Big news...

[bad_karma_2805a1]

Morning all my fellow pine heads. So I have been going back and forth on this one because honestly, I do not want to step on anyone's toes. But I have to get some thoughts on it from all of the Jedi Masters of Pine on here. So here it goes...

I am currently working with Derby Downs and the American Soap Box Derby, a track company, and some local sponsors...to well lay 1000 feet of track down the main hill at Derby Downs. Yes you read that right, a thousand feet of track! We have an August date, that we are looking at for the event and so far response has been positive. Council, District, and the Pack are all on board with the idea. Currently I am setting up a committee to help me with it, because at this point it has been just me running with the ball.

So there is the big news, a 1000 foot long pinewood derby track. I know other people on here are trying record attempts and I do not want to take anything away from them. But this is something that started months ago and finally has gotten the green light. I am really sorry if I am taking away from anyone else's record attempt.

So far a few questions have been brought up, not so much about can we do it, but will a car survive. The biggest debate has been will the wheels actually make it down a track that long. Some people think they will be just fine, some think the wheels will start to smoke, and well others think the things will actually melt down. I don't know what to think because I am worried more about the logistics of the whole thing...lol.

So what do you all think; Will the wheels smoke? Will aerodynamics come into play? What is the best way to lay out a car for a run like that? Heck can a car stay on the track that far? Am I totally off my rocker for even trying to do this? What are your thoughts on the whole thing? Help me out fellow pine heads, because I need it. Any ideas, comments, and suggestions are totally welcome.

[gpraceman]

I rather doubt that you'd get wheels smoking. You might get wheel bore damage. Maybe even enough to cause the wheels to seize up, but I sort of doubt it. Though, that is a long stretch to run on. You might want to test a car down that hill to see how it goes. Maybe lay out 1000ft of 1/4" x 1-5/8" lath for that test.

Aerodynamics come into play during a normal race (just not as pronounced as other effects), so I would think it would be more pronounced of an effect over that long of a run and at higher speeds.

Any details on the track? Wood or aluminum? How many lanes? Will a timer be used? Rules?

[Stan Pope]

So what do you all think; Will the wheels smoke? Will aerodynamics come into play? What is the best way to lay out a car for a run like that? Heck can a car stay on the track that far? Am I totally off my rocker for even trying to do this? What are your thoughts on the whole thing? Help me out fellow pine heads, because I need it. Any ideas, comments, and suggestions are totally welcome.

Sounds like a gas!

Do you know the total drop from start to finish? (Can't be too great or you wouldn't let kids run SBD cars down it.) But total drop would let you estimate the car's speed at the end.

As for making it all the way down ... that will depend on how good a job is done on the manufacturing and setting up the track. One "bad joint" could send a car that catches it wrong airborn. But if your track crew does its job well, most cars that could qualify to districts should make it without overheating or flying!

Good luck with it!

[dna1990]

I believe the drop (from the current starting point) is about at 50' overall vertical drop.

Our new SBD hill in Hockley is supposedly built with a similar profile. I would think the main drop (first thrid of the track) would see some decent speeds, not so much to melt anything...but i would wonder about track alignment. If not well aligned or joints not smooth, could see some derails.

I am anxious to hear more about this.

[Duane]

With a track that long, it may help to allow more than the usual 5oz total weight. It's the total mass which helps overcome friction effects (wheel or air drag).

Also, please consider oil lubricant. Loose graphite powder won't stay in place that long, I think.

Wow!!

[Stan Pope]

With 50' drop overall, you will get decent speeds from the well turned-out cars. Your challenges will be (1) to avoid track leveling and straightness issues that would cause cars to put their non-DFW wheels on the rail and (2) to avoid sharp slope changes with the center of curvature below the track that could put the cars airborn. Should "run the numbers" to see what the top zero-friction speeds would be and how small the radius of curvature could be without the track falling away from under the car faster than the car drops from gravity.

Also need a vastly improved braking zone that stops the cars gently enough. I don't think a jacket thrown across the track behind the finish line will hack it for this track! There will be a bunch of energy to scrub off... the car will be going approx 45 mph at the finish (if I remember the formulas correctly). Maybe the gang can suggest workable stop zones that will leave the cars able to make second runs!

[FatSebastian]

Will the wheels smoke?

I am inclined to agree with gpraceman in that I doubt wheels would literally smoke. Having said that, information about the height of the starting line relative to the finish line, and the shape of the track, I think would be needed to understand wheel survivability.

If you know the height, Stan suggests you can get some idea of the car's maximum speed, and then you can determine the maximum RPM of the wheel. From there, it seems straightforward to rig up a test with, say, a drill press to get an idea of what might happen to a wheel: spin up a horizontal platter in the drill press and rest a car/axle assembly on the spinning platter such that the assembly experiences the proper RPM for the supposed time of the race.

