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Wednesday, November 30, 2011

Traps: Trigger Delays

Adding a delay to a trigger pretty much just involves knowing how long some event takes to finish and setting up a mechanical test for completion. In pseudo-medieval settings, it's probably going to be one of these three:
  • Quantity: How long does it take for a container to fill or empty?
  • Consumption: How long does it take something to be used up?
  • Speed: How long does it take for an object to travel a given distance?
The quantity test usually involves a container sitting on a compression or pressure trigger (activated when enough weight has been added or removed,) or a container with a lever trigger inside it (activated when the contents of the container reach a certain height.) For example, if a trap designer knows how long it takes for water to drain from a barrel, the designer can place a float in the barrel attached to a lever, exactly as you would see in a toilet tank, and connect another lever trigger to a cork in the bottom of the barrel. When one lever is tripped by, say, an adventurer opening a door, the cork is pulled and the water begins to drain. When the barrel is empty, the lever on the float reaches its "triggered" position, triggering a trap to go off. This allows a trap designer to make a portcullis drop 1 turn after adventurers have entered a room, for example. Alternatively, a trigger can be designed that drains a small amount of water into a reservoir each time the trigger is activated; tripping the trigger a certain number of times fills the reservoir completely, raising a float lever to the proper height and triggering a trap. Other substances can be used, for example sand in a trigger that must sit unattended for years, or pebbles dropped one at a time onto a pressure plate.

Water that empties from a barrel can also be seen as a consumption test, which provides clues as to how to set up other such tests. For example, instead of draining a barrel, a trigger can merely open it and allow the water to evaporate, for a very long delay. Other consumption tests may involve fire; a candle attached to a lever pushes it down with its weight, but if it is lit, wax lost to melting reduces the candles weight, eventually activating a trigger. A simpler, more iconic method is the candle slowly burning through a rope; when the rope breaks, whatever it is holding up drops.

The speed test generally involves an object falling or rolling a given distance, triggering a lever or pressure plate when it reaches its destination. The mechanism is less complicated in some ways than quantity or consumption tests, and requires less material; a marble dropped into a grooved track is much smaller and will last longer than a barrel of water waiting to be drained. On the other hand, a speed test usually requires more space than the other two tests, especially for long delays. A variation of the speed test involves a waterwheel or windmill that can be connected to a series of gears arranged as a mechanical counting device. Tripping one trigger engages the power source to the gears; every time the first gear completes a revolution, it advances the second gear one increment, and when the second gear completes its revolution, it increments the third, and so on; this allows for more precise delays, but obviously involves more planning. And similar to the quantity test, the wheels can be set to advance every time an event occurs, instead of continuously after a single event, so that a trap can be set to go off after every 12 pulls of a lever.

The mechanism of any delay counts as a separate item that can be searched for, in addition to the trigger that activates the delay or the final trap triggered by the whole system. They are usually hidden inside wall or ceilings, or below floors, making them hard to see, plus the adventurers may notice an initial pressure plate and assume everything is safe when it is triggered from a distance, but appears to have no effect. There may be other clues to the mechanism's presence; water draining from a barrel may spill a little and seep through cracks, while a burning rope may give off an odor. Also, there may be a slight noise from water or sand falling, or quite a bit more noise from wheels squeaking as a stone weight tied to a rope descends, or a marble rolles down a series of ramps.

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