When using electric motors to power RC model aircraft you'll often hear the term KV so what is it?

In this video, I explain what KV is and how it can be used to calculate the RPMs of a motor when powered from a battery of a known voltage. I also demonstrate how to measure the KV of a motor when it is unknown although you can buy a KV meter which will do the job much more simply if you want.

I'm sorry that this video is a bit long I may reedit it later and shorten it up a bit.