Why this Rule - Wheels directly across from each other

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idpwdnut
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Why this Rule - Wheels directly across from each other

Post by idpwdnut »

This one pack that has this rule has no wheelbase limitation, no mention of having to use existing slots or any mention of drilling axle holes. So if wheels were staggered, what advantage would that give to a team, other than design feature and allowing them to be creative.
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Re: Why this Rule - Wheels directly across from each other

Post by Rukkian »

There have been sites that claim that if you stagger the rear wheels, it will help when you hit bumps (like at the seams of the track), the same way as most people go over speed bumps at a bit of an angle.

We tried it once, and could not get the alignment quite right, and it is against the rules in our old council as well.
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Re: Why this Rule - Wheels directly across from each other

Post by Darin McGrew »

I've used staggered axle locations as part of a design effect, but not as part of a speed optimization. (Our rules allow staggered axle locations, as long as the car fits the track.)

I've read discussions of 3-wheel designs that suggested moving the rear wheel opposite the DFW slightly forward. I forget what it was supposed to accomplish though.
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Re: Why this Rule - Wheels directly across from each other

Post by 3 Cub Dad »

Out of the four "Why this rule"s posted, this is the only one that I have seen routinely used and has a little bit of merit.

If you look at the pics on one of the "pro" boards, you'll notice that most of the 3 wheel rail rider super cars, literally have only 3 wheels. The removal of the non-dom front wheel can and does affect time. I've run the experiments my self. So why not say simply, "must have four wheels"? Look at some of the older pics and you'll see where the fourth wheel was included, but it was built horizontally into the body on the top where it would not impact airflow. So the rule ends up being written something along the lines of "each wheel must be free wheeling, mounted on an axle directly inserted into the body of the car at an approximate horizontal angle, (to allow for canting), with no more than 1/8" protruding over the surface of the car, (again for canting)". Which leaves a bunch of people scratching their head.

So why not say, just attach the wheels to the side? For a 3 wheel rail rider, if you move the non-dom wheel back to directly in front of the rear wheel, you can have a slight impact on time due to decreasing the low pressure gradient behind the front wheel and resulting turbulence affecting the rear wheel. It's slight, but it is real.

Also, if there is no wheel or other device opposite the front dominate wheel, when the car hits the stop section, it is highly likely to spin off and damage itself or other cars.

The last point is probably the most sound basis for the rule, and the pack or district may have had some history with it in the past.

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Re: Why this Rule - Wheels directly across from each other

Post by FatSebastian »

3 Cub Dad wrote:So why not say simply, "must have four wheels"? [...] when the car hits the stop section, it is highly likely to spin off and damage itself or other cars. The last point is probably the most sound basis for the rule, and the pack or district may have had some history with it in the past.
:overmyhead: Another "Why-this-rule post" unambiguously notes that "Cars will be allowed to have no more than four wheels." Thus, three wheels are seemingly allowed under the rules that idpwdnut is questioning.
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Re: Why this Rule - Wheels directly across from each other

Post by dna1990 »

A simple answer to all these 'Why This Rule' questions...because once upon a time somebody beat somebody with that design element, so it was quickly outlawed as the suspected secret out-of-the-box-thinking that made for the 'unfair' win. If this forum engine had the ability to spit, I would use it right here.

Go play FunFairSoccer if you want a trophy without doing any homework. Innovation has been on life support for so long, I wonder if we have any hope at all.

idpwdnut - I wish you the best of luck in restoring what is indeed a 'fair' set of rules that make sense and HIGHLIGHTs a scout's intelligence and imagination. It will be tough if these are the historical rules you have been dealt, but we are behind you all the way.

Otherwise, let's just all run down to WallyWorld and buy 100 identical matchbox cars, randomly assign them scouts, but let any scout trade theirs for another one if they don't feel good about the one the got. But everybody turn their back while the cars down the track, so in case one falls off - it won't embarrass anyone.
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Re: Why this Rule - Wheels directly across from each other

Post by rpcarpe »

At the workshops this weekend, we had a kid drill a weight pocket into his axle hole. Ooops!
Moved the the axle forward, should still pass inspection of 4 wheels, right & left rear, right & left front.
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Re: Why this Rule - Wheels directly across from each other

Post by idpwdnut »

Rukkian wrote:There have been sites that claim that if you stagger the rear wheels, it will help when you hit bumps...We tried it once, and could not get the alignment quite right...
I had not seen that claim before. I could see how in theory it might work, but in practice, alignment would not be fun.
Darin McGrew wrote:I've used staggered axle locations as part of a design effect, but not as part of a speed optimization. (Our rules allow staggered axle locations, as long as the car fits the track.)
This is allowing the build teams to open up their minds and make creative designs.
3 Cub Dad wrote:Out of the four "Why this rule"s posted, this is the only one that I have seen routinely used and has a little bit of merit.

