Of the 3 bodies styles shown which is the weakest?
- Thread starter 5KidsRacing
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I'm with OPA.. All will perform the same... the margin of error will be too small to come to a conclusive answer...
Just my 2
Just my 2
I think the reverse ladder would have the least bend with high torsional flex. The ladder high bend and flex. The xfactor 2nd in bend with low Flex. The xfactor has the best strength due to the weight triangle. Boxing any of these with cover plates significantly increases the strength.
Papa V Racing said:
Yes, that was my thinking, too. It's not like they're being cranked by a 500 cid mill! BUT, if the car is too flexible in that plane, I can see where it could set up a vibration that may slow the car. I'm curious to see what 5kids reports.
If anything, at the transisition, the chassis would look sway-backed I bet. Maybe oscillate a little vertically afterwards.
Dang, now I want to build a car that's super flexible just to see what it does! Where's Mythbusters with a high speed camera when you need them?
I also need to build a car with NO weight cantilevered, a triangle shaped body. Just to see what it does.
As far as JB07 is concerned, I can't see that the layover wheel is the reason for his success. I think he is a meticulous builder that has developed a near perfect prep process for his combo. I would have no faster car if I layed the wheel over than if I painted a white stripe across it's rear end! But I could be wrong! I'd be happy to be about .050 sec wrong! Stephen
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bracketracer said:
John, you have more experience in PWD than any of us......what are your thoughts on the subject?
I run a solid plank. I don't think it will matter. I think all it does it slightly change where your sweet spot is when putting in the weight. I do think the ladder style would be the weakest though. Very hard to tell which is the fastest.
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DerbyDad4Hire said:
I agree! I am not totally convinced having a rigid body/frame relates to a fast car. I have tried several bearing cars with an aluminum frame. There is very minimal flex in that frame. I have not had good results. I know Goat Boy has built several bearing cars using aluminum, but some how it seems we always revert back to good old wood! There are more important things that have to be in place to have a fast car.
Have you ever watched a top fuel car in slow mo making a pass down the 1/4 mile? If that frame didn't flex, that design would not work. I'm not saying PWD is the same thing as racing a top fuel car, but it's someting to think about.
Maybe that ladder frame has just the right amount of flex to work properly? Many guys recently have been using them with good results.
I say rigid is better and metal doesn't absorb vibrations as well as wood so it doesn't perform as well.
I personally don't think flex in the frame, or solid bodies matters.. It has to do with the way the block it drilled, car is weighted, wheels and axles prep. As well as tuning. I have several full bodies as well ladder. Both seem about the same. Although one ways less. So far I have had better luck out of full body cars. But this month I'm sending in a few of both designs. I have built 4 new ladder style cars since and before nationals. As well 3 full body cars ... Only time will tell. Builders are winning with both style. So it's a tough argument. But I will say this I have 2 new cars I built that has 4 more pieces of tungunten each them my other cars... Weight is power!!
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The rigid front is the important thing. I still remember long ago when I lost my front sway bar on my studebaker lark. The car was all over the place. You felt like you were in a boat and not a car. I did an experiment years ago with the pinewood derby cars where I sawed in the middle from the very rear of the car past the front weights to give it "independent" rear suspension. There wasn't any change in speed or time. The same experiment done to a another car but sawing down the front middle did slow the car significantly. Keep the front solid as possibe.
To reread 5Kids original post, all that he asked was: Which design is the weakest? I'm assuming as it is presented and not covered with anything in a race ready condition other than installed weight.
We've all put our thoughts in and maybe misinterperted the question. I think in a race ready condition it would be tough to say which one would be the weakest. And as few have mentioned, are we really flexing that much going down the track, likely not. Thinking out loud now, if there was absolutely no give in the car at all, would that not create vibration by itself? It would then depend on the track condition itself, right? I think we have all determined at one point or another that a lot of vibration in the design is not good for speed and try to simply minimize it all together, on purpose and by design.
I personally have not built a car with any of these designs, but have seen many build the ladder design with good results. I will be trying one of the new bodies that John has designed in the upcoming series. Just waiting for it to arrive. Time will tell.
We've all put our thoughts in and maybe misinterperted the question. I think in a race ready condition it would be tough to say which one would be the weakest. And as few have mentioned, are we really flexing that much going down the track, likely not. Thinking out loud now, if there was absolutely no give in the car at all, would that not create vibration by itself? It would then depend on the track condition itself, right? I think we have all determined at one point or another that a lot of vibration in the design is not good for speed and try to simply minimize it all together, on purpose and by design.
