# matching magnets



## leonus (Dec 17, 2013)

Hello all, hope you have a great weekend.

I was wondering, what's the best way, without a super expensive gauss meter, to test for matching strength in motor magnets??

I am beginning to think that when it comes to performance, this may be even more important than strength..

Anyone ever tried anything like seeing how many paper clips, or bbs they pick up? Is this a silly idea and not accurate enough?

Looking forward to expert opinions.

Thanks and God bless &#55357;&#56841;


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## dtomol (Mar 30, 2005)

*Matching Magnets*

I use a compass, take a 8 1/2 by 11 sheet of paper start with as large a circle that you can make then make corresponding smaller circles. Either number or letter them. Put the compass in the center of the paper now move your magnet closer to the compass till needle deflects then record the reading. Also some people use a in expensive postage scale with the plastic cover put the magnet on the scale and record the with reading the higher. These way work well you can also build an inexpensive gause meter the plans are on the web, I will locate them and post as well.


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## leonus (Dec 17, 2013)

Thanks, never thought of a compass, very clever


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## Rich Dumas (Sep 3, 2008)

The best thing to do is to use someone else's expensive gauss meter! Actually I have a magnetometer. A common practice is to get some small shims from a hardware store and see how many of those the magnet will pick up.
The magnets used in slot cars have irregular magnetic fields. If you use a magnetometer you can get all kinds of readings for the same magnet, so the technique that you use is very important. Using washers or scales you will only get a relative reading, but the field shape tends to factor out.
A few places sell "Magnet Matchers" that use a Hall effect sensor to give a relative strength reading, those are cheaper than magnetometers and I have an article on how to build your own.


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## Boosted-Z71 (Nov 26, 2007)

As for magnet matchers & pickup shims, bbs etc thats all relative numbers, I built a chassis jig and I measure and match in the chassis, Thats what I want to know is how matched they are in position, Like was mentioned these magnets have a variety of strengths and fields, all can be measured, but how is that relative to the arm in position. 

Boosted


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## clydeomite (May 5, 2004)

A speed secret i learned several years ago is to check magnets by pulling them apart first with both colored sides up and then flipping 1 magnet colored side down. Most pair I have found have greater strength with one colored side up and one down. Just an observation.:freak:
Clyde-0-Mite


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## Rich Dumas (Sep 3, 2008)

With the magnets used in pancake cars one end of the magnet is often stronger than the other end. Sometimes you can get better performance by turning one magnet upside down so that the strong end of one magnet is on the opposite side from the strong end of the other magnet.
When I match magnets I go by the highest reading that I can find in the middle of the side of the magnet that faces the armature, but I also determine the strength at either end of the magnet.


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## leonus (Dec 17, 2013)

Never thought of that..

Cool&#55357;&#56841;


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## slotking (May 27, 2008)

using a dyno, I can also check what is the best magnet setup for any car.
if it does not make a difference in motor speed/torque, I will face the strong side of the magnets down to increase downforce.

this works for pancake or inline cars.

I have also found that at times, I can get faster cars with unmatched magnets.
note : this is using stronger than normal mags. ie.. say my strongest matched magnets are at 1k gauss, I may replace 1 with a magnet at 1.2K gauss to get a faster car.


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## leonus (Dec 17, 2013)

When I started playing with these, I never would have imagined how much tweaking there is to be done if desired... Its almost endless.

Pretty cool.


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## Boosted-Z71 (Nov 26, 2007)

Careful your tweaks are leading you towards Fray car territory, That is a never ending journey, some enter, some stay forever, some leave immediately, some never understand why they are there to start with. 

There are all kinds of guides & tweaks out there to build a faster t-jet, That is what makes them a ton of fun to build, the real trick is figuring out the tweaks that are truly consistent in gaining speed, not everything works twice.

Boosted


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## leonus (Dec 17, 2013)

Nah, mine are all AFX cars, and a few AW clones.

I respect the knowledge and work that goes into the fray cars, and I'm sure the least of them could blow the doors off the fastest of mine, but they just look too unrealistic to me. Just a personal opinion, but I gotta have cool lookin, and fast, in a balance..


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## Rich Dumas (Sep 3, 2008)

Magnets are just another thing that you have to experiment with a little if you race your cars. If the magnets are too strong you car can loose top speed, even on a dyno. The ultimate test of how things work best is on the track.
If you are looking for speed tips the best people to talk to are usually the ones that win the most races.
I have written articles on tuning Aurora T-Jets, JL/AW ThunderJet 500s, T-Dash and Magnatraction/X-Traction cars. Those are available in the Files section of the HOCOC Yahoo! site, or you can drop me a PM with your e-mail address.


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## rodstrguy (Feb 14, 2002)

I use a trick learned here, inexpensive digital scale from Harbor Freight... has a tray that snaps off, but you leave it on. place magnets on cover and measure the pull that the magnet has in grams... Match up measurements. You can probably search for scale and find this tip.


