Gandy and Roberts actively participates in experimental siege engine research. In particular we have examined the performance characteristics of the trebuchet — the siege artillery of the middle ages. Starting with small models we have built several machines of ever increasing size. We have developed mathematical methods of predicting the performance of any given machine. This has demonstrated clearly that contemporary descriptions of the performance of trebuchets were not exaggerated. There is no doubt that large trebuchets would have been capable of throwing 50 kg stone balls over 200 m and demolishing castle walls. Select photos for a larger view then use browsers back button to return to this page.
Mark i
This simple fixed weight trebuchet was constructed on Christmas Day 2000 inspired by an SBS documentary. It was powered by a collection of nuts, bolts and washers. The device was capable of launching grapes and cherries from the kitchen table to the sink, a distance of approximately 4.0 m.
Mark ii
This trebuchet, constructed from 10 mm dowel, constructed over the 2000 new year break, was inspired by the success of Mark i. Mark ii stands 450 mm at the axle and is currently powered by a jar of five cent pieces. The original swinging counter weight consisted of a collection of sinkers. This machine is capable of throwing a squash ball the length of the drawing office (about 15 m). The most significant advancement was the pyramidal light weight frame. By leaning each triangular frame inwards the axle is shortened significantly reducing bending forces.
Mark iii
This trebuchet was the big brother of Mark ii, constructed from 22 mm dowel, was designed to be highly configurable in order to allow the investigation of different configurations. The machine was tested with a fixed weight, and a swinging counter weight. It was tested fixed to the ground and with wheels. This trebuchet demonstrated the benefit of a fixed counter weight and wheels.
Mark iv
Mark iv was constructed with Mechano more for comic relief than serious experimentation. The sole purpose of this machine is to fling small plastic cows. This is a fixed weight device mounted on wheels
Mark v
Mark v is the most agricultural machine in our family, it was built using tea tree rounds and a 4.5 m hardwood throwing arm. The swinging weight is a flour sack filled with rocks weighing about 60 kg. This configuration allowed a throw of approximately 70 m with a 0.75 kg rock.
Mark vi
The Mark vi was represented the next generation of throwing device, this prototype was designed to be portable (fitting in a small trailer) and to be highly configurable to allow further experiments into the efficiency of different configurations. The counterweight can be fixed to the arm, or be hung from it. The base can be on wheels or be bolted down to a solid base. Best throw so far is a bocce ball to 100 m.
Mark vii
This polite monster will fold flat, may be carried by two people, and transported to site on a 1.2 m square trailer. In experienced hands Mark vii is off loaded and ready to go in 15 minutes and can throw a missile every 40 seconds. This is a fixed weight machine mounted on four timber wheels. The length of the counter weight arm can be adjusted by altering the weight locations. With a 105 kg counter weight, the Mark vii lobbed a 750 g bocce ball 140 m on it's first outing. Subsequent firings with some fine tuning extended the range to 165 m. The frame is of 80 mm diameter pole construction with simple bolted connections, the two part throwing arm is a plywood box section. This machine is not an historical replica, rather it is engineered or maximum efficiency — designed for minimum weight and maximum range for its size.
Mark viii
Powered by a tonne of sand this beast throws 7.5 kg balls 200 m or 15 kg balls 140 m. Computers, toilet pans, and the like fly near 100 m to their spectacular doom. The disassembled machine fits on a small truck and can be erected in about 2 hours. The design follows historical lines though some modern steel components have been used for ease of assembly and safety. It is 3.5 m high to the axle, 8.3 m high to the tip and weighs 3/4 tonne exclusive of the sand in the weight box. This is not a "model" but a full sized replica — albeit at the bottom end of the scale for a medieval siege engine. Awesome is an overused word these days, but this machine truly is — when it fires, the sling whistles as it accelerates the missile to a speed of over 165 kph. The missile flies in a graceful arc before plummeting to earth. Solid balls hit the ground with an emphatic THUD you feel from the launch site. More fragile ammo explodes impressively on impact.
Ballista
The ballista is an ancient weapon used by the Greeks and Romans — a form of large crossbow. These were much more difficult to build than the later trebuchet, but less powerful. The power is provided by torsion in twisted skeins — the ancients used hair or animal sinews but we had to use rope in this replica. This is a full sized replica of a small machine. It is able to hurl walnuts 50 m, but the ancients could build them better than us — the ancient texts indicate that machines this size could fire large arrows 200 m.
