Magnet dimensions

[GriffinRU]

Well, I thought maybe that would be easy to explain by making it too simple. And when I was talking about magnet power, I was assuming that with segments you can easy pick up similar power magnets to achieve consistent magnetic field across wide selection. But that maybe not true, I haven’t measured magnetic field individually myself and haven’t compared one either.
When I was talking about magnet losing its power, I was thinking about high currents not high temperature. Magnet can be demagnetized with high current, especially when it is cool. While demagnetization with high temperature happens at relatively high temp, so before you reach one something will be smoking pretty well. But on other hand everything possible.

Usually, Eddy current losses in the magnets are ignored, due to the fact that magnet magnetic field and windings magnetic fields are synchronized. However completely cannot be ignored because of braking, accelerating and timing.

There are couple ways to reduce or eliminate Eddy current losses different motor manufactures use different approaches, based on their R&D data. It is known fact that Eddy current losses dependent on the magnetic thickness, air gap, magnet width etc. Eddy-current loss in the rotor can be reduced by either increasing the magnet thickness and air gap length simultaneously, or using segmented magnets for each pole. The increase in magnet thickness and air gap length effectively reduces the effect of armature reaction, while segmenting the magnets reduces the Eddy-current loop areas. Using a shielding cylinder around the magnets (aveox BL motors), segmenting and side-insulating the magnets are popular solutions as well.

Torque – more poles, big diameter, longer can, bigger magnets, smaller air gap
Speed – less poles, small diameter, shorter can, relaxed air gap

And building motor with small diameter but very long can not a good idea because of shaft flex.

Artur

[Serum]

I never heard about a neodym magnet loosing its magnetical strength caused by a too high current. It is know from loudspeakers that the relative poor quality grey magnets can loose some of their magnetic force by dropping them or just loosing strength during the years. Neodym is nothing like that from what i have read. Could you please share your source for the information you have got on these magnets?

[Dafni]

Ja, please share the source. I read many scientific puplications on magnets / rare earth magnets / motors or generators over the last few months, and this kind of information somehow got past me. Please share the knowledge.

[captain harlock]

Yes, please.

[captain harlock]

Probably you might find this site informative to some extent:
www.neodymiummagnets.info/neodymium-magnet.php

[Serum]

I was more interested in the source for the wisdom of griffinru..

[captain harlock]

Wisdom....wisdom?!!....may God grant us wisdom.

Since you have wisdom as well, Serum, may I ask you this question: is a rotor of thinner segments better than one with thicker segments? Daf said that the more thinner are the segments the higher is the effeciency and the weaker is the torque ( correct me please, if I misunderstood) and vise versa.
The kontroniks, the pletts and the lehners, by far ,are the only companies that uses segmented magnets, probably there are other companies I dont know about, but that is fine with me. Why I'm asking this question is because I need to decide whether I am supposed to go with the FUN600-13 with its low price or go for a 1950/10 motor and pay extra 200 dollars( though I know that the 1950 will take down the fun600-13 easily.) I'll be using one of these motors in my future heavy maxx. The fun600-13 is like a L wanderer motor with segmented rotor and the 1950...well, you know it better than I do. Please, answer it this time if you could not answer my PM.

[Serum]

It really isn't about the thickness of the layers in the segmented magnets, it is about efficiency of the motor.

From the experience of all the lehner 19/20 series users on this forum you can tell that the lehners are cool motors, also cool on partitial load, so based on that experience, you can jump to the conclusion that the lehners did a good job on the thickness of the slices.

I have got 0 experience with the kontronics, but my guess is, that they will be great as well. (better than the feigaos because of the segmented magnets) i would not be suprised if they would be simular in performance than the lehners.

I did not meant hisd wisdom in general, i meant his specific wisdom, regardig some stated 'facts' over the neodym magnets.

And i don't see why you need to push your question you did sent me with the PM. really no need for that.

[GriffinRU]

I wasn't focusing on neodym magnets in particular but to create a magnet you need apply current, so to destroy you can do the same. If you look on different magnetic material specs it would be clear that neodym magnets require higher current, but still current (current ratings depend on magnet size). And with stronger magnets what we do? We make motors smaller.
Some of my posts based on information obtain from different sources (some of them might be not available anymore :( ) and some of them from personal experience. Google search brought me this link http://www.cy-magnetics.com/hauptseite.htm some of the information and specs can be helpful.

Artur

[captain harlock]

Originally posted by Serum
It really isn't about the thickness of the layers in the segmented magnets, it is about efficiency of the motor.



And i don't see why you need to push your question you did sent me with the PM. really no need for that.

:) My appologies, modorator.

[GriffinRU]

After reading some posts here and there about which motor is good and why...

I have a question to those who used them and did felt or measured the difference.

What is efficiency difference (in %) between lehner, BK, Hacker, Feigao, Nemesis, Kontronik and Aveox motors.

Artur

P.S. similar size and maybe ratings...

[Serum]

Lehner and BK are the same, as are the nemesis and the feigao's.

I can tell you that normally a lower KV setup on a higher voltage gets less hot. The Lehner motors (19/22 series) are very good. They don't get too hot if geared with sence.

I can't tell you anything from the kontronik or the aveox motors, but like i said before, the segmented kontronik motors would not surprise me, if they are the same quality as the lehners (also being segmented)

Promod is the one who does measure his setup, he uses an eagletree system for this.

I also read that you stated that the Xl size motors (feigao/wanderer/nemesis) are rated for 1200 watts. i've seen a calculation of another member, that said it was capable of pushing out 2200 watts at 92 percent efficiency. not bad at all imo.

I prefer a higher voltage setup, with a bigger low KV motor (such as an 2240 on 6-8S lipo.)

[captain harlock]

I believe all feigaos, wanderers and hackers are similar in terms of effeciency, but the Aveox ( specially the sensored based ones) are weaker than the others. Probably the most powerful are the 19-22 series of lehners followed by Kontronik's full line of motors( all kontronik motors use segmented magnets) and the Tango is the only motor capable of challenging the 22 series ( the 2230 at least).

[captain harlock]

Oh, from what I understood from kontronik is that their motors' effeciency is near 89% at load.

[GriffinRU]

Higher voltage applications will always be more efficient then lower.

And let’s not be so biased with segmented magnets, we talking about 1% max difference. Do not forget about wiring (wire gauge, wire type, delta/star …)

So from what I am reading here looks like we have problem with correct gearing not motors. :)
Do not get me wrong; what I am trying to say is when we select gearing we look upon Kv ratings of particular motor. But there is another factor to consider, efficiency which is not linear at all. And sometimes we need sacrifice something in order to achieve another. Based on your feedbacks lehner motors have better efficiency across wider RPM/Load range then others.

But I am not convinced 100%. Because main argument for lehner and kontronik motors to be the best based on type of magnet used. Is it possible we are missing something?

Artur

P.S. My personal opinion Aveox motors are not that bad.