I've done this to simulate extreme "wear-in" or "break-in". In one case I allowed a graphite-lubricated wheel/polished-axle combination to spin for perhaps 10 or 15 minutes non-stop. I could not tell you anymore what the RPM of wheel was during the test, but I don't recall it coming close to getting hot, and I even recall that the wheels were even still usable after the experience (although far from performing optimally, as you might expect).

Will aerodynamics come into play?

[sporty]

we were there in 08, when my son won his local.

if you start from the very top, thats pretty steep, versus the starting gate area.

lane 2 after the repave is suppose to be pretty level now.

I asume you are talking with Huntsman or someone in the office or on the board.

Yes aero is a factor they for the soap box derby cars.

those cars go good there, but its not the fastest track we have raced on for soap box derby.

.Will they stay on the track ? I would imagine some may not, where others will do fine.

Not sure they will have a majority of them finish, its going to depend on there prep work.

There is also a cross wind there and somedays it is more of a factor then other days.



my son holding his car on the akron hill.


This sounds like a way for akron to get some funds, they are hurting ! all American is.

i think you will be okay and a good portion of the cars will finish !

setting up the track to be even and level, now thats gonna take some work !

Sporty

[FatSebastian]

With 50' drop overall [...] Should "run the numbers" to see what the top zero-friction speeds would be [...] the car will be going approx 45 mph at the finish (if I remember the formulas correctly).

The expression for maximum idealized "falling" speed is V^2 = 2*g*h, where g = 32.17 ft/sec^2. For a 50 foot drop, by my calculations that turns out to be V = 56.7 ft/sec (or 38.7 mph). The angular speed of the wheel would be V/r, where r is the wheel radius (~0.6" or 0.05'), which then rotates at ~1134 rad/sec, or 10830 RPM! At these speeds the effects of wheel inertia must significantly reduce the speed from the ideal...

To hurry calculations along, I built a quick simulation using Jobe's Virtual Race based on sporty's picture, modeling 500' of inclined ramp plus 500' of straightaway. The top speed was 37 ft/sec (23 mph) for the car design I happened to try (e.g., 3 wheeler, new wheels, reasonably aggressive COM), which by my estimate is ~742 rad/sec or 7090 RPM. IIRC, this is slightly more than twice the max RPM usually encountered on a conventional derby track, even though the starting height is 12 times higher.

[gpraceman]

Will this track have a traditional start section? If so, then the height of that section should be added for any max speed estimates.

[FatSebastian]

Will this track have a traditional start section? If so, then the height of that section should be added for any max speed estimates.

Point well taken, although I don't think BK has provided any detailed height data yet - I modeled the track as a 50'-over-500' incline, followed by 500' straightaway, simply based on dna1990's comment about the track. Of course my purpose is just to provide a starting point should somebody want to conduct a bench test regarding the survivability of wheels.

[bad_karma_2805a1]

This sounds like a way for akron to get some funds, they are hurting ! all American is.

Sporty

Yeah I know they are hurting, which is sad but like everything else...it comes down to the dollar. We all are hoping that it will bring some attention to Derby Downs. For a tag line we are thinking "The two greatest gravity races teaming up to set a record." I know it is long but something like that.

Lane two...I guess I know what lane to look at for laying the track now.

I am waiting to hear back on all the distances, when I find out I will let you all know. Then you all can work your formulas.

[Stan Pope]

Thanks for running thenumbers, FS! I gotta quit converting fps to mph inmy head ... or remember that 88 is closer to 90 than to 80! (88fps=60mph, a relation that sticks in my brain better than most formulae or constants)
The sim drop to 23 mph from 37 seems reasonable given likely friction and aero losses. 23 is about twice the small track speed of 11-12 mph, so the rest of the computation works. Whether the rpm's are 7K or 11K, the energy to spin 'em up is pretty serious. Doesn't that also follow a "v^2" law? If so, then it would take 4 times as much energy to get up to 23 mph vs 11-12 mph.

PE should not be an issue... with 50' of head, I doubt that any will stop on the track.

I wonder if the timer will have any problems with a 1/5 mile of lead between the start gate and the finish line? Might have to go to some form of wireless link to make it work. Might be cost effective. too, as the wiring expense starts to mount up ... probably in the range of $200.

[gpraceman]

I wonder if the timer will have any problems with a 1/5 mile of lead between the start gate and the finish line? Might have to go to some form of wireless link to make it work. Might be cost effective. too, as the wiring expense starts to mount up ... probably in the range of $200.

That is an issue. Most timers will only time out to just shy of 10 seconds. The Judge timer is the only one that I know of that will time out past that (up to about 99 seconds) and they offer sensors that can work in sunlight. You'd need an awfully long start switch cable. I'm not sure if that length would pose any problems for the timer to recognize the start. Maybe John Shreffler can chime in on that.

[FatSebastian]

Any ideas, comments, and suggestions are totally welcome. ...it comes down to the dollar.

BK, is this event limited to your Council, or might there be an open race for scouts / Scouters outside to Council to take a spin down the Centennial 1000? If so, will there be a fee to participate (and how much)? Could be an excellent fundraising opportunity...