82 The Woodworker & Good Woodworking August 2019 http://www.getwoodworking.com
FEATURE Building a giant trebuchet
hands of a clock, attached at a fulcrum; the long
arm holds the firing sling and the short arm holds
the counterweight. The trebuchet is prepared for
firing by lowering the long arm and raising the
short arm, usually with a winch but in the case
of the Warwick trebuchet, with the use of two
treadmills. When the counterweight has not been
tensioned, both arms hang plumb. When the arm
has been lowered and locked in place, the sling
is loaded with a projectile, which is then released
by the trigger causing the projectile to be hurled
towards its target (photos 3 & 4 ). The Warwick-
based trebuchet took eight men half an hour
(four men running on the two 4m treadmills) to
lift the counter weight, weighing 6 tonnes, ready
for firing. In 2006, the trebuchet proved to be the
most powerful of its type in existence, sending
a projectile weighing 13kg 249m at a speed of
121mph. The Warwick trebuchet also literally
hit the headlines when the Telegraph reported
around this time that: “Hundreds of tourists
have been evacuated from Warwick Castle after a
burning cannonball fired from the world’s largest
working siege machine destroyed a medieval
boathouse by fire.” This certainly demonstrated
the lethal potency of siege weaponry, even
in the 21st century.The Outlaw King trebuchet
As well as creating a new Guinness World Record
for the most powerful siege engine of its type, the
trebuchet also served to have a bearing on future
events, as Fergus Stuart would discover. In 2017,
Fergus received an unusual enquiry from LoudounProductions Ltd, who had been set up to
manage the feature length Netflix film Outlaw
King, about building a new trebuchet for the film.
In this film, David Mackenzie (Director) retells
the story of Robert the Bruce and his 14th century
defiance against the English king, Edward I, which
ended in a historic victory for Scotland. The film
encapsulates a world full of beards, smocks,
monks with tonsures, smokey bonfires, medieval
feasting and battle scenes, but alas, no scene
showing Robert the Bruce hiding in a cave with
a co-starring spider. It was Loudoun Production’s
job to recreate the period with sets and props,
costumes and whatever it took, so hence the offer
to Fergus and his team to build a replica trebuchet
for the crucial Stirling Castle siege scene. Fergus
explains: “They were familiar with the Warwick
Castle trebuchet and who made it.” The production
company had obtained full working drawings of
the trebuchet, which the Scottish Yard then used
in its construction. “We didn’t need to translate
them into ‘frame drawings’, which we do in a
conventional project, such was the detail of
their diagrams,” Fergus says (photo 5).
Although very similar to the Warwick Castle
design, the Outlaw King trebuchet differed in the
fact it was only two-thirds the height of the earlier
Warwick Castle reconstruction. This truncated
version was 4.5m in height and built of Douglas
fir rather than oak. The finish was to be ‘aged’,
so Douglas fir was more cost effective than oak
(photo 6). All the moving parts of the firing arm
were omitted. The moving parts you see in the
film, such as the firing arm hurling a burning12 The ladder frame’s main function is to support 13 The guide chute is positioned on top of the ladder
the two A-frames8 Edward cuts the securing rope to hurl the projectile
towards Stirling castle. These details to be later
added by CGI7 Edward I approaches the trebuchet. Detail of
firing arm and Stirling Castle to be added by CGI
Photographs courtesy of Netflix6 Completed truncated trebuchet at
reconstruction yard
11 Chassis and ladder frame assembled on site
10 The spine beam is scarfed together
9 Beginnings of the trebuchet base (half of)