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Russell Sheldon
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2,855 Posts
I don't profess to be a specialist with "magnet traction" chassis -- in fact all my attempts at building cars for this class have been abysmal -- but I would tend to agree that "lighter is better". Let the magnets do all the work!

In the Marconi Foundation for Kids Charity proxy event, there is a class for "extreme" magnet traction cars. Larry Geddes built this superb chassis, which ran very successfully:-

Since the magnets provide the traction, Larry positioned the motor up front, in order to move the physical weight closer to the guide.





This is Larry's explanation of his chassis design:-

"My current thinking behind magnet cars goes like this: the main objective is to keep the magnet(s) over the rails for as long as possible. If the magnets lose the rails a little, fishtail results, costing speed. If the magnets lose the rails completely, it's a deslot (all of a sudden, too).

The front motor design with wall-to-wall magnets across the rear solves these problems, I feel. The rear can slide a little & there will still be a magnet over the rails. And with as little mass as possible in the rear, the polar moment of the rear with respect to the guide pivot is reduced. This helps give the rear less tendency to slide out in the first place. I also tried to keep the overall weight low, because the heavier the car, the greater the centrifugal force generated, which aggrivates fishtail.

The main rails are 1/16" piano wire for stiffness. The side "pans" of PC board are just there to back up the body & mount the lead wires. I narrowed a portion of them because I didn't want the chassis TOO stiff. I used PC board because it's light & strong enough for the intended purpose. The gears are 11/33 & the car weighs 75 grams. I was hoping it would be lighter, but I didn't want to lose too much strength. The PC board is just to back up the body sides & anchor the lead wires.

One thing I think is important in these super-magnet cars is to reduce bearing friction as much as possible. I feel that the tremendous downforce would really be pressing the bushings down on the axles. Maintaining an oil film would be difficult or even impossible, & friction would be higher than desired. Because of this, I decided to use ball bearings on all four corners of the car (The front tires are fully functional, actually supporting the front end. This car is not a "tripod"). And since the pinion bearing is an "extra" (something you would not normally have in a sidewinder), I used a ball bearing there too. There is a lot of side loading on this bearing & again I wanted to minimize friction."


Kind regards

Russell
 

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Russell Sheldon
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2,855 Posts
Thanks for posting Larry -- and welcome to SlotForum!

Larry makes some interesting points. It's clear that conventional wisdom doesn't apply in setting-up a magnet-traction chassis. Getting the right amount of 'downforce' vs 'horsepower' is where there are gains to be made.

Kind regards

Russell
 
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