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

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pwrd by tungsten
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Re: Rail Riding - "How To Guide"

Post by pwrd by tungsten » Thu Aug 12, 2010 12:04 am

DFW on the right. It will gradually steer into the rail as the slope occurs.

I Drill rear holes canted at 3 degrees and use straight axles. Rear is symetrical.

Rear is full width. I like the rears to be equal spaced off the rail but it does not happen therfore I keep the wheel on the raised side a tad further from the rail.


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Re: Rail Riding - "How To Guide"

Post by ah8tk » Fri Aug 13, 2010 10:30 am

In the following drawing: figure A shows a pinewood derby car heading down the track from the front (see what good alignment it has it is going perfectly straight, and it was staged very well also). The car body is the 1 3/4” block with the axles drilled straight, the center rail on all tracks (that I’ve seen) is 1 5/8” wide so that leaves 1/4"(approximately, as there is also spacing between the wheels and the block, of 1/32” on each side, and wheel hub spacing)

Image
FinePine wrote:with the DFW riding the rail, what are the ideal locations of the other three wheels in terms of distance from the rails?
This depends on if the front of the car is narrowed to bring the following rear wheel out further from the center rail.
FinePine wrote:One thing that needs to be addressed first is whether, when in stable rail riding action, the car is still pointing straight down the track, only offset to the side a bit, or is the car angled to the left or right? From the viewpoint of the wheels and axles
If it is not pointing straight down the track you will have a very slow car as something would have to be rubbing considerably to offset the car from straight.
FinePine wrote: So, with that assumption in place, let's think about the rear wheels. How much clearance between the rail and the inside edge of the wheel should there be for each wheel? Should it be the same on both sides or asymmetrical? What should the total width between the wheels be?
See figure B&C, these figures show a PWD railrider with 2.5 degree angled rear (negative camber) and front wheels (one with positive camber, the other is raised), from the front and the rear, this should give an idea of where each of the wheels would be compared to the guide strip. Unless you offset the rear of the car the wheels could not be symmetrical to the guide strip, remember almost every set of PWD rules has “No less than 1-3/4 inches clearance between the inside of the wheels”. This rule is often tested with a 1 3/4" board, placed on a table that the car must roll over without binding.

Sorry I can only provide 2D drawings to show how this works. Hope this helps.
Last edited by ah8tk on Fri Nov 24, 2017 9:10 pm, edited 1 time in total.



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Re: Rail Riding - "How To Guide"

Post by FinePine » Fri Aug 13, 2010 2:02 pm

Thank you for the images. 2D views are the best way to show things, I think. I'll also have -2.5 degree camber in the rear, and +3.5 in the front.
ah8tk wrote: This depends on if the front of the car is narrowed to bring the following rear wheel out further from the center rail.
Well, what I'm trying to do is determine what the best placement for the wheels would be, free of any restrictions from the body, and then I'll shape the body to meet those needs. I'm thinking of the wheels determining the shape of the body, not the body determining where the wheels are.
ah8tk wrote: Unless you offset the rear of the car the wheels could not be symmetrical to the guide strip, remember almost every set of PWD rules has “No less than 1-3/4 inches clearance between the inside of the wheels”. This rule is often tested with a 1 3/4" board, placed on a table that the car must roll over without binding.
Here's what I have drawn up so far:
Image

This is a view from the rear of the car. The rear wheels are red, and the front wheels are black. The DFW (on the right) is against the rail, and the rears have equal spacing on each side of the rails. The rear to rail clearance is .130" (the short blue line). The red lines represent the 3/8" x 1-3/4" clearance required for the back, and the black lines are for the front wheels. Plenty of clearance at both ends. For us, clearance is only checked at these two locations, but clearance could still be made over a 1-3/4" strip of wood, even without angling the car to fit. Yes, the car block would need offsets and narrowing here and there, but that is easy enough. The question then isn't can it be done, but should it be done? Your drawings suggest that 1/8" clearance between the rail and right rear is plenty; is it enough for the left? I think that it probably is, but then my concern goes back to staging - with a narrowed spacing, the DFW will reach the rail sooner, which could slow things down.



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ah8tk
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Re: Rail Riding - "How To Guide"

Post by ah8tk » Fri Aug 13, 2010 9:12 pm

I made a new drawing from the rear showing what it would look like when the car was racing down the track. If the person staging the cars were to place the car on the track with the rear wheels spaced the same distance from the guide strip then the DFW would be at the rail the whole time.

