won’t foc decrease peak horsepower?
No, because the “additional power” in trapezoidal control is not torque generating.
how would adding iron for reluctance to the rotor affect the torque to weight ratio of the motor compared to sliding the stator in foc or bldc?
you know how you can make a chain of paper clips by sticking them to a magnet and can extend the magnetic field further than if the magnet were on its own?
Same idea, except you create an opposing field instead. Stator creates field in the rotor iron that opposes the magnets.
Pulling the stator out is mechanically complicated, that’s why no one does it.
threads on the rotor can of an outrunner would do it without adding iron or using a different controller.
such as when going from a hilly area to a flat area or changing from a bigger to a smaller wheel size you’d unscrew the stator to increase the kv…
found a post on endless sphere about why adjusting the stator position before a ride to tune the kv may beat field weakening control on esk8…
from endless sphere:
“One interesting thing I notice with phase advance/field weakening is that when you get to the motor’s base speed and keep accelerating you don’t notice any difference. But when you get off the throttle (i.e. motor current goes to zero) you get very strong braking as the inverter’s diodes rectify the motor’s voltage (now higher than the battery’s voltage) and feeds it back to the battery. Once you go under base speed it stops regen’ing.”
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Can you adjust stator position in the middle of ride?
No.
That’s a problem with the control algorithm; you’re not supposed to drive the power stage to high impedance in field weakening operation. Drive Q axis current to 0 to emulate coasting.
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One day, without needing a field weakening control algorithm in a hilly area, one could screw the stator full in for say 140kv in a hilly area for more torque.
The next day, in a flat area, before the ride they screw the stator out for 220kv, for a higher top speed but with lower acceleration and torque.
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And then you hit a bump and the entire mechanism either unscrews itself from vibration or straight up breaks.
Or you’re riding in a flat area and run into a hilly area and get stranded because now your motor stalls.
Your point?
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im on the fence whether it’s simpler to swap out the whole motor and/or change the gear ratio whenever riding conditions or wheel sizes change… i’m leaning towards it being simpler to turn a screw. (and i haven’t seen field weakening implemented on the controllers we use)
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Field weakening is impossible on the motors we use. No rotor iron
Use a higher pack voltage and lower kv.
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suppose someone’s using existing controllers with field weakening and some rotor iron, is it very safe for the electronics in the existing escs to have stray voltages from the rotor present that are much higher than the battery voltage while above base speed (especially if there’s some kind of fault? won’t the mosfets blow up? i believe shifting the stator for adjustable kv doesn’t necessarily create any voltages from the rotor that are higher than the battery.
The Axiom blog has a discussion of the problem of a fault while above the base speed and point out a couple of catastrophic possibilities.
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sine waves dont put out the same power as trap waves. trap waves have more current at the peak of the voltage output as apposed to sine which just touches upon the max current. you can see looking at their shape. be the same voltage and less current with sine.
adding iron to the rotor strengthens the magnets and will drop the kv without needing to do more turns of wire and the subsequent increase in winding resistance that comes from that. adding iron to the rotor is a great way to get a better motor and every motor out there could benefit from it. (unless its a true hallbach, not quasi, and all magnetic field is already trapped in the rotor that way)
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With my puny human brain, I’m trying to understand why less stator in the housing is faster? Someone break it down?
moving the rotor away from the stator decreases the back emf at the same angular speed, so it takes a higher angular speed for the back emf to equal the battery voltage.
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So if I ducktape nails to my rotor, KV goes down?
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the weight and imbalance might be a problem, and the risk of flying nails, but yes. ideally youd want the iron at the edge of each magnet where the magnetic field lines come off the magnet not centered behind each magnet