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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.
POSITIVE CAMBER: I'm trying to understand all applications where positive camber would be of benefit.
(1) I can see benefit if running a rail hugger (vice a rail rider) where you would tip the wheels in to track the rail.
(2) I can see benefit of putting postive camber on the lifted wheel on a three wheeled rail rider. to ensure it doesn't impact the track or rail.
(3) I can see the benefit above if you can put the wheel "on edge" and run the outside edge of the wheel tread against the track and the inside edge of the wheel tread against the rail.
However - if you must keep all four wheel treads FLAT to the ground (axle cant is fine as long as the wheel tread if flat), is there any situation where postive camber could be used beneficially?
*5 J's* wrote:However - if you must keep all four wheel treads FLAT to the ground (axle cant is fine as long as the wheel tread if flat), is there any situation where postive camber could be used beneficially?
Suppose that the axle on the DFW has slight postive camber.
When the car is "rolling free", where will the wheel go on the axle?
When the car is "guiding on the rail", where will the wheel go on the axle?
For each of the two extremes, what will happen if the wheel encounters a "rough spot" that pushes it away from the rail? How much mass will be moved by the encounter?
Stan
"If it's not for the boys, it's for the birds!"
When the car is "rolling free", where will the wheel go on the axle?
IN to the body
When the car is "guiding on the rail", where will the wheel go on the axle?
The toe of the DFW and the positive camber will try to make the wheel go into the body - however - the rail will be holding it back.
For each of the two extremes, what will happen if the wheel encounters a "rough spot" that pushes it away from the rail?
Well I'm not positive I know what extremes you are referring to - but I'll give it a shot. If the car encounters a rough spot that drives the opposite the direction the DFW wants to drive - the DFW will drive the car back to the rail - however - if the car encounters a rough spot that tries to drive the car in the direction of the DFW - then the DFW will try to drive over the rail - but the postive camber will hold the car back (?)
How much mass will be moved by the encounter?
Okay - I felt pretty good about my first answer - the second I felt I was climbing out on a limb - the third I was barely hanging on to the limb - now the fourth is going to be the one to break the limb - wait, what's that..................sorry about that I was hearing voices in my head saying "patience young padawan" ....... and hey where did all these BSA cars with Pinecar axles sticking out at various degrees of positive camber come from.
As the front wheels see 1/4 of the mass - I'm suspecting not a lot is moved in the encounter.
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?"
Stan
"If it's not for the boys, it's for the birds!"
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).
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.
In my one car test comparison for a ~0.75" COM, standard wheelbase, 4 wheels rolling RR, 32' wood track runs with positive camber on the DFW averaged ~0.025 less than runs with negative camber on the DFW.
quadad wrote:In my one car test comparison for a ~0.75" COM, standard wheelbase, 4 wheels rolling RR, 32' wood track runs with positive camber on the DFW averaged ~0.025 less than runs with negative camber on the DFW.
This is interesting, since I'm in a 3-wheeler world. If you don't mind me asking, do you recall the amount of drifit, if any, in each case? Also, do yo remember the amount of camber or axle bend in each case? If you'd rather not say that's quite ok too.
In my one car test comparison for a ~0.75" COM, standard wheelbase, 4 wheels rolling RR, 32' wood track runs with positive camber on the DFW averaged ~0.025 less than runs with negative camber on the DFW.
Interesting - how would you catergorize the conditon of the track and rail used in this comparison?
How was the front non DFW wheel aligned neutral toe/camber, or slight toe-out/slight negative camber?
The guide strip is 1/4" - 3/8" in height, which places contact with rail on the bottom 1/4"-3/8" of wheel. I would think, although minute, a negative cambered wheel offers less surface contact, in that tread rim is further from rail as opposed to [junk] cambered placing same in potential contact.
I seem to recall Joe experimenting and finding, regardless of camber, DFW will seek an equilibrium once contact is made and pull to ride flush with rail. I need to think this through more and probable consequence.
The guide strip is 1/4" - 3/8" in height, which places contact with rail on the bottom 1/4"-3/8" of wheel. I would think, although minute, a negative cambered wheel offers less surface contact, in that tread rim is further from rail as opposed to [junk] cambered placing same in potential contact.
But what is you must keep the tread FLAT on the track - now the camber is about position on the axle (IN/OUT) and the pro's and con's of being in each position at different moments or conditions.
But what is you must keep the tread FLAT on the track - now the camber is about position on the axle (IN/OUT) and the pro's and con's of being in each position at different moments or conditions.
In that case, I would opt for neg camber and keep wheel at axle head. Rail contact would tend to push in same direction why fight it?
quadad wrote:In my one car test comparison for a ~0.75" COM, standard wheelbase, 4 wheels rolling RR, 32' wood track runs with positive camber on the DFW averaged ~0.025 less than runs with negative camber on the DFW.
This is interesting, since I'm in a 3-wheeler world. If you don't mind me asking, do you recall the amount of drifit, if any, in each case? Also, do yo remember the amount of camber or axle bend in each case? If you'd rather not say that's quite ok too.
K
I have no trouble telling ... only remembering !
At that time I was following the "classis" RR setup using the RR Tool from DerbyWorx. (I remember their instructions being confusing about this and that was one of the reasons for the experiment.) 2.5 degrees negative cant on the rear axles, 1.5 degrees cant on the DFW, NDFW had no toe. The car steered straight w/o the DFW attached (similar to our alignment process with straight running cars) - though I would do different now with RRs. Then the DFW was attached and I expect toe'd for 2" in 4'. The track had fairly smooth edges on its guide strip. That's all I remember about it, but I was pretty convinced immediately to stop thinking of negative camber on the DFW. Just my experience with the one car, which was our first RR car.
It would seem there is an effective minimum camber angle required on the Fr Dom wheel of a 4 wheels touching racer to realize the benefits of [junk] camber. And a car running with rules requiring "flat 4 wheels down" might not be able to reach that minimum before being cited for a canting violation. In this case, a slight negative camber may be favorable on a rail hugger. Do I have that right?
This all would be fun to test sometime on the track since I do not believe I can model this on the computer with existing tools I have access too.
The addition of that 4th wheel into the mix really messes with things and introduces different "opportunities" to experiment doesn't it?
I wonder what percentage of Packs require 4 touching, 4 flat, or don't specify...?