Inrunner, outrunner, whats the dif?

[Varooom]

Sorry I posted this on the "build" area by mistake so I am posting again here where I should have posted it the first time.

Whats the pros and cons of these two types of motors?

When would I want one over the other?

thank you for your time,

Varooom

[kevinpratt823]

Type "inrunner vs. outrunner" in the forum search. There have been a few threads about it, though none very extensive. What I gather is, an outrunner is harder to cool, takes longer to spool up(reach max rpm), but is capable of more torque due to the larger rotating mass. An inrunner is easy to cool, spools up quicker, is capable of higher rpm, but not as much torque.

[keithbradley]

Outrunners have high pole counts in order to operate more efficiently in low RPM setups like planes and helis. They are less efficient at high RPM and also more prone to failure because the rotating mass is further from the center axis point. Air cooling is more effective because of their greater exposure to air and increased windage.

Inrunners are typically made for higher RPM applications and struggle at very low RPMs. The rotating mass is placed at the center of the motor, so centrifugal force is minimized.