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Ceramic magnets... "You've come a long way, baby"


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#91 Ron Hershman

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Posted 05 August 2012 - 08:37 PM

which is the more important - the leading or the trailing edge/rim??

which one do you want to match for the best result?


Leading edge is the most important when it comes to the highest strength. The hardest part of matching tips in a ceramic magnet either molded or machined is the tips on both sides being the same and also all the pieces being the same after machining.

All molded ceramic magnets are "machined" after sintering or as it is called in industry...."qualifying". The magnets after sintering have rough edges that have to be ground to knock off flash and to fit to finished dimensions. If you seen how this was done...you would laugh at how they do it...nothing precision about it..... the make a "fence" on the grinding table and usually push the magnets past the grinding wheel...... there is deflection and if a magnet has a "high side" on the edge up against the fence.... it takes off less material on the tip than a magnet with a lower side on it.

It's not very accurate nor precision and therefore you get un equal tips and tip dimensions among the batch of magnets.

Machined from block material magnets can have the same problems and seen this a zillion times at RJR when I worked there.

So if you have a magnet with a thicker tip than a magnet with a thinner tip.... you will find two different gauss reading/numbers.

Why you want the leading edge to be the stronger tip......... when the armature comes into the field ( this also has to do with magnet height, timing, air gap, wind just to name a few factors ) the leading edge of the arm laminations start to fire and you want to fire or charge the coil as the tips intersect. If you fire past this point or before this point....... loss of performance. You also do not want the arm firing or charging with the leading tip of the lams at the center point of the magnet either.... that's almost too late.

This is why certain arms with certain timing work with a certain magnet. There is a "sweet" spot for the firing/charging and over the years we have all figured out that a X-12 arm with 38 to 42 degrees is raceable versus a 50 degree X-12 arm. Sure you can use the 50 degree arm for drag racing or qualifying as it won't be ran long and get excessively hot and then fail.

Generally speaking.... the lower or shorter height of a magnet.... one has to reduce or retard the timing..... the taller the magnet more advance can be used.

But again this varies based on turns and wire size as well as air gap and magnet strength and energy.

Perfect example is the RJR Big Diameter 16-D arms.... being the tip width across the crown was reduced and a smaller width.... timing had to be reduced as the arms with 38 degrees and higher were firing way before the leading edge of the tip got to the leading edge of the magnets..... this caused heat and no RPM or torque. We reduced the timing to 32 and 36 degress and had a totally different animal and one that changed 16-D racing in a hurry.

So you always want the leading edge of the magnet tip to be the strongest. The "push pull" guys had it all wrong a few years back.
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#92 havlicek

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Posted 06 August 2012 - 06:06 AM

No it's not rocket science if you have the equipment to measure the "energy" of the magnet. Being I have done this before as well as every single magnet MFG..... it's not rocket science.


I beg to differ. I understand that you have worked for and with magnet manufacturers, but the theorey behind magnets, especially in a dynamic system like a motor with interacting fields of both the permanent magnets and the electromagnetic fields of the spinning armature is way beyond "rocket science" which is basically ballistics and Newton's laws of motion. What's going on here is still not well understood in some ways by physicists...certainly no one here and DEFINITELY not me! In a sense, it's not rocket science...it's black magic.

The grade of a magnet directly refers to the Maximum Energy Product of the material that composes the magnet. It in no way refers to the physical properties of the magnet. Simplistically, grade is generally used to describe how "strong" a permanent magnet material is. The energy product is specified in the units Gauss Oersted.


"Simplistically", I understand what grade means and refers to as I'm sure many here do as well. We're not talking about where the magnet's strength comes from, but rather how to accurately (enough) measure that field in a useful way. Saying that "measuring Gauss is not good" really has no meaning when it's all a slot racer can do.

Of course the "term "energy" you're using is unfamiliar and vague" to you...... have you ever sat down and discussed magnets and magnet manufacturing with a company such as Hitachi, TDK, Arnold??? I have..... I know this term and this term is used frequently in the magnet "world".


Again, in the physics of magnetics, the term energy is vague/general and when "we" set out to measure a magnet's field strength we deal with "Gauss". No, I have not sat down to discuss magnets with a manufacturer, but even if I had...I still wouldn't probably understand what's going on here. I do have a generally pretty good understanding of physics though. You and I get to these points sometimes where you seem to take offense at being questioned about such things. I am not questioning what you have done in the past...why would I? What I am questioning is a couple of particular statements about measuring magnets. This term "energy", other than it's general meaning, has no real meaning here. You may have used it before and even have heard it used by manufacturers, but if you can't define it or say how it is measured because "measuring Gauss is not good" (other than by a magnetometer or "Gaussmeter"...hall effect transducer), than what's the point?

