Building a SS for 63 foot Nationals Track

[GravityX]

BR we'll soon find out. I sent cars into Zeebs without changing anything from the 42 foot setup to see what happens. IMO I think the Unlimited cars will be the least affected by the added track length.

 

[B_Regal Racing]

I hope mine make it to the finish.

 

[Guest]

My hunch is that whatever the fastest setup is at 42' is going to be the fastest at 63'. I only say that because it appears to me that the car slows at the same rate per foot of track as soon as it's off the hill assuming it's not wobbling. It takes the most efficient chassis to win at 42 or 63 IMHO.

This makes total sense.
However, I have seen a few fast cars that wiggle near the end and nowhere else.
This could be a point at which the speed reduces enough to start he wobbles going the rest of the way.
I bet we see some races that have a car lengths difference in time.

 

[Guest]

There were a few in stable cars that won heats and were wiggling while a stable car nearly caught up at the finish. Having the longer flat you may see more lead changes in the flat. That was mostly middle if the pack cars though. The fastest were almost all running smooth the whole way through.

My hunch is that whatever the fastest setup is at 42' is going to be the fastest at 63'. I only say that because it appears to me that the car slows at the same rate per foot of track as soon as it's off the hill assuming it's not wobbling. It takes the most efficient chassis to win at 42 or 63 IMHO.

+1
I even saw the fastest SS wobble race before last.

Maybe it would not have done so well on the long track.

OHHHH so much speculation! I guess it always comes down to controlled/ predictable friction vs. riding balls out.

 

[Falcon777]

Also ....... surprised no one has addressed this - is wheel weight. Heavier wheels will act like a fly wheel and carry more inertia down track which will sustain more speed to the finish. While lighter wheels will get a faster start, they will also slow much faster especially at lengths greater than 42 feet. As of right now, ALL wheels have been optimized for 42 foot tracks. Food for thought.

 

[3phase]

It has,but not recently.

 

[Guest]

Also ....... surprised no one has addressed this - is wheel weight. Heavier wheels will act like a fly wheel and carry more inertia down track which will sustain more speed to the finish. While lighter wheels will get a faster start, they will also slow much faster especially at lengths greater than 42 feet. As of right now, ALL wheels have been optimized for 42 foot tracks. Food for thought.

TX Chemist ran the numbers a few months ago and figured that the track would have to be longer than a football field before weighting the wheels would be advantageous.

 

[Falcon777]

As John has said many times here, there is "theory" and there is "reality". Testimg has punched holes in that Theory.

 

[B_Regal Racing]

Do you by chance have access to any scales? If you do you can figure COM by using this calculator. Have fun... play around with it.

I tried this and it does not appear to be accurate. Using one of my current cars with a known COM, I checked the calculator. It computed I had a .1 COM , which was in actuality 5/8"; however, it did accurately represent which way the COM would move based on the weight change. Just the result COM result was in error. I was hoping to have a way I could calculate weight placement in relationship to COM in the X and Y directions. Ehhh...I'm now just doing what Kinser said, move weight, tune, then test, to find where the car runs best. I can not find a way to document the weight placement other than just record the weight on each wheel as I change the setup.

 

[txchemist]

Sorry Falcon- you confuse theory with physics. I think the times I calculated were super close to Zeebs track and should be even closer to the Nationals track. And wheel weight and inertia are all part of the equation. If your theory was correct, would you not have seen a fall off on the times of unlimited and eliminator with super light wheels compared to the BASX with heavy wheels?
It did not happen. You continue to be imagining mysterious properties that heavy wheels have. While it may be possible to make a faster car with heavy wheels and super low friction compared to lighter wheels and not so good friction, it was not due to the inertia effect in the last part of the race. You seem like a clever fellow, perhaps you can show us your math on wheel inertia and how it helps in a 63ft race.

 

[zeebzob]

I have to agree with txchemist. He was darn near spot on with his time estimates. We just did not see the fall off with light wheels on a 63 foot track.
The heavy wheel theory is fun to think about, but in the PWD world, it just does not come into play...EXCEPT in a turtle race. A few years ago I was in a turtle race and I added a lot of weight to the wheels so they would act like a fly wheel and keep rolling. I had employed a braking system that would try to slow the car down as much as possible after the hill, then I wanted to keep it rolling slowly, just enough to cross the finish line.
So, it is my belief that the heavy wheels only help when the cars get to a point where they are just barely moving. Think of it this way, light wheels - easy to start rolling, easy to stop rolling. Heavy wheels - more energy to start, more energy to stop.

 

[bracketracer]

Do you by chance have access to any scales? If you do you can figure COM by using this calculator. Have fun... play around with it.

