Swing bridges in Obduction are span-bridges which rotate around a center bearing and according to their position connect various passage points. There are two such bridges in the game, one is in Hunrath and one in Kaptar. Each one also defines a location of its Cell.
The swing bridge of Hunrath[]
This bridge is pivoted on a central column based on the riverbed with bearings above and below it. The upper bearing is fixed on two metal H-beams which connect to pillars on both sides of the river. A mechanism based on the waterflow of the river powers the movement of the bridge. Two vertical panels of corrugated metal on either side of the axis can be lowered or raised by a lever at the middle which is made of a small plane propeller.
When the right panel is lowered, the left is raised, and the waterflow tends to push the bridge to rotate 90° anticlockwise. When the left panel is lowered, the right is raised and the waterflow tend to push the bridge to rotate 90° clockwise. The rotation however is blocked by the upper bearing and can be unblocked by pulling a cable that is connected to a nearby lever on the bank of the river. The lever only permits a 90° move at a time. No movement is possible, however, unless the water has been diverted to the waterfall and the level of the river has risen.
Possible positions[]
The bridge can be rotated to three positions. The central one, which is its initial position, permits passage across the river banks, as well as connects a grated metal catwalk overhead that runs along the wall of Hunrath. The overhead passage is cut off if the bridge is rotated to either side. If the right panel is lowered and the bridge permitted to rotate by the lever, it swings anticlockwise and the path to the rear part of Hunrath is enabled. Later in the game the bridge has to be moved back to its central position and even later rotated clockwise so that the path along the opposite bank is enabled. Luckily, this move is blocked until a later stage in the game.
The swing bridge of Kaptar[]
Upon arriving in the cell of Kaptar, the only way forward is to cross a swing bridge pivoted on a lone rock between the two sides. The bridge has two arms at an angle and its center bearing is on a metal hub on the rock. The rotating mechanism is powered by a simple overhead propeller whose axis is at the very center of the hub. There is a little space on the rock to get off the hub and lock or unlock the movement of the propeller. If enabled, a lever that is operated while on the hub can move the bridge to rotate in either direction if the arms are clear of obstacles.
Possible positions[]
The intitial position of the bridge has it opposite arm in mid-air. A clockwise movement brings the opposite end on the ledge of a rock, but the arm we came from meets only solid rock. A further clockwise move is possible if a metal rod blocking it is pushed out of the way. The opposite arm moves a bit further on the same ledge and the arm we came from leads straight into a cell wall portal, initially disabled.
More about this bridge can be found at the Kaptar swing bridge puzzle (spoiler warning).