And at the top is a top view of the car body and how you would need to offset the body in the front and the rear (using the 2.5 degree rear - negative camber and front - single positive camber). with this setup the wheels would indeed straddle a 1 3/4" board for check-in.

Image
Last edited by ah8tk on Fri Nov 24, 2017 9:13 pm, edited 1 time in total.



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Re: Rail Riding - "How To Guide"

Post by pwrd by tungsten » Fri Aug 13, 2010 11:56 pm

Running the rail:

If you draw a line down the center of your car. The rears should be symetrical. in all ways. The block at the rears the full 1 3/4".

The DFW indented 1/16" to 3/32" of an inch.

3/32" height DFW
4/32" height raised
5/32" height rears

Drill rear holes canted negative at 3 degrees. Axles straight

Drill front holes straight. raised axle straight. DFW bent 3 degrees.

Most inportant thing is to have straight axles and well drilled holes.

Well drilled holes are the foundation of your car.
Last edited by pwrd by tungsten on Tue Sep 21, 2010 10:37 pm, edited 1 time in total.


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Re: Rail Riding - "How To Guide"

Post by quadad » Tue Sep 21, 2010 2:45 pm

pwrd by tungsten wrote:Running the rail:
...
3/16" height DFW
4/16" height raised
5/16" height rears
Wow ! I know you have mentioned it before, but assuming similar height wheels all around that puts the front of your car up on like a 1.6 degree angle. I know you are running fast, but I can't figure out how that doesn't make the bottom of your car a big wind catcher. What am I missing here ? :scratching:
pwrd by tungsten wrote: Most inportant thing is to have straight axles and well drilled holes.

Well drilled holes are the foundation of your car.
:bigups: Agree with you 100% there.



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pwrd by tungsten
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Re: Rail Riding - "How To Guide"

Post by pwrd by tungsten » Tue Sep 21, 2010 3:22 pm

It adds a little bit of toe-out. :-)

Think of a car with canted rears. As you lift the front you get some toe-out.


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Re: Rail Riding - "How To Guide"

Post by FatSebastian » Tue Sep 21, 2010 3:28 pm

quadad wrote:
pwrd by tungsten wrote:Running the rail:
...
3/16" height DFW
4/16" height raised
5/16" height rears
Wow ! I know you have mentioned it before, but assuming similar height wheels all around that puts the front of your car up on like a 1.6 degree angle. I know you are running fast, but I can't figure out how that doesn't make the bottom of your car a big wind catcher. What am I missing here ? :scratching:
I was also wondering if the divisors should be 32 rather than 16? Otherwise, wouldn't the clearance between a 1/4"-high guide rail and the rear of the car seem uncomfortably close to dragging? (Or is low clearance actually desired?)



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Re: Rail Riding - "How To Guide"

Post by asatxj » Tue Sep 21, 2010 4:08 pm

By raising the axles as high as possible you gain the ability to get more weight below the plane of the axles. This give some increase in stability and speed. I haven't tested it yet but many on other forums use this method exclusively. This season I may build a test car around this premise.


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Re: Rail Riding - "How To Guide"

Post by FinePine » Tue Sep 21, 2010 4:25 pm

To get a "level" car that has negative rear camber and positive front camber, the rear holes need to be a bit lower than the front to account for the angles of the axles. But all this "height of axle hole" talk is dependent on the shape of the bottom of the car. But even if it is flat, and it slopes down toward the back, this doesn't mean that the car necessarily has a larger frontal area. A wedge shape car is thicker in the back than in the front, so even with a "raised" front end, the top of the car could still be level, and frontal area would not be increased.

Still, need 3/8" bottom clearance by most rules.



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Re: Rail Riding - "How To Guide"

Post by quadad » Tue Sep 21, 2010 5:54 pm

pwrd by tungsten wrote:It adds a little bit of toe-out. :-)
I'm still scratching my head a bit about that. I drew up a car on the computer with axle holes placed as Pwrd By Tungsten described. It is possible to get the top (at least the front 4-5 inches) to be level or very slightly downward in this configuration. The bottom does drag (just under 1/4" clearance at the far back) unless you cut it - assuming you start with a 3/8" to 13/32" thick block. You have to work to make an acceptable shape AND provide enough room around all the axle holes (1/4" difference).
asatxj wrote:By raising the axles as high as possible you gain the ability to get more weight below the plane of the axles. This give some increase in stability and speed.
Yep, I have been a big proponent of weight below the axle holes, trying for very high percentages. I have been considering going up more like 15/64" though with the rear holes, which is greater than the 0.17" or so you get with the ProBody Jig, but not near the 5/16" Pwrd By Tungsten is suggesting. I can think through the 'How much clearance do I need ?' and "What weights will fit well under the axles ..." question, but my thick head is still mostly stuck on this toe out conversation. :pullhair:



