Thoughts on Kv selection

If you drop the voltage from 12s to 10s, and adjust your gearing to keep top speed constant, you lose about 1/6 of your torque. Some people will argue that your VESC will be less likely to fail at 10s though. I don’t know for sure. I’m going 12s on my flipsky 6.6 driven build and will watch long term how it does.

60,000 rpm, or maybe 60,000 erpm maybe would be the most efficient depending on the motor design and what loads are put on the motor.

the low kv has thicker wire and can take more amps but at the same time it takes more amps to make the torque and ultimately is the same heat produced. A motors km is winding or kv/kt independent.

10s need not be any less torque than 12s And it’s the amps that decide the torque. If u used an esc that could put out more amps Itll get more torque For ultimate efficiency Youd want to balance the copper losses with the iron losses but both are dependent on the situation and the torque and speed Of the vehicle. U can reduce your copper losses with greater motor speed so less current needed with a gearbox to produce the same torque but then the iron losses hysteresis and eddy currents are increasing with the erpm so there is the limit there as these iron losses also produce heat. It would be nice to see a breakdown of the losses, whether copper or iron, and if u work with the grin motor simulator u can see a lot by comparing custom motors. You can increase the poles there which is similar to having a gear or pulley. There really would be an ideal rpm for a motor for maximum efficiency but how likely are u to sit at that speed? Unlikely and u need to account for acceleration and top speed and slower speeds and steep hills. But if u wanted to set up a challenge where u wanted to get the most Mileage on a consistent maybe flat track at a consistent speed then u could tweek for that ideal speed But at the higher erpm there is greater switching in the esc and losses there too Really your best bet is a good aero tuck!


yup…exactly what I experienced

think you have a couple things flip-flopped

other way around, high kv has thicker wire and can take more amps. See the published specs for 6374 200 and 150 Kv motors. 200 Kv has 14 turns (i.e. thicker wire), 0.016 ohms winding resistance and 80A continuous current vs 18T, 0.021 ohms and 70A.

I agree that Km is independent of winding, but max current (and therefore max torque assuming you compensate for the extra speed with more gearing) is not.

Keep in mind that if you run 12s, you get 20% more motor speed, which you can generally trade extra torque with gearing. That’s what I mean by “assuming you gear for the same top speed.” The amps are deciding the torque at the motor, but because you have a more aggressive gear ratio in the 12s setup, you end up with more torque at the wheel. Since we’re bumping up against the current limits on our motors, in general I think going up in voltage is always a good thing (assuming the ESC doesnt blow).

As for iron losses, yeah I really need to get around to educating myself on those, I dont even know whether (at our speeds) they are 10% or 10x as big as copper losses, but I imagine (by conservation of energy maybe? ehhh… really getting vague with my physics here :grimacing:) that they must ultimately manifest themselves as heat as well, and therefore are already reflected in the max current specs provided by the manufacturers. Thus since the higher Kv motors are rated for more amperage, we can probably still assume that they are capable of more torque (net of gearing) despite the increase in iron losses.

I struggle to use the grin simulator because the motors we use aren’t in the system, and defining custom motors is difficult because I dont know which numbers are important, and what values to use in many cases.

O yea I flip flopped the kv and resistance as You say and more turns n resistance w the low kv but people often think u can get more amps in and more torque w the higher kv as it has fatter wire n less resistance but in equal measure it takes more amps for the torque n balances out.

And with 12s n gearing u can get more torque with still the same amp limit of the esc as you say

I’ll post up a comparison of efficiency of our motors using the custom motor option in the future. It can be worked to incorporate any wheel size n frontal area for wind resistance. I’m assuming that a non-hub motor can be represented on there actually. Hoping people will take it on too and we could get somewhere. It’s a great tool

Don’t think the Vesc is up there…I’ll see if I can get them to put it up if not and it should be

Oh I don’t feel so good. Could you guys already give an opinion in the context of I think so?

Higher kv, lower voltage, same wattage and geared for the same speed, what do you think about that?

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With higher kv motors they need more amps to get same torque. That’s not a problem if ur esc can do higher amps and should be maybe almost as efficient , maybe depending on the esc efficiency. But with the same esc , with say a 100 amp limit, with 10s vs 12 u won’t get the speed that can then be converted by a gear to torque. So less torque w 10s

But then again in use it could be more efficient depending on the speed ur using the motor.

@Blitz, I dont see any good reason to not go at least 10s

so your telling me 12s 100a is more powerful than 10s 100a?

Yea because if u geared it to have the same top speed that 12s speed is converted to torque

Let me rephrase so your telling me that 5040W (12s) is more powerful than 4200w (10s)?

Or are you saying that a higher gear is worse than a higher voltage for a certain speed?

I got a motor that is 245kv and cannot be run at a high voltage due to ERMP limits. but I can near max out its wattage with extra current. (lets pretend I got a focbox unity with a massive heat-sink.)

Is that just as good as running a higher voltage? (lets also pretend that the motor doesn’t heat up)


Im saying the efficiency could be worse running 12s if ur not going faster than u were on 10s in its use

If u can put the extra amps in it will be able to put out the same torque and power as the 12s. Maybe just as efficient too depending on how u ride …maybe more.

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Thanks for explaining!

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So, I was debating on whether go with 12s4p or 10s5p on a hummie deck… I guess that going with a 190kv motor with the 12s4p would be similar to a 245kv 10s5p (a little faster on the 245kv)… Would you recommend going 10s @Hummie?

Also what 6364 motor would you recommend? Sk3 or tacon 245k?

I dont know if the quality of the Tacon is higher or lower than the SK3. But assuming they are equivalent quality, 10s + 245 kv Tacon is the better setup there, unless you use a VESC 6 and can go above 60k erpm.

answering your question i think it would depend on the esc and how heavy you are and what hills or power you would do. Ive never had a temp shutdown riding around san Francisco doing laps on hills on 12s but some people have, and then putting more amps through the esc on 10s and getting it hot will decrease its life and I think be general electronics standards is being pushed beyond the usual safe margin in amps and voltage. really we want oversized motors and oversized escs compared to the amps they can do and then its most efficient, but what is more unsafe the voltage or the increased amps and heat…i think youre safer going with 10s for sure and pushing the motor and battery amp limits. maybe even a cheap 4.2 from hobbyking on foc could be fine with that or maybe you still should go for the 6 to be safe.

the tacon 245 is an awesome motor just by the looks alone. and of the few motors ive taken apart its the only one with pressed bearings and shaft. and the glue is very strong and thick. the only thing I don’t like are its motor leads which are just the magnet wire coming the whole way along out and to the plugs. its stiff and easy to rub off the insulation and short. its rare in that I think, but a super benefit is I think you could reterminate the motor to a wye. almost all the motors for sale are wired delta termination for whatever reason, and with the magnet wire coming the full length you can find the starts and ends of each of the 3 wires and bundle either the starts or ends, soldered, and drop the kv by some math I forget. instead of 245 my guess is… … 160.