# 6" Curve Theory



## Grandcheapskate (Jan 5, 2006)

Hi Guys,
A theoretical question for you...

In my layout, I have a couple places where I use 6" curves. In three of those places, I use them in a complete 180 degree turn. In two of those places, there is a lead-in 9" 1/8 curve and I have no problem navigating them with non-mag cars.

In the third location, there is a lead-in 6" straight. I have a very hard time getting through this turn on the inside lane as the rear spins out, especially with Aurora AFX cars (T-Jets and Magna-Tractions seem to have less of a problem). The only thing I can figure is that the lead-in 9" curve puts the car in a better position entering the curve.

In any case, here's a theory I came up with yesterday and I wanted to see what you think.

As you know, some AFX cars came with the pin style front axle. This is where one hub slides over the axle and the other gets pressed on. The hub/wheel which is pressed on must turn the axle while the other hub spins freely - so obviously it is harder for the one tire to rotate. I started to notice that when the press-on wheel is to the inside of the turn, the car will more easily spin out. Reason? Since the press-on wheel must turn the axle, it doesn't turn as freely as the other wheel. When you go around a sharp curve, I am thinking the car wants to use the inside tire as a pivot point and when it doesn't spin as easily as the outside tire, it allows the rear of the car to kick out.

Thoughts?

Thanks...Joe


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## Ralphthe3rd (Feb 24, 2011)

Nice theory, but then, WHY doesn't the solid axle T-Jet have the same problem ?


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## NTxSlotCars (May 27, 2008)

Joe,
Your theory would seem exactly right, on both. (the 9" curve lead in and the pivot point)
Have you tested your theory by flipping the front axle?

Ralph,
You have a valid point... if I understand your question right...
Why wouldn't a tjet with the same front end set up have the same problem?

To me, the AFX and Magnatraction cars are completely different than Tjets, especially handling.


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## Grandcheapskate (Jan 5, 2006)

Ralphthe3rd said:


> Nice theory, but then, WHY doesn't the solid axle T-Jet have the same problem ?


I believe on a solid axle car, both tires share the load of turning the axle equally. Therefore neither tire tries to use the other as a pivot point.

Think about this. If one front tire rolled and the other did not, wouldn't the car try to pivot around the tire that does not turn?

Rich,
I took out cars which have the press on wheel on opposite sides, but it is really hard to get a handle on how much effect this has. And this has to be done with non-mag cars as any kind of magnetic downforce would mask the effects. 

Thanks...Joe


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## Dslot (Sep 2, 2007)

I had a haunted killer-curve on one layout that we nicknamed "Undertaker's Bend." It was a short 6"R with 9"R lead-in. It shouldn't have been any worse than several similar neighbors, but even if you were ready for it and slowed down more than you ought to, it would still pitch you into the cornfield unless you were going dead slow. 

I dinked around with it, trying different cars, replacing the track section, but what it turned out to be was that the curve had a slight reverse banking - You couldn't see it, but putting a level across it showed the outside was just a little bit lower than the inside. I shimmed the outside with a matchstick or similar to give it a slight positive banking, and suddenly the spooks were gone.

Since then I've taken to giving all but the broadest curves a bit of shimming on the outside edge for a very mild bank. It really tames the 6-inchers, and seems to make more difference that I would have thought to the general flow and feel of the course.

-- D


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## tasman (Feb 17, 2007)

Grandcheapskate said:


> In the third location, there is a lead-in 6" straight.


What preceeds the 6" straight? 

As far as the wheel becoming a pivot point, what you propose might be true but I would think that the guide pin would have more of an effect as the pivot point. Do you have any better results on AFX/Magnas if you replace the "pin" with the "flag" side?


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## Hornet (Dec 1, 2005)

You're right Joe.
The guide-pin/flag is the pivot point on a slotcar.
One front tire is physically heavier then the other tire by being attached to the axle.
Couple that with the drag of turning the axle in the axle holes,one front tire is always gonna turn and respond to chassis inputs easier then the other front tire.
That goes right back to the rear tires when you apply power,under braking it's not a big deal but as soon as you apply power coming out of a corner,that heavy slower to respond front tire becomes a drag point,that the car wants to pivot or rotate around,and the guide-pin is the pivot point of the whole mass.
Rick


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## Grandcheapskate (Jan 5, 2006)

tasman said:


> What preceeds the 6" straight?
> 
> As far as the wheel becoming a pivot point, what you propose might be true but I would think that the guide pin would have more of an effect as the pivot point. Do you have any better results on AFX/Magnas if you replace the "pin" with the "flag" side?


