KB45 motor isn't notchy. Xerun 4274SL is. Why?
 

Hola amigos!

I had read before that quality brushless motors have a notchy feeling when the shaft is turned. So far I have only had my hand on the 1st gen Ezrun motors (4465SL) and KB45's... neither are notchy.

Yesterday I had a Xerun 4274SL in my hand and it was surely notchy... but why? The case is aluminium, the windings are copper. So whats the story... why is it notchy?

the newer motors have better quality magnets so the "notchy" feeling is greater.

Also the 4274 is a 4-pole motor, where as the kb45 and 4465 are 2-pole motors. A 4-pole will be twice as "notchy" as a 2-pole.

The "notchy" feeling is just magnetism as the rotor turns........

Aye, but what does the (increased) magnetic field interact with? Pure aluminium and copper isn't magnetic...

The only thing I can think of is that the windings might have iron cores? or maybe some other iron parts in the case to focus the magnetic field?

Yes...........All of this......+

The 4 pole motors have iron laminations in the field that the copper winding go around, much like the outrunner motor core that is shown in my avatar.

2 pole motors on the other hand, have only copper in their field winding. Their field winding are wound, compressed and baked, after being bathed in epoxy. This makes this type of field winding retain it's shape.

Ahhh goodie... we have a magnetic metal in play now :)

I couldn't wrap my basic physics around what I had seen in disassembled 2 pole motors and the nocthyness. Thank you Sikeston.