-john
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John Havlicek

#93 Fast Freddie

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Posted 06 August 2012 - 09:29 AM

Ron
If the .450 magnets make less energy than the .500 magnets why have so many trended to the .450 magnets? Is it just for the weight savings? Is that worth the loss in power? I think the biggest problem in motor building is finding the right arm for the setup. Many times I've built setups as identical as I possibly could but put arm A into setup A and it runs OK. Now put arm A into setup B and it runs so much better or worse. I've come to realize over the years that in slotcar motor building all else being equal nothing is the same. It takes time and patience and alot of trial and error. As far as tip orentation I use the push method like the late Monty Ohren he was a very good motor builder and racer. To each his own. I use to win more races when I didn't even match magnets, but then again I was 20 years younger and Gp12s were 1 second slower than they are today.
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#94 Mark Johnson

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Posted 06 August 2012 - 02:46 PM

I'm a push guy also , I run .450 mags on x-12 and swasp , long mags on s16c and contender .
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#95 CFL Mike

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Posted 06 August 2012 - 02:46 PM

A shorter length magnet will read higher gauss than a longer magnet made from the same material. BUT...... the shorter magnet has less "energy" than the longer magnet if using the same material.

The only way to get more energy with a shorter magnet is to change the material and that can only be done if new tooling is purchased to the tune of 10's of thousands of dollars.



The Ceramic magnets that are "molded" and used in slot racing are dry press. No wet press molded magnets... the magnet companies in Asia do not want to wet press a small arc like we use in slot racing.

Now wet press material blocks can be cut and ground and used, but they are not radially oriented like a pressed and molded magnet it.

Wet press molded magnets would have higher gauss and higher energy than dry pressed magnets due to better materials and better orientation when pressing wet.


Maybe I said that wrong, arent Muras "Wet Charged" then? The guy who runs my local track is the one who told me this, he said thats why everyone used to use Muras mags. He was also the one that told me Koford and ProSlots where made by Mura, and thats why it doesnt matter much better the 3s magnets.
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#96 Rick

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Posted 06 August 2012 - 03:07 PM

first off, why are you debating with Hershman who knows this information, first hand? He says they are dry press, take it to the bank, I think the old Champions were wet press type?

On to the push/pull debate. That has been going on as long as motor builders have been building motors. Now this is only my opinion but I think it doesn't matter if its push or pull, as long as the strong tips are oriented correctly. I think it is a wash of which is superior.

Its mojo, not rocket science, LMAO. As Fred says, you can build two identical motors and one will run better than the other? WHY?..........................MOJO!
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#97 Ron Hershman

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Posted 06 August 2012 - 08:03 PM

Maybe I said that wrong, arent Muras "Wet Charged" then? The guy who runs my local track is the one who told me this, he said thats why everyone used to use Muras mags. He was also the one that told me Koford and ProSlots where made by Mura, and thats why it doesnt matter much better the 3s magnets.


Mura magnets were NEVER Wet Press. They have always been Dry pressed.

Koford, P-S, etc once bought them OEM from Mura because they were the best performing Ceramic C can magnets at the time when these other companies used to purchase and use them in their production motors.

, I think the old Champions were wet press type?


The only "old Champion" magnet was the Blue Dots and the material had water added to the Powder to create a "slurry" before pressing into the mold.

All other Champion magnets were Dry press.
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#98 Gator Bob

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Posted 06 August 2012 - 08:23 PM

Ceramic is the binding agent ... no?

What is the iron to ceramic ratio?

BTW: I don't know Jack Shirt about magnets. >corrected<

Off topic...maybe... I saw that neo mags can be used on incoming domestic well water pipes to 'remove' iron and 'soften' water .... anyone know about this?
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#99 Ron Hershman

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Posted 06 August 2012 - 08:32 PM

Ron
1.If the .450 magnets make less energy than the .500 magnets why have so many trended to the .450 magnets? Is it just for the weight savings? Is that worth the loss in power?

2.I use the push method like the late Monty Ohren he was a very good motor builder and racer. To each his own.


1. Because of weight mainly...... sometimes a power "reduction" can be a good thing depending on the type of car and track. Maybe be easier to hook up with a bit less power.

2. Yes to each his own.... I have never matched magnet "tips" in the 30 years I have raced slot cars. Never knew about it for many years, once I found out about it..... I could never see much difference in readings and then never could see any difference on the track. Like I said earlier...... the tip profiles can be sanded/ground to get a better match, but in most classes this would be illegal to do so.... so why waste the time to do it if it's not legal to do so?

More on Push/Pull......... most everyone has it WRONG on this theory...even Monty.

Again like I said in a earlier post...... you want the leading edge of the magnet tip to be the strongest so when the leading edge of the arm is at the leading tip of the magnet...this is when it fires/charges..... once the arm fires/charges..... it needs to get out or leave the rest of the magnet field quickly.

If the trailing tip of the magnet is stronger than the leading edge.... you will have a magnetically "bound up" motor as the arm does not want to release as quickly due to the stronger trailing tip resisting a quick release. After the arm fires/charges it needs to get out and go to the other magnet on the opposite of the motor.

If the push method "really" worked the cobalt guys would still be doing it.... they aren't...why??? Because they had it all back wards.

Here is a test I did many years ago to prove to myself and others how push/pull doesn't work.

I took two pairs Mura Ceramic magnet and ground one tip flat or flush with the ID on both magnets.

I built two set-ups.......... same can.... same strength magnets.

