Four on the floor rail rider thoughts

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woodworx
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Four on the floor rail rider thoughts

Post by woodworx » Sat Feb 16, 2008 7:25 pm

Our pack and district mandates four on the floor no three wheelers. I have been reading all the comments on the rail riding theory and it makes perfect sence. The one thing i was wondering about was the fact that you are steering the car into the rail. Since we have to run four on the floor would it make sence to have the wheel that doesnt ride the rail steer the oposite tire into the rail?. I guess my thoughts are it would ride smoother into the rail not trying to climb it so to say. Not having a track to test this i would only be guessing and maybe taking a huge gamble testing in a race. So far straight alignment has one us first place the last three years running as well as pack champion, but we are not very competitive at the district level. I beleive we need to try something different to be more competitive in the next level.



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Re: Four on the floor rail rider thoughts

Post by Pinewood Daddy » Sat Feb 16, 2008 10:17 pm

If the dominant wheel steers into the rail it only contacts on the front inside edge of the wheel. If it hits aligned straight it will touch along the whole surface of the rail. I'd think touching the smallest amount of surface area to the rail will be faster.



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Re: Four on the floor rail rider thoughts

Post by Stan Pope » Sat Feb 16, 2008 11:52 pm

Aligning the non-RR front wheel straight-on seems to work fine. Joe suggests a slight toe-out for that wheel as a good bet to be better. Maybe not as aggressively toe-out as the RR wheel is toe-in. Maybe if 0.4 degre toe in on RR, then about 0.2 degr toe-out on the other?

All guestimation at this point. Maybe after next weekend I'll have some actual data to share. Depends on how well our Distr Derby Chair is doing his job! And not creating emergencies!


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Re: Four on the floor rail rider thoughts

Post by Pinewood Daddy » Sun Feb 17, 2008 12:12 am

But it makes sense that if the RR wheel is aligned straight more of the surface of the wheel inner edge will contact the rail. More surface contact equals more friction, however small it might be.



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Re: Four on the floor rail rider thoughts

Post by woodworx » Sun Feb 17, 2008 7:48 pm

yes i was wondering about more of the wheel rubbibg on the rail, But i was also thinking the fact that it wouldntnt be cutting into the rail might ofset the loss more than what you might think. just brainstorming here i apreciate the feed back



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Re: Four on the floor rail rider thoughts

Post by Pinewood Daddy » Sun Feb 17, 2008 7:53 pm

woodworx wrote:yes i was wondering about more of the wheel rubbibg on the rail, But i was also thinking the fact that it wouldntnt be cutting into the rail might ofset the loss more than what you might think. just brainstorming here i apreciate the feed back
It would also be less apt to dig into a gouge or joint in the track.

We can finally go 3 wheelin' and this comes up??!! :mrgreen:



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Re: Four on the floor rail rider thoughts

Post by quadad » Thu Feb 28, 2008 8:19 am

Pinewood Daddy wrote:We can finally go 3 wheelin' and this comes up??!! :mrgreen:
Yeah ! And I think there are plenty more Packs like ours that require 4-wheels down as well, so expect more comments like this !

... Seriously, thanks for the great help on many threads on this forum, they are REALLY appreciated ! :D



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Re: Four on the floor rail rider thoughts

Post by psycaz » Thu Feb 28, 2008 8:24 am

Pinewood Daddy wrote:If the dominant wheel steers into the rail it only contacts on the front inside edge of the wheel. If it hits aligned straight it will touch along the whole surface of the rail. I'd think touching the smallest amount of surface area to the rail will be faster.
Would that be the case though?

Just wondering if the both sides of the wheel would still make contact as the angle on the axle wouldn't be sufficient to prevent this - due to the play in the bore of the wheel.

You would hit the rail too hard by setting the toe that hard to prevent the rear portion of the wheel edge from contacting the rail.

Just thinking out loud.



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Re: Four on the floor rail rider thoughts

Post by Pinewood Daddy » Thu Feb 28, 2008 10:55 am

psycaz wrote:
Pinewood Daddy wrote:If the dominant wheel steers into the rail it only contacts on the front inside edge of the wheel. If it hits aligned straight it will touch along the whole surface of the rail. I'd think touching the smallest amount of surface area to the rail will be faster.
Would that be the case though?

Just wondering if the both sides of the wheel would still make contact as the angle on the axle wouldn't be sufficient to prevent this - due to the play in the bore of the wheel.

You would hit the rail too hard by setting the toe that hard to prevent the rear portion of the wheel edge from contacting the rail.

Just thinking out loud.
Very true!! Since it takes a 2 degree bend to take up the slack in the bore, and a 0.4 degree bend is required (per Stan) to properly turn into the rail, the clearance in the bore will allow the whole inside edge of the wheel to contact the rail.



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Re: Four on the floor rail rider thoughts

Post by FinePine » Sun Mar 02, 2008 4:57 pm

Pinewood Daddy wrote:If the dominant wheel steers into the rail it only contacts on the front inside edge of the wheel. If it hits aligned straight it will touch along the whole surface of the rail. I'd think touching the smallest amount of surface area to the rail will be faster.
If you could choose, you would want the only contact to be at the bottom of the wheel, where the speed and direction of the wheel surface matches that of the track, so there is no sliding between the wheel and the track. As the contact point moves up, the relative motion between the two increases, and friction too. Lacking a radius between the rail and the track, you can't have the best case, but if the wheel was 'flat' to the [edit:]rail, at least some of the friction would occur lower, with less relative motion. The amount of contact area isn't the issue.

