Do bigger motors deliver more torque at the same motor current?

[rusins]

Well, lower kv might not always be a bad thing. The main reason TO go high voltage is if your ESC is the bottleneck. So if motors weren’t a bottleneck in the first place, then maybe you can afford to go lower kv. (Although I do find it very funny when people do, thinking they now have more powerful motors, even though the size remains the same lol)

[mutantbass]

@ross_forp

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.

I want to go back to this. For the same wattage output on 12/18s, your motor current has to be 50% more on the 12s so motors will never be at the same current for the same speed on 12/18s so the comparison isn’t true. They will ramp up differently throughout the throttle curve.

[rusins]

@mutantbass

They will ramp up differently throughout the throttle curve.

Until battery bottleneck kicks in, they ramp up the same if you set the same motor amps.

[ross_forp]

@rusins

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.

False… increasing the kv decreases the torque of the motor for the same motor current, changing the gearing to compensate for the same top speed leaves you back where you started performance wise… same top speed, same acceleration.

[mutantbass]

@rusins

if you set the same motor amps.

But you won’t because that’s not the same total output watts

[rusins]

@ross_forp

increasing the kv decreases the torque of the motor for the same motor current

I know, but I’m highlighting how to make use of the extra current you have on 12s. Higher kv motor can take more current.

@mutantbass

STOP Saying Lower Kv Motors Produce More Torque

[mutantbass]

Whats the difference between these two systems?

18s

40 battery amps total.
20 motor amps each

12s
60 battery amps total
30 motor amps each

Assume everything the same except gearing is 50% higher on 12s.

[ross_forp]

@mutantbass

Whats the difference between these two systems?

18s

40 battery amps total.
20 motor amps each

12s
60 battery amps total
30 motor amps each

If those are the only differences, the 12S will have 50% higher torque on account of the higher motor current limit, and the 18S will have 50% higher top speed on account of the voltage increase.

[mutantbass]

@mutantbass

Assume everything the same except gearing is 50% higher on 12s.

I edited to say this

Assume everything the same except gearing is 50% higher on 12s.

They will feel the same.

[ross_forp]

Now you’re changing the voltage, gearing and settings which isn’t what was previously discussed, but yes, the same in theory, but the 18S motors will be running cooler on account of the lower motor current setting, so they will be a bit more efficient in the motor, so the 18s will give longer range and a little bit more torque on account of the decreased I^2R losses from the reduced motor current.

[mutantbass]

@ross_forp

Now you’re changing the voltage, gearing and settings which isn’t what was previously discussed,

It was exactly what was discussed. I said same top speed and same total wattage output.

@ross_forp

but the 18S motors will be running cooler on account of the lower motor current setting, so they will be a bit more efficient in the motor, so the 18s will give longer range and a little bit more torque on account of the decreased I^2R losses from the reduced motor current.

Now that we are getting into the nitty gritty, 50% gearing reduction isn’t usually possible due to the size of the gears so people are using lower KV motors which get hotter quicker so like I said before, we are back to square one.

[ross_forp]

@mutantbass

It was exactly what was discussed. I said same top speed and same total wattage output.

You spoke before about changing the battery current limit only, now you’re talking about changing both motor AND battery current limits… which changes the situation entirely.

[mutantbass]

@mutantbass

Whats the difference between these two systems?

18s

40 battery amps total.
20 motor amps each

12s
60 battery amps total
30 motor amps each

Assume everything the same except gearing is 50% higher on 12s.

Both variables changed. Maybe you misread.

[rusins]

TL;DR of all this:

• if the output power is the same (for example, battery is bottleneck, or you adjust motor settings like in @mutantbass 's example), 12s and 18s perform the same if geared the same
• high voltage allows us to increase the total output power when ESC is the bottleneck

Everyone agree? We can move on with our lives?

[mutantbass]

Good summary.

@rusins

ESC is the bottleneck

Nothing a 10 dollar heatsink cannot fix. And probably not an issue for most builds. Much cheaper than spending for 18s components.

[ross_forp]

@rusins

if the output power is the same (for example, battery is bottleneck, or you adjust motor settings like in @mutantbass 's example), 12s and 18s perform the same if geared the same

no even with the same motor current limits and same gear ratio, and you reduce the battery current of the 18s to the same peak wattage as the 12s, the 18s still gets 50% more top speed because the 12s is limited by the bemf voltage approaching the battery voltage, not by the wind resistance.

[rusins]

@ross_forp

same motor current limits

Then total output power is obviously different, like @mutantbass complained a dozen messages back

Okay fine, you gained some extra top speed. You could do the same by just increasing motor kv AND motor current on the 12s system. Why am I allowed to increase motor current? Because at the same speed I need less voltage now, so I need the extra current to compensate.

And if you still say – no, you’re not allowed to increase motor current – then fine, ESC is the bottleneck, of course upgrading to 18s will give me more power.

[mutantbass]

But they have the same top speed so the bemf will apply to both systems.

[ross_forp]

we’ve been through a dozen different scenarios, i’ve lost interest. bottom line, if you get a bigger, lower resistance, same kv motor and change nothing else, you will feel more acceleration on the bigger motor, because the same battery current limit puts more motor amps through the bigger motor.

[mutantbass]

Lol no shit.