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

[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.

[longhairedboy]

@TheBoardGarage

Someone in a YouTube comment said that all the best DIYers use 6384 and bigger motors now.

hilarious. I’m using 6374 190KVs at 60-70 motor amps and usually 35-40 battery amps. yeah they get warm, but by the time they’re too hot to touch the battery is drained.

@mutantbass

Honestly, anyone that believes that bigger motors give you more power is a fucking idiot. What you are essentially claiming is that you have discovered free energy. Ridiculous.

thank you.

@ross_forp

But if you instead use the same battery current for both motors, the larger motor will accelerate quicker, because the smaller motor is wasting more of that battery current as heat coming out of the motor.

how noticeable is this on the street though? Or is this one of those things where you would get better returns simply by eating less and maybe walking somewhere now and then? aka losing weight.

[rusins]

This weekend I promise to bench test my 190kv 6355, 190kv 6374, 170kv 6355, and 170kv 6374 Maytech motors and submit them to the motor dyno database. Then we can solve these mysteries once and forall for the most popular esk8 motor sizes.

ESK8 Motor Dyno - Requests and Discussion [SERIOUS]

[image] Electric motors are awesome, so awesome that we can accurately predict the performance with just a few basic measurements, this mean that anyone using a VESC or VESC based hardware and software or any other ESC that can measure and display phase current and rpm and a few minutes to spare can supply the data needed to plot all the performance metrics Before doing the guide on how to measure, I will show a result as an example, find it in the topic bellow that will be exclusive for the …

[noflers]

@mutantbass

Honestly, anyone that believes that bigger motors give you more power is a fucking idiot.

Honestly, remember that not everybody has the same understanding of electricity as you, and that doesn’t make them idiots…

[mutantbass]

Tbh my understanding of electricity is pretty basic. I do Know one rule of life though. There is no free lunch.

[rusins]

That one’s also complicated

No free lunch theorem

[mutantbass]

I am a simple man. Leave me alone

[Madmiah]

Pardon my naivety I’m a car and … guy before I found eskate.

Wouldn’t adding stickers that say things like GT or DRI etc etc add more Nm of torque at the wheels?

[Dinnye]

@rusins

The main reason TO go high voltage is if your ESC is the bottleneck.

An easy fix would be better cooling. The problem with higher voltage ESCs, is the higher RDSon of the mosfets - so unless the ESC has more mosfets to distribute the current draw, the power actually doesn’t really increase, or even if it does, not by the amount you expected it to! Remember…

@mutantbass

There is no free lunch.

[fessyfoo]

that moment i understood the dodging ESC/Motor current limits with higher voltage.

Battery amps vs motor amps vs voltage

I haven’t been able to stop thinking about this. pretty excited to understand it better. I did another version of the power curve comparator on desmos. parameterized it in terms of NsMp cell counts. and added a “gearing” component. In the default comparison, 10s6p (blue) and 12s5p (red) the power curves are the same. Red has more top speed but the torque/amps continues to drop as the rpm/volts (dutycycle * volts) goes down. keeping max power the same. (!!!) bingo light going offf for…

[mutantbass]

Any sticker in Red will do.

@Madmiah

Wouldn’t adding stickers that say things like GT or DRI etc etc add more Nm of torque at the wheels?

[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

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

The thing with both of these setups is, performance wise, they will be the same. Each set of motors is putting out the same mechanical power either way for any set of riding conditions, whether under acceleration or constant speed. But the 18s set of motors with less motor current will have lower I^2R losses for any identical performance condition. When you add up the I^2R losses and the mechanical output, it approximates the battery wattage. So essentially with the 18S option here, the same mechanical power is coming out of the motor, but less electrical power is going into the motor, because less I^2R losses are coming out of the motor in the form of heat.

So essentially these 2 setups give the same performance, but not the same electrical wattage for identical performance. The 18S draws less wattage from the battery for identical performance.

But while we’re on the subject, there’s no good reason to lower the motor current limit on the 18S option, so essentially, lowering the motor current limit is pointless, and when you don’t do that, the 18S option gives you 50% more torque if you gear for the same top speed.

Also I think you meant gear ratio is 50% higher on the 18S (not the 12S) for same top speed.

[Titoxd1000]

I don’t think anyone is running 190kv at 18s and spinning up the full RPM allowed. Usually people are going down in the 120-140kv range. Lower KV motors handle less amps.

[mutantbass]

@ross_forp

But the 18s set of motors with less motor current will have lower I^2R losses for any identical performance condition. When you add up the I^2R losses and the mechanical output, it approximates the battery wattage. So essentially with the 18S option here, the same mechanical power is coming out of the motor, but less electrical power is going into the motor, because less I^2R losses are coming out of the motor in the form of heat.

We talked about this earlier. The higher mosfet RDSon and lower KV motors having higher internal resistance would offset the 18s advantage.

@ross_forp

The 18S draws less wattage from the battery for identical performance.

This is just a claim that I have yet to see justified.

@ross_forp

But while we’re on the subject, there’s no good reason to lower the motor current limit on the 18S option, so essentially, lowering the motor current limit is pointless, and when you don’t do that, the 18S option gives you 50% more torque if you gear for the same top speed.

Umm there is. Those extra amps do not exist on the 18s setup. Your P count is lower.

@ross_forp

Also I think you meant gear ratio is 50% higher on the 18S (not the 12S) for same top speed.

@mutantbass

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

I said gearing higher, not higher gearing ratio. Gearing higher on 12s is saying the same thing as higher gear ratio on 18s. lol

[Gamer43]

@mutantbass

We talked about this earlier. The higher mosfet RDSon and lower KV motors having higher internal resistance would offset the 18s advantage.

Resistance in the motor goes up by a ratio of 18/12 = 3/2 if we adjust the Kv. (same thing applies to the battery)
Current goes down by a ratio of 12/18 = 2/3

(2/3) ^ 2 * 3/2 = 2/3.

Actually, if the Kv is the same. The resistance stays the same so in reality it’s 4/9 if you just change the gearing.

The problem is you need a multistage reduction at that point.

[mutantbass]

@Gamer43

The problem is you need a multistage reduction at that point.

Bingo. That is going to introduce it’s own inefficiencies.

I have gone from 6s to 10s to 12s. Zero difference when setup the same way. Only reason I run 12s is that my board is a travel lipo setup and 12 goes very nicely into 2/3/4/6.

[rusins]

@ross_forp

But while we’re on the subject, there’s no good reason to lower the motor current limit on the 18S option, so essentially, lowering the motor current limit is pointless, and when you don’t do that, the 18S option gives you 50% more torque if you gear for the same top speed.

Did you see the beautiful graphs @fessyfoo shared? They are excellent at highlighting how any extra speed is with less torque at the high end, or any extra torque on the low end ends sooner than usual.

And I will argue that you can achieve the same effects remaining on 12s by going higher kv, or higher kv with a larger gear ratio, as long as you can still increase motor current in your ESC.