Gravity needs the arrangement. A cabin suspended from a freely turning joint can remain upright because its center of gravity sits below the suspension axis, making the cabin behave like a pendulum. Geometry does the work. As the wheel turns, the joint lets the support rotate without forcing the passenger compartment to follow its changing angle.
Simplicity has its conditions. When a hanging cabin tilts, gravity produces restoring torque, which tends to pull its center of gravity back beneath the suspension point rather than leave the floor at an angle. Upright does not mean motionless. Wind, braking and passengers shifting their weight can make the cabin swing, so damping can reduce oscillations without replacing gravity as the leveling mechanism. Size alone decides nothing. A large cabin can still hang this way if its mounting provides clearance and its mass remains appropriately distributed below the pivot.
Motors buy architectural freedom. Where a capsule rides outside the rim or uses a mounting that cannot simply hang freely, powered mechanisms can rotate it relative to the wheel so its floor remains level. The distinction is mechanical. Depending on the design, sensors and controllers monitor cabin angle or wheel position, while motors counter the rotation that would otherwise tip the compartment; bearings permit the relative movement. Complexity brings maintenance obligations. Such systems require power, monitoring and fault protection, although mechanical leveling arrangements also exist, leaving the apparently effortless horizontal floor dependent on machinery passengers scarcely notice.
