JRH, can you explain a little bit about the difference between 2,4 or more poles as it relates to smoother start up vs the staggering of poles. Which seems to defeat the efficiency. I understand it also depends on esc software and circuitry.
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Every motor design is unique, but there are guidelines. Some respond better to staggering or skewing. The key element to how much efficiency is hit, is how far the slot skewing goes in relation to the “pole pitch”. Skewing is essentially misalignment of the motor where work cannot be done. In my brushed motors, I always skew 1/2 slot pitch or less to have the least efficiency hit while gaining most benefits, and I use it because there is no other choices left. Brushless gives more freedom of design and there are more stator choices, so there isn’t much reason for skewing IMO.
Higher slot rotors/stators can get away with less skewing on the steel for the same effect, with one slot pitch being maximum. 12 slot 4 pole motors have 3 slots per “pole pitch”, so a full slot pitch skew is only 1/3 pole pitch. A 3 slot 2 pole would be 1.5 slot per pole pitch, so a full slot pitch skew wouldn’t even be a full pole pitch skewing.
Since each magnet shape and lamination shape is different, detent force is not always affected as anticipated. A small amount of skew might make the motor worse, and I have indeed built 12 slot 10 pole motors where skewing was worse than none.
The hobbywing motor appears to have 1/3 pole pitch staggering, which makes the back EMF sinusoidal but didn’t seem to reduce detent. Maybe the motor was terrible beforehand though. Skewing would have reduced detent more, but magnets can be difficult to make this way. Skewing the rotor would work, but it is hard to wind and many stators have alignment nubs to prevent it during stacking.
I’m really quite puzzled as to why this was their choice. I’ve engineered plain old brushless motors with sinus bEMF for customers before. But it’s really not an issue to have a trap bEMF, in fact it makes more power dense motors and less esc losses to drive them. It’s not like existing 4 pole motors are uncontrollable, they are practically on par with brushed motors for 95% of driver. Just really seems like a solution looking for a problem. Or, marketing overstating these fantastic solutions to problems that nobody actually has.
