What is the maximum allowable Air gap(mag& stator) for GBx build?

[BlazerB52]

Got parts to build GBx motor. Single, Double and Triple and 22.7mm stators. When I try to use the magnets I have:

5x4x1mm flat
5x5x1mm flat
5x5x1 curved
5x5x2mm curved

I either have to big of Gap? Or the mags rub the stator. Do you have to turn down the stator.

Same problem with 20mm build also.

Using the bought stators, not stuff robbed out of cd-roms.
Thanks

[fly_boy99]

Your best answer is to go consult the GoBrushless rotor
calculator.

Try and get between .15 and .30 airgap... of course lower is better.

[olmod]

On the gobrushless site there is a caculator for working out drum sizes for flat magnets,the magnetic gap controls a ballance of torque and speed the closer the gap the more torque and efficiency is what ive found from experience generally speaking. do not try and turn the stator down the legs of the teeth will bend out of shape no matter what others say,what you can do is use a fine flat mill file or a diamond file and while spinning hold against the stator and you can reduce the diameter that way without distorting the teeth.hope that helps . cheers :)

[BlazerB52]

Wanted to ask because it seems that half the stuff I am building seems to have a rub issue. And have not read on here(rcgroups) people with this many problems. Just wondering if I am doing something wrong or is it just part of the build process. Have a 20mm double and can barely get a .002 feeler guage between the stator and mags. The stator ends do not have enough to file down to get bigger gap. Used 1mm curved magnets. Do they even make .9mm curved to use instead? :confused:

[BlazerB52]

The 22.7 stator build on GOBrushless site I was trying to duplicate build #GBL_00015 which is 14T of 24 Gauge(man that was hard to wind)WYE 5x5x1mm mags N48
12 magnet poles

Says I should have a air gap of .9928mm---seems large to me?

[peterp1964]

Wanted to ask because it seems that half the stuff I am building seems to have a rub issue. And have not read on here(rcgroups) people with this many problems. Just wondering if I am doing something wrong or is it just part of the build process. Have a 20mm double and can barely get a .002 feeler guage between the stator and mags. The stator ends do not have enough to file down to get bigger gap. Used 1mm curved magnets. Do they even make .9mm curved to use instead? :confused:

are you sure you don't have excess glue sitting on the magnets facing the
stator shoes ? what I do is this: when mags are in position I put a bead of
medium ca on top between mag and flux ring...once dry I remove the
magnet spacer, throw the can by the shaft on the dremmel and then I roll
the can by hand one rev while dripping thin ca as it goes around. Without
wasting time I grab a toilet-paper tube, put the can in it and spin it.
Finally, I use medium ca between the mags and spin that too with the
dremmel. After an hour or so I take an xacto blade and carefully clean the
mag surfaces...no rubs. The GBx stuff is designed for no rubs _provided_
the stator was not distorted during pressing it on the bearing tube.

Peter

[peterp1964]

The 22.7 stator build on GOBrushless site I was trying to duplicate build #GBL_00015 which is 14T of 24 Gauge(man that was hard to wind)WYE 5x5x1mm mags N48
12 magnet poles

Says I should have a air gap of .9928mm---seems large to me?

yes, this is too large a gap. If you're using the GBx bell+flux ring then you
should use 5x4x2 mags or the GBx curved mags from www.strongrcmotors.com

Peter

[BlazerB52]

I use the spin bell in drill with paper tube method. Also I go back with x-acto knife and clean any glue off magnet surface. I am using Black CA to glue magnets. Magnets that I was going to use are the curved 2mm magnets and I don't have a gap. When i put measurments in the gobrushless rotor calc says I have a negative gap. Put 2 magnets(oposite each other) in bell and slipped on stator and just barely able to go in. No gap. :confused: All my stuff is GBx.

[olmod]

try blueing the ends of the teeth with a black marker pen when dry try a turning fit into your drum then examine the rubs on the teeth ,you may have an off centre stator to bearing tube situation and the only way to fix is to dremel sand away the high spots that have rubbed and recheck.that is if the drum is true to the shaft.

