58 replies to this topic

[slotbaker]

Just a bit curious about magnets, and how they have changed/improved over the years with regards to our slot car motors.

Specifically for slot car motors in 1/24 scale, has anyone done a chart, or can provide some info like:
What are the best/strongest magnets available today?
What is their gauss rating, and at what distance?
Do we use any other form of measuring?

How do these magnets compare to common motors from the '60s, '70s, and '80s?

What would be the weakest magnets used in slot motors, and what are their relative ratings?

TIA.

[Russell Sheldon]

Hi Steve,

There are much better qualified people than myself on this forum who can answer all your questions but I would like to mention that most, if not all, magnets used in motors suitable for slot cars are of the sintered ferrite, or ceramic - whichever you prefer - type.

In the 1960s, cast Alnico magnets were mostly used. Cast magnets are manufactured by pouring a molten metal alloy into a mold and then further processing it through various heat-treat cycles. The resulting magnet has a dark gray exterior appearance.

Sintered ferrite magnets are mainly used these days and are manufactured by compacting fine Alnico powder in a press, and then sintering the compacted powder into a solid magnet. Ferrite magnets are sintered permanent magnets, composed of barium or strontium ferrite. This class of magnet, aside from good resistance to demagnetisation, has the advantage of low cost.

The very powerful "rare earth" or "Cobalt" types of magnets, as used in Eurosport "strap" motors, are a hybrid of casting and sintering but because of the many special steps involved in manufacturing, they tend to be somewhat expensive. As with everything, you pay for performance!

With kind regards,

[Cheater]

Rocky Russo (Prof. Fate) likely can provide some of the numbers you're seeking, Steve. He'll probably post to this topic when he sees it.

[Horsepower]

He didn't chime in......

[Prof. Fate]

Hi,

I don't have a chart, but I did post about a week ago on this subject on this board SOMEWHERE!

All gauss measured at the face. Magnetism has the property that it is an inverse square relationship. Double the gap, the strength drops by four. Thus, there isn't a lot of reason to measure at anything other than the face.

Vintage Alnico magnets from the day would only be in the 200 gauss range. Early ceramic Mabuchi are similar. In '66, in 16Ds, we had Hitachi with the "Hemi" and other aftermarket magnets go to about 350 gauss. '66-70, various manufacturerers got 16D magnets quickly from 400, then 500, then 650 gauss. At that point, the materials were at their upper limit. Modern 16D-sized magnets are still in this 400-600 range. Though about a decade ago, somone was offering "high saturated higher RPM magnets" that were 350 gauss and did give higher RPM! But that is another long story.

Cobalts can be 2000 gauss in the "P" can size (13UO and strap).

Modern FK motors, the "Cheetah" type, usually measure about 350 gauss. I haven't disassembled the new Slick7 or TSR to test.

One theory of motor building is to ignore the strength of the magnets as it is more important to have the fields relatively matched in strength.

My wife had a friend who was a health nut and who peddled magnets as promoting good health when placed on various parts of the body. The magnets she sold measured under 100 gauss. My wife joked that if this nutball stuff worked, I would be aging backwards.

Fate

[slotbaker]

Cool, thank you Russell and Rocky.
That all makes sense.


Hhmmm, aging backwards??
Does that mean you will be back in diapers soon??

[GT40]

Professor,

Some magnetic musings. Comments?

Don't the can material, can openings, and air gap from armature pole to magnet face influence the magnetic flux that interacts with the armature? How much do these factors influence the performance versus the magnets themselves?

Why is it said that a "hot" - presumably, drawing large currents - armature will cause a motor to overheat if the magnets are not strong enough?

At what temperature are magnets adversely affected and start to demagnetize? Soldering a motor can to a stamped steel chassis can raise the temperature of the can considerably. How much effect does this have on the magnets?

I recall when I was racing as a kid, the "hot" magnet setup was Champion Arco Blue Dots. What were these made of and what kind of gauss reading would they have been?

[TSR]

Modern FK motors, the "Cheetah" type, usually measure about 350 gauss. I haven't disassembled the new Slick7 or TSR to test.

You will be stunned.

[Rick]

I was stunned when I gaussed some of the new toy motors. FK Mabuchi, Ninco, and another brand I forgot, all gaused about 1100. Darn close to the new Mura/PS magnets...

Haven't had a Falcon 7 or TSR in my hands yet but I am guessing better than the above...

[Prof. Fate]

recall when I was racing as a kid, the "hot" magnet setup was Champion Arco Blue Dots. What were these made of and what kind of gauss reading would they have been?

 

I seem to rememer they were in the 450-500 range, similar to modern Super 16D magnets.

