Can one have to much magnet?

[mistairjoe]

Just replaced my broken original magnets with these curved ones,after opening the can slightely. The coging is enourmous, there is no rubbing even though the airgap is minimal.Did i over do it?

[Bruce Abbott]

You seem to have the same number of magnets as stator teeth, so I don't think it will work properly. How many magnets were there originally?

[mohillbilly]

A guy I flew with had a motor he made that could NOT be turned by the bell by hand at all! yet pulled his wing vert at under 1/2 throttle.

[KenSt]

Bruce is right, you have a 12 tooth stator and 12 magnets; It won't run! All 12 magnets line up with all[B] the teeth every time you turn it by hand.

Now, if you had the right # of magnets it is possible to have too much magnet. A proper balance between back iron (can), lamination and magnet is needed for effecient operation. Software is the predominant tool to achieve this nowadays. Magnets that are too thick or too strong are simply a waste of money and weight. More magnetic flux does not always mean more performance or efficiency

[KenSt]

---

[mistairjoe]

Yes,my bad. I noticed the number of magnets and the number of poles after looking at my own photo. So now i have to soak them out and start over.I dont remember how many magnets there were, do you think 14 would work? Thanks Joe

[jj1]

Number of magnets depend on winding schema...
10 , 14 or 16 are all possible and not always interchangeable with the same type windings
http://powerditto.de/Kombinationstabelle.html
Hopefully someone with similar motor can help..

-JJ

[KenSt]

According to the Plettenberg site, your motor had 10 magnets. Therefore, you must replace 10 magnets, since that's what it was wound for. (16 magnets would also work, but they won't fit without cutting) 14 magnets uses a different winding pattern (LRK) and also will not fit without modifying your magnets. I would suggest that you soak yours out, clean off all glue, and put 10 back in, spacing should be as even as you can get it.

[landru]

LRK winding (sps or dps) can be run with 10 or 14 magnets. 16 magnets requires a different winding scheme: ABCABCABCABC. The link to Kombinationstabelle.html above provides details.

Increasing magnet strength, increases the motor's torque producing capability, and lowers the motor's Kv. I have yet to test a outrunner motor in which switching to stronger magnets caused a decrease in efficiency. That being said, remagneting may necessitate changing prop size for best performance.

Andrew

[mistairjoe]

Thanks for ypur help.The can is soaking and i will put 10 back in, spaced.I will do a quick reading on a couple of different prop combination and report back.Joe

[galloping gimp]

For anyone interested, here's Ralph's Winding Table in English (http://www.powerditto.de/Kombinationstabelle2.html). The winding data is no different of course, but it's nice to be able to read the notes.

- Jeff

[osmium_192]

The strength of the magnet is what determines the strength of the motor. For example, we can take the extremes, from NO magnet to having a magnet. The stronger the magnetic field the more powerful the motor.

The formula for the force exerted on a coil in a field purpendicular to the coil.

F = n x I x l x B
Force = number of turns x Current x length (stator) x magnetic field strength

So the stronger the magnet the more power you get for the same input. BUT of course you can have too much magnet since it follows the diminishing returns principle - for a linear increase in magnet weight you will get a diminishing increase in magnetic field (for example having 12oz of magnet will give a bigger magnetic field but will not provide at least 12oz more thrust)

Usually a magnet of about 1.5mm thickness for a say 25-30mm stator is sufficient.

Owen

[pem]

@ airjoe

find a stator with 9 Teeth and the appropriate diameter. Then the bell will
do perfectly.

PM

[mistairjoe]

Thanks for the info. AS i stated i did pull the magnets out and will try 10 spaced. I did think of finding a different stator but it i found it to be to much hassle so i try this first. i will report back.Joe

[Al M]

You can get to the point where increasing the strength doesn't increase the motors torque when the iron becomes saturated. Increasing the air gap can help things then at least for efficiency.

[Littlescreamers]

I would be careful and take everyones claims with a gran of salt! I am not going to get in to the specs of motor design but if I had used the advice form all the people that thought they knew more then me I would not have the motors I have now. Please try new things and test new idea's as this is what will get you closer to what you want. Everyone knows Littlescreamers was first in production with the curved magnets and they were n50 to boot. Was called a lier from many on this forum that my motors could not do what I was claiming! :eek: Was fun to prove them wrong but a pain in the :censored: I thought what the "L" I have nothing to gain by lieing to my customers? I can say that better magnets do make all the Dif in the world. and air gap is very important. coverage is also top on the list. That is a good motor and you get the right ammount of magnets in there and you going to be all set!

