In the Hobbyking specs? I gave some speculation a few posts back.
Most spec pages I’ve seen don’t have this relationship.
Originally you were looking for an example, I gave you one. I’d love to completely understand what’s going on there.
On the Hobbyking page? My guess is like I said they just test motors at 12s and they draw way more watts with higher KV.
Another example would be using a 6374 to spin a prop.
A 6374 100kv run at 20s would spin the same rpm as a 6374 200kv at 10s and the load from the prop will draw the same watts.
Take the same example and run both motors at 10s. In that case the 100kv will pull roughly half the watts as it runs at 1/2 speed (ignoring any rpm/watt curves specific to that particular prop rpm range).
Okay so ignoring the kV, the 18g weight and 10A increase is all we should be looking at?
I would just look at the weight to get a sense of how much power the motor can supply without overheating. A heavier 6380 will run cool longer than a lighter 6374.
Weight would also be a good indicator of peak torque.
The KV should be considered along with the voltage to get a good rpm for whatever gearing and wheel are used. I’d expect a 100kv motor fed 20s to run equal more or less to a 200kv motor fed 10s in the same system with the same size motor.
All this is a roundabout way of saying an 18s esc is great for keeping the esc cool and maxing the watts it can output, but there isn’t an advantage or disadvantage at the motor provided the KV is adjusted down to match the rpm of a typical 12s system.
Should caution that running a low KV motor to make up for limited gearing to enable larger tires might not pan out well. Since the voltage is the same and the wire size goes down with the KV the heat produced at a given amperage increases.
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These videos lay it out well. Lots of other factors to consider like air gaps between wires of different sizes, skin effect, max erpm escs can handle, and “the magic erpm number”
Kv seems to be the most easily varied variable in a setup because they’re nearly efficient across the board as long as you choose the right kv for your purpose.
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Staying at higher Kv is fine but most of the 190 kV motors I’ve tested sound like an angry swarm of bees at 18-20s so I am not sure how long they will last in that operating range.
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I was asking about 16S though. Theoretically would they be fine, or does going up in Voltage mean going down in kV?
I’m asking because ideally wouldn’t we want to have a 80kph capable board that you’re mostly only riding at 40kph?
It just depends on the motor, the ESC will drive it fine but it becomes a question of whether the bearings are rated for that speed etc.
Having a board that is rated beyond the speed you plan to ride at generally means taking a hit to efficiency in the power stage of the ESC. So if you run into thermal problems with ESC you’ll want to go down in KV.
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Are you saying we shouldn’t ride slow? 
I’m saying you should design the max speed of your board to be a speed you plan on going. Instead of 190 kV motors on 12s I could rewind them to be 380 kv. Theoretically my top speed would double and the motors efficiency will remain about the same at the same speed and load, but I will also draw twice the amps at half the voltage from the ESC to get the same power. Twice the amps means four times the losses in the power stage.
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I think it depends on your goal and what you care about and are able to mitigate e.g. if I want a board that can go up to 80kph, then that’s what I build to.
That doesn’t mean I’ll spend a lot of time even close to that. In practice it may mean I spend a lot of time at 60kph and below, which is just fact for a lot of people not on a racetrack.
As long as I’m able to design my system to manage the heat generated, and I’m okay with the compromises, it shouldn’t matter how I use it.
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Yes definitely, but I generally don’t advise someone to build a board to go over 40 mph because it seems like a good way to crack your skull open and when you do it you end up wasting a bunch of power for your regular riding. You asked if you can do it, the answer is generally yes but should you do it I think the answer is usually no. But it all depends on goals, I just want to be clear that it is an engineering question and there are tradeoffs with efficiency.
Just like right now when people build 12s setups we tell them to go around the 150-210 kV range, when you go 18s I’d recommend to go in the 100-150 kV range. Everything still works if you don’t do that but you might get some undesirable performance trade-offs. I also don’t think any of us are yet sure what the long term effects of running a 190 kV motor at those higher RPMs will do to the bearings.
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By the sound of it, the recommendation for 16S should be 130-190 kV then.
I get there are engineering trade-offs, but then it also depends on how you use it and where you want your power to be.
I don’t care much for the 0-30kph acceleration and sustained speed, and having a system that has better acceleration and capability to maintain speed in the 30-60kph range would be better for me.
At the same time I also want to be able to crank it up a notch to 80kph on occasion.
I’m asking these questions in advance because obviously if I want to build a higher Voltage esk8, I need to think it through.
Your replies have been invaluable, just wanted you to know.
@BillGordon I’m wondering whether this conversation shouldn’t be in the 13S thread instead.
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Yes it should probably be moved, my bad for hijacking.
150 kV*12s/16s =~ 110 kV
210 kV * 12s/16s =~ 160 kV
It won’t behave quite the same way as gearing in a car would. You will get (theoretically) flat max torque across all speeds (except maybe the last 2-5% as you approach max speed). The torque will linearly be related to the max amps set and motor kV, but changing kV will change the max amps the motor can handle. In general for a given motor design there will be a fixed max continuous torque it can output if you wind it with the same amount of copper but different kV.
You run into trouble when the ESC starts becoming the thing creating the ceiling for your maximum amps settings, then you lose torque in the system you could otherwise be enjoying.
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Watch out for thermal throttling, and watch motor temp is what I’m reading.
Yes you could back calculate from the max continuous amps of the ESC and the winding resistance what an appropriate kV would be. Additionally losing efficiency is never nice if you don’t want to go fast so then the rule is just lower the kV until your max speed is where you want it.
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Now that I’ve taken the 2x Stormcore 100S on 20S1P LiFePO4 out for two rides, seemingly neither the 192kV 6374 SK3’s or the ESCs break a sweat.
They have plenty of power throughout the RPM range, and so far only luke warm to the touch. We’ll see how this changes as I go out for longer, faster rides.
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Anyone have much experience with the Trampa VESC 100/250 or know of any other suitable ESC’s for an 18S setup?
Ideally wanted to go for the Stormcore 100D but it seems they’re still ironing out all the issues.
Also @shaman 's Some New FOCers (84V VESC 6 based controllers) is still under development as well. Similar story with MakerX’s 100V ESC
Are there any others out there?
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I’d say the trampa has the best resale value
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