Fate

[MantaRay]

Rick,

What are you using for a gaussmeter?

[Ron Hershman]

Yes, the can material, design, openings, have an effect on what I call the "static gauss". Some cans allow for more leakage versus others. The more holes or less metal in a can, the less field gauss. Air gap affects the static and what I call the "field" gauss as well. Air gap does not change the static reading of the magnet itself. Air gap changes the field gauss where the arm lives. The tighter the air gap, the less amps the motor needs to spool up the armature. It's more efficient.

You always want to match the magnets inside the can you are going to use. Matching them outside the can will usually change the reading once inside the can and the magnets are repelling one another.

You could take ten motors cans... all the same design and mfg... put the same set of magnets in each can, take gauss readings and you will sometimes find different (of the same type and manufacture) cans give different readings. This has to do with the material in the can. Not all steel is the same out of the same sheet.

Now with that being said, a gauss reading does not tell the real story of magnets. What is important in a magnet of the same type, size, and material is two things... energy ( which you can not read with a gauss meter ) and loss of gauss when magnet gets heated. This can be measured. When a magnet gets hot, it demagnetizes or loses strength when getting hot. The way to check this is to put your magnets in a motor can, put can and magnets in a small toaster over, heat for five minutes at 250 degrees F (you want to try and duplicate what the motor sees on the track... example if you're running two minute heats, then stick set-up in oven for two minutes ) then pull set-up out of oven and take a gauss reading as quickly as possible. You will find that some weaker magnets do not lose as much gauss under heat compared to stronger reading magnets at room temp. This is showing you the resistance to the temp. So while a stronger mag (at room temp) may be stronger the first minute of a race, it could get weaker as the race goes on compared to a lower gauss magnet (at room temp) when heated up. Magnets lose gauss during this heat, cool-down, heat, cool-down cycle and hard hits knock the field out of alignment as well. When we zap magnets, we are realigning the field inside the cans and resaturating the magnet strength.

With that being said... different materials are used depending on the application. Ceramic magnets are the most popular in motors due to low cost and mass production. Ceramic magnets are used in the cheaper slot motors because of this and ceramic works well with Group 20 motors and down. Ceramic replaced Alnico because it was better and cheaper.

As a ceramic magnet gets smaller, it gains gauss, but loses energy. If you take a Mura ceramic magnet and shorten the length of it, you will find it has a higher gauss, but it has less brakes and punch due to loss of energy.

There are many different grades of ceramic material. The better the grade, the better the energy in most cases. Highest energy is best over gauss readings, unless you find two grades of material that have the same energy, then you want the higher gauss.

There are also two types of ceramic magnets... dry press and wet press. All ceramic slot mags are dry press. Dry press magnets have less piece loss during the manufacturing process compared to wet press. Dry press material is pressed into a mold using dry material.

Wet press material has water added to make the material into a slurry when pressed. Wet press magnets are stronger and have higher energy due to the alignment of the radial orientation during the manufacturing process. When ceramic magnets are pressed they are also kind of "charged" which turns the metal in the material into a radial arc if you will. It is easier to do this orientation when the material is wet versus dry. The better the orientation, the better gauss and energy. This is why you find different readings in magnets...some particles turned or aligned better in some magnets compared to others for what ever reason no matter if dry pressed or wet press. Wet press molds cost more to have made than dry press molds.

After the magnets come out of the molds, they are then "sintered". To find out more about the sintering process...... do a Google on "sintering".

There are also two type of ceramic magnets in the market place today. Molded magnets and machined magnets. Molded magnets are better as the flux lines in the magnets are radially aligned. Machined magnets are ground from ceramic blocks and the flux lines go straight through the material versus being radially aligned. Molded magnets are better performing, but cost more to make and you also have to buy a die. Machined magnets can be ground on a surface grinder with diamond coated wheels with no mold cost.

Some winds exceed the energy of ceramic magnets and that is a reason that cobalt material is used in other types of motors. Also, as motors got smaller, cobalts were used because they have higher energy in a smaller package while cobalt demagnetization is very high. Cobalt magnets don't lose their strength like a ceramic does under high temps. Cobalt and ceramic magnets gain back their strength when they cool down to a certain point.

All cobalt magnet in slot racing today or either ground to size or EDM cut from blocks of cobalt material. While pressed/molded cobalt magnets would perform better, no one wants to spend the tooling money to produce the various sizes and shapes used in cobalt motors today. Grinding or EDM cutting offers more options for the manufacturers at less cost.

