On Tue, 22 Jan 2013 16:13:30 -0700, Ashton Crusher
wrote:

Not only do I wonder *why* they change rotation, but *how*? I'm
guessing they use a shaded-pole motor (I'm not sure), and as far as I
know, those motors only turn one direction. Either CW or CCW.
Unless there's a belt driving them, there is not much room for any other
type of motor in the base of the oven.

Anyone know anything about this?

I see some suggest it's just random but I think it's random "on
purpose". In the old days they always went the same direction. What
I read was that they purposely make, or at least allow, them to revere
direction because they found that was a good way to dislodge crumbs
that would otherwise get stuck on/under the little support wheels and
make the turntable jerk/squeak/squeal.

Someone had their smarts working to figure that out....