MANGONEL (ONAGER)

Build your own Mangonel
The Mangonel (or Onager to some folks) uses a bundle of twisted ropes (known as the skein) for a type of power called torsion. 

This torsion engine is so powerful, a full-sized machine can hurl a bowling ball almost 1/4 of a mile!

Range and power were enhanced by increasing the weight at the butt end of the rotating arm.

This was accomplished by filling large continers, or hutches, with dirt or stones (some reports of using lead).

Initially these hutches were fixed in position in line with the axis of the arm. The added weight required design and construction of sturdy trestle frames.

The massive weights replaced the need for rope-pullers, but demanded mechanical mechanisms for lowering the the throwing end of the arm to allow loading its sling.
One such mechanism was the 'squirrel-cage' device shown here. It was used for many heavy-lifting tasks in the Middle Ages.

The fixed-hutch engine lurched when fired. This was dangerous to the nearby operating crews and was destructive to the engine, itself. Medieval military engineers experimented with suspended, swinging hutches that minimized the reactive jolts. The stability also allowed sustained firing upon the same target.