Musings About Magnets, Part 3

Part 3- Cost Containment and Regulation

by Bob Ward

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Perhaps the biggest, yet least appreciated purpose of traction magnets is cost containment.  It’s no secret that the cost of slot cars keeps going up.  The causes are many, and I won’t go onto them here, but there is no doubt that the introduction of rare earth traction magnets allowed basic mass-produced slot cars made for plastic track racing to make a big leap in performance without a corresponding increase in costs.  Magnets are literally the crucial difference between Scalextric, Carrera, and similar cars at $25 to $55 and Slot It, NSR, and comparable cars at $70 to over $100.  This is because magnets allow a car to achieve, on plastic track, a high level of performance while using less expensive components.  The magnetic downforce suppresses the vibration from the imperfect trueness and concentricity inherent in injection molded plastic wheels pressed on to knurled axles.  It also dampens vibration that may occur due to the somewhat loose axle-to-bushing fit required by the need for the splined portion of the axles to pass through the bushings.  Both of these, without the magnet, can cause chattering and wheel hop.  But these are issues inherent in these components and are present to some degree whether they are poorly or well made.

So, at the risk of committing slot car racing heresy… the key term here is less expensive, not necessarily lower quality.

There is a perception, common (though not universal) on slot car web sites, that the plastic wheels, press-on plastic gears, one-piece plastic chassis, plastic axle bushings, and related components found on most magnet-equipped basic slot cars are of poor quality compared to machined aluminum wheels and gears, brass or bronze bushings, drill blank axles, and podded chassis of higher-end slot cars.  This view misses the point.  Yes, Pioneer’s plastic wheels, for instance, are less expensive to make than NSR’s aluminum ones, but they are the very best plastic wheels Pioneer’s highly capable people can design and manufacture.  The same is true of Scalextric, Carrera, and others.  Pioneer, by the way, moved their factory from China to England at tremendous expense, and one of the major reasons was to be able to ensure the quality of their products.  Will plastic wheels pressed onto an axle ever be as perfectly true and concentric as machined aluminum ones on drill blanks? Will a one-piece plastic chassis ever be as tuneable as a multi-piece podded chassis?  Probably not, but magnets make those considerations largely irrelevant to 90-plus percent of all the slot car racers in the world.  For most of these hobbyists the less expensive parts, used with traction magnets, are as good as they need to be, and they help keep slot car racing affordable

Certainly, there are places in 1/32 scale home and club racing where high-end parts are really necessary, or at least inevitable.  One is non-magnet racing, often carried out on wood tracks.  There the precision of machined metal components really is critical and the tuneability of multi-part chassis comes very much into play.  Another is when cars are built with really extreme magnet downforce and motor power.  In some such situations the plastic wheels and other components simply can’t handle the stresses involved. (I know of a place in our local area where they run 600 grams of magnet and 40-50k motors in some classes.)  Yet another is where the hobbyists involved came to “Scalextric-type” slot car racing after a long history of commercial track and similar racing where high-end components are essential, and they want to apply all their experience to racing plastic cars or simply can’t get comfortable with less than pro-level parts.

By the way, even where high-end cars are allowed they don’t always prevail.  I once wrote an article for another web site on how to graft the entire rear end of a TSRF plastic chassis center section into a Carrera McLaren M20 CanAm car.  The build resulted in a one-piece chassis with an FK130 motor in a sidewinder mounting with a magnet right under the motor.  It used plastic wheels and press-on plastic gears.  The car is rocket-fast on my own track, but I have never raced it against other cars.  A while after the article appeared I got an e-mail from a racer who had followed the article and built an identical car.  He said he took it to race night at his local club, where everybody else was running Slot Its and other high-end cars, and just plain killed ’em.  Yes, this was on a plastic track and magnets were being used by all, but still, his car with all “low-end” plastic parts was nowhere near as expensive as all the ones he was racing against and it spanked the field.