I tried this and it does not appear to be accurate. Using one of my current cars with a known COM, I checked the calculator. It computed I had a .1 COM , which was in actuality 5/8"; however, it did accurately represent which way the COM would move based on the weight change. Just the result COM result was in error. I was hoping to have a way I could calculate weight placement in relationship to COM in the X and Y directions. Ehhh...I'm now just doing what Kinser said, move weight, tune, then test, to find where the car runs best. I can not find a way to document the weight placement other than just record the weight on each wheel as I change the setup.

BRR, I've used Minion's calculator on several cars and I've never seen it miss. Are you sure you're not seeing GIGO? If you want to post or pm the numbers I'd be happy to have a look at them with you.

 

[B_Regal Racing]

Thanks for the help. I was hoping someone would offer. In re-checking, I can not for the life of me, determine what I was doing wrong. It is spot on now. It is hard for me to believe one of my scales was that far off, but before posting this, I did re-calibrate both scales to be sure. Maybe I picked the wrong week to stop sniffing glue....

 

[Bullet]

I made my own sheet in Excel for calculating COM for width and length. The first time I went through it, I forgot to add in the diff of the DFW contact running on the outside of the wheel, it made a significant difference in the width calculation, nothing on the length obviously. My sheet gave a little different numbers than the calculator, but I take the actual measurements for each car to get dist between rear contact, DFW contacts, etc. Then I adjust this to a center line of the car body. With the DFW contact outside of the rear wheel contact, it makes a surprising difference in the width COM.

 

[bracketracer]

Thanks for the help. I was hoping someone would offer. In re-checking, I can not for the life of me, determine what I was doing wrong. It is spot on now. It is hard for me to believe one of my scales was that far off, but before posting this, I did re-calibrate both scales to be sure. Maybe I picked the wrong week to stop sniffing glue....

Good! Glad it's working for you now!

You're only using two scales?

 

[bracketracer]

I made my own sheet in Excel for calculating COM for width and length. The first time I went through it, I forgot to add in the diff of the DFW contact running on the outside of the wheel, it made a significant difference in the width calculation, nothing on the length obviously. My sheet gave a little different numbers than the calculator, but I take the actual measurements for each car to get dist between rear contact, DFW contacts, etc. Then I adjust this to a center line of the car body. With the DFW contact outside of the rear wheel contact, it makes a surprising difference in the width COM.

I believe Minion's calculator takes care of that also. You'll see a red line on the outer edge of the DFW and the inner edge of the rears to indicate the contact point.

 

[Bullet]

OK, thanks for the heads up! Need to look at it some more and compare. The numbers were actually close... It was just surprising to me how much the width changed even though the weight on the DFW is light...its the distance off the centerline.

 

[GravityX]

Just to follow up BracketRacer, I've used this calculator many times without fault. I'm no TXChemist, but from what I can tell this application is accurate as can be.

I'm not sure if the COM Visualizer, as shown, is representative of your values to the left of it.

From what I can see in this picture is that on the left side of the picture you have written in your document the wheelbase is 5-1/8" and in the COM Calculator shows you have input 5" as your wheelbase. COM value only changes slightly with this adjustment; from .5522" to .5556". Also, the weight on the DFW has a calculated value of .575 oz. and the value show input is .55 oz. The calculator rounds values to the hundredth, you can either go with .57 or .58 as the weight value. Doing this changes the COM once more from .5556" to .5824" with a weight value of .58 oz at the DFW. Looking further at the rear wheel positions if input as 3/4" this would move the COM to .5933".

As an example: without changing any weight at the wheel positions and moving the rear wheels back to 5/8" and using a 5-7/16" wheelbase you could achieve a .6295" COM. If you're looking for a 5/8" COM shorten the wheelbase.

This application is not fool proof. Making some input changes will change or alter measurements, in particular the wheelbase. As a preference I prefer to use grams as a weight measurement as opposed to ounces. Double check all values to make sure they are correct.

I hope this helps.

 

[B_Regal Racing]

You're only using two scales?

Yeah - I went cheap here. I weigh the whole car, then place each rear wheel on a separate scale, with the FDW resting on some CD cases to make the car level. I then calculate the weight on the FDW.

Thanks again BR and GX for checking on this. This tool has been exteremely helpful. It seems for me, I get better results with the COM centered as opposed to equal weight on the rear wheels. Its easier to get a rearward COM between 1/2 and 5/8, which could be the slight speed increase I see with the centered COM. Of course, the rest of my prep could be suspect making it "appear" that a centered COG is preferred.

Who knows; I'll keep building and testing...

 

[Kinser Racing]

I only use one scale. /images/boards/smilies/biggrin.gif