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I know there are a lot of guys on here that are no magnet but this question is for the magnet racer guys.

I just received a Fly Lancia from a member here. Its a great car and runs really well.

When I pulled it apart to clean it and oil it I found something I haven't seen before that got me curious about something I know nothing about: There was an aftermarket stronger (neodymium sp?) magnet in place of the original and stacked on top of that magnet were 4 round magnets, two on each side. My question: does stacking the magnets on top of each other like that make for stronger magnetic down force? Does it somehow magnify or increase the force of the bar magnet on the bottom of the stack?

This is just one of those things in life that make you go hhmmm :think: when you don't know the answer and have too much time on your hands, so what say you magnet or engineer gurus?

Thanks for the info.

Ventura Alfa

It depends on the grade on the original magnet but ,say assuming it is NdFeb, if you stacked an N35 grade on top of another N35 grade you would find the coercive force would increase by a factor of 1.2 and the intrinsic coercive force might be > 1.6, reading as KOe or KA/m respectively. The maximum energy pull would be increased in the 'all around' field rather than directional, ie not just downwards.

Stacking mags one of top of other is not an accurate way of 'tuning' the force. Better to use simple steel shims. One mag on top of the other is very hit and miss.

Tomorrow, if you like, we can move onto the relationship of magnet grades and the coercive force expressed in the KA/m vs. the KJm3 maximum energy likely properties in respect of atmospheric and TWdegsC environments and whether if you live in the Southern States you should consider a switch from Neodymium to Samarium-Cobalt magnets for their superior ability not to be affected by air temperature.

Jules

Is there a translator program here? :) Right after "depends on the grade of the original magnet" it went GREEK!

What is that word above "for dummies" ?

whatever it is, it's pretty darn small, as in 10-to-the-minus-9 power.
but didn't Robin Williams do something with 'nano-nano" in a sitcom years ago, where he played a humanoid alien? and he had a magnetic personality to boot, so maybe there's something there...

WOW Jules,

I knew we had some bright guys on this site but that takes it to a whole new level. :clap:

If I understand correctly running the magnets on top which are smaller and less powerful will have little to no effect on the down force of the larger bar magnet.

Nanu Nanu was from Mork and Mindy. Mindy was hot, Robin Williams was a goof ball alien. :lol:

Ventura Alfa

could have been Mork and Magnet maybe

My experience with magnets has shown me that the height of the magnet above the track has a greater effect than adding steel shims or stacking extra magnets. If I find the downforce is less than what our local club allows ( 4 x the cars natural weight ) I modify the magnet pocket to get the magnet flush with the bottom of the chassis and check the downforce at that position. If it is still too low I then sand the rear tires to a smaller diameter or switch tires to achieve the same result. If the downforce becomes too high I then adjust the magnet height carefully. This can only be done precisely if you have a magnet marshal available or some other tool to measure downforce. If modifying the magnet pocket would prove too difficult then I experiment with adding shims or other smaller magnets to get the same result. Smaller magnets are available from K&J Magnetics in a variety of shapes, sizes and strengths.

In the real world of slot racing, Modlerbob is spot-on. Quite simply, you can throw away the academic theory. It is all about distance from the metal rails.

The other problem is that, along with mini motors, the production tolerance levels on mass produced toy (not serious application) magnets is huge - between 5 and 15% or more of difference in one batch of motors (with mags) and button or bar magnets.

We have all run what we thought should be an identical model but it seems faster or sticks to the track better than the one we had last month. None of us would be prepared to pay top Dollar for calibrated motors or magnets. A small motor would cost $40+ and a calibrated magnet would be in excess of $25. I have already asked the question during my early research back in 2008. I went for the cheaper option which is: you get something approximately like what you asked for which translated to a 18k motor that might only rev to 16500 or might be as much as 19500 and an N35 bar magnet that should pull 250gms on a Magnet Marshal but might only pull 225gms or maybe even as high as 270gms. All these variance of product can come right out of the same supply batch.

Jules

.... or you could take them out and add lead, but if you're looking for a denser material you could try uranium or one of the isotopes...... dang, it's the same thing only in reverse :lol:

For me, adding lead creates a problem with momentum. The magnet creates artificial weight and if /when the car breaks loose it reverts back to it's normal weight and loses momentum much quicker than if there are 300 gms of lead in the car. In my experience the cars suffer less damage in a crash because they weigh less.

Jules, Besides being smart you build great looking cars. I just got the #17 Jerry Titus car in the mail from inaslot. :D

Sweet looking, can't wait to try it tonight.

I took the magnets off the top of the bar magnet on the Lancia. No drop in lap times and didn't seem to be any looser than with them on. If this were myth busters I would say that Jules was proven to be correct. :clap:

Thanks for all the replies. It was an interesting subject.

Ventura Alfa

hey Bob,
just curious: is your magnet marshal broad enough to take into account the effect of the motor?
speedy

The metal bar in the magnet marshall is as wide as the steel rails on the track so the effect of the motor is measured. If you put a car on it's roof and weigh it then put the car with no magnets in the slot there will be an increase in apparent weight due to the magnets in the motor.