Notes on magnet downforce and the USD rule - Part 1
Posted: Mon Nov 30, 2015 4:51 pm
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.
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.