Now if the car were a free-rolling car, no rail, the least rolling resistance for a given turning circle would be where the axes of wheel all intersect at the centerpoint of the arc. Thus, the inside wheel would have more toe in the direction of the turn than the outside wheel. If only one wheel were to be toed (and in the absence of being able to test to be sure), I'd choose the inside. Just toeing the outside wheel will create a lot of scrub across the surface of the treads, and not much turning.
Last edited by FinePine on Mon Mar 03, 2008 12:24 pm, edited 1 time in total.



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Re: Four on the floor rail rider thoughts

Post by Stan Pope » Sun Mar 02, 2008 6:11 pm

Keep in mind that even with all 4 wheels rolling, they are not all necessarily bearing weight. Track irregularities may even cause the weight to shift left and right on the wheels.

If one front wheel is bearing weight and the other is just rolling along beside the car (but constrained from rolling away by the axle), can we call one of those front wheels "dominant?" Which one? Which has the greatest input into steering the car? If one front wheel is controlling the steering (getting the car to the rail and keeping it there), what is the best direction for the other front wheel?

Here is an exercise that puts four of those cheap Harbor Freight scales that you bought to good use: Lay out the scales so that your 4-wheeler sits with one wheel on each scale. One of the front scales will show more weight than the other. (Almost a certainty!) Start sliding pieces of paper under the front scale that reads lowest weight until it starts to increase. Now shift your attention to the readings on the rear scales as you continue to add a few more sheets to the pile under the front wheel. Do the rear scales stay the same? What about the total of the two rear readings ... does the total stay the same? How about the total of the two scales on the side that has been jacked up?


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Re: Four on the floor rail rider thoughts

Post by FinePine » Mon Mar 03, 2008 10:50 am

I had started to type a disclaimer that my previous post assumed even load left to right, but didn't because I think the statement about all axes intersecting at a single point would still be true even if the loads are not even. Maybe not, though, as hub friction changes; I'd have to think about that some more.

Corner weighting a real car is a pain, but is done with 4 scales like you describe. You have to work the diagonal pairs a lot. Each height adjustment throws off the alignment, so there is a lot of iteration.



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Re: Four on the floor rail rider thoughts

Post by joe » Mon Mar 03, 2008 11:34 am

If only one wheel were to be toed (and in the absence of being able to test to be sure), I'd choose the inside. Just toeing the outside wheel will create a lot of scrub across the surface of the treads, and not much turning.
These are interesting observations. We're trying to get to a point where this is possible with a 4-wheeler. One of the problems is getting both front wheels to accept weight, and to stay that way all the way down the track. Otherwise, if your inside wheel is dominant and steering, and the rubbing or "outside" wheel is floating, then you at least run the risk of scrubbing the outside wheel when the tread is not contacting the track, this is not ideal. This is probably not so much a concern on a smooth aluminum track, but it is a big problem on wooden tracks because you are playing with thousandths of an inch, and most wooden tracks don't have that sort of tolerance. Who knows, it might work, and it's worth a try since there's no weight, or at least not much, on that wheel!

On the other setup, the problem with having the dominant wheel rub the rail on bottom at a point is that you have to cant the axle down and run on the outside edge of the wheel -- two potential problems. Potentially though, a fix for those tracks with rough or protruding joints. You'd think this might avoid the big bumps at offset track sections.



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Re: Four on the floor rail rider thoughts

Post by FinePine » Mon Mar 03, 2008 12:27 pm

FinePine wrote:Lacking a radius between the rail and the track, you can't have the best case,
Ah, right. Positive camber will do this. Thanks.



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Re: Four on the floor rail rider thoughts

Post by PWD_addict » Mon Mar 03, 2008 1:32 pm

woodworx wrote:Our pack and district mandates four on the floor no three wheelers. I have been reading all the comments on the rail riding theory and it makes perfect sence. The one thing i was wondering about was the fact that you are steering the car into the rail. Since we have to run four on the floor would it make sence to have the wheel that doesnt ride the rail steer the oposite tire into the rail?. I guess my thoughts are it would ride smoother into the rail not trying to climb it so to say. Not having a track to test this i would only be guessing and maybe taking a huge gamble testing in a race. So far straight alignment has one us first place the last three years running as well as pack champion, but we are not very competitive at the district level. I beleive we need to try something different to be more competitive in the next level.
In general, when rail-riding with a 3 wheeler, the dominant front wheel doesn't just rub the rail at the bottom front, it tends to pull parallel to the rail and rub on most of the bottom inside, correct? This has the tendency to make the same side rear wheel rub the rail as the front wheel wants to become parallel to the rail (thus twisting the car). That's why we tend to trim off 1/16 from the dominant front side.

So, let me think about this out loud:
Now, if you had the rail riding wheel aligned straight, but the other front side steering it into the rail, you could possibly avoid the rear "twist" that you get. So, three wheels would be aligned straight and going straight. Which would seem to be faster than one wheel going straight and the back two slightly sideways.

You would want to make sure that the side rubbing the rail didn't rub in the back. This may happen anyway as the steering front wheel tends to twist the rear RR side away from the rail (due to steering front wheel toe-out). Of course, if that happened, then you are back to the rear wheels being slightly sideways anyway . . . . no potential speed gain from straight aligned wheels.

But, if you didn't get that rear twist, and you could keep the RR rear off the rail, you might get a little more speed with three wheels tracking straight.

Does that make sense or have I missed something completely?

Another thing about District Woodworx, are there any rules that you aren't taking advantage of and do you have a relatively aggressive CM? There could be other ways besides RR in which you are giving up speed in the Districts.



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