[peterp1964]

IMagnets that I was going to use are the curved 2mm magnets and I don't have a gap. When i put measurments in the gobrushless rotor calc says I have a negative gap. Put 2 magnets(oposite each other) in bell and slipped on stator and just barely able to go in. No gap. :confused: All my stuff is GBx.

something's wrong...the ID of the GBx can is 27 mm, the stator OD is 22.7,
with 2mm curved mags you have an airgap of 0.15mm. The GB calculator
only works with flat magnets. Can you post a link to what can you have ? is it
like this ?

http://www.gobrushless.com/ccp51/media/images/category/CCDR_logo_lg.gif

Peter

[BlazerB52]

Here is pics of some of my stock. Measured cans and these are the measurements. They are GBx.

27.15
27.17
27.13
27.18

22.64

[peterp1964]

you got the right parts...I guess you have to determine where the rubs are
to figure out whether the flux-ring got distorted upon pressing it to the end-bell
or the stator got distorted or the shaft is out of alignment.

Peter

[BlazerB52]

I use a small pinion press. And when I spin stator in the bell. I dont see any wobble. Feeler gauge seems to be the same all the way around bell between mags and stator..

[peterp1964]

I use a small pinion press. And when I spin stator in the bell. I dont see any wobble. Feeler gauge seems to be the same all the way around bell between mags and stator..

so what makes you say you have mags rubbing on stator ? sound ? can it
be coming from the bearings ? the 2mm curved mags make the can slam
onto the front bearing if you don't hold onto it as you're inserting it.

Peter

[BlazerB52]

The feeler gauge I am using is only .002". For 20mm motor.

And that is even a chore to get it in it.Thats why I was asking the original question.

That is why I think it is why it is still rubbing. Put some marker on stator and is okay hand turn. But when I chuck it up in drill it rubs a little in the center where two stators are joined. I have sanded it down as much as I feel safe. That is why i was asking for help was not sure if my parts are the right stuff(magnets,ect.)

Some of the confussion is my fault I am building two motors at the same time a 22.7mm and a double 20mm. Both have same issue: 20mm has magnets glued and rubbing, but 22.7 does not have magnets glued due to fit issue.

By the way I appreciate the help.

[olmod]

After filing or sanding make sure you get rid of the dust,i use on the end of a wooden skewer a dollop of automotive sticky black putty that i force into the nooks and crannys of the drum ,and compressed air for the stator, ;)

[BeavrdamElectric]

The 22.7 stator build on GOBrushless site I was trying to duplicate build #GBL_00015 which is 14T of 24 Gauge(man that was hard to wind)WYE 5x5x1mm mags N48
12 magnet poles

Says I should have a air gap of .9928mm---seems large to me?

The motors using 5x5x1 magnets are GBv motors, using the stock can. 22.7 GBx motors should use 5x4x2s as Peter stated.

If it's any consolation I've had problems with GBx endbells too. One of the first motors I got was a triple that has never run, it has .003" runout in the face of the endbell. I got a lathe so I could make my own parts but haven't gotten around to fixing that problem yet. I've had less problem with the Strong setscrew versions but you have to be very careful with the tiny set screw. It's a fine line between slipping and stripping. A flat spot on the shaft would help.

Good Luck!

[ImaBiggles]

On the gobrushless site there is a caculator for working out drum sizes for flat magnets,the magnetic gap controls a ballance of torque and speed the closer the gap the more torque and efficiency is what ive found from experience generally speaking. do not try and turn the stator down the legs of the teeth will bend out of shape no matter what others say,what you can do is use a fine flat mill file or a diamond file and while spinning hold against the stator and you can reduce the diameter that way without distorting the teeth.hope that helps . cheers :)

The only problem with grinding the teeth is that you will typically grind them and increase the electrical conductivity in the head. The more conductivity you have, the thicker the stator laminate 'appears' to the motor. The net result is that you rob the motor of some efficiency. Not a big deal, but something to be aware of. . . .

[Ron van Sommeren]

The bigger the magnet-tooth gap, the higher Kv and the lower Kt, the motor character changes, that's all.
Ironlosses will go down, hardly noticable though.

