In the assembly above there is a sleeve, a shaft to which a disc is integral, and two gears pivoted on two holes on the disc.
The two gears are constrained to each other and to another gear, part of the sleeve.
If I keep the disc steady, and rotate the sleeve, the two gears move as expected.
If, on the other hand, I keep the sleeve steady and rotate the disc the motion of the gears is... wrong.
I'd like to know the reason for this strange behavior.