King Arthur (KA)

The Hurl Wiki » Trebuchets » King Arthur (KA)

Super propped trebuchet where the arm is locked to the hanger when cocked with the arm pointing almost straight down, and the hanger almost straight up. The hanger is released first and when it gets to a certain point it pulls the secondary trigger releasing the arm. Invented by Chris Gerow who built the original King Arthur (Lots of great information on his site) pictured on the right. Also see the Floating Axle King Arthur

Machines

Mini KA

Power Source

Gravity

Advantages

Long drop for maximum energy
Small counter weights can yield very large distances
Very tunable

Disadvantages

Requires some extra complexity
Can be hard to cock

Triggers

There are two triggers for KAs, the primary and the secondary. The Primary holds the hanger inline with the arm initially. It usually consists of a rod through the arm and hanger. With the design, the trigger load is inversely proportional to it's distance from the hanger axle. The secondary trigger is much more complicated. It has to release the arm (allow it to rotate forward) at just the right time, and prevent if from rotating backwards. It is usually released by a line attached to an extension of the hanger (beyond the hanger axle). In the pictures below of mini-ka, it is a thin blue thread. This line is usually attached to a rod (like a nail) that holds the secondary closed.