Musings About Magnets

Part 1 – Civilizing the Magnet

by Bob Ward

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Probably the longest-running controversy in slot car racing is about traction magnets.  There are diehards on both sides – magnet and non-magnet- and many other hobbyists somewhere in the middle.   I’ve raced and won, at one time or another, with just about every kind of slot car there is, both with and without magnets. That includes non-magnet cars that corner as hard as any magnet car I’ve driven.  I’ve also raced countless times on both plastic and wood tracks and enjoyed all of them.  We here at VLH don’t take sides, but we do know from experience, both racing and selling slot cars, that at least 90 percent, probably more like 95 to 98 percent, of all slot car racing in the world is done with magnets on plastic track.

For those new to the slot car hobby, “magnets” refers to the practice of placing a neodymium or other rare-earth magnet low in the car, usually toward the rear, where it interacts magnetically with the steel strips that carry the electric current in plastic track systems.  The magnetic attraction thus generated creates downforce.  Magnetic downforce in slot cars is in many ways comparable to aerodynamic downforce in full-sized race cars and in some kinds of slot cars.  Either kind presses or pulls the car down onto the track surface, increasing tire grip and, therefore, cornering force.  Magnets differ in strength, and cars differ in where their magnets are placed and how close to the track they are positioned.

I find the whole magnet thing interesting partly because it’s very commonly simplified into an either-or proposition. Actually, it’s anything but that.  It’s not a simple continuum with drive-the-car-on-the-ceiling magnets on one end and no magnets at all on the other, but a more complex matter of what kind of driving characteristics you find satisfying (or necessary to be competitive) and how you get to them. If you have ever watched 1/24 scale “wing” cars on a commercial raceway track and then watched strongly magneted cars run on a plastic track you will recognize that the difference is not in how stuck down they are but in how all that cornering grip is achieved. The main issue with both magnet and non-magnet cars is the same – generating and using downforce, but there are also related issues of drivability, realism, crash impacts, and – are you ready – cost containment.

One development that has, or should have, made a big difference in the way slot car hobbyists view magnets is the introduction, some years ago, of the Magnet Marshal.  The MM, essentially a modified digital scale, is a game changer because it gives racers, not to mention rules makers, a reliable way of measuring and therefore limiting magnetic downforce.  I turns out that Demon Magnet CAN be tamed, after all, and you can put him to work creating magnet-equipped cars that do have to be driven and can, to a surprising degree, drive much like non-magnet cars but with higher limits.   The vast majority of racers can also use him, usually along with just tire options, to “tune” slot cars inexpensively to a performance package they like.  You can even use him, along with regulations on tires, motors, chassis configurations, controllers, and other factors, to create a coherent racing class structure that fits the needs of your racing program.

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Admittedly, the MM’s impact has suffered from limited availability, as only 1000 of them were made.  (As this is being written a more advanced MM is being developed and production may not be too far off.) However, it put to rest the biggest knock against magnet racing.  That’s the notion that magnetic downforce always escalates until the cars get so stuck down they largely don’t have to be driven, with its almost inevitable follow-on that magnets take all the skill out of driving.  I take no position on whether that’s true, but I do think it’s no longer very relevant.

With the problem of limiting downforce addressed we can look at the other issues related to magnets.  The first one mentioned above is drivability.  The first really stout magnets put into 1/32 scale slot cars had the shape of a disc or very short cylinder.  They provided downforce over only a small part of the car’s width, about 7 to 8mm.  In cornering centrifugal force makes the rear end of the car slide toward the outside of the turn.  With these magnets it didn’t have to slide very far before the magnet was no longer over the steel strips and the car abruptly lost most of its grip and snapped into a spin with no warning to the driver. This made these early strong-magnet cars very hard, unforgiving, and quite unpleasant to drive at the limit.  Small rectangular magnets 10 to 15mm long followed, yielding some improvement.  Still, the width of the magnet was little if any greater than the width of the track’s contact strips.  The thinking appears to have been to use a small but strong magnet to hold the rear of the car over the contact strips, producing on-rails handling.  This was fine up to the point where centrifugal force finally overcame the magnet and the car instantly turned into an unguided missile.  The magnet was working against the car’s natural tendency to corner tail-out.

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Scalextric, meanwhile, had been fitting its cars with transverse bar magnets around 24mm long by about 7mm wide.  These magnets were the old ferrite ones and were simply too weak to be much better than no magnet at all.  Finally somebody at the factory fitted the same size neodymium magnet to a car.  At last a car had real downforce over a significant portion of the normal arc through which the car slid under cornering.  The change was transformative.  Now the magnet was at least partially working with centrifugal force in the corners instead of against it.  Scalextric made neo bar magnets standard equipment on all cars with room to fit them and leaped to the head of the mass-produced slot car pack in cornering.  The difference wasn’t in absolute magnet strength but in drivability.  You could slide the rear of the car to a reasonable degree without losing grip. This made the car much easier and more pleasant to drive.  It inspired confidence in the driver.  Most Scalextric cars have had these magnets ever since.

There’s a story that illustrates just how much difference the long neo bar magnets make.  Years ago I was writing a column on slot cars for a hobby industry trade publication.  I heard about a hobby shop owner who had raked in amazing money one Christmas season by selling several brands of 1/32 scale race sets in temporary mall kiosks. I called him up to get the full story for my column.  The story, however, was not the tale of triumph I expected.  Sure enough, he had sold a lot of sets in just a few weeks.   However, the mall required all the kiosk operators to stay open for a week after Christmas to be available for returns.  Starting the day after Christmas, sets came flooding back in.  The complaint was the same with almost all of them.  The cars had such poor cornering grip that the kids for whom the sets had mostly been bought couldn’t drive two laps in a row without deslotting. Tears and tantrums followed.  By the time he closed his kiosks he had taken back almost all the sets he sold under the mall’s no-questions-asked return policy.  All, that is, except for one brand – Scalextric.  He got very few Scalextric sets back.  The one big difference between the cars in the Scalextric sets and the others was those long rare-earth bar magnets.  They were what made the cars drivable for all those children and beginners.

It probably shouldn’t but it surprises me that none of the manufacturers has taken the concept to the next logical step and used a bar magnet, or magnets, spanning the whole width of the chassis. That should make a car even more drivable, with downforce over practically all the reasonable cornering angles.  It might require two magnets or even three, and that might create a cost barrier.  There may be practical limitations I’m not aware of, but I have pursued it experimentally far enough to know it is workable.  I never really developed it fully because there is no place I could have raced a car with full-width magnetic downforce.  Still, for the mass market, where the key to success is a good experience for kids and beginners, the concept seems like a worthwhile one to pursue.

So far, however, the only manufacturer that has even followed Scalextric’s example and used a 24 or 25mm by 7 or 8mm bar magnet is Pioneer, and that was because its initial goal was to make better Scalextric cars than Scalextric does, even to the point of adopting Scalextric’s plug-in digital chip system.  In recent years Carrera has also gone to longer (but narrower) bar magnets, but most if not all Carrera cars tend to be significantly overweight, so much of the benefit of the better magnets is wasted.  More about the relationship between magnets and car weight a bit later.

Your experiences and opinions may differ from mine.  As always, I invite your comments, requests, questions, and suggestions at the bottom of this post or at productsupport@victorylaphobbies.com and I look forward to responding.

.In Part 2. We’ll look at the realism of slot cars and how magnets have affected and can affect it for worse and, more important, for better.

Copyright © 2016 Robert M, Ward

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