I personally have not built a car with any of these designs, but have seen many build the ladder design with good results. I will be trying one of the new bodies that John has designed in the upcoming series. Just waiting for it to arrive. Time will tell.
pony express said:
That statement makes me wonder if the lifted NDFW was able to vibrate more, since it was cut partially free? Or if it just changed the alignment after the cut
Too much flex will slow you down I do know that for a fact. Insuspense started off building cars with "independent suspension" and they sped up as soon as we took the flex out of them. I don't know the exact point when it has an impact but too much flex is definitely bad.
THE RESULTS:
WINNER: REVERSED LADDER
HONORABLE MENTION: X-FACTOR
LOSER: LADDER
The Reversed Ladder is twice as rigid as the ladder and 50% more than the X-factor.
The following bodies were modeled in Pro-Engineer and analyzed in Pro-Mechanica. All bodies were analyzed with the same materials, loads and same constraints. The scales on the results are all the same and show least stress at dark blue to most stress at bright red. The highest stress for each body style is the number shown at the top of the scale. The first plot of each body type is the stress and the second is the deflection.
How rigid the bodies are and the amount of deflection is basically based on how the stress travels from the rear axle line to the DFW. The more material in this direction, front to back, will make for a stronger body with less deflection. The ladder body has the least amount on material in the front to back direction and therefore performs the worst in this test. The rungs do very little to help transfer the stress from the rear axle to the front of the car. These rungs only keep the body rigid left to right and during a run there isn’t much force trying to bend a car in this direction.
The reversed ladder body has the most material in the front to back direction which makes it the strongest body of the three examples. The X-factor body falls in the middle because the part of the “X” that travels towards the lifted wheel does little to help transfer the stress to the DFW.
This body would be ideal for this test:
The real question is how rigid do you need a pinewood derby car body to get it down the track without flexing? The size of the tungsten weight and axle holes dictates how thin you can make a car body and normally you wouldn’t get it thin enough to cause an issue when it runs down the track. The DFW has very little weight on it and doesn’t need much support from the car body. The biggest issue with running a body like these would be damage from the stop section and vibration. The advantage of using cut-outs is that you can add weight to the rear and also change the weight ratio on the rears and DFW. You don’t have to run a hollowed body to win at the NWPDRL, but it is fun to try different body styles and see what works for your build style. Drilling the axle holes correctly is most important and depending on when you drill you want your body very rigid at that point. When you take a lot of material out of a car body there is a chance for twisting and warping of the wood and that is not good for alignment.
WINNER: REVERSED LADDER
HONORABLE MENTION: X-FACTOR
LOSER: LADDER
The Reversed Ladder is twice as rigid as the ladder and 50% more than the X-factor.
The following bodies were modeled in Pro-Engineer and analyzed in Pro-Mechanica. All bodies were analyzed with the same materials, loads and same constraints. The scales on the results are all the same and show least stress at dark blue to most stress at bright red. The highest stress for each body style is the number shown at the top of the scale. The first plot of each body type is the stress and the second is the deflection.
How rigid the bodies are and the amount of deflection is basically based on how the stress travels from the rear axle line to the DFW. The more material in this direction, front to back, will make for a stronger body with less deflection. The ladder body has the least amount on material in the front to back direction and therefore performs the worst in this test. The rungs do very little to help transfer the stress from the rear axle to the front of the car. These rungs only keep the body rigid left to right and during a run there isn’t much force trying to bend a car in this direction.
The reversed ladder body has the most material in the front to back direction which makes it the strongest body of the three examples. The X-factor body falls in the middle because the part of the “X” that travels towards the lifted wheel does little to help transfer the stress to the DFW.
This body would be ideal for this test:
The real question is how rigid do you need a pinewood derby car body to get it down the track without flexing? The size of the tungsten weight and axle holes dictates how thin you can make a car body and normally you wouldn’t get it thin enough to cause an issue when it runs down the track. The DFW has very little weight on it and doesn’t need much support from the car body. The biggest issue with running a body like these would be damage from the stop section and vibration. The advantage of using cut-outs is that you can add weight to the rear and also change the weight ratio on the rears and DFW. You don’t have to run a hollowed body to win at the NWPDRL, but it is fun to try different body styles and see what works for your build style. Drilling the axle holes correctly is most important and depending on when you drill you want your body very rigid at that point. When you take a lot of material out of a car body there is a chance for twisting and warping of the wood and that is not good for alignment.
When I was looking at the given body structures in my mind, I only thought of the twisting of the body left to right and not the bend of the body front to rear. No contact to the track on the NDFW side of the car is why I was thinking primarily of twist. Interesting either way. Do we have a new body style to try out now??? Thanks for the research 5Kids.
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So like most things in Pinewood derby the one that is the worst will be the fastest and the one that is suppost to be the best will be the slowest!
Quicktimederby said:So like most things in Pinewood derby the one that is the worst will be the fastest and the one that is suppost to be the best will be the slowest!
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