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Post by pwrdbytungsten on May 24, 2006 2:32:37 GMT -6
I have usually made wing cars. I am looking into making something more three dimensional. I was wondering what the ideal vertical COM would be for a PWD car and/or what vertical COM has worked for others.
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Post by slkrnsntracing on May 24, 2006 10:18:30 GMT -6
I have usually made wing cars. I am looking into making something more three dimensional. I was wondering what the ideal vertical COM would be for a PWD car and/or what vertical COM has worked for others. pwrdbytungsten, I think the answer to that question is a question. HOW LOW CAN YOU GO?You can still have a wing, and put your weight low. Go for it! You can still be yourself, and have a fast car. Best of luck Phil
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Post by SpeedGeek on May 24, 2006 18:50:12 GMT -6
A physicist or engineer could prove that (theoretically) lower is faster. The real question is: how big a difference will half and inch really make?
A heavier car is faster, no doubt, but unless you have a car like Warp or 234, the difference between 4.9 oz and 5.0 is very small compared to the other improvements you could make.
I say make the car as you want. If you lose the big prize by 3 or 4 milliseconds, then you can kick yourself...
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Mr. Slick
Head in the Pine
www.PwdRacing.com
Posts: 151
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Post by Mr. Slick on May 24, 2006 20:26:08 GMT -6
COM, such a weighty topic. . . A few things I have learned (may have to unlearn later.) A shorter distance from the point of rotation the less energy lost when rotating the body. A higher COM will travel a shorter distance. Farther down the track at the start and shorter circumference on transition. Lower is more stable. Design influences the location. . . some designs can increase the level of difficulty in placement of COM. More time spent building than racing so go for the design you want. Empirical results on COM location and amount later this summer . . . Best solution: build two cars one high and one low!
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Post by SpeedGeek on Jun 2, 2006 17:22:38 GMT -6
See May's race result in the stock race. Sudden Impact won first place at a weight of 4.9 oz. By theory and conventional wisdom, Malibu (5.0 oz) should have won because "heavier cars are faster".
Heavier cars are faster, lower CG (COM) cars are faster. The question is: how much faster compared to the other factors like alignment and wheels and axles, and wind velocity and phase of the moon, and, and, and... ?
IMHO, the speed effect of vertical COM, mass, etc are real, but very small compared to other, more difficult to measure factors.
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234
Addicted to Speed
Posts: 79
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Post by 234 on Jun 2, 2006 20:48:59 GMT -6
SpeedGeek
A heavier car is not necessarily faster. Malibu is a Pinewood Derby standard wheelbase car that has not been lightened in any way. She benefits from near perfect wheel alignment and proper wheel & axle preparation.
Sudden Impact on the other hand is a much lighter car that has been hollowed out. I think the body after sanding was just a hair over 1/2 ounce allowing me to place more tungsten in the engine room giving her a little more horsepower despite being 1/10 ounce lighter. Getting a very light car to run stable is the tricky part. You have to have the wheel/axle alignment as perfect as you can get them or you can forget it.
Take care, Leo
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Post by pwrdbytungsten on Jun 3, 2006 3:11:39 GMT -6
234
I really like Malibu. The paint job is amazing. It also really shows the potential that a wing design can have in that it is so fast. It is nice to hear that it is not hollowed out.
I have been wondering about the importance of the concentrating of mass. In particular the importance of minimizing the weight of the wood, maximizing the weight of the tungsten and then placing the tungsten in as small of an area as possible
-Eric
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Post by SpeedGeek on Jun 3, 2006 6:01:55 GMT -6
Leo,
You said it better than I did: heavier cars are not necessarily faster. I've observed that people (not you, of course) tend to focus on one thing and ignore everything else. There is more than one factor that affects the speed of a car and the magnitude of each effect is different. Personally, I don't think that weight has a very big effect, as long as the car is reasonably close to 5 ounces... Same thing with vertical location of COM; I wouldn't let it affect the car's design too much.
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Post by SpeedGeek on Jun 3, 2006 6:05:44 GMT -6
PS - I almost forgot: Malibu is one hot car; very nice paint job!!!
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