Now in the new Falcon and TRS "FK" motors, they have Neodymium magnets. Neo magnets (depending on the grade used) are much stronger than ceramic magnets and in some cases stronger than the best cobalt grades. Neo mags are used in HO cars for traction magnets, not motor magnets. While Neos are very strong, they have very little resistance to heat. When a Neo gets hot, it loses its strength and the gauss does not come back like a ceramic or cobalt magnet does. Some Neos do not re-zap or magnetize very well after getting hot. You be the judge... take a Falcon 7 type "FK" magnet or motor, stick it in your oven at 250 degrees F, let it set for three to five minutes, take it out and take a gauss reading. Then let it cool down to room temp and take another reading and you will find it was not as strong after a heat cycle as it was when first read at room temp before sticking in the oven.

I did a test last month on some C-can sized Neo magnets... at room temp they had a gauss reading of 1400 (compared to a ceramic magnet reading of 800) I put them in the oven at 250 degrees F for three minutes, took them out and the reading was 400. When the Neos cooled to room temp, the reading was still 400. A ceramic magnet that read 800 at room temp, dropped to 730 at 250 degrees F for three minutes, but went back to 800 when cooled to room temp.

Neo magnets are not used in most slot motors for this reason. While they may be stronger, they have no resistance to heat. They have produced better grades over the years, but they are still not close to cobalt materials in heat resistance.

Champion Blue Dot magnets were the same material as the Champion White Dot magnets. Champion had the magnet manufacturer make a batch of magnets using the same material, but adding water to produce a wet press magnet. The magnet mfg told Champion they would never do that again as the magnets size specs were off and it damaged the die. The Blue Dots were stronger due to the wet press process, but Champion didn't want to spend the money at the time to make a correct die to wet press magnets. Today's Mura, Pro Slot C-can sized, dry press magnets are still better than a set of Blue Dots and that's because the material used today is much better than what was used 30 or so years ago.

To knock a ceramic magnet close to completely dead in gauss reading, you must get the magnet to over 400 degrees F. Your armature will be melted before your ceramic magnet ever gets that hot.

Soldering motors into chassis don't affect the gauss too much, unless you hold the iron on the motor for 4 or 5 minutes. A 30 to 60 second motor change doesn't affect the mag readings too much.

[Rick]

I use a modern 16D for my mule set-up when I check zappers, and it gausses at 1100+, many time over 1200.

I use a NY meter, the best the industry has to offer. Made by John Acello.

New Muras will gauss 1200+ on a new zap.

[Ron Hershman]

Are those new Muras being checked inside or outside the can???

Not all gauss meters have the same readings. What is 1200 on Rick's meter may only read 700 on a different meter.

Use "your" meter as a reference tool.

[Rick]

Any and all meters are relative to the user. Doesn't matter what they read as long as you use the same meter on your stuff. I have arm meters and magnet meters. who cares what gauss they read, just match the numbers and race em...

I read all magnets in a can. NEVER OUT...

[Ron Hershman]

Smart man!!!

I would say if 1200 is high/good on your meter... then it would read 980 or so on my meter.

[Hworth08]

Thanks, Ron! Your post answers a lot of magnet questions. Very good information!

[S Forsyth]

Rick or Ron,

Are you guys reading only the center of the magnets while in the can, or do you read the tips as well?

I use a Wright Way gauss meter, and I'm able get on good magnets D-can or C-can magnets at 1150 to 1200 on the tips, and then orientate the magnets in the can. I never read the centers; is this wrong?

[Ron Hershman]

Thanks Ron! Your post answers a lot of magnet questions. Very good information!

Thanks and I am sure someone will come in and add something I may have forgotten or overlooked.

[Hworth08]

Thanks and I am sure someone will come in and add something I may have forgotten or overlooked.

Ron,

Well, you might want to mention the relationships of different cans, magnet strenghts, arm timing, gearing, bodies, tires, etc... How they work with each other and different track power to effect slot cars.

Just joking!

It may be true that a lot of racers in the built-motor classes use a "common" air gap so their arms can go from setup to setup.

[Cheater]

Don,

Just to be picky, one doesn't need the same air gap, but they need to be close.

When I was building C-cans, I used air gaps from .535" to maybe .525" and could interchange most arms.

[Zippity]

Ron,

Great information - thanks.

Have you, or anyone, compiled a comparison chart that compares todays available C and D can magnets in priority of strength to weakness? Is such a comparison possible?

[Zippity]

Blue dot, orange dot, white dot - the list goes on ad infinitum.

Can someone please tell me which is the strongest, which is the weakest, and what is there in-between

[TSR]

The D3 mags are the strongest.

[GT40]

I don't have a gaussmeter, but that is certainly my impression in comparing the TSR D3, the Falcon 7, and the Pro Slot 4002, both on the dyno and on the track.