14 replies to this topic

[olescratch]

I'm in the process of getting ready to try my hand at building a few motors.  I recall seeing a device that could be used to determine the polarity/gauss of magnets, and was wondering if anybody was able to point me in the right direction to locating such a device.  Thanks in advance for any and all replies.

[Pablo]

Polarity can be determined simply by using a compass.

Gauss is a different story.

 

If you are just starting out building motors, I doubt you need a gauss meter yet.

There are many things you need to learn before matching magnets comes into play.

 

Just my opinion.

[havlicek]

There are several different kinds of magnet "matchers" or "meters" and the ones I've seen will also read polarity.  A compass will work also of course, but here's the thing, if you flip the magnets, you can always make up for that by just flipping the lead wires.  The one thing you CAN'T make up for is if you glue two of the same polarity magnets in a setup...like two norths or two souths, although I guess you could just have the setup zapped if that ever happened.  I'm sort of on the fence regarding Pablo's feeling on all this.  If you plan on building motors as a continuing thing, a good meter is a handy thing to have, but so is a zapper.  I have the RGeo "Mag Blaster" and it works very well.  Most magnets will hold their charge for quite a while with no noticeable drop unless they're abused, but testing magnets strength (for matching) and polarity is something that comes up often.  One more thing on the magnet zapper, the common ones won't do neos or cobalts, and the old Mabuchi magnets (pre-"Arcos") don't take kindly to zapping, at least not with the common type.

Making motors uses a lot of the same tools many slotters have anyway, but also some different ones.  It depends on how deep you want to get into it.  If you DO decide to get a magnet matcher/tester at some time, they're pretty pricey and range from $90 to $180 or so.  eBay has a bunch as well, buyer be ware!

[Pablo]

This is silly. What does "try my hand" mean ? Where I come from, it means "I've never done this before".

As in, "I want to try my hand at making quilts"

 

The title of the post is "Polarity tester". You can determine polarity with a compass.

 

You want to get a gauss measurement tool and you've never even built a motor before ?

That's like saying "I want to try my hand at winding armatures - can anybody tell me where to buy a comm tab welding device ?"

[old & gray]

John,

 

My two cents for what it's worth after many years of not building anything...

The motors I was building were ceramic magnet Group 12's and the matching of magnets was a significant factor. I was having magnet zapped and read by those who were reconditioning my armatures. Finding one of my setups that didn't seem to run well had a mismatch in the magnets was quite enlightening.

 

If you want to try this for a science experiment, here's a possible low cost alternative:

http://www.coolmagne...om/magmeter.htm

 

Bob

[Guy Spaulding]

Same circuit, different packaging

 

[olescratch]

WOW!  In no way did I want to start an argument or have my question referred to as silly!  If that's the way anybody felt, they could have just went on to the next post.  I wanted any info on the question that I asked, and if that was something a person felt was silly, stupid, unnecessary, whatever, let it be so.  As I stated, it's something "I" wanted to try, and I think I have a right to try any and all aspects of this "hobby" that I want to.  Once again I would like to thank all that have given "positive" responses, and those with "negative" responses need to get a life!  I always wondered why a lot of the bloggers on this site seemed to have the same "negative" comments aimed at the same person!?   Now I see why!  Mr. H thank you for hitting the nail on the head, I am trying not to make the mistake of building a motor with magnets not only having identical polarities, but with close to equal magnetic strength.  Boy, all I want to do is try, is there any harm to anybody's ego in that?

 

 

 

BTW   I tried my hand at replacing the engine in a 1994 Chevy Step side that I was told wasn't worth the time or money.  Now I love the looks Ole Blue gets when I take her out for a drive around town!  I guess I just like doing things that others think would be a "silly" thing to do! 

[Geary Carrier]

Dr Stewart,

 

This is another inexpensive alternative... http://www.kjmagnetics.com/blog.asp?p=gaussmeter

 

I predict that you will in point of fact build your motors.

 

Please keep asking your questions, as the only one that could ever stop you from building your motors is you...