If you look at the pics on one of the "pro" boards, you'll notice that most of the 3 wheel rail rider super cars, literally have only 3 wheels. The removal of the non-dom front wheel can and does affect time. I've run the experiments my self. So why not say simply, "must have four wheels"? Look at some of the older pics and you'll see where the fourth wheel was included, but it was built horizontally into the body on the top where it would not impact airflow. So the rule ends up being written something along the lines of "each wheel must be free wheeling, mounted on an axle directly inserted into the body of the car at an approximate horizontal angle, (to allow for canting), with no more than 1/8" protruding over the surface of the car, (again for canting)". Which leaves a bunch of people scratching their head.

So why not say, just attach the wheels to the side? For a 3 wheel rail rider, if you move the non-dom wheel back to directly in front of the rear wheel, you can have a slight impact on time due to decreasing the low pressure gradient behind the front wheel and resulting turbulence affecting the rear wheel. It's slight, but it is real.

Also, if there is no wheel or other device opposite the front dominate wheel, when the car hits the stop section, it is highly likely to spin off and damage itself or other cars.

The last point is probably the most sound basis for the rule, and the pack or district may have had some history with it in the past.

3 Cub Dad
I can see making sure that the car stays on the track and break section is extremely important. Thats why most if not all of the "pro" board 3 wheel super cars have a guide peg of some sort. If we need to have two wheels on each side for safety, then say that, but why limit design creativity by saying they have to be directly accross from each other.
FatSebastian wrote:
3 Cub Dad wrote:So why not say simply, "must have four wheels"? [...] when the car hits the stop section, it is highly likely to spin off and damage itself or other cars. The last point is probably the most sound basis for the rule, and the pack or district may have had some history with it in the past.
:overmyhead: Another "Why-this-rule post" unambiguously notes that "Cars will be allowed to have no more than four wheels." Thus, three wheels are seemingly allowed under the rules that idpwdnut is questioning.
When asked about having only three wheels, they said that was not allowed, however there rules did not state that. ( to clarify, these rules come up at a roundtable on PWD, these two rules that FS is talking about are from the same pack, some of the others are not from the same pack.)
dna1990 wrote:A simple answer to all these 'Why This Rule' questions...because once upon a time somebody beat somebody with that design element, so it was quickly outlawed as the suspected secret out-of-the-box-thinking that made for the 'unfair' win. If this forum engine had the ability to spit, I would use it right here.

Go play FunFairSoccer if you want a trophy without doing any homework. Innovation has been on life support for so long, I wonder if we have any hope at all.

idpwdnut - I wish you the best of luck in restoring what is indeed a 'fair' set of rules that make sense and HIGHLIGHTs a scout's intelligence and imagination. It will be tough if these are the historical rules you have been dealt, but we are behind you all the way.

Otherwise, let's just all run down to WallyWorld and buy 100 identical matchbox cars, randomly assign them scouts, but let any scout trade theirs for another one if they don't feel good about the one the got. But everybody turn their back while the cars down the track, so in case one falls off - it won't embarrass anyone.
I think this is the most accurate answer. It reminds me of my Boy Scouts who say we cannot take milk on a camping trip because it goes bad, its not because he left it on top of the ice chest in the sun, it because of the camping. I would think adults would put a little more critical thinking into it.

Sorry dna1990 to get the blood pressure up, lets both go to our happy places. Thanks for the support dna1990, hopefully we will get the rules fair, sensible, and allowing for some imagination.
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Re: Why this Rule - Wheels directly across from each other

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Our pack requires use of the pre-cut axle slots, and 4 wheels touching, and no camber. So I've not studied RR and other advanced designs. But now we're going on to the district race with looser rules, and there is no rule against building an entirely new car. District says 4 wheels touching the track, but wheels can be anywhere within the 7" box, and camber is not mentioned. The track is Freedom Series, with a long gradual curve.

So I'm thinking about mounting 3 wheels at the extreme corners, and mounting one front wheel halfway between front and back. On the curved section of track, that middle wheel would be lifted just enough to not be touching. This would delay the onset of the wheel getting spun up to max speed, until after the car reaches the flats. During the curve, the car would have more of its momentum energy in forward body motion and hence be at higher velocity than a non-staggered 4-wheels-touching car. On the initial straight ramp and final flats, the car's angular and linear momentum and velocity would be the same as a non-staggered car. But the time spent at higher velocity would give the car a permanent head start on the flats. Or so I hope!

I think it would be safer to stagger the front wheels than the back wheels, given that most of the weight is on the back.
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Re: Why this Rule - Wheels directly across from each other

Post by Stan Pope »

Duane wrote:Our pack requires use of the pre-cut axle slots, and 4 wheels touching, and no camber. So I've not studied RR and other advanced designs.
Rail guiding is effective even without camber and with 4 wheels.
Lifting a wheel is effective without rail guiding.
Cambered axles are effective without rail guiding.
Duane wrote:I think it would be safer to stagger the front wheels than the back wheels, given that most of the weight is on the back.
If your goal in staggering is to temporarily lift a wheel, then you are correct. However, I think that if you look at the energy equations, you find no value unless you are able to avoid "spin up" of the lifted wheel. Lifting a spinning wheel, for instance, does not avoid the bore-axle friction losses for the duration of lift... it exacerbates them! Total losses from the bore-axle frictions of the weight bearing wheels is increased since the weight bearing wheels now carry the weight of the lifted wheel. But also, there is friction loss as the lifted wheel spins down. Then the wheel gets to spin up again when it touches.