Prettig weekend ;) Ron

[olmod]

The only problem with grinding the teeth is that you will typically grind them and increase the electrical conductivity in the head. The more conductivity you have, the thicker the stator laminate 'appears' to the motor. The net result is that you rob the motor of some efficiency. Not a big deal, but something to be aware of. . . .
Its not electrical conductivity you should be concerned about,its magnetic lines of flux shorting accross the laminations and if you wish to remove any burring, the area can be washed with a little hydracolic acid and thoroughly rinsed with water after the acid has done its job ,but ive tried both and found no difference to performance, the reason may be that the lines of force prefer to travel in a straight line accross the magnetic gap just like iron fillings between the ends of 2 bar magnets held apart with a small gap.

[ScubaSteve]

BeavrdamElectric, pm me mailing info and i can replace that endbell.

[fly_boy99]

excess glue on the magnet faces? possible spacers getting
in the gap?

Most likely the shaft is not true and is hard to tell from just looking
at it. Get a dial indicator guage and check for true-ness.

B

[BlazerB52]

Started to measure everything again. Found what was throwing me off. The magnets were suppose to be 1mm thick but are actually 1.2mm thick. Guess I will have to wait till I come across some stators (from junk cd-rom drives)that will fit better.

[Ron van Sommeren]

It's not electrical conductivity you should be concerned about,its magnetic lines of flux shorting accross the laminations ...ImaBiggles was right, insulation between laminations is needed to reduce eddy currents (= losses). The magnetic field is not bothered by the insulation between laminations.

Prettig weekend ;) Ron

[BlazerB52]

Gave away my dial indicator gauge to a friend. Never used it. Wish I had kept it now. If I keep building I think I will get another one.

Thanks for input Guy's!!

[peterp1964]

Started to measure everything again. Found what was throwing me off. The magnets were suppose to be 1mm thick but are actually 1.2mm thick. Guess I will have to wait till I come across some stators (from junk cd-rom drives)that will fit better.

this can't be it...flat 5x5x1's will give you 0.9 mm airgap while 1.2mm flats
gives 0.7mm airgap...both way too much.

Peter

[olmod]

ImaBiggles was right, insulation between laminations is needed to reduce eddy currents (= losses). The magnetic field is not bothered by the insulation between laminations.

Prettig weekend ;) Ron
If that is so why :) ImaBiggles remarked on electrical conductivity :confused: you can place an ohm meter accross most stators and have continuity,most are shorted electrically,the surface finish on the laminations is to try and stop random lines of flux escaping sideways into adjoining lamination ,eg think about mfg of motors like used in mains powered tools they grind grooves into stator heads to ballance their armatures and cause laminations to have continuity.

[BeavrdamElectric]

If that is so why :) ImaBiggles remarked on electrical conductivity :confused: you can place an ohm meter accross most stators and have continuity,most are shorted electrically,the surface finish on the laminations is to try and stop random lines of flux escaping sideways into adjoining lamination ,eg think about mfg of motors like used in mains powered tools they grind grooves into stator heads to ballance their armatures and cause laminations to have continuity.

The laminations do have contact in spots, like where the alignment dimples are and where they contact the support, so they are not totally isolated. But in general they are isolated from each other so the currents can't go straight from one to another in any area. Hope that makes sense.

Good Luck!

[olmod]

Correct beav' im just pointing out the misconception between electrical conductivity and magnetic flow :)

[BeavrdamElectric]

Eddy currents are electrical, aren't they? :confused: If they can flow at the stator tips wouldn't that make the stator act more like a solid piece?

Good Luck!

[peterp1964]

Eddy currents are electrical, aren't they? :confused: If they can flow at the stator tips wouldn't that make the stator act more like a solid piece?

Good Luck!

the laminations help increase the resistance of the core (hence reduce
eddy currents, which are little whirlpools and don't flow in the usual
sense) by providing many paths of small cross-section for the magnetic
flux to travel over. Ideally, there's supposed to be insulation between
the laminations...but in our stators there isn't any that one can
see (right ? maybe the lams are painted with something ?). The dimples
and the sanding of the stator shoes are not detrimental. Maybe that's why
the doubles with cheese came to be preferred over doubles with no cheese.
The cheese (plastic) acts to reduce eddy currents from those in a no-cheese
double of the same thickness.