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## Rich Dumas (Sep 3, 2008)

That should work quite well. When I weigh cars with powerful motor and traction magnets I always put an inch thick non-magnetic spacer, like a piece of foam, between the car and the pan to avoid getting bogus readings. Turning the car upside down works too.
As an experiment you could try moving the magnet around to different places on the pan to see if that affects the reading. If it does you could mark off an area on the cover and always read the value in that place to minimize that problem.


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## tasman (Feb 17, 2007)

*Is the premise of this thread correct?*

Is it true that 2 weaker magnets well matched to each other will provide superior performance than 1 stronger and 1 weaker magnet?


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## slotking (May 27, 2008)

> Is it true that 2 weaker magnets well matched to each other will provide superior performance than 1 stronger and 1 weaker magnet?


Not really. It can be misleading. and kind of depends on what you mean?

For example. I can build a Fray car.
I can add 2 weak (normal t-jet magnets) to the car. on the dyno, it will show as faster than my fray with 2 strong (dash) magnets.

But on the track, the t-jet mags will lack the torque to make the car as fast as the DASH magnets. if you use 1 of each most times, the car is faster than 2 t-jet mags. but I have had it be slower as well.


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## Boosted-Z71 (Nov 26, 2007)

slotking said:


> I can build a Fray car.
> I can add 2 weak (normal t-jet magnets) to the car. on the dyno, it will show as faster than my fray with 2 strong (dash) magnets.
> 
> But on the track, the t-jet mags will lack the torque to make the car as fast as the DASH magnets.


This is because your Dyno is not loading the car, (torque), and the free-spin reading is really telling you nothing relevant to the cars performance. I have one of those dyno's as well, and that is why I built my own dyno where you can load the car accordingly, as I saw the same results as you in testing & wanted real, useful data. I can test 2 cars, if the data, RPM, output voltage, & power are relatively the same, the cars will perform almost identical on the track, likewise if one produces more rpm, output voltage and power on the dyno it will be faster on the track. The real trick on the dyno is getting measurements in a small enough scale for these motors to register the minor tweaks, either an increase or decrease. 

For testing on a no-load dyno you can build hot dyno queens all day, all you need to do in that case is increase the motor rpm, easily done by lessening the magnetic field to a point, or slight decrease brush tension, and they will show as a screamer on these types of dynos, however they will all be track dogs, just as you stated. HP & RPM is great, but Torque moves the world.

Boosted


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## Boosted-Z71 (Nov 26, 2007)

Leonus: some of the most fun cars that I have are highly tweaked AFX's & Magna-Tractions, arms vary from red-devils, mean greens, to 4 ohm re-winds, poly mags, shunts, tiger tails etc, lots of mods, but yes they are smooth, fast & fun to drive, just very enjoyable cars.

One of my favorites is a nasty magna-traction Buick GN, body is lowered and it has plenty of power to overcome the traction of the wide sili-sponges on the rear at any time, so I understand you wanting more from your later generation pancakes, the tweaks only make them better. 

Boosted


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## slotking (May 27, 2008)

> This is because your Dyno is not loading the car, (torque), and the free-spin reading is really telling you nothing relevant to the cars performance


the issue is time
on very long strait the weak mags may get the car up to speed just like on a dyno.

I use my dyno to 1 see how fast the car tops out; that tells me the torque
but the key to a dyno is not to compare car 1 to car 2, but to compare car 1 to car 1 after making tweaks


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## Boosted-Z71 (Nov 26, 2007)

slotking said:


> but the key to a dyno is not to compare car 1 to car 2, but to compare car 1 to car 1 after making tweaks


Its really nice when a tool designed to measure output will do both accurately and match track results.

I agree on the weak magnet car eventually reaching speed, but any turn or release of the trigger and your for the most part starting over to reach that top speed again, as the weak torque comes into play.

Boosted


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## tasman (Feb 17, 2007)

slotking said:


> Not really. It can be misleading. and kind of depends on what you mean?


Let me re-phrase...

I am not questioning stronger vs weaker magnets I am asking......

Is there any evidence that matching magnets' strength improves performance?


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## Dragula (Jun 27, 2003)

I faintly remember an old trick to balance the magnetic field by using a flux bar (not sure if that's the right term). In essence it would bleed or balance the 2 magnets strength by making the field a complete circle.I could be wrong,i was once before.
Christian


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## Rich Dumas (Sep 3, 2008)

There have been a number of HO cars that used flux collectors, but I have never heard of a pancake car with a flux collector. The addition of a flux collector would not be leagal under any set of rules that I am aware of and any magnet shims must be made of non-ferrous material. If you were not worried about rules a flux collector might be something that you could experiment with.
I do not own a dyno, if I did it would be one that can load up the motor so you would have an indication of power, not just RPMs. I have a flowing track where power is as important as handling. One of the guys that I race with makes dynos and he uses one of his all of the time. His track is much more technical than mine, which makes it more difficult to evaluate a motor on the track. His dynos do have an adjustable drag feature, but his dyno readings have led him astray a few times.


