a bigger motor could be more or less efficient than a smaller oneā whichever has the lower resistance for the same kv uses less power for the same acceleration, but itās easier to achieve lower resistance when constructing a motor if the motor is larger.
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The cost of the extra materials isnāt much more but its harder to assemble. Also more possible to demagnetize the smaller sideways magnets if exposed to a strong enough magnetic field as well but would have to be extreme
Typical outrunnersā back iron far from holds all the magnetic field in. U can see as it will attract iron on the outside. Lost wasted magnetic field that if it had been contained would ultimately produce less heat.
I donāt know why it hasnāt been done. U could likely strip the motorās magnets with acetone and rebuild w those and off-the-shelf thin ones between. Curious how much the kv would drop. Maybe worth getting a motor an extra 50kv too high or something.
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The motors are both 190kv I was just curious Iām coming from gas engines have little to no knowledge on ev so if theirs little to no change in range thatās all I needed to know
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What I originally had explained still stands true.
What @professor_shartsis had corrected me on was this statement, as the opposite is true in the properties of BLDC motors.
I made an incorrect assumption that the larger motor would be higher resistance, but there are other factors.
This difference in efficiency (regardless of which way) would be minor in comparison to the stated factors above.
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if you can halve the resistance for the same kv by using bigger motors, the copper heating losses are 1/2 for the same acceleration or constant speed. the losses in watts are I^2R=W. halving the resistance of 2 same-kv motors is equivalent in terms of improved efficiency as switching from 2wd to 4wd with the same size motors but using half the motor current per motor. in either case, total heating is cut in half for the same acceleration or constant speed.
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Another question are pulley covers worth 3d printing or are they not nessary as I see most builds donāt use them
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It really depends on your setup. @SeanHacker named his last board RockSlut because it would just feverishly guzzle rocks, every single ride, until he put a cover on it.
More info on what youāre looking to build would help give context.
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Landyachtz evo 40 tb218 tb rear mounts dual maytech 6374 abec 11 107mm focbox unity 12s4p 30t
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I would personally run covers on a belt drive PU board, just because of how close to the street you are. I do fine without them on my bigger pneumatic boards
Printing them is perfectly fine if youāre into that kinda thing too!
Sounds like a sweet ride! This is your first esk8 build?
Yes Iām currently riding a 12s China built hub board
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Iām not into 3d printing I was going to pay someone to do it I donāt know of any other option for getting pulley covers
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Does anybody know of any good quality 12mm X 28mm bearings for MBS matrix IIās that are cheaper than these?
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So in theory, it also makes it more viable to use lower A rated cells, for more mAh, i.e. I run 12s6p 30Q (72 cells, 778 wh, 120amp cont. is safe)
Say I switch to 40Ts in 15s4p (60 cells, probably less space, 864 wh, 140amp cont.)
So it will have more range, and will be even faster accelerating because it can use the same amps for more speed at a higher voltage. Even at a 30a max at 20s that would probably dust any board we have atm? Am I understanding this correctly?
And at 20s, 50e 20s3p (60 cells again, 1080 wh, 30a cont.) It would make more sense because we would be taking a fraction of the amps it would takes us to accelerate the same at 10s/12s but accelerate even faster because it can access more amps and yet have a higher top speed. We would probably never ever hit 30a at 20s anyway on an esk8 right? Even at a 30a max at 20s that would probably dust any board we have atm? Am I understanding this correctly?
I did this all w/ same gear ratio and wheel size. With increase in voltage that mean we could have an absurd increase in amount of torque with same top speed (higher gear ratio), or a massive increase in both (what I stated above), or have a deadly high top speed (lower gear ratio)?
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Doing my last build now The Kraken is complete It was to be a evolve gt rebuild but adhd and a busy mind got in the way. Parts on order TB40 deck and precision trucks this is built for speed and dont want dkp speed wobbles. Motors I have 4 x 6354 spare but want to try just 2 x 6380 or 2 x 83100. I have had issues with 6374 and loose magnets so shyed away from larger motors. But i need more power and dont want to do 4 motors.
Battery will be a 12S8P 21700 littokala 4000Mah cell pack 32000Mah total and on paper should do 320AMP but would be happy if it spits out 80 without sag. Cells were super cheap ($260) so its worth the risk. Wheels will be tb110 blue on order also fit kraken. With the ability to change down to cugamas. Vesc new makerX 6.6 dual.