Any questions please PM me

Scott

[ImaBiggles]

Everyone knows Littlescreamers was first in production with the curved magnets and they were n50 to boot.

Scott

Well, not really but we will give you credit for it anyway so you dont hijack this thread with the 'Im the Man' stuff again. Ever open up larger brushless motors? Curved mags in LOTS of them. I have a 10 year old Hard drive motor - curved mags too. But I agree, you were first.

[pem]

ah yeah

and george from engconcepts had them for sale long before
Having no story to tell these later new economy
spring offs. Only marketing speech.

But as long as mistairjoe does not report new facts .....

could have some fun

:)

[mistairjoe]

a picture tells .......feel free to add your own captions

[ScubaSteve]

Well, not really but we will give you credit for it anyway so you dont hijack this thread with the 'Im the Man' stuff again. Ever open up larger brushless motors? Curved mags in LOTS of them. I have a 10 year old Hard drive motor - curved mags too. But I agree, you were first.
LOL :p

[Littlescreamers]

Well, not really but we will give you credit for it anyway so you dont hijack this thread with the 'Im the Man' stuff again. Ever open up larger brushless motors? Curved mags in LOTS of them. I have a 10 year old Hard drive motor - curved mags too. But I agree, you were first.

You guys don't really know now do you? I have spoke to George in length about this and you can ask him! He was the first to have them produced, And has told me I was the first to have them in production motors. I am still only one of a couple motor makers that have a full ring of magnets and have since the first day, I wish you guys would talk the truth insted of out your :censored:

Scott
Littlescreamers.com

PS
You show me who was first then?

[Littlescreamers]

This is from George)
(6-22-04)

Scott



Give me the dimensions for the ring and I will let you know. There are maximum thicknesses that limit what can be done with multipole magnets. Also, please mark the direction of magnetization. Typically it is multipole through the thickness. For motors you might be wanting radial magnetization and the neo material cannot be magnetized like that. However I have had great success with arc segments. Now we might be able to make the arc segments into an assembled ring for you If the quantity justifies the setup costs.





Hope you are having fun!



Thanks

George Mizzell

Engineered Concepts

1836 Canyon Road

Birmingham, AL 35216

[Littlescreamers]

"Quote" (From George) you might be wanting radial magnetization and the neo material cannot be magnetized like that.

well we are doing it.

I have taken a step further now! Now for sure I am the first on this design so I really don't care. Funny how people know more about what I have done then me?


Scott
Littlescreamers.com
#1 in micro power

[ScubaSteve]

What does that have to do with the price of tea in China?

You've got a point though, I'm pretty sure every motor manufacturer buys their arcs from George, so if he said you were the first, I guess you're the first.

Honestly this is pretty sad. How about NOT hijacking this thread.

[latrans]

Scott,

I generally try to ignore you and your B.S. but I can't let this one go, Did you seriously post George's cell phone # on the web just to make your point? That sucks.

[Littlescreamers]

You know how all this started? It was not me! I just tried to defend myself and this is what I get? First time I was called a liar was on this site. I don't take that well :mad: First time was a couple years ago and I was posting the results from my testing on the new motors with the new magnets and I was called a liar by many that my numbers were doctored and that my motor could never do what I was claiming! I tried everything to get them to believe in me, But to no avail. So I ended up sending one to the good O Dr. Kiwi and only after he posted that he was getting the same
as I did everyone stop saying I was full of bull :censored: Now I have to do it all over again with my designs?

I have nothing to gain by lying about what I am doing or have done. :confused:

Scott

[ScubaSteve]

I notified the mods to delete George's cell. Also let George know in case his phone starts ringing. :(

[kcar]

Well, it happened. Scott hijacked another thread. Is anyone
else getting sick of this bullpucky? I was reading a thread about
'If it is possible to have too much magnet', and now it's
this infantile stuff about who was first to have curved mags.
Who cares Scott?!?!? Start your own thread called
"I was the First....bla bla bla" then go on to toot your horn some more.

