The Build
Woof Justice
Woof Justice planned to go with a centrifugal mortar. Their design would rely on holding the basketball ammo in cages mounted at each end of a rotating arm.
To spin the arm they wanted to use a motorbike. Once the mortar was spinning, the cages would be opened and the basketballs should shoot out on a lobbing arc. It was a clever design, but accurately timing when to open the cages was always going to be difficult.
They got off to a fast start with Ian finding cable trunking for the cages and scavenging lots of strong steel for the framework of their mortar.
But while the scavengers were having some success, expert James was already finding out what Woof Justice's weakness was – the boys loved to talk about the plan, discussing every option in great detail before proceeding. James knew that time would be tight and they needed to just crack on.
With the addition of a decent moped to turn the arm on the shaft, the mortar should have come together quickly, but the A-frame which would hold the spinning frame took them hours to prepare, frustrating James and puzzling the judge.
So while the boys finessed their welds, James moved onto the cages that would hold the basketball ammo. The idea was that the spinning arm would fly past a catch, which when operated would clip the doors holding the balls open. It was a clever design, but would it stand up to the rigours of the test?
When Woof Justice had finally completed the A-frame for the arm to spin on there was still a ton of work to be done. They needed to get the shaft fitted, the arm fitted to the shaft, a wheel fitted onto the shaft and the bike fitted to friction drive the wheel. Phew! The crew looked on in horror. There was no way this was going to happen if the lads kept chatting.
But as it dawned on them how much time they had left, Woof Justice picked up the pace, managing to get the bike mounted and the arm and trigger mechanism working. Sadly the bike's engine was dead – it looked like it was flooded or fried by the welding. Unlike the Bus Boys next door, there would be no reassuring test fire in the build bay. Tinker time would be very important for the boys in blue.
The Bus Boys
The Bus Boys' design was much more like a traditional barrel mortar. But instead of using explosives, their mechanical approach relied on a tensioned spring that would then kick on a pivot, smacking the ball up and out of the barrel. It was a simple idea, but with so many interacting parts it was going to be a challenging build.
Captain Paul and expert Mike nab a metal frame from just outside the build bay to serve as the framework to hold all the moving parts. Out on the 'heap Pawel comes up trumps, finding some bearings for the kicking arm to pivot on and some leaf springs that will put tension into machine.
Pretty quickly the Bus Boys amass an amazing selection of metal and set to work with little talk and lots of grinding and welding. While Mike worked on the pivot the other lads mounted the leaf spring and made sure they would be able to get tension into it by building a cam into the design.
A cam is any device that converts rotary motion into linear motion. When they rotated the cam it pushed the spring into tension, cocking the arm ready for firing. It was a great idea, but sadly the cam they chose was so big and put so much tension into the mortar that it jammed up.
There was nothing for it but to cut off the large cam and fit a smaller one, undoing hours of work. So while the lads went back to the drawing board, Mike fashioned a trigger mechanism out of some chain and a pair of pliers (very ingenious) and made sure the lads had a frame that would aim the mortar in the right direction.
As the last hour ticked away the Bus Boys were working like a well-oiled machine. With the second cam and the trigger mounted they finished their mortar and even had time for a successful test fire. Things were looking good for tomorrow.
