# Why low KV and high voltage selection?

Since my thinking is so far away from what everyone is doing – I’d rather ask and be wrong rather than spend a grand before finding out that I was… I’ve been poking around and it seems that all the boards use quite low KV motors <300 and quite high voltages, 8-12S. What’s the logic behind this – in particular- since electric motors have a fairly flat torque curve (particularly compared to IC engine) wouldn’t a 1000-1500KV motor running at 2-4S voltages allow for a much wider selection of motors and ESCs? I know you would draw more amps from the inescapable P=IV, but unless you’re dealing with really crap batteries 30-40C will give all the amps needed – unless my math is wrong (40C * 10amp * 14.8volts gets around 6kw to play with)

so TLDR; why not use higher KV motors with lower voltage systems to achieve performance with more selection of parts?

It’s simple, more amps = more heat

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The problem of the current is not only on the batteries, every part of the system is subject to I^2R loses, só going lower voltage increases the heat produced to the square to keep the same power, also to handle more current you would need more MOSFET’s in parallel, that will add cost and also more heat dissipated inside the enclosure

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Most of the vescs on the market can handle around 50a before they start heating up. Sure you can create a heatsink housing like the one from @Kug3lis which would allow you to get more amps out but even than I think with 90amps you on the limit. 90*14,8=1332w … far away from the 6k😉

I’m seeing 160a 4s ESC for around 60\$ — seems like I could get 2 of those for less than the cost of vesc and spend the leftovers on an aluminum enclosure for the motor controller to handle the heat.

that was an additional question, I suppose - why the fixation on vesc? - I get that it’s a nice bldc esc, I’ll probably pick some up for a couple of robotics projects come spring. Is the vesc considered so far superior for e-skateboard applications that little else gets considered?

not arguing or trolling-- I’d like to understand the cause of common design decisions that I’ve been seeing.

so far, heat.

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One thing you missing is that current = torque. Those high kv motors don’t have that much torque and just spins fast, to achieve same torque you would need to spin in its effective voltages and the apply aggressive 1:100 gear ratios to decrease RPM to suitable for esk8. Then you also need ESC which would be able to spin motor at these kinda high ERPMs I am talking >300-500k

So in the end its not worth it. Plus you cant use those high kv motors with low voltage they will not even start spinning.

Any other ESC not made for esk8 will have brakes so hard that every time you just push it sligtly you will fly forward also it misses all goodies and etc

No for sure you not fixed on a vesc. But at the moment I think there is no other esc which gives you all this oportunitys to fine tune all the settings you want to get in place for a nice smooth ride. You can adjust your brake forces, you amp limits your throttle curves etc. etc. I‘m not into all this car esc so i can’t say anything about it. The hobbywing max6 seems to be a good one thou.

Interesting – one reply I’m getting RC ESCs have too strong of brakes, and the other is saying way too weak.

I totally get that the vesc is really configurable. most RC ESCs give about 5 settings for brake strength.

It’s important to think about wattage when thinking about “horsepower”. @Kug3lis couldn’t have said it better, rpms are a limitation as well as amp throughput. But don’t be discouraged, @MoeStooge runs high kv motors, and he slays like it’s his job.

1s battery, 2200kv motor, esc that can do 1200 amps, a voltage potential across the motor enough to supply the needed amps for the equivalent torque as 12s n 200kv n 100amps from a capable esc (can u get that current across the motor …will you have the voltage potential and is it just ohms law at the motor or is the rest of the system needed to be incorporated)

Such a setup would be a huge esc. Huge battery. But regular motor n gearing.

Well I think @MoeStooge runs something in 800kv at 30V range so it is not bad compared to 2000kv

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So far: It’s looking like heat is a common concern with higher amp/lower voltage.

braking may or may not be a concern.

RPMs could be problematic.

any other reasons? and thank you all for the information so far!

Another thing, try loading these 60 usd 160a esc for more than a few seconds and see what happens, or they will heat up a lot and shutdown or you have a nice firework at your feet

In the beginning when vesc was just starting a lot of people used car/boat esc’s and there was a resistance to switching, but look now, only a few people go for them

What is better? It’s smooth, it’s predictable, all that because it’s made for what we are using it for, others esc was never made to propel a 100kg piece of meat uphill

I really recommend you to read the VESC thread at endles sphere

(Keep in mind that the video is just an example, the esc used is not a cheap one)

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1s battery, 2200kv motor, and an esc that can do 1200 amps,?

can u get that current across the motor …will you have the voltage potential and is it just ohms law at the motor or is the rest of the system needed to be incorporated). If so could get same performance I think

Such a setup would be a huge esc. Huge battery. But regular motor n gearing.

nice @Pedrodemio! I suspect leaving the cooling fan open to debris when kicking up gravel had more to do with that failure than anything else – but I’ll start my reading! Makes one consider the water cooled motors and ESCs for boats (easy to water-proof:grinning:)

the battery would be exactly the same size 12s vs 12p, btw

True. Yea.

Yeah, that could have part, I don’t remenver if @Nowind said anything

I think that any losses are energy that could make you ride farther, it’s the same think with electric cars that some manufactures didn’t realize yet, the cheapest way to increase the range is to lower the drag and rolling loses, not increase battery capacity

This . Don’t use an ESC not specifically designed for esk8. You can use an esk8 ESC on anything else, though…

Most of the value of VESC comes from the free and open-source software and not so much the hardware…

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Amps does not build heat. Resistance builds heat.

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