The sequence is as follows:

9" 90 left ==> 6" st ==> 6" 180 right ==> 6" st ==> 9" 90 left

I can replace the whole sequence with a 24" straight, but I really like the way it looks.

Whether using a pin or flag does not seem to matter.

D,
I thought maybe a slight "banking" to the curve might be a solution, so I'll give that a try. Maybe a popsicle stick would be about the right height.

Thanks guys...Joe


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## alpink (Aug 22, 2010)

the right 180 will always be a little more challenging to negotiate because of the rotation of the armature. that has been my experience and I have no data or theorem to back it up. LOL, your mileage will vary!


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## Grandcheapskate (Jan 5, 2006)

Slightly banking the turn doesn't seem to have much effect. It's still a handful with most AFX cars. Unless I can figure a way to get a 9" curve lead-in, I'm thinking this section may have to be removed. So while the turn sequence looks good, if you can't drive it, it's got to go.

The differences in non-mag pancake cars can be so varied it can drive you nuts. Some of my (non-mag) AFX cars are very rear end happy and will spin out if you breath on them, while others are fairly stable. One car will sometimes forget there's a slot when entering a curve and just keep going straight. I guess some playing around with shoe adjustments might have an effect.

Joe


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## pshoe64 (Jun 10, 2008)

What Ohm rating is the controller? Maybe a higher ohm will give you some more range at the lower end and make the NMT chassis a bit better in the handling dept. I love those 6" turns, keeps you on your toes!

-Paul


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## alpink (Aug 22, 2010)

limiting the shoes by bending the top and making the "window" smaller is a must for handling.


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## TUFFONE (Dec 21, 2004)

Use one of those center line guardrails that I see pop up from time to time...


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## Grandcheapskate (Jan 5, 2006)

pshoe64 said:


> What Ohm rating is the controller? Maybe a higher ohm will give you some more range at the lower end and make the NMT chassis a bit better in the handling dept. I love those 6" turns, keeps you on your toes!
> 
> -Paul


Good thought Paul. The current controllers are 60 Ohm running off a 20v power source.

Al,
The shoes will definitely be an area I fiddle with before abandoning the curve.

Thanks...Joe

Joe


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## Grandcheapskate (Jan 5, 2006)

I may have gotten the 6" curve to the point where it is driveable with AFX cars. I spent a couple hours tuning a few AFX cars, getting them to the point where they ran as good as the stock parts will take me. This alone makes them more driveable on smaller curves, especially when you can get them to move easily in the first 1/4 or so of trigger travel. I then elevated the curve as suggested by Dslot and the combination of those two things seems to have made it a manageable curve.

I think the key is getting a car to utilize the entire band of your controller so you have control of the car at very slow speeds.

Thanks...Joe


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## NTxSlotCars (May 27, 2008)

Well, because its a slow corner, with so many joints, you may wanna double check your slot for snags.


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## LDThomas (Nov 30, 1999)

Sounds to me like the biggest problem is a controller with too many ohms.


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## rbrunne1 (Sep 22, 2007)

I had a similar problem on my track...the joints had worked loose and the guide pin would get snagged.


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## Grandcheapskate (Jan 5, 2006)

My issue is not a snagging guide pin, although that can happen more easily on a small curve and with a pin rather than a blade (I've been changing all the AFX to blades). A non-mag car needs to have smooth acceleration to handle sharp curves. A car which goes from stop to fast can't negotiate these sharp curves. As I have tuned these cars more and more over the past few days, I have made them more responsive at the lower speeds, allowing me to go slowly around the curve.

If anything, a problem with a controller would be one with too low an Ohm rating rather than one with too high an Ohm rating. If the Ohm rating is too low, there may not be any way to get the car to go slow.

The other factor is the volts on my track. I am feeding in 20v-22v on a fairly small road course, so I never get near 100% thottle anywhere. Maybe on a course like mine, cutting the voltage down would help on the tight curves.

Joe


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