weight placement

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itgl72
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weight placement

Post by itgl72 »

Quick question on weight placement. I understand you're looking to put weight towards the back and get a center of gravity around the rear wheel more or less. My question is, do the type of weight placements matter? I can put the weight into the body of the car and then wood seal it, or grind out a slot area under the car and put in the flat weights. I would assume weight is weight whether its inside the body or applied to the bottom. Your thoughts?
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Vitamin K
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Re: weight placement

Post by Vitamin K »

Conventional wisdom is that energy transfer is most efficient, the closer the weights are to the track (that is, the bottom of the car). That said, a lot of people have had good results using tungsten canopies on top of thin cars, so the horizontal placement seems a lot more important than the vertical.
itgl72 wrote:Quick question on weight placement. I understand you're looking to put weight towards the back and get a center of gravity around the rear wheel more or less. My question is, do the type of weight placements matter? I can put the weight into the body of the car and then wood seal it, or grind out a slot area under the car and put in the flat weights. I would assume weight is weight whether its inside the body or applied to the bottom. Your thoughts?
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Re: weight placement

Post by Speedster »

Who are "a lot of people" and what was their competition? No matter how slight something may be, you cannot break The Laws of Physics.
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Noskills
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Re: weight placement

Post by Noskills »

This could be a tricky question. An easy answer is anywhere you can fit it. Assuming you are going for top speed then you are looking at a thin car. A thin car by nature has to have the weight within the body unless you glue it to the top. Putting it on top has the potential to to decrease stability.

Yet to comment on the previous two posts if your competition is not great you can likely do very well with an aggressive COM well build car with the weight either on or in the car.

I once bought a canopy and I am dying to try it out.

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Scrollsawer
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Re: weight placement

Post by Scrollsawer »

Noskills, our orange car this year has a 2.5 oz. tungsten disk in the rear (that I got from Mid-America) along with 4 cubes. I'm really curious to see how it performs.

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Speedster
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Re: weight placement

Post by Speedster »

itgl72, I was Off Topic. Sorry. I'd like to try to answer your question. By the Type of weight placement I take it you mean the area you place the weight. Yes, it matters a lot. Weight is weight is correct. A pound of feathers and a pound of tungsten weigh the same. However, their density is not the same. An Example. You cut 1/4" off the short end of the block and move it to the front. That will move your balance point 1/4" higher up the arc. You now have 5/8" of wood behind the rear axle slot. Let's say you want 2 ounces of weight behind the rear axle slot and as low in the car as you can get it. 3/8" by 1 3/4" lead rod weighs 1.1 oz. Four of Maximum Velocity's 3/8" x .40" tungsten cylinders weigh 1.858 ounces. 2 rows of 6, 1/4" tungsten cubes weigh 2.036 ounces. You have gotten rid of as much wood in your car as you can and your car resembles a Hershey Bar. What are you going to use for weight? Now we move to the front of the rear axle slot. "More or Less". It's not "More or Less", it is an exact spot chosen by you where your car will balance. 1", 3/4" 5/8", 1/2" or any number in between in front of the rear axle slot. It's your choice and your going to use tungsten cubes again which will allow you to stay as far back as you can in the smallest area and as low as you can. As far as I know, that set-up is the ultimate. When you deviate from that in any way you are taking speed away from your car. That's Physics. The science of Matter and its Motion. Sure, we now move on to other Topics such as alignment, bore prep, wheel roundness, railriding, axle prep, are we going to use blue or red wheels, etc. If you want even more speed you install fenders. If you do it right maybe you'll save .002 more seconds.
A few days ago at our workshop a gentleman came up to me and asked, "Why do you have all this stuff? 5 ounces is 5 ounces". How hard do you think it would be to beat his car in a race?
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itgl72
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Re: weight placement

Post by itgl72 »

Thanks for all the comments folks.
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Re: weight placement

Post by Speedster »

Maximum Velocity Newsletter, Volume 13, Issue 9, January 22, 2014.
http://www.maximum-velocity.com/pinewoo ... mes-v13i9/
Was my answer to itgl72 correct because of only .0016 seconds?

