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Bob Chapman
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I have found lead also works to lessen the magnetic effect .
Bob
 

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Well... lead shouldn't. Again, I'd have to wonder about thickness. Next time you find that, compare with the same thickness of plastic or paper. Also try sticking a magnet to the "lead" -- it may have been a mixed metal.
 

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Kevs Racing Bits
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Next time down the club I'm going to test some of these seemingly daft ideas for reducing the magnetic effect. Lead, plastic, sellotape. I doubt I'll see any significant reduction with these but I'd love to be proved wrong.
 

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Kevs Racing Bits
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Pre-armed with physics facts:

Why can't I just use lead or copper or aluminum foil for magnetic shielding?
In the strictest sense, magnetic shielding is not truly shielding at all. Unlike the way a lead shield stops X-rays, magnetic shielding materials create an area of lower magnetic field in their vicinity by attracting the magnetic field lines to themselves. The physical property which allows them to do this is called "permeability".
faq8.gif
Unlike X-rays, sound, light or bullets, magnetic field lines must travel from the North pole of the source and return to the South pole. Under usual circumstances, they will travel through air, which by definition has a permeability of "1". But if a material with a higher permeability is nearby, the magnetic field lines, efficient creatures that they are, will travel the path of least resistance (through the higher permeability material), leaving less magnetic field in the surrounding air.

Here's how the permeabilities of some common materials compare:
Air ........... 1
Copper ...... 1
Aluminum ... 1
Tin ............. 1
Lead .......... 1
Nickel .................. 100
Commercial Iron ... 200
Stainless Steel ....... 200
MagnetShield ........ 4000

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That means lead has zero effect, it may as well be fresh air.
 

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It's amusing that their list skips from Stainless to their product. I wonder how it rates against what I'm recycling from tuna tins?

Do honour us with some tests once you get the shield, Grip. Could be good fun. YMMV, but it's the tuna tins here that tend to be very thin and highly magnetic, compared to others.

General note for people reading along: Stainless Steel is often, but not always, non-magnetic. So expect mixed results. Also it's a common sales trick by fridge & oven sellers to use a magnet to demonstrate how the unit they're trying to sell you is "real" stainless, unlike their competitor's.
 

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Kevs Racing Bits
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I used tuna tins too, as they're mild steel they are perfect but there's not much that's actually flat enough even if you try to peen it flat. Stock steel shim is cheap enough and available in numerous gauges (thickness). I've used up to 0.4mm thick shim, and don't think it should always be under the motor, you will see measurable magnetic effect reduction if you put some on the sides or even the top of the motor...I've used our clubs magnet downforce checker to prove this.
 

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Here's how the permeabilities of some common materials compare:
...............
Stainless Steel ....... 200
Giving one number for stainless steel is very misleading. Stainless steels covers a wide range of alloys. There is a very wide spread of magnetic properties depending on the alloy and for some grades. heat treatment can make a big difference to the permeability.
 

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I digress, but am I the only racer that wants the cars to corner at realistic speeds? The slower the better as far as realism is concerned for me. ...............................(New topic perhaps?)
Quite a lot of modellers would agree slower the better. Not sure how many racers would say slower the better. Arguably, good racing needs a field of cars with similar cornering speeds, individuals will have different takes on how realistic the speed is.

Yes that might be better as a new topic
 

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Kevs Racing Bits
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I know that, it's a copy and paste, it's a generalisation...but it's a far better option than lead.
 

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I was going to say check out Mu Metal. It's the ideal magnetic field blocker and comes in very thin strips.

But then I looked at the price for the first time in decades...
 

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Rich Dumas
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There are different types of stainless steel and often they are less "magnetic" than mild steel. 304 SS is commonly used for things like kitchen appliances and that is magnetic. For chemical reactors and the like that must stand up to more corrosive materials 316 SS is used and that is not magnetic.
 

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Discussion Starter · #34 ·
If "Magnet Shield" does what it says on the tin (no pun) then we can forget all of these other materials. From post #24 it's 20 times more magnetically permeable than iron. I found it for sale after a cursory internet search at about £5 plus postage for a piece 300mm x 75mm x 0.25mm (approx.) it shouln't affect the ground clearance significantly, so should be a simple add-on.

i will report in due course.
 

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Discussion Starter · #35 ·
The Magnet Shield sheet just arrived. I have done a quick rough test with the BRM can. It works.

Using the tesla meter on an Iphone, I held the can above the screen and got a reading of 250 micro tesla's at a height of 31 mm. I then placed the motor on the corner of the sheet and repeated the test. The 250 reading was at 23 mm. I conclude that the material therefore reduced the magnetic force to 23 squared/ 31 squared of its original value, i.e. 0.55. A reduction of 45% on this crude test gives me hope, so when I get a bit of time (ha!) I will wrap a short piece around a can in a real car and see what happens when tested on a piece of track.
 

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Kevs Racing Bits
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I wonder if wrapping it round a motor with weak magnets would actually prevent the magnetic field escaping and thereby improving the motor's performance.
 

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Kevs Racing Bits
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...and how does that compare to using a similar thickness piece of steel shim?
 

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Discussion Starter · #39 ·
I will wrap a short piece around a can in a real car and see what happens when tested on a piece of track.
Experiment now done on Ninco track. I installed the BRM motor in an anglewinder NSR Mosler with about 2 mm ground clearance. The static rear axle weight was 48 gms. With the unsheilded motor the axle weight registered 126 gm. With a single wrap of Magnet Sheild the value dropped to 71 gm. The magnetic effect was therefore reduced from 78 gm to 23 gm., a 70% reduction. This is now within the realms of motors which are not advertised as "magnetic effect"

Impressive. It remains to be seen what the actual effect on driving is.

Keith.
 
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