Benefit's of Positive Camber

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Stan Pope
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Re: Benefit's of Positive Camber

Post by Stan Pope »

*5 J's* wrote:
Then let me rephrase ... When guiding by the rail, the DFW on a marginally positive cambered axle might go to the extreme of holding to the car body, or to the opposite extreme of holding to the axle head. The "rough spot" on the rail usually pushes stuff away from the rail. What reasonably happens for each of those two extremes when the DFW encounters the "rough spot?"
Let me try this again. This time looking at the system as a whole.

You start with a given amount of Potential Energy based on the mass of the car (and its placement) and the height of the track. The goal is to minimize any losses that are not used to pull the car to the finish line as quick as possible.

I'll start with the possibility that the positive camber holds the wheel to the axle head. If you hit "rough spot" on the rail that pushes the wheel away from the rail - the wheel in turn pushes against the axle head (that it is already against) which in turn pulls the nose of the car (and it's mass) across the track.

Next what if the positive camber hold the wheel to the body. If you hit "rough spot" on the rail that pushes the wheel away from the rail - the wheel will slide across the track until it comes against the axle head (that it is already against). <-- No! Cut and paste error?

Much less energy is lost in the second scenario as the wheel only has to slide across the track. In the first example the entire nose of the car would have to slide across the track.
This is it! And the difference would seem to be significant. Now the question is, "Where does the wheel really want to stay?" I think that there are several factors involved, including the magnitudes of the toe angle and the camber angle as well as front wheel load and any rear wheel steering influence. Multiple factors suggests that a variety of test cases would be needed to determine with confidence ... unless someone can formulate the full detail of the physics involved.
Stan
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Re: Benefit's of Positive Camber

Post by *5 J's* »

yes, cut and paste error.

Yes -I would like to hear if any others have experiment with this, and what their results were.
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Re: Benefit's of Positive Camber

Post by doct1010 »

Stan Pope wrote: ... When guiding by the rail, the DFW on a marginally positive cambered axle might go to the extreme of holding to the car body, or to the opposite extreme of holding to the axle head.
I am having difficutly imagining a [junk] camber bringing wheel to axle head. Maybe "marginally" is the operative term here, ie enough to lift tread from track?
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Re: Benefit's of Positive Camber

Post by doct1010 »

The longer I ponder the question of benefits of positive camber the more disadvantages come to mind.
1. Riding outer edge, risk of nubs contacting (especially if a bit aggressive with pro shaver) exception may be ultra light 1g's, where the rigidity of wheel face is needed to prevent deforming under load..
2. Body contact as opposed to nail head, may be mitigated a bit with body cone ala SSnakes' method.
3. On FDW, seems to encourage more surface area contact and
4. Working counter to drift of toe pushing wheel

Pleae inform, what am I missing?
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Stan Pope
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Re: Benefit's of Positive Camber

Post by Stan Pope »

doct1010 wrote:Pleae inform, what am I missing?
Since the wheel "must roll flat" on the track, it can't "roll" against the rail.

That seems to leave a tendency for the wheel to stay near the body except when pushed away by rail irregularity as the possible saving feature. Pushing only the wheel instead pushing the entire front of the car should save a bit!
Stan
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Re: Benefit's of Positive Camber

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Stan Pope wrote: Since the wheel "must roll flat" on the track, it can't "roll" against the rail.

That seems to leave a tendency for the wheel to stay near the body except when pushed away by rail irregularity as the possible saving feature. Pushing only the wheel instead pushing the entire front of the car should save a bit!
That makes it a bit clearer. We are talking minimal camber, just enough to change orientation on axle, not enough to lift wheel.
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Stan Pope
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Re: Benefit's of Positive Camber

Post by Stan Pope »

doct1010 wrote:
Stan Pope wrote: Since the wheel "must roll flat" on the track, it can't "roll" against the rail.

That seems to leave a tendency for the wheel to stay near the body except when pushed away by rail irregularity as the possible saving feature. Pushing only the wheel instead pushing the entire front of the car should save a bit!
That makes it a bit clearer. We are talking minimal camber, just enough to change orientation on axle, not enough to lift wheel.
Yup! "Flat on the track" was a condition expressed by *5 J's* at the start of the thread.
Stan
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Re: Benefit's of Positive Camber

Post by pwrd by tungsten »

*5 J's* wrote:
i always run positive camber on BSA wheel cars...
On all wheels or just the DFW on a railrider?

Do your rules permit enough camber to run the wheel on edge? (no four wheels flat on the ground rule)

Do elaborate.
Just the DFW... Learned it from very fast folks... Wheel does rub on body.
W Racing!!!!
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Re: Benefit's of Positive Camber

Post by Speedster »

This is a very interesting Topic for those who are required to have all 4 wheels touching and roll. Don't ask me why they put in the rules "and roll".
Info: I use the axle bender where the nail is put in the tool and you pull up on the handle to get the bend. Rear wheels and dfw are bent to 1 1/2 degrees. Rears are set with Negative cant and Dfw is set with Positive cant. When the car is sitting on its wheels they will look very close to be sitting straight up and down. The rear wheels must be adjusted so they are running parallel to the body.

This is only the 3rd time I have ever been involved with a scout in the only District (not my District) in the Erie council that requires 4 wheels yada, yada, yada. This scout is so wanting speed I finally gave in.

The Physics has always been there but we have gained more knowledge. Here is Kenny's statement that I invite you to think about - "The addition of that 4th wheel into the mix really messes with things". That is a huge understatement.

My experience. We set up a 3 wheel rail rider, set the drift for 2" in 4' on the test board, took it to a section of a "Best" track and it rolled with only the Dfw touching the guide strip. Time for the 4th wheel. First, get it on the ground. Second, set it with Negative cant and slight toe out to have it help the Dfw and keep it off the rail. We are dealing with .010 clearance between the axle and wheel bore on each of these wheels. Took it to the track and the non dfw became the dfw and the car now drifted the opposite way 2" in 2'. We were out of time, race was next day, car took 2nd place. Don't ask me how.
The scout has left the car with me and I have put countless hours in it. I changed 2 of the wheels and all of the axles. The wheels all are .002 or less Out of Round. I used the nails for truck racing. I sanded the nails with 3000 grit and polished them with Novus 2. The non dfw is set with .5 degree Negative cant and I tried to set it so the wheel would run straight. I got everything to work on the test board and then took it to the track. Everything seems fine. I believe the non dfw is hanging on the nail but it took me forever to get it there. The body of the car was not narrowed 1/16" behind the Dfw. The rear wheel following the dfw is spaced .060.
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