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## Dragula (Jun 27, 2003)

If you think about most people on here they don't race under sanctioned clubs,so a flux bar could really smooth out otherwise jumpy or doggy cars or turn a set of otherwise useless magnets into usable pieces.and yes all shims must be non-ferrous material in every rule bound class I have ever raced in.Just throwing in my 2 cents.


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## Boosted-Z71 (Nov 26, 2007)

I built sole purpose drag car (my first) for Sgrigs contest on here a while back. I used ferrous shims behind the magnets to create "flux shields", it definitely improved the magnet field by near 25% total, per my readings on my BRP magnet matcher, these were checked with the magnets in position on a test chassis jug that allows you to measure the total field for both magnets or individually. 

These were high rating JL mags, sorted from about 20 pair to find the absolute best, The numbers with the shims were approx 25% greater than without the shims, that mean green arm would take all the magnet you could throw at it. Polys were not legal, the shims were. I had poly mags that without the shims did not measure in total field strength as high as the JL's with the flux collectors.

I tried to build a ferrous shield that would cap the top of the magnets under the arm plate as well, but never got that to work how I wanted it without major magnet mods. I had already milled out the arm plate for cooling, so doing some type of metal inlay into the top plate was out of the question at the time. 

I think the flux collectors were a major factor in the success of this car. 
As was mentioned I know of no class racing that allows the shields like this, I have also played around with various metalized plastic films for shims, and there are a couple plastic metalized shim materials that produce similar results to the steel but not quite as good as a true ferrous material shim. But it does work.

Boosted


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## ruralradio (Mar 11, 2011)

Steel magnet shims are sometimes used in A/FX based gravity unlimited race cars. Shim placement can also deflect the magnetic field to prevent the car from picking up the "lift pin".

As far as checking relative strength and "matching" magnets, I use the el-cheapo digital scale method. To me, the biggest advantage of "matched" magnets is smoother power delivery, nice when road racing cars with no magnetic downforce and 3-4 ohm armatures.


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## Rich Dumas (Sep 3, 2008)

Matched magnets is not something that I have experimented with in any systematic way. In theory at least if one motor magnet is a lot stronger than the other the armature would be pulled to one side and some power would be wasted. How big the mismatch would have to be before the drop in track performance would be measurable has never been determined as far as I know.
A few years back I read about a rather interesting experiment. Someone used one motor to spin a second one. With the drive motor held at a constant speed he could measure the voltage produced by the driven motor. It would be reasonable to expect that a driven motor that produced a higher voltage would be faster on the track, but maybe not. Another thing that he did was to connect the driven motor to an oscilloscope. For each revolution of the motor you see three pulses, like you get when you only have half wave rectification in a cheap power supply. Ideally the three pulses would all be the same height and width. If they were not the same you would expect performance to be degraded somewhat. There are a number of things that might contribute to the irregular wave shapes, among those are armatures with poles that have different resistances and commutators that are not symmetrical or are warped or tilted. In addition some armatures have more or less metal on each pole. I have seen all of those problems with pancake armatures.
I suppose that the Holy Grail of slot racing is a way to measure cars on the bench that will always predict how they will run on the track.


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## slotking (May 27, 2008)

friend had a car he built in college, it was as fast as a tyco inline on the track!
it had the normal rear magnet and 2 magnets in the front. with 2nd front magnet drop down to act also as a traction mag.

The arm shaft was the size of a needle.


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## Boosted-Z71 (Nov 26, 2007)

I am not an inline guy, I have some, modified a couple, The pancake drag car I built was faster than any inline I own, Tyco, Tomy etc, and that was faster by quite a bit, say 4 feet in a 15 ft straight line. 

Years ago, I should say many years ago I built a t-jet with 4 magnets, all circling the armature, I never completed it and I still have it, I may have to get it out just for fun. I will post some pics.

I really like to see the scratch build ideas, where guys let it all go on the car. 

Boosted


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## ruralradio (Mar 11, 2011)

*Like this, Boosted?*

Note the steel shims...



....along with a few other small tweaks....


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## Boosted-Z71 (Nov 26, 2007)

Awesome car !!!!!!!!

Exactly, only I used a t-jet, a ton of epoxy, I built mine as a teenager, skills were not quite what they should have been then, you know, idea, get it done as fast as you can, get discouraged add more glue etc. 

Great job on the pan as well

How does it run?

Ruralradio you made my morning

Boosted


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## ruralradio (Mar 11, 2011)

Runs pretty well with just a mean green in it on my twisty short-ish track, really doesn't handle any better then my other gravity cars. I think it'll do better on a long fast track, which I'll see in Denver next Thursday. Going to stuff a 3.5 ohm custom wind in it just for fun before I go....


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