Help - Magnet replacement and installation

[_Dekker]

The magnets are the original ones, so I have 4 left for each motor.
Benefits:
-Less eddy current losses (=heat)
-hopefully a little bit more efficient.
-lighter motor

[powercroco]

Originally Posted by _Dekker

The magnets are the original ones, so I have 4 left for each motor.
Benefits:
-Less eddy current losses (=heat)
-hopefully a little bit more efficient.
-lighter motor

what I miss in berts post
(basing on our findings in the same experiment some years ago)

in positive effects:
-less work for the esc (5/7 switches per round compared to 14poles)

negative effects:
- only 10/14 of magnetic conterpower because of less magnetcoverage caused by using the original magnets = less torque power for the same winding
- longer way for magnetic field lines in the backiron = more losses there
- without additional backironthickness = more fluxdensity there
- more turns are needed for the same n spec = higher internal ohmical resistance + higher copper weight

without rewinding someone will get a slightly lighter motor (4magnets removed = -23g of the 500g motorweight = -5% for P 800) with about 20% higher n spec and less torque and better low load efficiency by about 3-4% at low load and will pay for it with a lower efficiency at high load.
for the normal pilot it can bring about these 3-4% in flight duration.
with a normal esc at higher rpm easier handling, less warming in esc.

combined with an improved rewinding and the right magnetcoverage the way from 14 to 10 poles can be a sensful solution for someone.

btw. it's the same, what kontronik did by developing the 10 pole "pyro 30-xx" basing on its 14Pole predesessor "kora-top".

[omerco]

If the motor is used for a heli (governed headspeed) the work on the ESC will not change much:
lower magnet count will give higher KV, which leads to lower pinion and higher motor RPM so the magnetic RPM will be +- similar (compared to 14P lower KV highr pinion and lower RPM).

[1BOHO]

Does more copper winding weight for the same Kv in the lower pole motor necessarily mean a heavier motor in spite of the absence of 4 magnets?

In the case of governed head speed if the Kv is higher,rpm is faster for the lower pole can we assume in that scenario that the lower pole motor never had the extra winds put on it to match Kv? So wouldn't it be lighter in this case?

How does power to weight play into aircraft?

Seems like a comparison was made at the same Kv then one at different Kv . Which is the fair comparison what are the controls?

[omerco]

If you put less windings you use thicker wire so copper will roughly weigh the same

And if you use 10 magnets instead of 14 you will want to maintain the magnet coverage so it will also weigh the same roughly, unless you just pull out 4 and re align the rest which will give less torque

[1BOHO]

No question about reducing the windings on the 10 pole for higher Kv. It's already higher than a 14 pole with the same amount of winds. In your scenario I thought your post proposed a smaller pinion to match head speeds. In that case wouldn't the 10 pole motor be lighter simply because it has 4 less magnets?

Does the required extra windings to match the 14 poles lower Kv on a 10 pole motor weight more than the 14 magnets on less winds?

As far as magnet coverage is concerned.
I was under the impression that Dekker used the original magnets in his reduction from 14 poles to 10 poles by the statement "the magnets are the original ones...."

[omerco]

I was referring to what The discussion Powercroco wrote and not necessarily to what Dekker did - If you keep the magnet coverage as you should changing between 10-14 they will weigh the same.

If you keep the copper fill, as you should, also the winding will weigh the same for the same kv. The wire size will change.

[1BOHO]

Can you have a magnet much wider than the arms hammer on FSCW motors slotted stator and not begin to have a significant change in the BEMF signal creating detrimental effects on some ESC's ability to time correctly?

If the wire size went smaller and length longer for more turns wouldn't all that add up to more resistance and less current carrying capability in the 10 pole motor? Wouldn't it be better to leave it lighter as would be seen with the native wind and use the smaller pinion to let it run at the higher rpm to help negate the effects of it's higher cogging torque?

[omerco]

For the first question I have no knowledge to answer.

For the second - yes it would and would be possible on a heli. Also when I wind for heli I aim for the lowest pinion I can allow mechanically in order to get the highest kv = the widest and shortest wire.

But that is not always possible with a plan when the prop dictates a certain rpm with direct gearing, and also on some helies, like the logo 690, where the pinion has a mechanical minimum limitation.

[kircoff]

hi , i have a 850mx and magnet fail . where to buy the magnet?

