Rail Riding - "How To Guide"

Secrets, tips, tools, design considerations, materials, the "science" behind it all, and other topics related to building the cars and semi-trucks.

Have you had success with a "rail rider"?

Yes
90
49%
No
8
4%
Somewhat
12
7%
Haven't tried yet
72
40%
 
Total votes: 182

*5 J's*
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Re: Rail Riding - "How To Guide"

Post by *5 J's* » Thu Apr 07, 2011 4:18 pm

Duane wrote:
derbyspeed wrote: if it works it doesn't matter if science agrees or not.
Yes. Better said as 'if it works, it doesn't matter if theories agree or not'. Science is more about the repeatable experiments than the theories. The theories are added, just to have some way to predict the results of the experiments, and maybe understand them too.
Ahh - yes, I agree 100% Duane, but your statement was that the Dr Jobe and other experts on the physics of these cars... not the theories. Are Doc Job and the experts stating the laws of physics or conjecturing theories, or hypotheses....

Duane - after reading this it sounded a bit argumentitive to me. Know that it is not meant to be argumentitive, rather I see a lot of theories on this forum - which is great - but some need to be taken with a grain of salt. Some of the quoted theories have been disproven in real worlld application. Obviously science and physics prevail, but some peoples interpretation may be deficient.



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Re: Rail Riding - "How To Guide"

Post by Duane » Thu Apr 07, 2011 7:04 pm

*5 J's* wrote:Some of the quoted theories have been disproven in real world application.
I wonder now, about the theoretical claim that total friction is independent of the area of the contact surface.
I've merely been parroting that statement without knowing any facts about it, or what the exceptions are.



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Re: Rail Riding - "How To Guide"

Post by FatSebastian » Thu Apr 07, 2011 7:55 pm

:offtopic: Recent comments have apparently wandered pretty far from the topic of this "sticky" thread, Rail Riding - "How To Guide". May I suggest that this interesting line of discussion be continued as a separate thread? (Perhaps gpraceman could port recent posts into their own topic.) Having said that...
Duane wrote:I wonder now, about the theoretical claim that total friction is independent of the area of the contact surface. I've merely been parroting that statement without knowing any facts about it, or what the exceptions are.
A brief presentation by Doc Jobe of the hows and whys of friction versus contact area can be found in this lecture. The context of this physical effect is seemingly limited to certain types of sliding friction (rather than rolling friction) between dry surfaces without lubrication. Outside of this context, one liability stated by Jobe regarding grooved axles of which I am aware is that they can serve to trap un-crushed graphite.



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Re: Rail Riding - "How To Guide"

Post by *5 J's* » Fri Apr 08, 2011 5:25 am

FatSebastian wrote::offtopic: Recent comments have apparently wandered pretty far from the topic of this "sticky" thread, Rail Riding - "How To Guide". May I suggest that this interesting line of discussion be continued as a separate thread? (Perhaps gpraceman could port recent posts into their own topic.) Having said that...
Duane wrote:I wonder now, about the theoretical claim that total friction is independent of the area of the contact surface. I've merely been parroting that statement without knowing any facts about it, or what the exceptions are.
A brief presentation by Doc Jobe of the hows and whys of friction versus contact area can be found in this lecture. The context of this physical effect is seemingly limited to certain types of sliding friction (rather than rolling friction) between dry surfaces without lubrication. Outside of this context, one liability stated by Jobe regarding grooved axles of which I am aware is that they can serve to trap un-crushed graphite.
I am going to post on Stan's friction post as I think we need to look beyond static friction and consider rolling friction, which is largely ignored in these pinewood theories.

For example take two identical basketballs, one full of air and the other slightly deflated. Roll them along the ground with the same initial velocities. Which will roll furthest? The one that is more full will. What is the difference between the two balls? They both have the same weight. The only difference is that one has more contact surface area than the other.



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Re: Rail Riding - "How To Guide"

Post by Slalom » Sat Apr 23, 2011 9:24 am

For example take two identical basketballs, one full of air and the other slightly deflated. Roll them along the ground with the same initial velocities. Which will roll furthest? The one that is more full will. What is the difference between the two balls? They both have the same weight. The only difference is that one has more contact surface area than the other.


I would think it is because a deflated basketball isn't perfectly round? A solid ball rolls faster than a limp ball



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Re: Rail Riding - "How To Guide"

Post by FatSebastian » Sat Apr 23, 2011 10:15 am

*5 J's* wrote:I am going to post on Stan's friction post ...
which can be found here.



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Re: Rail Riding - "How To Guide"

Post by PWRookie » Thu Mar 01, 2012 8:59 am

Great web site. I am a rookie, but have been reading this thread and a question popped in my head.

What if you consider the glued wheel to be a "feeler" like the kind discussed in the Pinewood Derby Times article below:
http://www.maximum-velocity.com/pinewoo ... _v6_i7.htm" target="_blank

If you get a speed advantage with a "feeler", why not utilize the glued wheel as a "feeler" by aligning the car to ride on it instead of the rotating wheel?

