First some testing.
Here you can see the clutch.
When it's open the arms and the gondolas doesn't spin but the whole ride spins as one.
When it's closed everything spins.
On the left end of the horizontal boom you can see 3 gears that changes the
direction of the main axle for the left arm. First I thought I can save 3 gears
by changing the direction inside of the arm. However this caused a strange
phenomenon: one arm was turning faster than the other. This was not good. Both
gondolas should be down at the same time in order to load the passengers. Then
I understood: the other arm was turning in the same direction as the main axle
which causes it to turn faster while the other arm was turning against the main
axle direction which causes it to turn slower. So I had to put those 3 gears there.
Photo from the homepage of Mel Park