Magnetic force measuring.

[rex craemer]

[rex craemer]

[rex craemer]

[WesR]

A ball magnet rolling on the track would eliminate the problem of maintaining an accurate gap between magnet and wire but if you place the ball magnet (I had some 6mm diam. ones) on the wire, the friction/pull is such that the car would hardly run.
I guess perhaps with a smaller ball and heavier/larger car with more power it might work. If the wire were below the track surface, by say 0.5mm, the friction would be reduced but then you are back with the need to maintain the 0.5mm accurately.
The rolling ball would also make a noise.

[goatdope]

Hi Fellas, In regards to the optimum pickup shoe height. My oval raceway uses standard magracing wire layed in a grooved plywood surface. After alot of testing and trial and error I found the range is .011 to .020 inch from the bottom of the shoe to the top of the track with the wire right underneath. Most of the cars run at .015 - .017 in. but some need more clearence , some less. I fashioned a jig to measure this and use paper of known thickness as feeler gauges. A micrometer is needed for this. I have 13 cars and no two handle exactally alike. The reason could be the fact that all the chassis had to be "stretched " in order to fit the various wheel base stock car bodies that I use. Of course you must check that the magnet is at least flush with the plastic and not indented or below the surface of the arm. Most of mine are protruding at least a little. Good luck. Ken

[HeliumFrog]

Just a couple of ideas that might help.

Magnet force measurement
Magnetic force measurement could be carried out by inverting a piece of track and pulling on the magnet with a hanging weight. With a little paper cup suspended you could gradually add in nuts and bolts until the magnet fell. By placing the track at 90 degrees you could also measure the side shear force of various magnets and wire combinations.

Roller Magnets
I was looking at some small magnets for another project and these might be suitable. They are called "magnetic clasps" and are used in jewellery. You might find one type that has a hole in the centre. Drilling holes in magnets is a non starter as they are brittle and machining a magnet often destroys the magnetic force.
Another possibility is to mount the magnet as a conventional magracer, but have a small rolling bearing just in front to maintain a nice working clearance. I'm thinking of something like a small 681XZZ 1.5x4x2 mm Miniature roller. (google or ebay "681 miniature")

[WesR]

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Good thinking here! I have thought about supporting the guide magnet arm with a wheel but didn't think of small ball races.
I have ordered one of only 4mm diam. so I will give it a try soon. One advantage of this idea would be that the magnet would not need to be inline with the front wheels, i.e. it could be further forward which would leave more space in the chassis. The wire would still need to be flush with the track surface but if it were a little high, the magnet would be lifted up.
I did experiment recently with a hinged arm (see photo). The idea being to have a low friction spacer under the magnet but the friction developed was too much for the low grip rear tyres. I guess if we had rubber rear tyres they would overcome the friction, as slot cars do, but then we would be back to 200 mph cornering speeds!

[WesR]

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My 4mm ballrace arrive today so I gave it a try. The car follows the wire ok but lane changing not so good. Probably because the wheel (ballrace) has to be dragged sideways to do this. We would really need some sort of castor wheel I think.
This is in aid of making tracks less precise and therefore easier to build I guess. I have another experiment ongoing however using even thinner wire (.020") which I find the cars will run over without the need for a slot or plastering level. Just a couple of coats of paint will do. Should have it sorted next week.

[Ned]

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My 4mm ballrace arrive today so I gave it a try. The car follows the wire ok but lane changing not so good. Probably because the wheel (ballrace) has to be dragged sideways to do this. We would really need some sort of castor wheel I think.

A very small piece of ultra-high-molecular-weight polyethylene (UHMW) may work better than a round ball caster wheel. Mounted just in front of the guide magnet, and beveled on the edges to prevent any snagging, it could prevent the magnet from coming in contact with the wire, where the wire may be a little high. By a little, I mean .005" (.13 mm). That's enough to cause a car to freeze to the track at slow speeds with low traction rear wheels. I doubt that the guide arm would have to be hinged. It is already flexible enough. In fact the current flexibility is a primary reason the car will freeze to the track where the wire is a little high. The reduced clearance between the guide magnet and a high wire causes the guide arm to flex more. Initially I'd mount the UHMW so that the bottom of the UHMW slide is about .002" below the bottom of the magnet and adjust the height of the guide arm so that normally the UHMW doesn't touch the wire. That way the UHMW slide would only touch the wire at places in the track where the wire is unusually high. It also would prevent the magnet from coming in contact with the wire. UHMW is extremely slippery and very abrasion resistant.

[Keld]

My wife working with pearls, i think some of those could give the same effect as the roller ball, but they are round so maybe they are better at lane change, and if we just has to make them in UHMW