please help me to understand this motor

[sss]

hello guys
i'm trying to figure out this motor before applying any voltage .
It's an NSK industrial motor , used to drive precision industrial robot .
it has 2 windings , one on each side , and a huge bearing in the middle .
It seems that the larger windings are the usual 3 phase , all 6 wires are available at the connector .
the smaller winding have 4 wires available ,per my resistance measurements it looks like they are connected in Y config (thus 4 wires...) total of 11 wires available (extra wire for case ground)

the motor is an outrunner .

The main issue for me is i don't see any magnets or field coils . Also the teeth on stator and rotor make it look like a stepper motor .
i removed the metal laminates on the smaller coil (see pics) and its just... well ... metal .

anybody have any idea how does it operates without magnets (maybe they are inside somewhere) and what is the purpose of the second coil ?
thanks

 

[fechter]

That's pretty interesting. It's a switched reluctance motor.
https://en.wikipedia.org/wiki/Switched_reluctance_motor

It works by the stator pole just becoming and electromagnet when energized and attracting the iron in the rotor. No magnets. It is just a large version of a stepper motor.

It takes a specialized controller to deal with the non-linear BEMF, which is probably the main reason you don't see them on bikes yet. That one certainly resembles a bike hub motor and might work as one with the right controller. If there is ever a magnet shortage, this is one way around it.

It's hard to tell about the coils. The smaller coil may be a feedback mechanism for the controller.

 

[mxlemming]

Are there actually no magnets or are the magnets axial to the machine? I.e. do other bits of iron/steel stuck to the rotor.

It looks very stepper motor like, which I guess is a sub set of reluctance machine like fechter says.

"Modern"steppers are hybrid steppers... They work on combined reluctance and permanent magnets.

First time I've seen inside one of these. Nice one! Thanks!

 

[sss]

so i read about srm yesterday , pretty interesting .
srm needs precise positioning feedback , so i guess the smaller coil is really just an encoder .no other encoders were attached to it , except a homing sensor .

yes there are no magnets . unlike stepper motor , this one spins freely without cogging .2 of those motors are used in a robot like this one :
https://www.youtube.com/watch?v=pEm7vuASVfM

they are designed to operate many years without any service . very heavy duty (and heavy) so not the best option for an ebike.


now for controlling it , unfortunately using regular esc or stepper controllers wont work . i saw the basic control of srm and it seems pretty simple . i don't understand yet why 6 switches are used , instead of just 3 , as polarity of the phases seems not important here .