Advice i am after motor recommendation and where do you get the plates that sit on the tops of you deck the through truck bolts sit in any recommendation thereā¦this build will now have zero evolve parts. Gear drive? Which one
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We can definitely deliver more Watts from the battery to the ESC with less loss if we are at higher voltage because Watts are a product of Volts x Amps, so we increase amps then we can decrease volts and end up at the same value. For a real world example say we have 50V and 20A thatās 1000W, if you were to double the voltage up to 100V itās only 10A to deliver the same 1000W (since we are cutting the amps in 1/2 we should have 1/4 the loss to heat from internal resistance in the cells, wires, and other components, for the most part, and yah less strain on the cells, so less voltage dip/drop under load)
Down sides I think are most the components to support higher voltage are also bigger https://www.goldenmotor.com/ <-- can see some crazy big powerful motors here and other downside is the higher voltage is considered more dangerous (primarily the arcing from shorting things out and other battery explosion risks) https://www.ecmweb.com/safety/article/20897929/nfpa-70es-approach-to-considering-dc-hazards
Some discussion about it here will loop back around to thinking about this more but itās not 100% clear to me with regard to the voltage pulsing and frequency how exactly that effects the amperage (especially with the motor being an inductorā¦ I need to read more to add anything else 
)
most of the losses occur in the motor, and for the same acceleration or constant speed, increasing the battery voltage doesnāt change the efficiency at all in the motor.
the esc steps down the voltage that it delivers to the motor, so if it takes 10v instantaneous effective voltage to supply the desired 60a motor current at a particular rpm (factoring the back emf voltage generated by the motor), it will still take 10v, whether you increase your battery voltage from 50v to 70v or not. yes you will get slightly less heating in the battery wires, but it doesnāt change the overall efficiency very much since most of the I^2R=W losses are occurring on the motor side.
on the other hand, if you increase the voltage and then gear down for the same top speed, then you increase the efficiency, because it will take less motor current to deliver the same wheel torque, reducing the I^2R=W losses in the motor for constant speed or acceleration.
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So higher voltage (w/ gear down) = increase in efficiency and torque while keeping same top speed?
Is the efficiency not being affected at all by requiring less amps to deliver the same power? (What am I missing here)
I think what the professor is saying is the losses from heat in the components up to the motor side of the ESC are mostly negligible which I think is probably true aside from maybe the heat in the cells from the resistance of the cells themselves, the wires we use are large gauge from the battery to ESC so should be low resistance and little loss anyway so we would save something but not appreciable compared to the change in efficiency on the output side of the ESC.
Ultimately the coils in the motor just need to handle whatever current flows through them but the ESC is varying the average voltage (up to the battery voltage, Iām assuming it doesnāt act as a boost converter, but could be wrong) and the coils have fixed resistance so the changing voltage also results in changing amperage. Strength of the magnetic field I believe is proportionally related to the square of the amperage, but the back EMF generated from the motor acting as a generator is a bit hard for my brain to deal withā¦ Anyhow I concur for as much as I can grok.
@Resonant @wafflejock here is a comparison of 50v, 60a motor current, 2.375:1 gearing vs 100v, 30a motor current, 4.75:1 gearing:
^bottom left chart shows identical performance, but motor heating in the bottom middle chart is 1/4th and the green efficiency line in the top left chart is increased with 100v
so for identical performance with increased efficiency and higher voltage, you increase the voltage, gear down and drop the motor current (in this case, twice the voltage, twice the gear ratio, and half the motor current for 1/4th the motor heating and same performance)
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Thanks I think Iāve seen you share this before but didnāt understand the context in the past, makes sense to me 
This sort of begs the question why not go crazy reduction but I guess that just requires more complex multi-stage gearing once the size of the pulleys/teeth becomes an issue and running higher RPM means higher frequency noise and I guess more loss as heat from friction so thereās some balancing point.
Another more practical question what are the real limits with regard to the BLDC motors and voltage, from what Iāve read doing a bit of searching here the max voltage is something like 300V+ before arcing will happen through the enamel coating on the coil wires on hobby motors(according to people on the internet), but of course with enough amps flowing through them you will melt things, I also wonder when people start hitting limits of ability to grip (I personally use nothing near any of these power requirements for cruising around town itās just interesting to me).
To summarize you spin the motor faster (with higher voltage) but then increase the gear ratio effectively reducing the wheel speed but increasing the torque and so can effectively keep the output torque constant to the ground even though the motor is say half the torque itās double the speed so we can trade that speed for torque in the gearing.