Randy, what track and length? Would there be a larger difference between the Best track and Freedom track? It would be interesting to see what the test results would be if the tests were done on both tracks.
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Re: weight placement

Post by MaxV »

The test was performed on a 32 foot aluminum freedom track. I doubt the the length of track would make any difference, but that is just speculation.
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pwrd by tungsten
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Re: weight placement

Post by pwrd by tungsten »

I have thought about this a lot. My recommendation is to place at least 3.5 ounces of added weight into the car. With razor wheels I have even gone 4.2 ounces. And to concentrate this weight in as small of an area as possible. I also will not design a car where more than half the added weight is behind the axle. The weight being low rule serves people well as long as they do not get disqualified for clearance sakes. However I have both had success with and seen cars with the weight centered on the rear axles (from a vertical perspective). I am ok with either method on a best track etc. However on a lower quality wood track I still feel that lower helps. My new go to build is cubes behind and in front of the axle. In a way I have mellowed in my approach and allow myself the use of cubes which aren't as dense as say a proper tungsten 1" disc. The cubes should still be as close to the axles as possible. Of course my kids choose their own weight method.
W Racing!!!!
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Re: weight placement

Post by Speedster »

Randy's test was for height. Nice Job. He stated in the Newsletter, "unless the track was very short the LCG car will overtake the HCG car". A good reason to keep it low. The test was performed with a Round. You're trapped using one piece of metal shaped a certain way. Would you get the same results if the test was performed with cubes? Between two perfect cars, one with the round high and one with the popular 2 rows of 6, 1/4" cubes, etc., would Physics demand the cubes will win?

pbt, why wouldn't you put more than half the added weight behind the rear axle? If all you could add is 3.8 ounces, why wouldn't you place 2 ounces behind the rear axle? The car is going to weigh 5 ounces. How would you distribute 3.8 ounces? I think DT'ers who finished in the top 12 at the Mid America, Adult graphite division, had 4 ounces of added weight on scout wheels.
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Re: weight placement

Post by Scrollsawer »

Speedster,

I placed twice in the top 12 (albeit in the 6th - 12th range) with 23 cubes. 12 in the rear, and 11 forward of the axle.

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Re: weight placement

Post by Speedster »

I happen to be well aware of that. You have very nice looking tail lights. Great Job !!!!
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pwrd by tungsten
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Re: weight placement

Post by pwrd by tungsten »

Speedster wrote:
pbt, why wouldn't you put more than half the added weight behind the rear axle? If all you could add is 3.8 ounces, why wouldn't you place 2 ounces behind the rear axle? The car is going to weigh 5 ounces. How would you distribute 3.8 ounces? I think DT'ers who finished in the top 12 at the Mid America, Adult graphite division, had 4 ounces of added weight on scout wheels.
I guess if it is just .2 ounces I might do it, However I have found that in all cases I can move the weight to be centered on the rear axles or ahead of the rear axles by lightening the body of the car. To go the full circle too much wood means all of the added weight behind the rear axle.

I do know that cubes in place of tungsten rounds are good enough. They will not be a limiting factor in your car design if placed close to the rear axle. Of course leave room for a rear axle. Which on a 5/16" car means that the weight is pretty close to being centered vertically on the rear axle.

One caution is placing the weight to far away from the rear axle. This can slow the car in the transition. Think of an ice skater spinning. they bring there arms in to speed up and out to slow down.
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Re: weight placement

Post by Speedster »

PBT, I've been thinking of what you're saying since you posted this. I've got an open mind. I'm not arguing with you and I'm not trying to prove any point. Let's take a scout car, stock wheelbase of 4 3/8", slots, no fenders and you can start with any weight and design for the wood. You will be running 40' on an aluminum Best track. How exactly would you set it up telling me the weight of the wood you start with. We're using stock wheels and axles and can't do anything to them so I already know what they weigh. If you would draw me a picture of what the block would look like after you cut it I would appreciate it.
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