I built a set-up with the un ground and stock tip as the leading tip and the ground tip as the trailing edge. Pull/Push

I built the second set-up with the ground tip as the leading ledge and the trailing edge stock tip. Push/Pull

Then I had two set-ups that would use the same endbell, arm, brushes, springs on both.

Went to the track and the stock tip leading edge set-up was a ballistic missile rocket ship.

Then switched to the ground leading edge set-up and this was a complete turd even with many gearing changes to try and regain the lost Torque, RPM's and overall power.

Of course this would not be legal to do in most D or C can classes so it's not very applicable to do. It can be done in Int 15 and the cobalt classes, but not the Box 12 or scale ceramic classes.

Now all of you think back to the different magnet profiles we have seen in the last 20 years..... Champion Force magnets with their ground back tips top and bottom.....RJR...same as the Force magnets and then the Pro-Slot SMQ's.....none of those worked very well when compared to "full" tip Mura magnets.

Why didn't Force magnets work? Not long enough tips.

Why didn't RJR magnets work?? Not long enough tips and not radially oriented. Very Very good material.

Why didn't SMQ magnets work??? The big notch in the back reduced the energy of the magnet too much to be effective.

So Ron.....why was the magnet you describe never made?? Production issues and magnet retention inside the can. Would be/work great if the magnets were epoxied in place in production motors but can't be done for cost reasons.

Yes any company making ceramic magnets could have one tip ground back on their production magnets and offer them, but this is costly to have the grinding done as second operation.

Yes they could be molded but no one has ever wanted to "flip" the tooling costs to do so plus there could be a "orientation" problem with two different tip dimensions in a molded magnet. I never talked to a magnet engineer about this, but I am sure it would lead to problems when orienting the magnets in production.
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#100 Ron Hershman

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Posted 06 August 2012 - 08:38 PM

Ceramic is the binding agent ... no?

What is the iron to ceramic ratio?





Yes ceramic is part of the "binding agent.

What is the ratio of ceramic to iron? Depends on the "grade" of the material and other materials used other than ceramic and iron. ;)

A good primer here for those not knowing "Jack" about Ceramic Magnets..... http://en.wikipedia....Ferrite_(magnet)
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#101 CFL Mike

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Posted 06 August 2012 - 10:35 PM

Thanks for the information Ron, on how the magnets and armature interact. The only thing I dont quite understand, is what part of the magnet is considered the lead edge and the trailing edge.

Also just to clarify, "wet press" and "wet charging" are the same thing? Or is "wet charging" a non-exsistent term?
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#102 Ron Hershman

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Posted 06 August 2012 - 10:49 PM

The leading edge of the magnet is the top edge/tip as the armature rotates in the running direction of the motor.

Wet charging is not a term or process.

More info....

General Information

Ferrite magnets are sintered permanent magnets composed of Barium or Strontium Ferrite. This class of magnets, aside from good resistance to demagnetization, has the popular advantage of low cost.

Ferrite magnets are very hard and brittle, and require specialized machining techniques. Moreover, they should be machined in an unmagnetized state.

Anisotropic grades are oriented in the manufacturing direction, and must be magnetized in the direction of orientation. Isotropic grades are not oriented and can be magnetized in any direction, although some degree of greater magnetic strength will be found in the pressing dimension, usually the shortest dimension.

Due to their low cost, Ferrite magnets enjoy a very wide range of applications, from motors and loudspeakers to toys and crafts, and are the most widely used permanent magnets today.


Manufacturing Methods

Pressing and Sintering:

Pressing and sintering involves pressing very fine ferrite powder in a die, and then sintering this pressed magnet. All fully dense Ferrite magnets are produced this way. Ferrite magnets can be wet pressed or dry pressed. Wet pressing yields better magnetic properties, but poorer physical tolerances. Sintering involves subjecting the material to high temperatures to fuse the pressed powder together, thus creating a solid material. Magnets produced through this process usually need to have some finish machining, otherwise surface finishes and tolerances are not acceptable. Some manufacturers extrude instead of press wet powder slurry and then sinter the material. This is sometimes done for arc segment shapes, where the arc cross-section is extruded in long lengths, sintered, and then cut to length.

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#103 CFL Mike

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Posted 07 August 2012 - 10:39 PM

Since it seems like you pretty much run the slot cat magnet industry Ron (I know hyperbole, still take it as a compliment) I would really value your opinion. I was reading through this thread earlier, and I think you said, even today you prefer Mura magnets right? Or which ones do like/use most often?
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#104 Gator Bob

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Posted 28 August 2012 - 04:30 PM

Did Mura sell them as Yellow Dots?



Help - I forget.

Orientation ???

dots face the can bushing ?
with the two dots at the (rear on a AW) side of a Mura C can with the axle clearance cut out ?

Or what?
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#105 Rick

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Posted 28 August 2012 - 06:55 PM

Be bold, turn the dots one way on one side and opposite on the other. heheheh
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#106 Gator Bob

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Posted 28 August 2012 - 07:10 PM

Be bold, turn the dots one way on one side and opposite on the other. heheheh


Then paint new dots? ;)
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Bob Isrealite
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