Now try it with 18s, 260Kv, and an absurd gearing and see what you get.
You’re better off with a multistage reduction at that point because with the torque involved you want as many teeth in mesh as possible
Let’s turn this into an online calculator.
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The calc is inaccurate, see ohms law…
As one example, with 64.8v and 98mOhm, max possible motor current is 661.2a, not “162.6a”
I suggest starting a new thread since this has gotten far off topic.
But to summarize the answer to the OP’s question, 10-12lbs additional thrust @ 15mph is plausible by dropping the motor resistance from 70mOhm to 20mOhm with a larger, same kv motor and changing nothing else. I assumed 2 motors, 12s, geared for about 40mph, with 30a bat and 80a motor limits per motor. At 15mph, they’d be hitting the battery current limit and not the motor current limit, and essentially the lower resistance motor has more motor current at that speed than the higher resistance one on account of lower I^2R losses (both have less than 80a motor current available at that speed on account of the 30a battery limit, but the lower resistance motor’s motor current is higher).
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If you’re getting 162.6a motor current with a motor that isn’t turning, and you have 98mOhms, then the voltage to the motor is 15.9v. (see ohms law) That’s also 2590 watts. Since the battery voltage is 64.8v that works out to about 40a battery amps.
If one takes electric skateboard design to the extreme we end up with an electric car.
Those use in the neighborhood of 400v, 25-35kv with low resistance and 9:1 reduction.
The 25kv motor gives very high torque per motor amp, the 400v lets it rev to 10000rpm, and the 9:1 reduction gives a reasonable top speed given the wheel diameter. They don’t want the motors to go much higher than 10000rpm because things start getting inefficient mechanically and with iron loss.
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This is we’re I’m slightly out of my depths but magnet size and heat do play a factor but we talking small amounts.
Larger motors have larger surface area to shead heat.
Larger core takes more to saturate.
Longer starters make a more powerful magneti fielded
The issues is there’s a efficiency point and things can have negative effect
Longer started have a higher resistance due to winding length.
More mass to move decreases acelaration.
Many more I’m guessing John @hummieee can give you a more detailed answer
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How?
Winding size and length determin the max amps not KV
Lower KV at same fill% requires you to have a longer wire (more turns around the iron cores). This can only fit by using a thinner wire, which is also slightly longer. Again, all this is assuming same fill %.
With the same fill, the lower kv handles less amps, but more torque per amp, so you get the same torque for the same heat either way. with higher voltage, a lower kv motor can spin just as fast as a higher kv motor, and produce the same torque for the same heat. by going lower kv and higher voltage, you end up with less losses on the battery and controller side, because less motor current and less battery current is required for the same performance, efficiency & heat on the motor side.
If every thing was equal from what Iv seen going over 60v mosfets are less efficient and produce more heate. I can say the same with motors we are slowly going down in KV from the old 210kv to 190kv now 170kv even dabbling in 140kv as they get better. there is still material limitations that makes the higher vk more efficient. 12s is still a better balance in my opinion as it’s a higher efficiency. I can say the same with higher gear ratios needed for high voltage have more losses in them. Less wast means more power out the wheels.
Keepin it on topic smaller motors are more efficient as a general rule but you still got to balance the system for optimisation. Bare in mined There is all ways exceptions to any rule you can apply.
The big part is power curves on a motor output x wattage in dose not always equal the same amount of power out at difrent rpm why power graphs exist.
Yes but the controller losses are tiny compared to the motor losses, so if you improve the motor efficiency with higher voltage and more gear reduction (less I^2R loss in the motor) for the same performance, and the controller losses increase by 1w, overall the efficiency has significantly improved. not to mention the effect in the controller of reducing the motor current for the same performance (when 18s is geared for the same top speed as 12s), I suspect the reduction in I^2R controller losses outweighs the effect of the increase in 12S->18S mosfet contoller losses.
No the larger motors are more efficient… lower I^2R losses at the same kv and torque, because the windings are thicker — lower resistance.
So why are we not flying around the world on large motor drones? Small ones are so easy to make lift yet large ones with large motors and props struggle
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Because with land vehicles at constant speed, the weight doesn’t affect the efficiency as it would on a flying vehicle that also needs to produce its own lift.
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So larger motors been less efficient don’t matter?
Larger motors only matter if that’s you limiting factor no point in going overkill it adds other factors in that are detrimental. You need to have a balanced system
Just simply calculate the I^2R losses of 2 motors (same kv) at a given speed and torque… a larger one with lower resistance and a smaller one with higher resistance. You will see the mechanical output (and motor current) is the same, but the I^2R losses of the smaller motor are higher, resulting in lower efficiency… you need more current from the battery to supply the same performance plus the additional losses of the smaller motor.
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