2 pole vs 4pole motor torque?..

[RC toy]

Hello my fellow physicists

Recently, I found some info about how poles affect torque/RPM. As you probably know, that is 4 pole motor will have twice the torque and twice less RPM as a 2 pole would have.
Also that 4 poles make about 3ft/lb while their high reving brothers make 1.5ft/lb of torque per horsepower (I think he was talking about AC motors)

Then i remember an old thread: http://www.rc-monster.com/forum/showthread.php?t=28030

This message to be exact.

Originally Posted by nuz69

Have faith ;)
The amp your motor will eat does not depend only on the gear reduction, the 1518 will produce more torque for the same amp rating, that's why it will consumme the same current for the same top speed than the 1515.
More over, the 1518 will have a better efficiency because it will handle the same power in a bigger size and at a lower RPM, so longer runtimes and lower temps ;) I warranty you the result ;)

Now if the mentioned 1515 and 1520 consume the same amount of amps, how does one make more torque than the other? I do realize it has a longer rotor, but the two different statements contradict each other. Im confused.

Please explain. Or is it a different story with AC motors? (like they have size standards or something?)

[snellemin]

Simplest way to explain is that the 1520 just makes more torque vs the 1515........

With the same continuous load the 1520 will waste less power in heat vs the 1515. So for 30A load, the 1520 will make more use of it vs the 1515.
See what works for you man. Sometimes the lighter weight of the 1515 is preferred for better handling.

[nativepaul]

To make a 1520 with the same KV as the 1515, they will use less turns of fatter wire, this fatter wire has less resistance and leads to better efficiency at high amp levels, also the fatter wires and bigger thermal mass mean it is capable of more amps than the 1515. So it it capable of delivering more torque than the 1515 and more efficient when producing it.

It is not a win win situation however. The bigger magnets of the longer 1520 rotor are harder to spin increasing the no load current and making it less efficient than the 1515 at low power levels when it is not producing all the torque it is capable of.

Which is more efficient depends on what you are driving, your gearing and your driving style.

In relation to the title question, the higher the pole count the harder the motor will try to achieve its unloaded RPM when loaded, (assuming similar quality for the motors and the same KVs the KTs (torque/amp) will be similar) they will draw more amps doing so.