction value equates to less kinetic energy LOSS, this is a very good thing.Therefore, One must explore possible scenarios for COOLING the axels. At first glance, It may be better to COOL the actual wheels since they also contact the track, but this may be simply impossible due to the obvious fact they are rotating, so by focusing on cooling the axels, one might find yet another way to make your pinewood derby car faster. We @ PinewoodProfessor.com are conducting experiments at this time to implement into our VIPER unlimited Series (using channels to cool the axels) High tech ... No Im not going to explain it here.

 

Remember - Friction is your enemy!

 

Our Axel Modification section combines the Basics of Friction Reduction for beginners as well as Full-on axel and wheel modification for advanced pinewood racers. It's definately one of the most informative documentations you will see on the subject, For Beginners and Advanced Pinewood Racers - everyone can learn something.

 

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