 

Nice job on the Step Side; I put a small block Ford in an Austin Healey 3000 and we all know how foolish that was.

 

 

Thanks,

g

[Rick]

John, I built one of gauss meters and they do work,.I did it just for the hell of it too. You'll have to forgive Pablo, he gets cranky................

[havlicek]

Look...Pablo has been through all this and "did his time" winding arms and digging in to motors.  If his response above seems a bit testy, he's just (IMO) probably being more "just a little realistic".  "Building motors" can mean all sorts of things now...from sticking a different arm in a setup (hey, I built this motor!), to REALLY spending time and going over every aspect to get a motor as perfect as it can be.  I have no problem with any of that and I always encourage people to rip open these little buggers and find out what makes them tick.  When someone expresses interest in building motors, I'll just give them all the information I can because we're all grownups here and can make our own decisions on how far to take things.  One person may start doing this stuff and get discouraged...the next may find it all fascinating and keep at it.  That's what makes a horserace.

On the magnet thing, a couple of bullet points:

1)When a pair of magnets are properly of opposite polarity, both concave surfaces will be attracted (as will both convex surfaces).  Easy.
2)It seems clear *to me* that magnets are more closely matched in terms of strength will be a plus.
3)Magnets that are beaten up looking can still work well.  A magnet can be tested for strength, but there is no reliable way to test the field shape of a magnet this side of NASA that I know of...or to predict what effect that will have on a motor's performance.  As with all of this stuff, the true test is when you put the motor in a car and then put the car on a track and squeeze the trigger.

4)A motor is a complex system, really complex.  In simple terms though, there's a balancing act...a kind of "dance" going on here.  The motor will work best if the strength of the magnets isn't so far beyond what the arm can do. 

 

[olescratch]

Once again, thank you to the ones that provided some positive response to my OP!  Due to the fact that my memory has faded a bit, I couldn't remember where or when I ran across a device that was being sold with the ability to identify the polarity and strength of a tested magnet.  It was a small instrument, combining a single probe and a LED readout.  I was only trying to get a lead as to where I may have seen it offered as either a new item or one in the process of construction.  Hell, I may never get pass the point of taking motors apart and reassembling them, but I get to make that decision, and for someone to classify it as being "silly" is a bit much!  We speak about what may have been the cause of the decline in the interest of this hobby back in the sixties, I bet situations like this had a major effect!

[olescratch]

I finally located the item I was looking for.  It is a Go Fast Gauss Meter.  This is the one.  Thanks to everyone for their input, now I will go back to my usual position in the slot car world!

[swodem]

....The motor will work best if the strength of the magnets isn't so far beyond what the arm can do. 

 

 

This I'd like to understand a little more...

[havlicek]

 

This I'd like to understand a little more...

 

 

Hi Steve.  Basically (*because that's all I myself understand about all this), a motor is a balancing act, a sort of "dance".  The permanent magnets exert a field opposed to... and attracted to in sequence...the changing fields created by the electromagnets of the armature's poles.  If the armature can't generate a field as strong as it needs to be, it will at least partially be fighting rotation (*think about those crazy-strong solid neos with a dinky #30 armature).  If the magnets field strength isn't strong enough, you wind up with loads of revs and a decrease in torque/horsepower because of the opposite effect.  

***Now it may be that having the arm a little stronger or the permanent magnets a little stronger is a good thing as far as efficiency is concerned, or even possibly for just the slot car motor application...beats me.  One thing I know for sure (*and only because of experience), you can quickly get to the point of diminishing returns when the magnets are THAT much stronger than what the arm can do at 12V (nominal) and with as much current as the motor could use under load.  The "best" balance is something racers look for and probably get pretty close to when spec-ing out setups.  Of course, the can itself comes into play, as well as the stack length, the shape of the magnets, the gear ratio, the weight and design of the chassis and the body.  I know nothing of all that stuff.

[Phil Hackett]

Here:

 

Look at the uncalibrated meter. You can use it to check field strength with a simple fixture. Also check out the magnet paper at the bottom of the page.