[1BOHO]

@Kircoff

Wow, Beautiful rewind. Did you do it? Is "850 MX" an align motor? Try Align for replacement if that's the case.
http://www.align.com.tw/contact-en/

@Omerco
In my mind the benefit of a motor with better a better n spec would be you could get the benefit of more torque (lower KV) with larger wire and less turns. This way you can really carry the amps to develop strong torque.From what I hear there are a few advanced engineers/motor builders that have actually built and run direct drive heli.

SCHWEIZER 300C RC SCALE MODEL HELICOPTER WITH DIRECT DRIVE / Treffpunkt Modellbau Paaren 2016 (5 min 53 sec)

You can see direct drive 250kv motor in snapshot and at 1:57 mark in video

[kircoff]

thanks ,yes align 850mx and gma is my logo for motor rewind
but is second case the magnet fail on this model

rewind is 6+5 yy x1.40

[1BOHO]

Cant tell from photos what actually happened. Did pieces of the magnet just break off?

[omerco]

Originally Posted by kircoff

hi , i have a 850mx and magnet fail . where to buy the magnet?

It was hard for me to find magnets. Aligns are not the best quality and I think they sell. You could try...

I found many on aliexpress but can't guarantee the quality and shipping rates were very high

From your pictures we can see the can hit the stator. Bearing issue? Alignment issue?

On the one I got the can wasn't glued straight into the can causing similar marks.

[omerco]

Originally Posted by 1BOHO

@Kircoff

@Omerco
In my mind the benefit of a motor with better a better n spec would be you could get the benefit of more torque (lower KV) with larger wire and less turns. This way you can really carry the amps to develop strong torque.From what I hear there are a few advanced engineers/motor builders that have actually built and run direct drive heli.

You can see direct drive 250kv motor in snapshot and at 1:57 mark in video

You need to relate to the torque at the end of the drive train: if you take a higher kv 10 p motor with less torque compared to 14p with higher torque you use different gearing to get similar rpm on the heli's main shaft. This gearing will also give similar torque on the main shaft.

But the difference will be in efficiency- to my understanding from this forum and inspecting some wind calculators a 14p motor is less efficient than a 10p one. Same as if I need to rewind for lower kv with thiner and longer wire.

Eventually I did do something similar to your suggestion - if I rewind that motor it would go in my logo 690 where I need around 430-440 kv. With the 14p I can use thick wire to get that.

For the direct drive use: we use a reduction of more than 10:1 on our helies using 12-14 Lipo cells. To reduce kv in such a way without using a bigger much heavier motor would be impossible imo.

Also note that direct drive train heli uses only 3 cell Lipo. It is probably unable to use higher count cells due to the direct drive and also no higher amps and power due to that.

[kircoff]

hi, in one case the magnet is cleavage , in the sencond for my opinion is internal bearing and damage the magnet. so how to find magnet ? align is not send magnet . Alternatively I would like omerco 14 magnets but do not know where he found them

[omerco]

Those are scorpion magnets. You could try them

[powercroco]

GMA = Mauro Ghezzi?

[1BOHO]

@Omerco

"But the difference will be in efficiency- to my understanding from this forum and inspecting some wind calculators a 14p motor is less efficient than a 10p one. Same as if I need to rewind for lower kv with thiner and longer wire."

Same as? If you had to rewind for lower kv longer and thinner wire to mathc the Kv wouldn't that actually make the 10 pole less efficient than the 14 pole? it would be a higher resistance but the same Kt.

I can also believe as it is stated in post #22, that at hi loads the 14 pole would be more efficient. I believe this is partly because at high loads the rpm could concievably be less and the 14 pole has less cogging torque (wind calculator shows a higher LCM for 12N14P). From my understanding the motor with higher cogging torque will suffer more from torque ripple at lower rpms. In essence if you are already geared for a higher Kv 10 pole it would be better to step up to 14 poles and rewind shorter and larger wire to match the Kv of the 10 pole. The extra work placed upon a properly designed esc can be managed to a degree by selecting the appropriate PWM frequency, and quite naturally the lower resistance wind can carry more current before loss.

PWM frequency=Kv x Volts (nominal you are using) x Pole count / 20

[omerco]

Forgive my English : by same as I meant you would loose something in both cases. I can't say where the loses will be higher.

And you contradict yoursels writing once the rpm would be lower and then that you would use the same kv. The second option is the one I would use. Always aim for the smallest pinion getting lower resistance.

Most of the better manufacturers use 10p. Isn't there a good reason for that? Also I can tell you an engineer friend of mine has tested many motors lately for a specific project and found the kontronic 14p producing a problematic behavior effecting especially on the efficiency side. He showed the results to kontronic who were very puzzled of his discovery and couldn't well explain it.