Correction. I just checked some newly-trued MJK rubber tyres on a Scalextric Nissan and I'm getting a coefficient of friction close to 1
How much friction does a slot car need to go round a banked corner?
The orange blur in the pic above is a Slot-it Porsche going around a home-made 45degree banked corner at 5m/s (16.4feet/sec). To my surprise it makes no difference if you remove the magnet. It still goes around at 5m/s!
This got me thinking. How much lateral friction do you need to go around a banked corner?
I crunched a few numbers and got a theoretical answer: in the above scenario you need a coefficient of friction of 0.6
This is a very low number. Even if you double it, it’s easily achieved. Decent tyres give more like 2.0
So why did I spend so much time gluing steel wires under the copper foil? A waste of time. Live and learn!
Here’s a graph showing some other data points. The data point for the Porsche is arrowed.
Thanks for reading!
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That's 30 seconds I'll never get back 
I'd say they would have been no faster with aerodynamic wings.
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Avus 1955. From Wikipedia.
Avus 1955. From Wikipedia.
Yes, if the banking is very steep you get the sense that the car is pushing very hard into the track and the clickety-clack of my plastic track gets a little too loud for comfort.
The lesson for me is: it's better to have the 45deg banked corner without steel under the copper tape so the magnet cars have less bogging down. The rest of the track can have rails that attract magnets. A hybrid layout is best.
Agreed. I have moved the arrow on the graph below to the 20deg line which shows that my Slot-it Porsche, with magnet, could still go full beans around the banking.
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My method for finding coefficient of friction
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Keep tilting the track till you find the point where the rear end starts to slide. The coefficient is the ratio of rise over run, a.k.a. gradient, a.k.a. the tangent ratio of the banking angle.
E.g., when rise and run are equal the coefficient is 1
if rise is twice run, the coefficient is 2
if the pic above was where sliding began, the coefficient would be around 0.5
The mass of the car makes no difference. Put the body on the chassis and you get the same answer.
What other methods are there for measuring level of grip?
Keep tilting the track till you find the point where the rear end starts to slide. The coefficient is the ratio of rise over run, a.k.a. gradient, a.k.a. the tangent ratio of the banking angle.
E.g., when rise and run are equal the coefficient is 1
if rise is twice run, the coefficient is 2
if the pic above was where sliding began, the coefficient would be around 0.5
The mass of the car makes no difference. Put the body on the chassis and you get the same answer.
What other methods are there for measuring level of grip?
wasn't aware MJK made rubber tyres. All the ones I have bought have been urethane>?
Usually we're looking for tyre grip to act downwards and stop the car from spinning out. On a wall of death you're looking for tyre grip to act upwards.
I've added a 85deg line on the graph below. All of the friction needed is negative - it needs to act upwards.
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The place where you need zero lateral tyre grip is like where the arrow is pointing; i.e., the speed is "just right" so tyre grip is needed neither up nor down the slope! At the arrow, 45deg bank, my Porsche at 2.5m/s could take the bend even if it was made of wet ice.
I've added a 85deg line on the graph below. All of the friction needed is negative - it needs to act upwards.
The place where you need zero lateral tyre grip is like where the arrow is pointing; i.e., the speed is "just right" so tyre grip is needed neither up nor down the slope! At the arrow, 45deg bank, my Porsche at 2.5m/s could take the bend even if it was made of wet ice.
All I know is when I was running my LMP cars on the Carrera banking in the summer those with anything less than very grippy tyres (no magnets) would "fall" down the slope. Hence the short strip of border to nudge them back on.
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When I added a straight section between the curves it was obviously much more notable, but I soon learned - in the interests of not having to get up and re-slot the car - to keep a good speed up in the banking and hope physics was my friend.
Great fun though.
When I added a straight section between the curves it was obviously much more notable, but I soon learned - in the interests of not having to get up and re-slot the car - to keep a good speed up in the banking and hope physics was my friend.
Great fun though.
Here is an HO track with a very serious banked corner. I believe that it is 56 degrees.
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This is the HO version of the famous 1/24th scale Purple Mile Sovereign tracks. It is located at LenJet Raceway and shares a building with Modelville Hobby that I think has the last 1/24th Sovereign.
I have only raced on the HO version a few times, but both higher downforce and gravity type cars are slower through the banking than they are in the straightaway.
There is a difference between a continuous banked corner and two banked corners that are connected by a banked straight section. The cars will tend to slide out more in that straight section.
This is the HO version of the famous 1/24th scale Purple Mile Sovereign tracks. It is located at LenJet Raceway and shares a building with Modelville Hobby that I think has the last 1/24th Sovereign.
I have only raced on the HO version a few times, but both higher downforce and gravity type cars are slower through the banking than they are in the straightaway.
There is a difference between a continuous banked corner and two banked corners that are connected by a banked straight section. The cars will tend to slide out more in that straight section.
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