Stator width vs turn count vs KV, Cromotor vs MXUS 3000

[zombiess]

This is a tech question for those with a deeper understanding of motor theory than myself.

I just started following the MXUS motor and saw the KV on a 4T per tooth has been measured as 9.0 KV and it has a 45mm wide stator.
The Cromotor has a 48-50mm stator (depending on version) and is also 4 turns (18 strands), but it is 9.35 KV.

If turn count stays the same and stator width increases, KV goes down (double the stator count = half the turns for the same KV). Why isn't this motor a faster than 9.0 KV? I would expect it to be > 9.35KV due to less stator width. What other factors are at play that effect the motors KV rating?

 

[John in CR]

Yeah, I was thinking those motors seemed to have a low Kv too. There must be some other differences in the motor. FWIW, the similar motors I've had for years have a 40mm stator and they have a Kv of 16, and though I've never unwound one, I'm fairly certain they're a 2 turn motor. Mine are the standard diameter with 51 slots and 48 magnets.

 

[zombiess]

Yeah, I was thinking those motors seemed to have a low Kv too. There must be some other differences in the motor. FWIW, the similar motors I've had for years have a 40mm stator and they have a Kv of 16, and though I've never unwound one, I'm fairly certain they're a 2 turn motor. Mine are the standard diameter with 51 slots and 48 magnets.

Your numbers make sense, my 40mm motor I have is 13.2 KV and is a 3 turn so your other 40mm motors were probably 2 turns. I was hoping it was higher quality than what it turned out to be. I've now opened up a number of motors and seen an array of quality, even on similar motors that look almost the same. I've also seen a mix of KV at similar size. I'm trying to find out the KV of the Crystalyte 40xx motors to compare as well. I'm curious to the variances and if there is any correlation to magnet quality, stator teeth, air gap, efficiency or other factors. I don't know enough in this area.

Another interesting thing to see of several 40-50mm stator motor is their efficiency, even a simple no load current test on motors with same number of turns.

 

[bigsi]

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[Punx0r]

Surely the pole count affects KV?

 

[nieles]

magnet strength influences KV. if you have stronger magnets in an otherwise identical motor, KT will be higher, KV lower

 

[Punx0r]

Good point...