Ye Olde



by Stan Moore -- August 9, 2003

The trebuchet is a medieval engine of war used during the siege of a castle to knock down its walls.

They were huge machines in which the beam (throwing arm) was often a whole tree trunk, and objects of several hundred pounds were thrown.

This trebuchet is designed for the more modest goal of launching golfballs, and can be disassembled for storage and transport.
Here is a stroboscopic diagram of a trebuchet firing a projectile. The ball starts in a sling laying in a trough. When the counterweight is released, it swings the beam around whipping the sling up and over where the missile is released, and shot off toward the target.
Diagram from Trebuchet Simulator by
Donald B. Siano


Here all of the trebuchet's wooden pieces are identified...


And here the small parts are identified...



The trebuchet is assembled as follows ...

treb06 Screw the trigger to the underside of the rear crosspiece.
Lay the rails and 3 crosspieces out as shown.

Start the center crosspiece into the slots in the rails, then start the front and rear crosspieces into their slots.
treb08 Slide the rails together until all crosspieces are seated.

Then use a rubber mallet to gently tap taper pins into the front and rear crosspieces.


Insert the braces into the center crosspiece slots.

Seat the braces, and secure them with taper pins under the crosspiece.

Now find the upright with two small holes near the lower end. This is the right-rear upright. Insert it into one of the crown pieces.

The uprights without any small holes are the front ones. Select one and insert it into the crown piece.

Adjust the uprights until they protrude the same amount above the crown piece.
treb10 Secure the uprights with taper pins above the crown.

Repeat this process for the other crown and uprights. The upright with one small hole is for the left-rear.


Set the beam rightside up.

( the bottom of the small end is rounded over)

Insert the axle into the beam, and slip a spacer on each end.
treb12 Now stand the two upright/crown assemblies up about a foot apart, and insert the ends of the axle into the crown pieces.

Be sure the uprights with the small holes are in the right relative positions, and that the beam is rightside up when pointed to the rear.


Lift this assembly up and lower it onto the rails.

Carefully work the uprights into the slots in the rails while guiding the tabs on the braces into their sockets in the crown pieces.
treb14 The dowels in the rails should fit snugly into the notches in the lower ends of the uprights when the uprights are properly seated.


Temporarily tie the beam to the uprights with the lanyard, and place 2x4 blocks under the rails to make this step easier. treb18
treb19 Insert the lanyard guide thru the small hole in the right-rear upright below the rail, and secure with washer and hex nut.
Insert the free end of the lanyard thru the guide, and then thru the small hole near the tip of the trigger.

Secure the lanyard near its end by wedging a turn under the plastic disk on the front of the trigger.


treb21 Secure one end of the sling to the end of the beam with the bent throwing pin and hex nut.
With the beam pointing to the rear, rotate the pin so the bend points up before tightening the nut. treb22


treb4 Load the three bricks into the counterweight (CW) cradle, and push the cap down over the four dowels.
Align the holes in the cradle arms with those in the cap, and tap the keeper into place. treb05


treb16 Place a 2x4 across the rails near the center.

Set the CW on the 2x4, and position it so the holes in the cradle arms line up with the hole in the large end of the beam.

Insert the CW-pin to secure the CW to the beam.
Remove the 2x4, and install the trough. The rear end of the trough should be flush with the back edge of the rear crosspiece.

This completes the trebuchet assembly.



The trebuchet is now potentially dangerous.
A misfired ball may fly backwards or even straight up.
Never stand in the plane of the beam -- either in the front or rear.
Never fire the trebuchet without a golfball in the sling.
Leave the beam pointed straight up when not in use.

Operation of the trebuchet

Setup the trebuchet on level ground in an open area free of people and animals or objects which could be damaged by a golfball.

Insure that there is a clear path of 100 yards or more to the target area, and provide at least 5 feet of clearance behind the trebuchet to allow for sling travel.

When relocating the trebuchet, it is easier and safer to remove the counterweight, and re-install it prior to use.

Removing the CW-pin, and keeping it in a safe place will discourage unauthorized use of the trebuchet.

treb30 Route the lanyard over the rail, and lay it on the ground to one side
of the trebuchet.

The trebuchet may be operated from either the left or right side.



treb25 Grasp the beam near the small end, and pull it down.

Insert the throwing-pin thru the free end of the sling, and then thru the hole in the trigger.

Push the safety-pin thru the small hole in the upright, then under the trigger, and thru the hole in the far upright.
Always leave the safety pin in place until the area is clear, and you are ready to fire.


treb28 At this point the counterweight is fully raised, and has the most potential energy.
Be especially careful whenever the CW is raised.
Place a golfball in the pouch of the sling, pull the lines taut, and position the pouch in the trough.
This trebuchet was designed for golfballs ONLY.
Do NOT attempt to throw anything other than golfballs.


Be sure the lines are running parallel, and are not tangled.

Tangled lines can result in a dangerous misfire.
To fire the trebuchet, remove the safety-pin, stand to one side, and gently pull on the lanyard until the trigger releases.


Now Go Forth and Conquer the World !

But be careful doing it !