Notes on magnet downforce and the USD rule - Part 1

[gordon]

Notes on magnet downforce and the USD rule - Part 1

In magnet racing, a huge part of the performance of our slot cars is the amount of downforce generated by the strength of any installed magnets. In fact, this plays a more important part than tyre grip, car track width (the distance between left and right outer tyre edges), ground clearance and centre of gravity. Its the single most important factor in a car's ability to stay in the slot. The stronger the magnet(s), the quicker the lap time.

Magnets come in different strengths, even in the case of otherwise identical magnets with the same shape and dimensions. As a result, the downforce on two cars of the same type and manufacturer can - and often does - vary, resulting in better performance for one over the other. This presents a big problem with presenting a level playing field for everyone.

For a long time, I had been scratching my head trying to find a way to eliminate this potential handicap/advantage, when I finally discovered what we now refer to our upside-down rule (USD rule). In one club that has been racing with this rule for years it is referred to as the "One Gee" rule (in other words, gravity). Using this rule is the simplest way to reduce any advantage gained by stronger magnets. It allows anyone to set up a car for passing this rule with minimal equipment. All that is needed is a piece of Scalextric Sport track.

Its not perfect though. For example, in its current implementation, weight can be added to the front of the car to help gravity overcome the magnetic force and dislodge the car from the track rails. This allows the car to be set up with stronger magnet strength than would otherwise be possible. On top of that, a longer car will have a potential advantage over a shorter one because less weight is needed through the simple principle of a lever - the longer the arm, the stronger the force. For cars with equal amount of weight added to the front, the longer one will be able to run with stronger magnetic downforce and still pass the USD test.

So, what's the solution? Well what about lightly holding the tip of the front of the car in place when doing the USD test? This would eliminate weight added to the front or near-front of the car having an impact on the test. It would not matter how far back the magnet is placed since the lever effect will no longer apply.

I plan to do some tests using this technique and will get back here with the results.

[RameshB]

Hi Gordon i think you are on a good course of deduction , and the USD rule really only applies to two classes, MP AND RGT and looking from past entries these classes are technically competitive and thus have a very low competitor entry , the USD rule is supposed to make regulation and preparation much more user friendly.I do hope to see more entries in 2016 , like Obre coming out with his Subaru , I feel that the magnet position rule should not count since USD rule is now in effect. This will encourage a lot more inline MP cars to take part .

[gordon]

OK guys. I've done several tests with a number of cars, ranging from cars using the current version of the USD rule right down to standard out-the-box cars with 100% standard parts. The bottom line is that this idea of holding the nose in place while doing the USD test will NOT work. Even the standard cars I tested this way will not fall off the track and pass the test.

This means that the current method of performing the test is the only viable way to do it, so there will be no change in the way the test is performed.

[steveaca]

Okay, that means that the classes subject to the USD Rule and the magnet positions need to be finalized. My feelings for the following classes, subject to the USD Rule are as follows:
-Mod.Prod. should stay as-is .
-RGT magnet placement should be free.
-Historic Saloon could be mag.less. If not mag.less, I'd support Gordon's suggestion of magnet to be placed ahead of midpoint of wheelbase.
Steve

[Luke]

Hi GG,

I haven't been racing much recently (giving one reason or the other) in most of FRC's well arranged class groupings ... Yet records will show I have raced in all these classes before and starting with LMP and maybe the RC classes - they were the only two I didn't have cars race ready for and look how it has gradually grown listed below in green ...

• Mixed GT IROC / Scalextric GT Challenge IROC
  Restricted GT
  
  Historic Saloon
  Vintage Sports
  Group 5 Sports Cars
  
  Mini Challenge IROC
  Rally Car
  
  Modified Production
  F1
  
  Nissan GT-R Super Series IROC
  Slot.It Challenge
  
  AM
  GT
  LMP

I kind of reckon there's enough setting up, tinkering and tuning with these 132 cars already and records will also show in 2015 - each one of these classes/groupings has only played out 3 times (few of them 4 times) this year.

Being one of your most establish FRC racers and appreciating all you have done and doing for this hobby - believe I can suggest that tuning of cars could remain the way they are for another year.

Luke

[arden100]

I agree with LukeT. Let's leave the rules as is for 2016.