Has a study been done to see which produces less friction or has less impact on slowing down the rotating wheel? I would think the less friction (by the rail in this case) placed on the rotating wheel the better.

I haven't tried either yet, but would be interested if anyone has any experience in this.

Stan Pope wrote:
Ten Thumb Tom wrote: If I understand correctly, the scenario you are both describing is a car that is not a rail rider, but a three wheeler with alignment so dead on that the raised wheel would not touch the rail, and that under these conditions, the car could benefit from less vibration by gluing the wheel down rather than allowing it to rattle.
No, the car is almost certainly a 3-wheel RR with the dominant front wheel (DFW) toed in a bit to keep it against the rail. Dead-on alignment will almost always touch both sides of the rail somewhere along the run down the track.

Since the DFW is lightly loaded (almost always carrying less than one ounce), the friction losses from it rubbing are small. If you add a bit of positive camber to the DFW so that it touches below the top edge of the rail, the situation may even be better ... it will be rolling on both the track and the side of the rail, though there is also some sliding on the rail.

The value of glueing the wheel down is probably very slight. It was probably done to "show off."

If the DFW were sufficiently lightly loaded and if the car's inclination to "run to the rail" could be controlled through the rear wheels' differential friction, then you could probably get by with glueing in both front wheels and letting the DFW slide down the track. But that would take a whole bunch of tuning to get it right and fast. And, it would be showing off. Don't think we really need that. :(



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Re: Rail Riding - "How To Guide"

Post by Stan Pope » Thu Mar 01, 2012 12:30 pm

Interesting thought, PWR.

I'd analyze the comparison by asking first if there is a difference in the amount of force between the rail and either wheel. Then I'd ask if that equivalence in force translates into equal frictions. Then I'd ask the distance over which the friction acts.

These questions are important since the energy used up by this friction is the product of force of friction and distance over which applied.

The fixed 'feeler" wheel slides against the rail for a distance equal to the distance from the start line to the finish line. A Dominant Front wheel with negative camber slides also, but I'm not sure how to interpret the distance, since the the wheel is turning and sliding at the same time... I think that the distance might be almost as far as the distance from start line to finish line. However, a Dominant Front Wheel with positive camber is sliding a much smaller distance... since it is almost rolling on the rail.


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Re: Rail Riding - "How To Guide"

Post by derbyspeed » Thu Mar 01, 2012 1:38 pm

Stan Pope wrote: However, a Dominant Front Wheel with positive camber is sliding a much smaller distance... since it is almost rolling on the rail.
I think this is the secret to your answer. Stan brings up a good point, the dominant wheel is rolling and the "feeler wheel" would just be sliding. I'm definitely not an engineer but just think of a grocery cart that has a bad wheel and it slides on the Wal Mart floor :scratching: it's drag creates a lot more friction then when it is able to roll.

From what I saw in the test from Maximum Velocity, he only used the rolling bushings with the BSA wheels, he didn't test with the nylon line, which would have been stationary, possibly causing more friction unless you can make it and keep it super slick.

A lot of rules do prohibit bushings. Even though that may refer to bushings in the wheels I'm sure they would relate that to any bushing on the car.

But I may be way out in left field on this one :wall:


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Re: Rail Riding - "How To Guide"

Post by PWRookie » Thu Mar 01, 2012 10:38 pm

Sorry, still getting used to posting...

QUOTING Derbyspeed: From what I saw in the test from Maximum Velocity, he only used the rolling bushings with the BSA wheels, he didn't test with the nylon line, which would have been stationary, possibly causing more friction unless you can make it and keep it super slick.

You are correct about them not testing the nylon line with BSA wheels, and I didn't catch that detail. That could be a significant detail I will need to ponder further. However, they specifically conclude their study by stating: "Apparently, the BSA wheels generate significant losses when they contact the guide rail, so much so that the bushings provide a big advantage."

Thinking out loud, when tested on the Outlaw wheels, the nylon (fixed) was significantly slower (0.103 seconds) than the bushing (rolling). But both were slower than no feeler at all (rolling wheel contacting rail). Since the article doesn't state otherwise, I assume that the car was aligned straight up, with all 4 wheels on the ground. Therefore, both wheels probably were rolling and at least one likely contacted the rail.

I assume the alignment for the BSA wheel test was the same as I assumed above for the Outlaw test. With the BSA wheels, the opposite thing occurred, the bushing (rolling) gave a 0.043 second advantage over the wheel (also rolling) rubbing against the rail. I think it would not be stretching it to posit that the nylon (fixed) touching the rail would provide a similar, but not as significant, advantage over the rolling wheel contacting it. Extending this further, a glued wheel properly polished and lubricated on the inside (acting as a feeler) would yield similar results to the nylon feeler.