Peter

[olmod]

Eddy currents are electrical, aren't they? :confused: If they can flow at the stator tips wouldn't that make the stator act more like a solid piece?

Good Luck!
No beav' if it was we could put a wire on each end of a bar magnet and use it as a power scource :)

[BeavrdamElectric]

the laminations help increase the resistance of the core (hence reduce
eddy currents, which are little whirlpools and don't flow in the usual
sense) by providing many paths of small cross-section for the magnetic
flux to travel over. Ideally, there's supposed to be insulation between
the laminations...but in our stators there isn't any that one can
see (right ? maybe the lams are painted with something ?). The dimples
and the sanding of the stator shoes are not detrimental. Maybe that's why
the doubles with cheese came to be preferred over doubles with no cheese.
The cheese (plastic) acts to reduce eddy currents from those in a no-cheese
double of the same thickness.

Peter

Hi, Peter :)

The only partial stator I have right now is a Komodo stator which appears to have a coating on the "exposed" lamination. It isn't conductive except where it's scratched. I'm not going to tear apart a GB stator right now but I'd think a higher quality stator would also have insulation.

I hadn't heard that a double with cheese was preferable, I thought replacing the cheese with lams was. :confused:

No beav' if it was we could put a wire on each end of a bar magnet and use it :)

I'm not sure what you mean. Are you talking about using magnets for stator teeth? :confused:

Good Luck!

[peterp1964]

I'm not going to tear apart a GB stator right now but I'd think a higher quality stator would also have insulation.


thanks Bob...I have a GB stator in pieces and yes, the lams are insulated
with something invisible (I had to really press with the probes of the
VOM to get a resistance reading, even the dimples/bosses are insulated).
So OK on the insulation score, and scratch the cheese stuff I said (it was a
deduction based on a wrong premise!)

But I still don't see much detriment to having the shoe faces shorted out...
Sure, eddy currents will be set up on the shoe areas facing the magnets
as the rotor goes around but I think this isn't that bad.

Here's a way to actually feel the eddy currents (or, rather, their braking
action): let two of the three input plugs touch and try to spin the prop...it
won't spin as much as it will when all three phases are open !

Peter

[BeavrdamElectric]

OK, I'm open to how bad it actually is. Theoretically it's a problem, but maybe not something you could actually measure.

Isn't the resistance to turning a shorted motor caused by generator/motor effects? How do eddy currents affect this? :confused:

Good Luck!

[ImaBiggles]

Its not electrical conductivity you should be concerned about,its magnetic lines of flux shorting accross the laminations and if you wish to remove any burring, the area can be washed with a little hydracolic acid and thoroughly rinsed with water after the acid has done its job ,but ive tried both and found no difference to performance, the reason may be that the lines of force prefer to travel in a straight line accross the magnetic gap just like iron fillings between the ends of 2 bar magnets held apart with a small gap.

I used to always grid a Gbv as it was easier than trying to center the bell. For grins, and since I had about a dozen kits around, I made my "standard" motor (16Turns 26 awg) benched the heck out of it, then ground a couple of the teeth down, benched it again.

Correct beav' im just pointing out the misconception between electrical conductivity and magnetic flow :)

I realize that it is not electrical connectivity, rather some magnetic deal that I dont fully understand- just easier to explain and think of it as electrical, wrong in theory I realize - but what I found was with very modest grinding and no deburring - an 8% drop in power out to the prop with the same power in (lower efficiency). The KV also decreased, despite having slightly larger air gaps on the ground teeth.

