Most setups aren’t hitting their top speed because of wind resistance, its because the bemf v produced by the motor approaches the battery voltage close to top speed. there are exceptions to this depending on gearing but that is generally the case with the setups we use. if you go from 12s to 18s, it takes 50% more speed before the bemf approaches the battery voltage, essentially giving 50% more top speed before this happens.
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Wouldn’t apply if they have the same top speed.
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If you go from 12s to 18s and have the same
top speed because you changed the gearing, then you have 50% more torque with the same motor current on account of the gear ratio increase, and you also have 50% more peak power with the same settings, because same battery current limit setting delivers 50% more power with 50% more voltage.
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Thats just not true. The Vesc is a buck converter. The motor doesn’t give a fuck about your battery voltage.
This has been discussed at length here. The takeaway is that you can use thinner wires/smaller connectors on a 18s. lol
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Suppose you are presently being limited by a 30a battery current limit setting per motor (no motor current limit), and you increase the voltage from 12S to 18s, you have 50% more power coming out of the battery.
Well duh. Of course. You have more cells. But I specifically said same top speed and same total output wattage.
Thing with esk8 is you are limited to a certain amount of space under your board. You can play all the Tetris you want but if you have room for 108 cells under your board, you can make a 12s9p or a 18s6p. They will have the same total watt output. I don’t see what is so difficult to understand about all this. 
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Yes but even with the same peak wattage from the battery (on account of battery current limit change) and same top speed on account of a gearing change, switching from 12s to 18s will still give you 50% more torque at the wheel with the same motor current on account of the gearing change which will be very noticeable.
Where are you getting this extra current for the 18s? You have a lower P count so less amps available.
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What extra current? The 18s uses less battery current for the same wattage. At low speeds you aren’t using peak wattage from the battery. The motor is spinning 50% faster at the same ground speed on account of the gearing change when you’re limited by the motor current setting, so it’s outputting 50% more power for the same torque, at the same speed.
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That only applies if you have small motors which you cannot drive with any more current. Yes, the change in gear ratio will give you more torque if you are driving your motors to their limits. But you could solve this on the 12s system by just getting a bigger motor to handle the extra current it has available. (Or if you don’t have room for a bigger motor, then higher gear ratio and higher kv, which would be able to take that extra current)
The simplest way of thinking about this is that your battery, no matter its configuration, can only output X watts of power. Which means that if your boards are setup for the same top speed given the battery voltage, they have the same amount of acceleration at that top speed. Assuming no losses, the output power will be the same. No free energy!
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he changed the gearing so they both have the same top speed
18s would have more torque cause its the same watts but gearing is for more torque
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If the battery voltage is higher, and the top speed is the same, it means the gear ratio is increased.
Accelerating through the same low speed (say 5mph) at the same motor current, the higher voltage system is drawing more wattage from the battery, because it has the same motor current, but it’s spinning 50% faster, resulting in greater acceleration and wheel torque for higher voltage but the same top speed and the same motor current.
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Oh, acceleration on startup. Sure, I’ll agree there that when the battery isn’t the bottleneck, yeah, higher gearing will give you better torque. Motors are the bottleneck at low speeds.
But you can solve this on the 12s system by also having a great gear ratio, and just increasing motor kv to compensate for the lost speed.
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Electrical power = current x voltage. Mechanical power = tork x rpm. They may be directly related but both are separate cans of worms.
Compared to smaller motors, are bigger motors more efficient at converting electricity into mechanical motion? I think that’s a better question.
Jus sayin.
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No. It would be the same wattage.
At slow speeds, let says motor is at 12v 50A, the 12s battery would pump out 12A at 50v while the 18s would pump out 75v at 8A. Lets assume no voltage sag for now. Whats the difference?
I believe that is what @ross_forp was talking about before the conversation switched to 12s vs 18s. And I think he is right in larger motors being slightly more efficient. Question is if it’s noticeable.
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Nah he’s right here because he was comparing a board with higher gearing to one without, and using max motor current to go at a constant speed. So although motor currents are equal, the motor is spinning faster due to the gear ratio, thus drawing more power. (It’s going up a steeper hill, we could imagine)
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But on a 12s for the same top speed/wattage, you would have to setup your motor settings higher than an 18s so the ramping curves would not be the same.
I will die on this hill. 16s/18s is just marketing hype.
At low speeds motor settings are the bottleneck, and those remain the same in these comparisons.
But yes, you are right about it being overhyped, because the solution on 12s is to simply increase motor kv and increase the gear ratio. Boom – same speed, more startup torque. Or increase motor size, if your ESC can push more current still.
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Moreover, its highly unlikely you will be able to reduce gearing alone by 50% on the 18s due to gear sizes so you will end up with a lower KV motors which usually have higher internal resistance resulting in heat loses so we are back to square one.
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