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 Sep 23, 2010 5:27 am

Yes there is a loss in camber as the wheel attempts to lay flat to the track. This causes the wheel to roll on two points once you pass the critical angle of 1.9 degrees - the inner/bottom of the bore and the outer/upper of the bore as the axle sits diagonally across the bore. This loss of camber also allows us to run 1.5 degrees of camber - but keep the tread flat to the track as required per our council rules.

Note that this 1.9 degrees is calculated on nominal values of an axle diameter (0.087") and hub bore (0.096") and bore length (0.273"). This gives 0.009" of bore slop to be taken up over a bore length of 0.273", which gives an axle angle of 1.89°. Any differences is these values would change the critical angle. With the older style wheels without the 0.02" step - the bore length was 0.293" which gave a critical angle of 1.76 degrees.

This is illustrated in this post.

Note that this is not true in the other plane, or toe. With toe, the axle will remain in the bore valley such that wheel toe angle = axle angle.



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Re: Rail Riding - "How To Guide"

Post by FinePine » Thu Sep 23, 2010 9:12 am

Thanks for the link. Later in the same thread, Stan's casual observations match my own, which is that the wheel tilts up to match the angle of the axle.

There are three moments acting on the wheel that determine whether it lies "tread flat" or is angled (car at rest on a level surface). If you look at these, it seems that they will cause a rear wheel with negative camber to tilt. One moment is from the weight of the wheel, one from the weight of the car, and one from the nail head preventing the wheel from traveling up the axle (if you roll the car a bit to allow it to get out there). I think the latter two are stronger than the first. It could be calculated easily enough, but I'll leave that to someone else. At low angles, friction may be high enough to prevent the system from reaching its lowest potential energy state.



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Re: Rail Riding - "How To Guide"

Post by *5 J's* » Thu Sep 23, 2010 9:48 am

yea, I have never gone with more than 1.7 degrees of negative camber due to our rules requiring the wheels to sit flat on the track. With 1.7 and less the wheel do sit flat - perhaps at greater angles above 1.9 - wheel angle = axle angle.



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Re: Rail Riding - "How To Guide"

Post by FinePine » Thu Sep 23, 2010 10:04 am

I'd be interested to know: if you push the top of the wheel in to match the angle of the axle, does it stay there? And if you then roll the car a bit, what happens?



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Re: Rail Riding - "How To Guide"

Post by *5 J's* » Thu Sep 23, 2010 10:32 am

I have a bit of my daughters car running during the alignment process
Imagehere

The cars can be seen here and here

I will have to see what happens when I push the wheel to match the axle angle.



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Re: Rail Riding - "How To Guide"

Post by *5 J's* » Tue Sep 28, 2010 10:06 am

FinePine wrote:I'd be interested to know: if you push the top of the wheel in to match the angle of the axle, does it stay there? And if you then roll the car a bit, what happens?
With 1.7 degrees of negative camber the wheels will match axle angle if you push the wheels "hard" against the axle head. However, this is an unstable position. As soon as the car starts moving a bit the wheel will come slightly off the axle head and the tread will sit flat in the track.



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Re: Rail Riding - "How To Guide"

Post by Slalom » Sat Mar 26, 2011 12:03 pm

New to this board I have 2 questions:

1. First year doing PWD, placed 3rd in district ( 2brothers placed 1st and 2nd hmmmm?) We have a RR Why are so many against the bent rear axles? what is the benefit of angled holes?

2. How do you turn the axles with needle nose pliers without damaging the axle head? is the only option slotting the head for a screwdriver?

3. Is there any benefit to tapering the outer circumference of the axle head to decrease it's catching on the inner bore?


Thanks in advance for your help!!!



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Re: Rail Riding - "How To Guide"

Post by 5kidsracing » Sat Mar 26, 2011 2:05 pm

Slalom wrote:New to this board I have 2 questions:

1. First year doing PWD, placed 3rd in district ( 2brothers placed 1st and 2nd hmmmm?) We have a RR Why are so many against the bent rear axles? what is the benefit of angled holes?

2. How do you turn the axles with needle nose pliers without damaging the axle head? is the only option slotting the head for a screwdriver?

3. Is there any benefit to tapering the outer circumference of the axle head to decrease it's catching on the inner bore?


Thanks in advance for your help!!!

You can drill angled holes very acurately.... using bent axles is hard to tune and hard for a novice to get right.

The Khouse Groove works excellent (screwdriver slot in axle head)... I drill holes in the bottom of the car exposing the ends of the axles and turn them from there...

Yes, angling the axle head is good... do it..


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Re: Rail Riding - "How To Guide"

Post by Stan Pope » Sat Mar 26, 2011 2:18 pm

Slalom wrote: New to this board I have 2 questions:
Then I'll try to give you 50% more than you ask for. :)
Slalom wrote:1. First year doing PWD, placed 3rd in district
Excellent!
Slalom wrote:( 2brothers placed 1st and 2nd hmmmm?)
They probably have the same mentor!
Slalom wrote:We have a RR Why are so many against the bent rear axles? what is the benefit of angled holes?
"Angled holes" allow "mass production" and "plug and play" builds. If the results don't "play" they can be round filed without significant loss. "Bent axles" facilitiate tuning of "one of a kind" creations. Both work.
Slalom wrote:2. How do you turn the axles with needle nose pliers without damaging the axle head?
Not all damage interferes with operation. If minor defacement of the axles heads does not touch the wheels, then no problem. Tapered underside of axle head naturally avoids contact with the wheel.
Slalom wrote:is the only option slotting the head for a screwdriver?
No. I cut a thin "wrench" slightly smaller than the diameter of an axle. The thickness of the wrench was less than the wheel-body clearance planned. Then I filed 1/32" wide notches right where it would stick out of the car body.
Slalom wrote:3. Is there any benefit to tapering the outer circumference of the axle head to decrease it's catching on the inner bore?
I need clarification of this one ... unless you are referring to the possibilty of the axle head catching on the sides of the indented hub face. Gotta keep the head diameter small enough to prevent touching the wheel.


