then for direct drive / hub you want the lowest kv, lowest resistance motor that gives adequate no load speed for your tire diameter, since lower kv motors have more torque per motor amp and you’re stuck with 1:1 gearing. most people select kv’s for direct drive between around 60-90kv so none of the motors you listed are in that range (they’d overheat the controller with adequate acceleration because they have lower torque per motor amp - they’re appropriate with gear reduction because via gearing you can trade their higher angular velocity at the same voltage for the same wheel torque with less heating, since gear reduction multiplies the motor torque at the wheel, but reduces the angular velocity)
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The first one I listed has 100Kv but that’s already too high. That’s why I said I’m not sure if there is a motor with such low Kv to achieve like 20km/h top speed on 1:1 ratio. I’m planing to use 125mm wheels. The motor Kv should be around 25.
Or I go 6S2P 50Kv. This should be possible.
if you want to the limit the top speed you can lower the voltage and use a higher kv than 25kv - it will be technically slightly less efficient than 25kv and 12s but still within reason. that said i’ve never heard of a 25kv motor on a skateboard. the way lower kv is achieved is by using more turns of thinner wire on a same size stator, which increases the resistance, which is why higher kv with gear reduction is ultimately more efficient.
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another point to consider is for the same amount of copper on the same size stator with direct drive, changing the kv doesn’t change the efficiency in the motor for the same acceleration or constant speed… same heat is produced in the motor regardless… the increase in amps with higher kv is cancelled by the lowering of resistance as far as heat production is concerned in the motor… but on a direct drive when you double the kv, the heating in the controller is quadrupled for the same acceleration or constant speed, because the controller resistance doesn’t change and with double kv you have to use double the motor amps for the same constant speed or acceleration, and since controller heating is proportional to the square of the amps, doubling the amps quadruples the controller heating according to I^2R=W.
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So what do you suggest?
if you’re having a custom motor made for 1:1 direct drive and all you care about is efficiency use the highest voltage battery and lowest kv motor that gives adequate no load speed for the tire diameter with the largest possible copper and stator volume.
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the only thing that fits this bill is hummie hubs atm.
Otherwise you’re going with torqueboards DD
Or Elofty DD’s
All at very different pricepoints
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Sure, but I don’t have a motor, that’s the whole point I started this thread. I was hoping somebody can recommend me a motor.
I theory I know it would be best to go with 262V and 1Kv, but I never saw a motor with less than 60Kv and I’m also limited to 12S- max. 14S in due to the VESC. I just can take what the market offers.
They are way too powerful. I think a smaller motor would be more efficient. I will build the DD or hub myself. Just need a efficient motor.
your options are quite limited by the direct drive requirement. if you know how to wind motors you can take your pick of any motor and rewind it for lower kv.
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I could use belt drive, but I think it would be less efficient.
no, with belt drive the highest kv with the highest gear reduction that gives adequate no load speed is most efficient as i previously mentioned — certainly more efficient than your direct drive options.
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Even with the friction loss?
Not sure if it’s falls in this topic of efficiency, what about a lower kv vs a higher kv with more amps capabilities?
Best for torque?
friction loss with a belt drive is insignificant compared to copper loss with your available direct drive options.
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for the same size stator with the same copper volume and same gearing—doubling the kv requires twice the motor amps for the same torque, but since the resistance is 1/4th (twice thicker & twice shorter windings)… the heating is the same in the motor for the same constant speed but the controller heating would be quadrupled as previously mentioned.
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Let me ask another way, the same stator, rewound with both more copper mass and a different amount of turns giving it a higher kv and higher amp, vs stock lower kv. I’m really wondering if the higher amp will give more torque then the lower kv I started with.
usually they try to maximize copper fill so typically you can’t add more copper unless its poorly wound to begin with
It was a skullboard hub so I was able lol