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If Carrera could be persuaded to adopt my “hybrid” chassis configuration they would leap to the head of the line in basic magnet car performance ad you would literally see $37 Carrera cars beating $70 Slot Its.  And if they could also be persuaded to put their cars on a diet and get overall car weight down to where Scalextric cars are, well…

Which brings me to the subject of magnets and car weight.  The great thing about magnets is that they add downforce and cornering grip while adding very little to the car’s mass.     A well-magneted production slot car might have a net Magnet Marshal reading (total MM figure minus car weight) of around 200 grams.  If the car weight is 80 grams to start with the total MM figure of 280g equals almost 10 ounces or well over half a pound.  Try ballasting almost any basic slot car up to that weight and see how well it gets around the track and for how long.  Because magnets increase downforce without increasing weight and mass the gain in cornering grip is essentially free as long as your motor and track power are stout enough not to lose too much speed to magnet drag on the straights.  At 200g downforce most RTR car motors do just fine, at least in my experience.

The real end point here is to look at how we write rules to regulate magnetic downforce.  All the magnet racing programs I have been in limit downforce to a fixed amount over car weight, whatever the car weight might be.  That’s fine as long as the cars all weigh the same or close to it, as in a one-make, one-car type event.  However, where that isn’t the case the racer gets the most benefit from the magnet by making the car as light as possible, any way he can.

This has several undesirable effects.  First, racers will go to extreme lengths to lighten the cars.  This can easily make preparing a car much more time and labor-intensive.  It also can mean replacing stock components with lighter ones, increasing cost and leading to squabbles about ultra-light, sometimes not very good-looking components like vac-formed interiors and windows.  It also means that cars are harder to equalize at a given performance level since certain brands of cars that are lighter to begin with come from the factory with a built-in advantage.  It’s especially hard to equalize the performance of dissimilar cars that historically raced with each other but as slot cars may differ significantly in size and weight.  One of the worst effects is that kitbashed cars with lots of bodywork or resin bodies tend to be heavier than comparable RTR cars, making them uncompetitive.  That discourages creativity and diversity in your race fields.

There is no perfect solution to these problems, but one thing that should go a long way toward one is to make the maximum net MM value a figure that goes up or down in proportion to unballasted car weight.  To continue with the figures used above an 80-gram car with 200 grams of downforce has 2.5g of magnetic downforce per gram of car weight or a downforce/weight ratio of 2.5:1.  Then somebody comes along with a 65g car.  At 200 grams of downforce for only 65 grams of car weight its ratio is 3.08:1.  It’s not hard to figure out which car is going to be faster, all other things being equal.  If, instead of a set figure of 200g we state the downforce limit as 2.5 times car weight the 65-gram car will be limited to 162.5 grams of magnet.  The lighter car might still have an advantage but it should be much smaller, very possibly too small to make much of a difference.

It is, of course, possible simply to have a minimum weight rule, but this will set off a scramble to find the lightest car eligible for the event or class and then ballast it up to the minimum, placing the weight where it will do the most good. This happens all the time in 1:1 scale racing.

One variation on this idea is to let the added grams be in the form of a combination of magnet and ballast to provide more tuning options.  Our 80-gram car above might be given 175 grams of magnet at the rear and 25 grams of weight, distributed about the car, to make up the 200 gram maximum.  I haven’t tested this, but it would be interesting to explore.  Just make sure the ballast isn’t in the form of more magnets.  You also want to examine all cars carefully both before and after the race to make sure there have been no shenanigans pulled.

There are, of course, many things besides magnets that play into slot car performance, but magnets are one of the biggies.  I think they deserve to be looked at more closely and in different ways than perhaps they have been, with a view toward getting the most from their potential to make the hobby more attractive to the widest possible range of hobbyists.

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.

Copyright © 2016 Robert M. Ward

One thought on “Musings About Magnets, Part 3

  1. Very interesting series. We at Fairways Racing Complex (FRC) used the Magnet Marshall method in one class for a year or so, but it was difficult for drivers to set up cars at home since the MM was based at the track. Around 2016, we introduced an idea taken from another club which we call the “upside down” or USD rule, which basically says that a car must drop away from a piece of Scalextric Sport track when held in an upside down position. We then differentiate classes by limits on how far back in the chassis any traction magnets can be located. It works very well and allows cars from virtually any manufacturer to be competitive within a given class. You can see our class rules here:

    http://ggonsalves.com/frc/forum/viewtopic.php?f=5&t=1268

    (Ignore the IROC classes where this topic is concerned)

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