Kcar

[ImaBiggles]

HERE YE HERE YE!!

LET IT BE KNOWN TO ALL THE SCOTT IS OFFICIALLY 'THE MAN' - HE INVENTED N50 MAGS, MADE THEM CURVE, AND WAS FIRST TO PUT THEM INTO AN OUTRUNNER MOTOR. HE WORKED WITH AL GORE TO INVENT THE INTERNET. HIS CNC SKILL ARE BETTER THAN N.A.S.A.'s. HE DEFINES CUSTOMER SERVICE. HIS TECHNOLOGY TOPPLED SMALL GOVERNMENTS. ALL OTHER BRUSHLESS MANUFACTURES BOW DOWN IN AWE AND FEAR!

So it has been said, so it is done!

[ScubaSteve]

lol, don't forget the flaming cartwheel. Too bad Bam Bam Bigalow stole it... ;)

[sniderea]

I just read through this thread and it seems like Littlescreamer Scott "started" it again. I could care less who was the first to do X. I just care who does X the best now.
I agree with latrans, why post someone's cell phone # and invite people to call for reasons that don't help George's business at all. I hope you've offered to pay the cell bill.
You don't have anything to gain by lying, but you have a lot to lose with all the ranting. Grow some thicker skin and learn some humility. I bet it would improve your business. I'm certain my next motor won't be a little screamer.

[latrans]

So are we now the ones hijacking this thread? Those that live in glass houses.....................

Lets get back on topic people this is a subject that I have an interest in.

Latrans

[ScubaSteve]

From what I gather from my countless years of experience ;) there is, as mentioned, a point of diminishing returns when referring to magnet thickness. I know there are some LRK motors out there using 3mm thick mags. Most you'll see though is 2mm. With motors our size, going 3mm adds more of a weight penalty than a benefit.

In larger motors, where keeping weight to a minimum isn't always the first thing on the list, people sometimes choose larger magnets thinking bigger is better. All depends on your application I guess. Remember that the stronger your mags are, the hotter you must wind the motor to achieve the target RPMs/volt (aka "Kv").

[KenSt]

The answer to this question was handled fairly well in the first page of posts. To summerize: Too much magnet is possible, whether they are curved, straight, Neo or ceramic. Diminishing return for your money and weight are the result. Once the iron in a motor is saturated, no further increase in the field will increase perfomance.

Scott, please try to stay constructive and on topic, you're only hurting your own business. A good product should speak for itself. If you think yours does then just relax.

[latrans]

Ken,
I gathered all that but I wonder if there isn't more to. I think that its more than just magnet size but also strength, shape, air gap, space between magnets, # of magnet poles, flux ring thickness, size in relationship to stator heads etc. etc. all play a role in a larger equation. By example read post #138 in the link below

http://www.rcgroups.com/forums/showthread.php?t=454407&page=10#post4874946


Latrans

[Littlescreamers]

Quote!
why post someone's cell phone # and invite people to call for reasons that don't help George's business at all.


I agree that was lame and I will remove it!

Scott
Littlescreamers.com

[Littlescreamers]

OK
I will stay out of this thread. But If I was not attacked I would not reply?

Scott

I'm on the phone with george right now, And he says no problem on the phone # And told me "Get over it" They don't know

Scott

[landru]

Increased weight, higher cost?

Perhaps more important than either of factors is another effect that hasn't been mentioned here yet: elevated Io. Stronger magnets increase the no-load current of a motor (Io) and thus decrease the motor's maximum efficiency — and move the point of maximum efficiency higher in the current range.

In practice, the operational efficiency of the motor depends on the load, too. For that reason it is hard to generalize on the effects of stronger magnets. For example, I have tested cases where switching from 4mm wide N50 magnets to 5mm wide N50 magnets caused a significant drop in part throttle efficiency, but also a significant increase in efficiency at WOT (for a given prop, all other factors being equal). Of course, the maximum achievable efficiency dropped slightly becasue of the higher no-load current.

Another way to think of all this is that changing magnet strength significantly changes the power curve of the motor. That change in motor characteristics can be used to advantage. Conversely, it may be detrimental.

I can post some graphs if there's any interest.