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Re: Rail Riding - "How To Guide"

Post by pwrd by tungsten » Tue Sep 21, 2010 10:34 pm

FatSebastian wrote:
quadad wrote: Wow ! I know you have mentioned it before, but assuming similar height wheels all around that puts the front of your car up on like a 1.6 degree angle. I know you are running fast, but I can't figure out how that doesn't make the bottom of your car a big wind catcher. What am I missing here ? :scratching:
I was also wondering if the divisors should be 32 rather than 16? Otherwise, wouldn't the clearance between a 1/4"-high guide rail and the rear of the car seem uncomfortably close to dragging? (Or is low clearance actually desired?)

You are correct:

5/32" on rears
4/32" on raised wheel
3/32" on DFW

Sorry about that...

I have updated my origonal post. I got these numbers from one of the finest PWD tuners in the world. ;)


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Re: Rail Riding - "How To Guide"

Post by *5 J's* » Wed Sep 22, 2010 9:40 am

FinePine - are you taking into consideration that 1.9 degrees of the canted axle will be taken up in the "bore slop" such that 2.5 degrees of axle cant will provide 0.6 degrees of wheel cant? (Somebody here can probably put this better into the Pinewood lexicon)

I am following this as this year we are going to pay attention to where on the block we start our holes. I may also modify a Pro-Body Jig to include provisions for drilling 1.5 degrees of negative axle cant, so I need to figure out the best spot for the bit to exit the Jig and enter the body. We can only run with a max of 1.9 degrees of axle cant as we need the wheel to stay flat on the track. I don't want to be on the edge - or worry about the "bind" having both the inside of the bore rolling on the lower edge of the axle and the outside of the bore rolling on the upper edge of the axle.

I have no particular reason for 1.5 other than it should provide enough to keep the wheel on the axle head but keep me safely away from the 1.9 degree critical angle.



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Re: Rail Riding - "How To Guide"

Post by *5 J's* » Wed Sep 22, 2010 11:36 am

FinePine wrote:To get a "level" car that has negative rear camber and positive front camber, the rear holes need to be a bit lower than the front to account for the angles of the axles.
A car with straight axles and axle holes will sit at a height of approximately 0.5435" minus the depth above the bottom that you drill the axle hole (using a nominal wheel of diameter 1.183" with a nominal bore of 0.096").

If the rear axle has a 3 degree negative cant it will only lower the rear 0.0016" (using 1/32" wheel to body gap).

If the DFW axle has a 3 degree positive cant it will only raise the front 0.0192" (using 1/32" wheel to body gap), and that is assuming all 3 degrees of the bent axle is used to provide positive cant, when in reality some will be used to provide toe-in for steering to the rail.

So if drilled all your axles at the same height and had 3 degrees of negative cant on the rears and 3 degrees of positive cant on the DFW the front would only be 0.0208" (less than 1/32") above the rear as measured at the axles. Or another way to look at it is the body would tilt up approximately 1/4 of a degree.

If you wanted to level the car - you would want to drill the rears 0.0208" below the front. However, PBT drills the rears 1/16" above the DFW which will further lower the rear. Using the quoted three degrees of cant I calculate the body will tilt up 1.12 degrees if a standard wheelbase is used. This will give a bit of toe-out on the rears as PBT states. Note sure how this equates to speed. I would think trying to set up level would be best - but PBT has much more experience than I, and experience beats theory anyday.

Somebody may want to verify my math.



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Re: Rail Riding - "How To Guide"

Post by FinePine » Wed Sep 22, 2010 4:26 pm

*5 J's* wrote:FinePine - are you taking into consideration that 1.9 degrees of the canted axle will be taken up in the "bore slop" such that 2.5 degrees of axle cant will provide 0.6 degrees of wheel cant?
I haven't observed a loss of camber. If the contact point of the wheel to the track is vertically between the ends of the bore (and if there is enough weight on that axle), the angle of the wheel should match the angle of the axle, no? The front, with positive camber and a deep dish wheel, and light axle weight, may be different. My car is in the display case now so I can't pull it out and have a look for a few weeks. Anyway, things will change when the car is moving, which is the part that actually matters.



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