Stan
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Re: Rail Riding - "How To Guide"

Post by FatSebastian » Sat Mar 26, 2011 3:34 pm

:welcome: Slalom!
Slalom wrote:2. How do you turn the axles with needle nose pliers without damaging the axle head? is the only option slotting the head for a screwdriver?
This thread mentions various options.
Stan Pope wrote:I cut a thin "wrench" slightly smaller than the diameter of an axle. The thickness of the wrench was less than the wheel-body clearance planned.
Discussed here I think.



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Stan Pope
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Re: Rail Riding - "How To Guide"

Post by Stan Pope » Sat Mar 26, 2011 5:47 pm

FatSebastian wrote:
Stan Pope wrote:I cut a thin "wrench" slightly smaller than the diameter of an axle. The thickness of the wrench was less than the wheel-body clearance planned.
Discussed here I think.
I'll get better info sometime... The "wrench" is back home, now, and the tooling to prepare it is in the tool chest. Only lacking a sample axle to photograph.


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Re: Rail Riding - "How To Guide"

Post by Stan Pope » Mon Mar 28, 2011 11:07 am

Not everyone is allowed to narrow the front end of their racer in order to achieve the desired offset of DFW to rear wheel. Here is some info from a spreadsheet to help plan how to achieve the same result:

Image
(Right click and save the "Open Office" spreadsheet here.)

The numbers are for standard wheelbase. Extended wheelbase numbers are similar.

The "Offset Angle" value is how much the rear axles need to deviate from perpendicular to the car's center line in order to cause the rear wheel behind DFW to stay off the rail by the "Offset" amount. This can be accomplished either by precisely drilling the axle holes at angle or by bending the rear axle to at least that amount.

Another interpretation of "Offset Angle" is how far the car's center line is angled away from "straight down the track." To "fix" the visual incongruity, one might redefine the car's center line accordingly. It is conceptually simple (though not so simple in practice) to layout and cut the car's body based on this altered "center line."

The "Deviation in Overlap" value is the amount to rotate the drill press table, measured by a dial indicator, in order to accomplish the "Offset Angle".


Stan
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Re: Rail Riding - "How To Guide"

Post by rpcarpe » Mon Mar 28, 2011 11:22 am

Turning axles... I'm not promoting the vendor(s)... but somebody out there makes special Axle Pullers and/or Axle Pliers.
Hold on, I just looked it up.
Axle Puller - Derbychamp.com $13.95, DerbyMonkey $14.95
Axle Pliers - Maximum Velocity $19.95

I got the Axle Pliers and I've been very pleased with them. When the tuning table gets set up... out come those special pliers.


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Re: Rail Riding - "How To Guide"

Post by Slalom » Mon Mar 28, 2011 11:24 am

Thanks guys, think I will slot the heads with my dremel (steady hand required), probably take some beta blockers before hand:>

two more questions, one relates to this thread, hope It's not a violation to stray.

1.I already have the body built and drilled, with a mighty fine paint job, retrospectively i would have drilled holes with camber using SP's technique, I alas have to use angled axles. Why can't grooved axles be angled? Is the force of the bending traslated to the grooved area causing bending around the groove? Why is 2.5 degrees the recommended Rear axle measurement, seems to me the 1.5 degrees would accomplish the same effect, what is the science?

2.I bought some Krytox and ran pack with that, now am seeing the krytox/"secret blend" mix, is this the new gold standard? Should I switch to this? Will it decrease times?


Cheers!

P.S. After reading through these threads for many hours over the past weeks, I feel like I am brushing with celebrity getting advice from Stan Pope and A pinehead legend.



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Re: Rail Riding - "How To Guide"

Post by Stan Pope » Mon Mar 28, 2011 11:58 am

Slalom wrote: Why can't grooved axles be angled? Is the force of the bending traslated to the grooved area causing bending around the groove?
Grooved axles can be "angled" and they can be "bent". I think "bent" is what you were axking about, right? But I'd have qualms about trusting the Pro RR Tool to do it well. I fear the axle ends up "curled" where the wheel bore rests. So, think about other ways to bend 'em!

The grooves for twisting axles (using the wrench described a few posts earlier), are right where the bend needs to be, and they can easily be added either before or after the bend is made.
Slalom wrote:Why is 2.5 degrees the recommended Rear axle measurement, seems to me the 1.5 degrees would accomplish the same effect, what is the science?
The extra degree seems to lift the wheel up on edge more reliably. I suspect that it relates where the wheel touches the track in relation to where the wheel bore touches the axle... a stability issue. At the same time, the shallow angle does not create great force against the axle head.

Slalom wrote:2.I bought some Krytox and ran pack with that, now am seeing the krytox/"secret blend" mix, is this the new gold standard? Should I switch to this? Will it decrease times?
Marginally, I'm told. The added surfactant needs to be carefully metered. Too much and the krytox fails. Too little and there is no benefit. Is it stable (on the shelf and in the wheel bores) for an acceptable period? Dunno.

My feeling is that most of us have so many "higher payoff" opportunities to improve our cars that buying the "latest and greatest technology" is probably wasteful.
Last edited by Stan Pope on Mon Mar 28, 2011 12:23 pm, edited 1 time in total.
Reason: lift


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