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Post by Threader on Aug 10, 2004 14:52:25 GMT -6
I have been conducting some experiments with weight placement have have a few conclusions.
1. If the weight is way in the back creating a CM at 20mm from the rear axle the car becomes unstable! There seems to be little benefit, I can't find any, to putting the weight this far back.
2. Moving the weight so your CM is set at 30mm seems to give the best reselts so far.
3. Keep the weight in the smallest area. I will be working on this more later.
That's all for now, comments?
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Post by jwavra on Aug 10, 2004 16:12:28 GMT -6
I agree. I placed the weight as far back as I could last month. the car didn't accelerate well and lost speed in the flat despite good alignment.
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Post by Panzer on Aug 10, 2004 16:33:07 GMT -6
I've found optimum CG also depends on the car length and wheelbase. Longer wheelbase cars seem to prefer CG location farther forward of rear axle. The trick is to find the sweet spot, far enough back for good energy transfer ballanced against far enough forward for good running stability. Your testing appears to confirm this. Running stability becomes even more importent on longer tracks.
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Post by PinewoodPerformance on Aug 10, 2004 17:29:16 GMT -6
guys, look at the track, look at it's aspects, how it's constructed. The cars function will follow the form of the car, why would rear weight placement make any sense? I can say no more! Lets use our brains and get away from common concepts and move towards adapting our cars to the tracks we race on... Piadosi Oars Tracks don't translate, not because of material but because of format...
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GILLS
Pine Head
Posts: 49
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Post by GILLS on Aug 10, 2004 19:45:23 GMT -6
Threader, I thought that a heavily rear weighted car was better also, but I learned last year that it wasn't. From a common sense point of view, you start the race uphill, so the more weight you have at the highest point up thehill,(the rear of the car), the more gravitational downhill push or speed you have. As ya'll stated, in the flat you lose speed. My son had a heavily rear weighted car that won his pwd, and we created the same car for our R.A. assoc. race that he won as well. If it sounds like I am contradicting myself I am. When we raced at my church with our own R.A.'s, he got beat 4 heats straight. You can see his cars at www.grandprix-race-central.com. The car that beat him was equal to us in axle and wheel prep because I preped them! The difference was the other car had most of his weight between the axles in the bottom of the car, and maybe 1 to 1.5 oz. in the rear. Yes we were faster at the top , but we got beat in the flats! We did'nt lose by no more than an inch at most, but thats enough!!! Try spliting your weights in this similar fashion and see what results you get! Sorry, the car that beat us was a wedge. And my sons cars are labeled as Brett's cars. Good luck!!!!
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Post by TurtlePowered on Aug 11, 2004 7:14:41 GMT -6
A lot depends on geometry of the track. More specificly, how much slope length vs how much straightaway. And you can get a way having the weight farther back if the track is good and smooth vs bumpy at the joints.
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Post by parrish on Aug 11, 2004 7:45:55 GMT -6
Case in point... My cars are very aggressively rear weighted for our home track. It is approximately 42 ft. long. The length of slope vs. flat almost equally split. My cars run consistantly 3.07/3.09 on our track, but that translates to 3.13/3.15 on the WIRL track. I will order the extra 7 ft section from Best Track this week, take over the other side of the basement, and start testing weight placement.
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Post by woodenwonder on Aug 11, 2004 8:21:41 GMT -6
Threader, What length wheelbase? It will make a difference. I know Stan Pope and others keep quoting 1 oz on front wheel as about optimal. If you have a standard 4 3/8 inch wheelbase that translates to a cm of 7/8 in front of rear axle (about 20 mm) with a 5 1/2 in wheelbase that translates to 1.1 inches (slightly less than 30 mm). I know we just built 3 identical shaped cars with 2 standard bases and 1 extended. The bottoms were hollowed the same so I could put the weight pretty much where I wanted it. The extended was hollowed slightly more due to more area between wheels. I put 3 ozs in the same place in all three cars then slapped some wheels on them to weigh and add more weight to reach optimal 1 oz on front wheel. On the 2 standard cars there was 35 grams on front wheel, on the extended car there was only 24 grams. 1 oz = 28.35 grams. On th 2 kids cars we had to drill holes behind the rear wheels to add 1/2 oz. This put 33.4 grams on front wheels. The extended required 3/4 ozs to bring it to specs and I had to put it 1/2 inch in front of other weights and weight on front wheel is still only 28 grams. Point is cm is farther back on the standard wheelbase cars than it is on the extended. Don't know how they will run, will find out this weekend. If mine is any good it will probably be at WIRL next weekend. Maybe Derby Master or Peede could let us in on where their cm is located . Good Luck to all!
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Post by Threader on Aug 11, 2004 10:27:00 GMT -6
Thanks for the input eveyone! ;D
Current experiments on my M1 car, which de-railed at WIRL showed the alignment was on.
I even got it to de-rail at home. After moving the weight forward it never did it again.
I will be looking at some of the concepts you are talking about.
Any more ideas or input?
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GILLS
Pine Head
Posts: 49
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Post by GILLS on Aug 11, 2004 10:35:44 GMT -6
A lot depends on geometry of the track. More specificly, how much slope length vs how much straightaway. And you can get a way having the weight farther back if the track is good and smooth vs bumpy at the joints. Turtlepowered, You are correct, track does make a difference in the car's performance. All three of our races were ran on a modern style track, about 48" at the start and falling about 12 to 14 feet to the flats, and having about 26 to 28 degrees of slope. All three tracks were a good smooth plastic laminate track and one was 32' with the last three feet being the stop section, and the last two tracks were 32' and had a seperate 3' stop section. The R.A. cars were set wheel spacings at4 3/8", the pwd car was on a spread wheel base.
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Post by Threader on Aug 11, 2004 10:54:44 GMT -6
A lot depends on geometry of the track. More specificly, how much slope length vs how much straightaway. And you can get a way having the weight farther back if the track is good and smooth vs bumpy at the joints. Turtle, My track is an Aluminum 32' with a extra 3' stop section. It is smooth........ WIRL track is the same but 7' longer. Maybe I took the weight to the extreme back, but it made the car unstable under those conditions. I had 12 T cubes behind the rear axle and about 14 T cubes right in front of it.
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Post by SpeedGeek on Mar 13, 2005 11:59:15 GMT -6
A recent car of mine had the same problem: CG too far back ( about 18 mm front of rear axle). The car was stable and very fast down the hill and went unstable and slowed on the flat.
Can anyone contribute the technical reason for having a LOW CG?
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Post by Sssnake on Mar 13, 2005 12:49:17 GMT -6
Think of the car as a pendulum. if you move the weight down on a pendulum the weight will travel farther through it's arc. The longer it travels the more it will accelerate. Also the weight actually falls further on the the low weighted car due th the perpendicular orientation of the weight to the track.
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Post by Nimrod on Mar 19, 2005 16:19:48 GMT -6
Hi all Yall. My name is steve AKA Nimrod. Nimrod is my online gaming name, I enjoy playing Ghost Recon. This is my first post and I will start by saying this forum has been a wealth of information. Here is a picture of the car I am working on. There is about 2 oz above the rear axle and 2 below. The last Awana race I ran had the same concept without the 2 below and we took first in speed by at least a car leingth. That car is going to run in a South FL race in April with all the South FL Awana groups that run Grand Prix. My goal is to beat the car we just ran. Thanks for looking, talk to Yall a little later. Steve
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