If your goal in staggering is to avoid losses due to joint irregularities which would give simultaneous roll-producing impulses, then the loss is linearly related to the load carried by the affected wheel and, I think, inversely related to the distance from the CM to the wheel. If this analysis is correct, then staggering the rear wheels on a car with typical 1:4 fore-aft weight distribution is worth much more.

The loss depends on the distance that the CM is raised and the time during which it happens. So, while staggering the rears lifts the CM the same total amount, the duration of the lift is doubled, which halves the energy required to move the CM. At least, that is how I recall the analysis.
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Re: Why this Rule - Wheels directly across from each other

Post by FatSebastian »

Stan Pope wrote:So, while staggering the rears lifts the CM the same total amount, the duration of the lift is doubled, which halves the energy required to move the CM.
:thinking: Regarding joint irregularities, I have wondered if a wheel lifting the CM travels a slightly longer distance (by virtue of having gone up and/or down) or, analogously, slows down a bit because of the energy exchange. If so, is there risk of a staggered rear wheels wanting to steer the car one way and then the other when encountering a seam because of the lack of simultaneity, possibly inducing a stability issue with a lightly loaded front end?
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Re: Why this Rule - Wheels directly across from each other

Post by Stan Pope »

FatSebastian wrote:
Stan Pope wrote:So, while staggering the rears lifts the CM the same total amount, the duration of the lift is doubled, which halves the energy required to move the CM.
:thinking: Regarding joint irregularities, I have wondered if a wheel lifting the CM travels a slightly longer distance (by virtue of having gone up and/or down) or, analogously, slows down a bit because of the energy exchange. If so, is there risk of a staggered rear wheels wanting to steer the car one way and then the other when encountering a seam because of the lack of simultaneity, possibly inducing a stability issue with a lightly loaded front end?
Interesting questions!

First, yes, the distance of travel is increased slightly, and forward energy is diverted, netting a slowdown! I think the total is the same regardless of the presence of stagger. Delaying the slowdown would be a plus!

The impulse from one or more rear wheels hitting a bump creates a transient increase in the weight carried by all of the wheels, temporarily upsetting the balance of the steering effects of each because, I think, there is a phase difference between the changes at the various wheels.

The possibility of steering due to the slowdown of one wheel seems very real. I don't know how this energy loss compares.
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Re: Why this Rule - Wheels directly across from each other

Post by Duane »

Stan Pope wrote:
Duane wrote:I think it would be safer to stagger the front wheels than the back wheels, given that most of the weight is on the back.
If your goal in staggering is to temporarily lift a wheel, then you are correct. However, I think that if you look at the energy equations, you find no value unless you are able to avoid "spin up" of the lifted wheel. Lifting a spinning wheel, for instance, does not avoid the bore-axle friction losses for the duration of lift... it exacerbates them! Total losses from the bore-axle frictions of the weight bearing wheels is increased since the weight bearing wheels now carry the weight of the lifted wheel. But also, there is friction loss as the lifted wheel spins down. Then the wheel gets to spin up again when it touches.
I think the energy lost to sliding friction between the axle and the (temporarily) lifted wheel will be an order of magnitude less, than the kinetic energy that would otherwise be immediately sunk into spinning that wheel at full speed. Why: sliding frictions in fully-loaded cars is less than the rotational energy sunk into spinning BSA standard wheels. And here, the lifted wheel has only its own weight to cause friction, not the normal weight including the front corner of the car. And on Freedom tracks with long curves, the wheel gets lifted early, before the car has picked up much speed and before the wheel has spun to higher speeds. And yes, all the rotational energy that the wheel did acquire before getting lifted will likely be entirely lost to friction, before the wheel touches down again. If the friction slows down the free wheel much, that lost rpm will need to be repaid again when the dropped wheel syncs to the track. Repaid by drawing down the car's total linear kinetic energy. So the energy lost from the free wheel's own friction gets subtracted twice from the energy total, not just once. I hope it is still small.

Yes, there is energy lost to added axle friction at the remaining 3 weight-bearing wheels, because the lifted wheel is no longer supporting its own weight. But this is just like the case of normal 3-wheelers.

To maximize the time that the wheel is lifted, I hope to set the middle wheel so that it barely passes the rolling test on flat tabletops. I.e. it is not bearing any car weight when on the flat; the axle is near the top of the wheel bore and is just nudging the wheel along.

This trick, if it works, is not nearly as effective and efficient as true 3-wheelers. 3 wheelers never divert any energy into spinning up the 4th or missing wheel, so they enjoy a higher speed all the way to the end. In this car, the diversion still happens at the start at low speeds, and again (in a full amount) when the flats are reached at max speeds. It merely delays, not avoids, that energy diversion. For tracks with long ramps, the delay in that diversion could give the car a (temporarily) higher speed than otherwise. Maybe.
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Re: Why this Rule - Wheels directly across from each other

Post by Stan Pope »

Duane wrote:... free wheel's own friction gets subtracted twice from the energy total, not just once. I hope it is still small.
Time to haul out the text books and do some serious computation?
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