BLDC Rotor Design

[The-Axial-Hunter]

Hello everyone,

I am working on building a new rotor for a small brushless motor used for a radio controlled boat. I am stuck in how to create the core of the rotor. I have been looking into some of the designs that are used in existing motors but I can’t tell exactly what they are made from. I hope someone here can help me.

Firstly, I disassembled an old rotor that was used in a motor that I burned out some time ago. The motor uses a lamination stack that is pressed onto the steel shaft of the motor. Then the magnets are glued in.

In my research, I looked at Neu motors rotor but it looks like the shaft and rotor core are once piece. Ie. The shaft was originally the diameter of the rotor core and then turned down at the end of the magnets to make the desired shaft size. Similarly, I watched a shop tour of Cordova research and there rotor core also looks to be one piece with the shaft.
Can anyone confirm if this is a viable way to do it or does it need to be lamination to reduce losses? Or am I looking at the parts wrong and they are indeed laminations, not one piece?

I have added some photos. For reference the shafts are 5mm on the Neu (black) and 8 on the Cordova (bare rotor core, no magnets). I believe the inside diameter of the magnets is approximately 10-12mm.


Thanks!

 

[amberwolf]

Note that the laminations would be in the stator, rather than the rotor, generally.

Generally the laminations are there to reduce fields / currents flowing in places and directions that don't help the motor move, and can counter some of the fields / currents that make the motor move.

Having those stray fields/currents reduces the amount of power that acutally moves the motor, and increases the amount of power that becomes waste heat.

The thinner the laminations, the less of these fields / currents there are, and the more efficient the motor can be...the faster the motor spins the more important this may be.

but the thinner they are the more of them there are and the more tiny wasted spaces there are between them (coatings, airgaps, etc), thus the less dense the flux may be for a given mass, and at some point it may affect efficiency.

it also costs more to use laminations both to make them and to assemble with them.

So a really cheap motor a company builds lots and lots of may not use lams just to save a penny or few on every motor, whcih adds up to serious money pretty quick.


There's some threads about laminations / etc around the motor technology subforum, and some discussions with in specific motor threads here and there, including some hubmotor discussions (like the one for the leaf hubmotor)

BTW, your pics are too blurry to see any detail in them, and the 3266 pic is so far away from the item being shown that it doesn't show anything. Both of them have sharper stuff in the image than the item being imaged, so the camera *can* do it, it's just not being focused on the item in question.

I recommend taking your pictures outside in direct sunlight, no flash. This usually makes the camera / phone focus much better on the subject, and especially with phones makes the shutter response much faster when you touch the "button", so there is a lot less time for shaky hand movement to blur the image.

Something to securely hold the camera *and* the subject in fixed positions relative to each other will also help.

 

[The-Axial-Hunter]

Note that the laminations would be in the stator, rather than the rotor, generally.

Generally the laminations are there to reduce fields / currents flowing in places and directions that don't help the motor move, and can counter some of the fields / currents that make the motor move.

Having those stray fields/currents reduces the amount of power that acutally moves the motor, and increases the amount of power that becomes waste heat.

The thinner the laminations, the less of these fields / currents there are, and the more efficient the motor can be...the faster the motor spins the more important this may be.

but the thinner they are the more of them there are and the more tiny wasted spaces there are between them (coatings, airgaps, etc), thus the less dense the flux may be for a given mass, and at some point it may affect efficiency.

it also costs more to use laminations both to make them and to assemble with them.

So a really cheap motor a company builds lots and lots of may not use lams just to save a penny or few on every motor, whcih adds up to serious money pretty quick.


There's some threads about laminations / etc around the motor technology subforum, and some discussions with in specific motor threads here and there, including some hubmotor discussions (like the one for the leaf hubmotor)

BTW, your pics are too blurry to see any detail in them, and the 3266 pic is so far away from the item being shown that it doesn't show anything. Both of them have sharper stuff in the image than the item being imaged, so the camera *can* do it, it's just not being focused on the item in question.

I recommend taking your pictures outside in direct sunlight, no flash. This usually makes the camera / phone focus much better on the subject, and especially with phones makes the shutter response much faster when you touch the "button", so there is a lot less time for shaky hand movement to blur the image.

Something to securely hold the camera *and* the subject in fixed positions relative to each other will also help.

Hi, thanks for your reply! Sorry about the images, I know they are blurry but I could only get screen shots from a video I found. I wanted to include something haha.

The cheap motor I took apart did have laminations in the rotor, while the other more expensive ones do not appear to have any laminations at the core of the rotor (just the material of the shaft). Does that not affect performance since the rotor moves with the magnetic field? I would assume that if the laminations offered a benefit the more expensive motors would use them.

I just want to make sure I am understanding you correctly.

I will search for some other threads.

Thanks again for your detailed response