Now is 8% significant for 40 watts when it comes to flying? Heck I dont know, but I tinker with motors for a hobby and building as best as I can. The big unknown still for me is how much efficiency and power changes in flight. I even put a wattmeter on my plane and video'd it with my cvs cam in flight. Interestingly - static WOT amps were 13.7 at 10.0V bench - in air WOT resulted in about 10% less watts than bench. Hardly conclusive and it was not the same number with different pitched props - but thats another story . . .
B

[peterp1964]

I realize that it is not electrical connectivity,

actually it is electrical conductivity that one is concerned with as far as
eddy currents go. Steel has high conductivity but putting together a
stator from insulated laminates (instead of making the stator solid steel)
serves to reduce the conductivity of the assembly relative to the conductivity
it would have if it was a solid stator of same dimensions. Hence, eddy currents
are reduced (J=sigma x E, where E is the electric field induced by the motion
of the magnetic field over the stator and sigma is the conductivity).

Peter

[BlazerB52]

peterp1964,

The 1mm thick magnets are curved also. went around each tooth after I filed a little and can see a air gap on each hammer now. Going to wind 11 turns of 24 Ga. This is a double stator.

[peterp1964]

The 1mm thick magnets are curved also.

now I'm at a total loss :confused: My GBx curved magnets are 2mm thick and
there's no rubbing !

Peter

[BlazerB52]

Maybe i am the one being confusing. The pic above bottom left show a stator and bell at the top of pic. It is a 20 mm double same bell front and ring as the 22.7's right below it in picture. Is the 20mm not suppose to be refered to as a GBx also?

[peterp1964]

Is the 20mm not suppose to be refered to as a GBx also?

No :p But it looks very interesting in this pic:

http://www.rcgroups.com/forums/attachment.php?attachmentid=962699

Did you buy this 20mm bell ? where ?

Peter

[BlazerB52]

All my parts are from 3 places. Others were the same appearance,ect. So I got confused and thought they were the same motors. Having same trouble with 22.7mm as the 20mm.

www.cdmotorworks.com
www.strongrcmotors.com
www.gobrushless.com

[NumbSkull]

Okay...

So, I'm a bit confused here.... I have a small rubbing problem in a GBx motor. I've read that it is okay, and that it isn't okay to file/sand the stator teeth a bit.

If I needed to take off a few microns of material from the stator teeth, is it okay to sand/file? I plan to chuck it into a power drill or a dremel, and use some emery paper that I have on hand.

I'm new to this so any advice would be great.

[BlazerB52]

I hope it is okay too. Because I already did it.
And getting ready to wind 20mm double with 11turns of 24 Ga.
I hope all i will lose is a little effeciency and not a smoking motor in the end.

[peterp1964]

All my parts are from 3 places. Others were the same appearance,ect. So I got confused and thought they were the same motors. Having same trouble with 22.7mm as the 20mm.

www.cdmotorworks.com
www.strongrcmotors.com
www.gobrushless.com

OK...how many setscrews, and what size, are there on the 20mm endbell
from cdmotorworks ?

Peter

[BlazerB52]

It has 2 set screws(2.5mm?). Had to add 2 more(2mm) because one was stripped when I got it.

[peterp1964]

It has 2 set screws(2.5mm?). Had to add 2 more(2mm) because one was stripped when I got it.

thanks!

Peter

[ImaBiggles]

actually it is electrical conductivity that one is concerned with as far as
eddy currents go. Steel has high conductivity but putting together a
stator from insulated laminates (instead of making the stator solid steel)
serves to reduce the conductivity of the assembly relative to the conductivity
it would have if it was a solid stator of same dimensions. Hence, eddy currents
are reduced (J=sigma x E, where E is the electric field induced by the motion
of the magnetic field over the stator and sigma is the conductivity).

Peter

See, I told ya I really dont understand it ;) . Anyway, the take home point of my test is that teeth, when ground, can rob you of efficiency.

[ImaBiggles]

Okay...

So, I'm a bit confused here.... I have a small rubbing problem in a GBx motor. I've read that it is okay, and that it isn't okay to file/sand the stator teeth a bit.

If I needed to take off a few microns of material from the stator teeth, is it okay to sand/file? I plan to chuck it into a power drill or a dremel, and use some emery paper that I have on hand.

I'm new to this so any advice would be great.

The motor will work, yes. As I mentioned above, I have many GBv's with ground teeth. As worse, it will rob you of some efficiency - significant is a matter of judgement. Certainly better than having a motor that rubs which can not be used ( or at least can not be used for long).