[Phil Appleraily]

Hi,

I have 8 different Scalextric cars with the original magnufacturer magnets. On service sheets, the downforce mentioned is different for each car.
I suppose this is due to car weight, wheel width, ...

But how can I get the downforce of a magnet ALONE (without being fitted on car) (any formula ?) ? I use W8475, W8449 and W8695 magnets
Is there a web site or a tool to get this ?

Thank you so much.

Cheers.

 

[300SLR]

The magnetic attraction between the magnet and the rails of plastic track depends how on the gap between them.
(To be technical, it follows an inverse square law - although this is something of a simplification when things are very close)
Try putting the magnet on the rails and you'll feel the attraction at its strongest, as soon as there is a slight gap the attraction reduces and gets smaller the further the magnet is moved away.
This can be used in car tuning by moving the magnet up and down to adjust the amount of attraction.
Obviously there is a practical minimum ground clearance under the car, so the maximum attraction is a good deal less than when stuck to the rails.

 

[Phil Appleraily]

Thank you for the explanation.

What i'm looking for is the absolute value of each magnet without being fitted on any car, like you said being posed on the rails.
Some magnets are stronger than others. Like you say, you can feel this just by placing the car on the track.

But how do you determine its strenght ? expressed in tesla ? in mg ? in gms ?

Is there any data about the standard magnet i described ?

Thank you so much.

 

[300SLR]

Magnetic attraction is a force, so it should be measured in units of force.
For slot car use it is usually expressed as grams. (Physicists among us will know that's not correct, it would be better given grams force, but most people just call it grams.)

There is a tool called a Magnet Marshall which is used to measure this force.
Magnet Marshalls are often used in scrutineering for races where the rules limit magnetic attraction.

 

[RichD]

A Magnet Marshall is used to measure the attraction between the magnet(s) and the rails with the magnet(s) in the car. If you want to know the strength of the magnet itself you need to use a magnetometer (gauss meter). Magnets from the same source can vary in strength by a significant amount, however the location of the magnet in the car can be more important than the strength of the magnet, therefore Magnet Marshall readings are probably more relevant.

 

[MrFlippant]

Even if you had magnets you believed to be identical (which is hard), AND cars which are seemingly identical, just a fraction of a mm difference in ride height can make one car have noticeably stronger magnet traction than another with the same set up. Like Rich said, it's more useful and important that the entire unit be measured on something like a magnet marshal. There are some DIY solutions out there if you can't find, or don't want to splash for a brand name Magnet Marshal. As long as all cars are measured on the same device, and made to be as close as possible, it's all good. Remember, lots of things can change magnet traction, such as braid thickness/springiness, front wheel trueness and/or diameter. rear wheel true and diameter, chassis cup or bow, or even chassis flexibility, bushing play, not to mention the track itself having spots where the surface is high/low, or the rails are high/low. ;-)

 

[Abarth Mike]

As has been said it will be very expensive to buy a Gauss meter to measure your magnets and even then it won't mean much.

What you CAN do is to determine which magnets are stronger and/or equal. Do this by simply dipping each magnet in a pile of small nails/tack/ball bearings and count how many each magnet picks up. This will obviously be a relative and non-dimensional measurement ( in the accepted sense) but may suit your purpose. If you have a scale you could measure the weight of the nails.

Again as has been said to do this scientifically you'll need to buy a MM or make your own. There are threads about DIY magnet marshals.

 

[Abarth Mike]

ISP unresponsive again!

 

[RichD]

I have a magnetometer and they are rather costly. You can buy a Hall effect sensor and make your own cheap magnetometer. A home made magnetometer is good for determining the relative magnetic strength. We used home made equivalents to the Magnet Marshall before those were available, there was one for each track and there was a standard magnet so that they would all read the same.

The device did not tell the whole story, however. Where the magnet was located was also important and we had to change our rules to take that into account. Eventually we got away from using magnets.