Perhaps, and Mr. Pope posits, the alignment and cambering made to intentionally rail ride will make the losses of the dominant wheel less than what the fixed wheel would be (even if the fixed wheel were polished on the inside where the contact would occur)?

Further thoughts or comments?



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Re: Rail Riding - "How To Guide"

Post by derbyspeed » Thu Mar 01, 2012 10:58 pm

PWRookie wrote:Perhaps, and Mr. Pope posits, the alignment and cambering made to intentionally rail ride will make the losses of the dominant wheel less than what the fixed wheel would be (even if the fixed wheel were polished on the inside where the contact would occur)?

Further thoughts or comments?
I also believe the dominant wheel, when aligned to ride the rail, will also act as somewhat a shock absorber for joints/bad spots in the rail, whereas a fixed wheel or otherwise would not be as forgiving.

You also have to remember, the main reason (at least in my opinion) for rail riding was to keep the raised wheel from touching the rail to almost take that wheel out of the friction equation (you still have weight and some spinning involved) and that's a pretty big improvement to beat. Not to mention keeping the heavily weighted rear wheels off of the rail.

You would most likely need 4 spots on the car with nylon or your feeler of choice to keep the car centered and off of the rail, I would think that, that would cancel out any improvement upon riding the rail with just the one wheel. :idk:


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Re: Rail Riding - "How To Guide"

Post by PWRookie » Fri Mar 02, 2012 3:20 pm

On a similar note, a Rail Riding article is posted at the following location: http://www.maximum-velocity.com/pinewoo ... _v8_i4.htm" target="_blank

Within this article, the author states that:
"Now let's add one other factor: a raised wheel. The purpose of the raised front wheel is to reduce the energy required to start the wheels rolling. If the raised wheel can be prevented from spinning, an advantage will be gained. But if the raised wheel contacts the guide rail, even one time, the advantage will be lost."

Is this sound reasoning? If so, I would think gluing the wheel to prevent it from rolling would help as well...?

Just to clarify, I am not advocating the use of a feeler or bushing, just hypothesizing whether or not steering the car to the rail towards a glued wheel could serve the same purpose as a feeler, and offer a benefit greater than steering the car to ride the rail with the dominant (rolling) wheel.

I don't have a track set up to attempt such an experiment.



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Re: Rail Riding - "How To Guide"

Post by FatSebastian » Fri Mar 02, 2012 3:45 pm

:welcome: PWRookie
PWRookie wrote:Is this sound reasoning? If so, I would think gluing the wheel to prevent it from rolling would help as well...?
You might want to review this topic, and direct additional comments and questions about glued wheels there?



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Re: Rail Riding - "How To Guide"

Post by FatSebastian » Fri Mar 02, 2012 4:33 pm

derbyspeed wrote:You would most likely need 4 spots on the car with nylon or your feeler of choice to keep the car centered and off of the rail, I would think that, that would cancel out any improvement...
MaxV's 2006 study did well to show that stationary "whiskers" were slower relative to rotating bushings. I liked derbyspeed's response, which highlights the fact that the study really did not involve rail-riding at all. To draw additional conclusions about the benefits of rail guides within the realm of rail-riding then, an apples-to-apples test would be helpful. One appropriate test might be to affix a rail rider with a roller bushing behind the non-DFW. In one test, tweak the toe of the DFW to let the roller bushing take on the rail (without spinning up the non-DFW!); in the other case, let the DFW take on the rail. (We wouldn't need to complicate this test by adding bushings on all corners; almost certainly more bushings would just drag down the car down even more as derbyspeed suggests.)

In this situation, I would suspect that the car could be slowed by roller-bushing contact with the rail. While we take away some sliding and rolling friction between the rail and DFW, we add sliding friction between the bushing and its large-diameter pin and rolling friction between the guide and the rail. The change in performance (good or bad) would likely be a function of the size and type of bushing, etc.

And as was mentioned, even if a guide bushing could be made faster, it would probably be ruled illegal as most rules prohibit "bushings."



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Re: Rail Riding - "How To Guide"

Post by derbyspeed » Fri Mar 02, 2012 9:27 pm

FatSebastian wrote: I liked derbyspeed's response, which highlights the fact that the study really did not involve rail-riding at all. To draw additional conclusions about the benefits of rail guides within the realm of rail-riding then, an apples-to-apples test would be helpful."
Actually in all fairness the test does involve railriding it's just a different element riding the rail instead of the wheel (albeit it may not keep continuous contact with any one feeler all the way down the track), but I like the test scenario you have put together Sebastion to see if keeping all 4 wheels off using just one bearing would be significant.

I think this experiment would be a good test comparing it to one wheel riding the rail if he could've taken the same car and tested again without the feelers (bushings) and adjusting the Dom wheel to ride the rail.

That would give us a better idea on how big of an improvement (one wheel) railriding is or is not. If that makes sense? :2cents:


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