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Post by resophonic1 on Jun 13, 2009 15:14:05 GMT -7
What's the science behind weight placement being to the bottom of the car as opposed to the top. Which method of placement is stated as the best. Not having a test track just limits what you can test on a car.
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Post by Carolina Gravity Sports on Jun 13, 2009 18:28:42 GMT -7
I center mine, there is just as much above the axle as there is below.
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Post by W Racing on Jun 13, 2009 23:59:04 GMT -7
Reso,
Go with Carolina!!!
There are three choices.
1) Weight above the axle. 2) Weight centered on the axle. 3) Weight below the axle.
Physics favoring choice 1 is that the weight being higher up travels a shorter distance in the transition of the track.
Physics favoring choice 2 is that in the transition less energy is used to rotate the weight. Less energy used in rotation equals more energy left over entering the flat.
Think about an ice skater spinning. As they extend their arms they slow down. As they bring them in they speed up. Centering the weight brings it in and during the rotation uses less energy...
Physics favoring choice 3. The car sitting at the pin has more potential energy with the weight below the axle than either centered or above. The amount is small but real.
I was a fan of mixing 2 & 3. Placing the Vertical COM of the weight lower than the axle but not much so... Mostly dropping down a 1/16 or 1/8 of an inch.
Coal Car has a 4.1 ounce disk and it is much lower than I have ever placed it... Making what I thouhgt was good use of the PDDR rules...
I am Changing closer to #2 every day and perhaps my next car will be pure #2
Putting it all together.
Each car has a certain amount of potential energy at the starting pin.
You want to maintain that energy across the finish line. Alignment, polish & lubrication all help keep the energy.
Weight below the axle increases potential energy however you will expend more energy in rotation.
Weight centered on the axles equals less potential enegy at the gate and less loss of energy in the transistion.
Choice 1 has been mostly disproven.... (I know what you are thinking K :-)
Choice 2 speaks for itself. Carolina is blazzing fast...
Choice 3 is the most common held belief. It results in a car with more potential enenergy. But greater loss of energy in the transition when the weight rotates.
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Post by resophonic1 on Jun 14, 2009 6:22:59 GMT -7
Carolina....Your speed on the track could never be questioned.
W Racing...Thank you once again for your technical prowess.
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Post by W Racing on Jun 15, 2009 6:07:56 GMT -7
I am going to enter two or more cars for August.
For the new car I am for sure changing my car to be center weighted (Vertical). Also changing it to be a plank style.
The rule of thumb should be centered or lower a tad. Don't go higher. Most cub cars are built with vertical COM higher than the axles because althought the weight may be centered or below the axle. The car body itself is mostly above the axles (And weighs a substantial amount...).
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