How does a corn or wheat combine work?

How a combine works. Rotating drums pull the kernels off and they are threshed. Considering how hard it is to take kernels off by hand, I'm surprised how simplistic this rotating drum mechanism is. Seems like the combine gets several chances to separate kernels from chaff and silage.


This animation shows the inner workings of a wheat threshing machine, without the machine. Nice way to illustrate it.


http://youtu.be/Q74eWEfO4Ho
http://youtu.be/RMU0goBWRjY

7:38 through the rotor, onto the chaffer, then the sieve, then up the return elevator, through the cycle again, with the grain elevator taking kernels to the tank. 

https://youtu.be/vHAyaiNbqiE