The kv of the motor does not equate thickness of the motor winding,rather the amount of turns the winding does around the core. (Ofcourse a simmilar motor would have a thinner wire if its a different kv or viceversa.)
Any kv motor really is equally efficent in terms of power in-power out. If they are run at their optimal rpm and optimal amperage. However one should make sure the kv is fit for the load and speed. This is pretty difficult to approximate but basically if you are running low-kv motors and really topping them out your back-emf is gonna increase a ton. So your cruising speed might be really inneficent because the rpm is too high. Then it would make sense to go for a higher kv motor.
Anyway,what in trying to say is that kv does not tell tou how efficent a motor is without looking at the gearing and assumed speed of the board
Keep in mind this was for the hw 4.x
Think he set the variables with high regard to erpm in that article if I remember correctly, ERPM went up on the vesc6
But as he states somewhere, more copper=moar better. Got probed with that info when I studied as well.
So it seems 8600 was the magic RPM number back then. Do we have any info on what the current magic number is on 14 pole motors?
It would be great to standardize this, thank you for linking that article; it confirms a lot of ideas suggested here and weeds out some misinformation.
Iâm going to keep calling it âmagic erpmâ to differentiate.
Is Vedder referencing erpm or rpm in that article? Iâm assuming erpm because he is specifically talking about motors and not wheel sizes but he also repeatedly uses rpm and not erpm.
As Jan says after 60k ERPM losses start to stack up. If you would completly ignore the losses and only intrested in the max RPM calculated from ERPM. 150k would yield roughly 21400 rpm.
Since the losses increase exponentially, running at that speed under load wouldnât be possible for very long and would require a very reliable motor etc.
Maybe 100k erpm is more realistic, that would yield roughly 14200. Iâm just spitballing here.
If someone has a 12S (13S even better) battery at full charge and a VESC laying around do this test. Preferably one that is know to support higher rpm
With no belts, first let the motor spin to warm it up a bit, them set progressively increase the rpm and take note at the power usage at each level, let it stabilize a bit first, plot rpm versus power.
Testing more than one Kv for the same motor would also be good, something higher than 190 Kv so we can see what happens at higher rpm. I only have 10S battery and 190 Kv motors on hand
Change the KV of the motor. Yes, this can be done quite easily without rewinding the motor. Almost all outrunners are connected using a delta-connection. By removing the heatshrink of the motor wires, they can be split up and reconnected in a star-connection. This reduces the KV by a factor of sqrt(3) = 1.73.
Ooh, would be cool to see someone do this on direct drives for more torque. TB 90KV ones would go down to 53, and 60âs would go down to 35
On the other hand, if you donât go full speed most of the time, would your ride be more efficient using higher kv motors? In particular on a mountain board where youâll be pulling full current at moderate speeds, and pulling a lower current when you actually get to cruise at full speed?
Yes, however you can never have too much torque on a mountainboard, so people are still going to go with lower KV motors because their ESCs are the limiting factor.
Edit: ESC + gearing is the limiting factor. Otherwise yeah you could pick a KV so that the speed you use the most is at that 8600 RPM sweet spot.
Do t know what u mean but high kv or low doesnât matter if same amount of copper. At least in the motor. With low kv n more resistance itâs more torque per amp n view versa. They magically get same heat to torque
Heat dissipation âŚthicker wire is better as less insulation between. But not a big deal
I^2R. related to current and resistance. Equals the copper loss. Our by far biggest loss
Must have all been Sharts claiming then, didnât mean to drag your name around man. I agree with your most recently stated point of view as the rest of the discussion has unfolded.
Honestly at this point there are so many factors at play that itâs not as simple as âchoose this motor for this battery/esc combinationâ until real world loss values can be calculated with belt drag, bearings, friction, etc.
This seems difficult to capture in real life so I will stick to what is âknownâ for now and just fucking skate.
No prob. Iâve read if u want max power instead of max efficiency a higher kv is better as less voltage sag since w less resistance. But thatâs an extreme goal n not efficiency. If u look up the grin motor calculator it can reveal a lot although itâs a whole system efficiency and donât think can isolate the motor. As far as I understand the kv shouldnât determine motor efficiency and youâll get the same losses to torque output as long as same amount of copper. The rest of the system will be effected. And most efficient running at like 80% of no load speed shows most efficientâŚwhich kinda contradicts kv being unimportant.
I read through this thread and was shocked to see no shartsis theoriesâŚ
This is one of the more concise, to-the-point technical discussions that Iâve seen here in a while.
The kv effixiency falsehood seems to ignore that this is all about balance. Different riding style and motor combinations will dramatically affect this flow:
Wow thatâs a solid link. Interesting turnout of energy loss breakdown.
âfull-load efficiency of motors increases with physical size and rated output of motorâ
Combined with
Makes me wonder where the total rated output of a motor actually comes from. Seems like manufacturers often skew label ratings to be safe or impressive.
I imagine that photo is for a specific motor and not all of course
