no, usually when people realize they’re in error they STFU to put it politely, in my experience
Okay fair. But in all seriousness, any physics professor would back up sharts. Hummie is claiming a momentum loss in motor unexplained by electrical resistance and motor bearing friction. We’re not talking about fission and dark matter here, that is a loss that literally cannot be explained by science in the way he is stating it. Which either means Hummie discovered a 4th state of energy, or… he might be off.
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i will grant he did mention hysteresis which isn’t electrical resistance or bearing friction, but it isn’t eliminated with the elimination of cogging
Cogging results from uneven magnetic field distribution within the rotor-stator assembly as a result of magnet shape and placement. There are sharp changes in flux at the edges of the magnets. This obviously results in larger eddy currents inside the stator iron compared to a motor that has a more even magnetic field distribution.
It’s a reluctance effect, and not the good kind.
Because there are larger eddy currents in the stator iron, this results in less energy being returned during the “springing” action.
In the case of transmissions such as belt drives, the sudden acceleration and deceleration due to cogging causes the belt to rapidly tension and release, resulting in internal friction losses within the belt.
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@Gamer43 would you estimate the unpowered friction losses in a belt significantly affect the efficiency (powered or unpowered) of a hub motor?
The eddy current effect is even worse in a hub motor because it has WAY more stator iron.
is that effect eliminated via the techniques which are used to eliminate cogging?
I am not aware of any techniques that can be used to eliminate cogging aside from changing the magnet shape and placement.
@hummieee previously specified using techniques such as “skewed“ stator teeth or filling in the gaps between the teeth with iron.
Well of course, that evens out the magnetic field distribution. The shape of the stator teeth also affect the magnetic field distribution from the reluctance effect, forgot to mention that.
would using those techniques reduce eddy currents and thusly improve unpowered efficiency while coasting?
Theoretically, yes.
in your view are the unpowered cogging losses mainly a result of increased eddy currents?
That’s what I think it is, there might something else I am forgetting with regards to reluctance effects or possibly even mechanical effects in the rotor itself.
in your view does reducing the unpowered cogging losses also improve the electrical to mechanical efficiency under power?
Well yes, there’s less of a parasitic reluctance effect, this also impacts the eddy currents generated from the phase windings.
Some prototype flipsky motors use convex magnets that achieve this, provides smoother torque generation and lower noise at the cost of slightly higher Kv.
do you know of any published papers addressing the powered/unpowered cogging losses topic?
I remember seeing one, I can’t be bothered to go find it again.
thanks for the info. much appreciated.
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Could switch to AC induction motors. 0 cogging, 0 resistance when de energized