Andrew

[ImaBiggles]

OK back on topic. I believe you can have too much magnet coverage based upon my experience with the original komodo double. The curved mags has next to no gap between mags in them. It would have a tendency to freak out some ESC's. It is a combination of stator laminate thickness, mag coverage, mag strength etc I believe. There is a thread about the originat Komodo singe that has a very good discussion about mag coverage and laminate thickness. Worth a read. That being said, I believe the easiest way to determine the answer is through experimentation on a motor. What may work well for one motor (like 100% coverage) may blow chunks on another with a different stator.

[KenSt]

Laterns, YES! :), all of that! The number of equations is so big that there are software companies out there whose sole product is magnetic analysis programs to help optimize the magnetic circuit. In fact, I just sat through a demo of one just the other day here at work! (I am a tool designer of a DC servo motor company here on the east coast and get involved with motor design from time to time) There are equations and tests you can do to solve all of the variables you mentioned and that's what they did before computers. Software just gets you a whole lot closer on the first shot before investing $$$$ in prototypes and trial and error.

Little things can make a difference. For instance, in an outrunner motor, the outer can thickness can be proportionally thinner than a brushed two pole motor such as Astro flight makes. The reason is that opposite pole magnets are right next to each other in the outrunner, so the flux only has to go a short distance. With the brush motor, all of the flux has to go half way around the motor. Mr. Boucher knows this and machined his housings to be thicker at the best point and thinner where he didn't need as much flux carrying capacity and thereby saved weight!

So,... if you use a NN, SS, set up for your outrunner magnets, technically the can should be slightly thicker than one that you have for the standard N, S, alternating pole set up because the stronger flux of the combined magnets has to travel between four magnets not two.

Each variable you mentioned has its own set of consequences if not done optimally. Lamanation material alone has its own industry and science. There are dozens of lam materials to chose from, and thicknesses. China can't get some of the stuff we can here in the states. Some of it is very expensive but does a fabulous job. I could go on for hours.....

Ken Stinson

[Ron van Sommeren]

Thanks for the info. AS i stated i did pull the magnets out and will try 10 spaced. I did think of finding a different stator but it i found it to be to much hassle so i try this first. i will report back.JoeDon't forget to glue them in alternatinly: N S N S ...

Do-it-yourself motor homepages, manuals/tutorials, checks and tests in the first message of this motor builders tips and tricks thread. The checks and tests may save you from frying your controller. Thread is active, bookmark it for future refence and subscribe to it:
http://www.rcgroups.com/forums/showthread.php?t=240993


Vriendelijke groeten ;) Ron
• diy motor building tips & tricks (http://www.rcgroups.com/forums/showthread.php?t=240993)
• diy outrunner discussion group (http://www.yahoogroups.com/group/lrk-torquemax)
• int. E fly-in & diy outrunner meet (http://home.hetnet.nl/~ronvans/), June 25 2006, Nijmegen, the Netherlands

[ScubaSteve]

LOL honestly i was wondering when Ron was gonna pop in with the tips and tricks thread. ;)

[mistairjoe]

Well to throw you a curve...Has anyone come up with this layout and what effect would it have ?

[olmod]

I havent but i did the same to the laminations on a 20mm thick stacked stator :)

[sneu]

Well to throw you a curve...Has anyone come up with this layout and what effect would it have ?


Less cogging--and a little less efficiency.

Steve

[kcar]

What advantage would mags on a diagonal be?
And how would the ESC cope with it?
Or are you just joking? April fools a little early?

Kcar

[Ron van Sommeren]

Linear motors have diagonal magnets for less cogging. Better accuracy (e.g. the motors in www.asml.com or industrial textile inkjet printers www.stork.com).

It would be difficult to position the magnets diagonally in the motor before glueing them in, even curved magnets.

Vriendelijke groeten ;

[INewton]

kcar,

Skew rotors reduce the ripple in speed which is important in some applications. Unfortunately motor power is also reduced. :(

[Micro Dan]

I don't have and high tech explanation but i have noticed in the countless number of tests i have done, that the smaller the gap is between magnets the better the motor performs.
Dan

[jj1]

Agreed, smaller AG/or better magnets increases noload current, but maximum power will be even more better or the same thrust can be achieved with smaller current. Have some data here:

Same stator, 4 different Bells, 7Volts, Gws 8x4,3 300g thust on Imax:


Bell 1, N45 5x4x1,5 AG 0,11mm Io 0,45A Imax 6,0A
Bell 2, N45 5x4x1,5 AG 0,23mm Io 0,40A Imax 6,2A
Bell 3, N50 5x5x1,2 AG 0,65mm Io 0,35A Imax 6,9A
Bell 4, N45 5x5x2,0 AG 0,18mm Io 0,52A Imax 5,8A


-JJ

[KenSt]

Dan, you are correct, but there are some specifics to it. The flux chooses the path of least resistance. So the air gap between the rotor and the magnet must be less than the air gap between two adjacent opposite pole magnets. If this is not done the flux will cross the air gap between them and short out the magnetic circuit, instead of going through the lams like we would like. I would think there is an optimum ratio for this but I don't know what it is. I'll ask around here at work to see of anybody knows, unfortunately the Engineer I used to talk to has moved on.

[Micro Dan]

that is very interesting.
i hope you can find the optimum ratio to share with us.
thanks
dan

Dan, you are correct, but there are some specifics to it. The flux chooses the path of least resistance. So the air gap between the rotor and the magnet must be less than the air gap between two adjacent opposite pole magnets. If this is not done the flux will cross the air gap between them and short out the magnetic circuit, instead of going through the lams like we would like. I would think there is an optimum ratio for this but I don't know what it is. I'll ask around here at work to see of anybody knows, unfortunately the Engineer I used to talk to has moved on.

[ImaBiggles]

Dan, you are correct, but there are some specifics to it. The flux chooses the path of least resistance. So the air gap between the rotor and the magnet must be less than the air gap between two adjacent opposite pole magnets. If this is not done the flux will cross the air gap between them and short out the magnetic circuit, instead of going through the lams like we would like. I would think there is an optimum ratio for this but I don't know what it is. I'll ask around here at work to see of anybody knows, unfortunately the Engineer I used to talk to has moved on.


Is this why the orginal Komodo double had some issues? the mags of opposite poles touched.

[Ron H]

Experiment gone awry. Motor was a Mabuchi 300 to start with, can kept but mags were replaced with n-50. Gap huge, so armature replaced with a rewound (several times) VCR motor and checked at different voltages. At no time could the motor keep up with the stock magneted motor. Amp draw did drop, but heat went way up. So much so, the testing was abandoned.

Magnet arrangment was tested from 4x4per pole, to 10x1 and any configuration in between.

Conclusion was the brushes cannot support the current of the now far stronger motor.

[KenSt]

Imabiggles, its not a big problem, it simply weakens the magetic field to some degree. All of the original ring magnets from CD ROM drives have this condition since they are magnetized all at once. Weak magnets like those don't show much difference but stronger ones will. It all depends on the rest of the design as well. Its that magnetic software thing I keep preaching about. :)

[adam_one]

I think the strength of the magnets and the size of the stator are interdependent for better efficiency and power/weight ratio.
To get the benefits of the stronger magnets it's needed more current and also a bigger stator core so it doesn't get saturated.
jj1 got the same thrust with smaller current because stronger magnets reduced the motor's Kv.

[Ron van Sommeren]

I don't have and high tech explanation but i have noticed in the countless number of tests i have done, that the smaller the gap is between magnets the better the motor performs.
DanReluctance (= 'magnetic resistance') is lower -> higher flux -> more torque and lower rpm. I.e. as long as there is no magnetic saturation of the iron anywhere in the magnetic circuit. At the cost of slighty lower efficiency due to higher iron losses.

Prettig weekend ;) Ron

[mistairjoe]

Here are my results with 10 cuved magnets.At start up motor haunts quiet a bit at low throtle. Prop 9.6, volts 10.8 from a 9 cell 1100GP nimhs, Watts 135 Max, Amps 18,. At this point the motor cuts out, it did get a little worm but will restart again . 25 CC esc is used did not get hot.

[Ron van Sommeren]

Houw many statorpoles?
What winding diagram?
Magnet wrong way round: N S N S etcetc.

Vriendelijke groeten ;) Ron

[ScubaSteve]

...the air gap between the rotor and the magnet must be less than the air gap between two adjacent opposite pole magnets...
Rotor and magnet or rotor and stator?

Also, I've got a letter from George regarding magnet thickness and the "point of diminishing returns" I meant to bring to work with me... Good info, I'll post tomorrow.