Flame Flingers

Semi final two, and it's third time out for the Anoraks, already victorious in the sand racer and power rowing challenges. The Up 'n' Atoms took the bowling and spy car contests. Their challenge this week is to build a motorised flame thrower, which will burn up targets at a range of distances.

The Atoms are joined by Richard Little, who knows his engines. The plan here is to power two sets of wheels on a frame, feed in the projectiles from the back, and have it spat out at high speed from the front. Richard's initial plan is to power the top set of wheels only, which might be bad for direction and distance.

The Anoraks have Paul Denny, an expert in siege weapons. Paul plans to keep it simple, with a motorised sling - a revolving steel bar, mounted on the rear axle of a van, spinning at several hundred RPM, and released by a mechanical contraption.

This pair of experts met in the Car Flinging Challenge in the 2002 series, when Richard's ramp beat Paul's collapsing trebuchet.

Quickly, the Atoms find the wheels they need, and the Anoraks find a taxi that might well provide the axle they need. Less quickly, the Atoms find an airport conveyor belt. It's long, it's reasonably thin, and it's going to be a great base on which to mount their contraption. If they can move it back to base, naturally... This is a non-trivial task, as even though Atom captain Ali thinks he's driving in reverse, it's going forward. With only a little help from Lisa, the conveyor eventually arrives back at base.

In order to maintain structural integrity, the Atoms need to balance the weight of their fireball on their arm, otherwise the machine will vibrate itself to bits. They decide to balance the fireball with half its weight, so that the arm is never perfectly balanced, but the shock of losing the extra mass won't be so large. They also chop their taxi in two, but don't have enough ground clearance.

Problems, problems. The Anoraks need a trigger, the Atoms could use an engine that clearly works. The Atoms are a little lost, concerned about whether their engine will rotate in the right direction, but the Anoraks seem to be completely stuck without a trigger. It's a good job the Atoms checked - they were all set to build for an engine going clockwise, but their experiments showed the engine goes counter-clockwise. With that known, it's relatively plain sailing.

The Anoraks are in trouble - they've managed to weld some of their components back to front. Nasty. With barely one hour to go, their trigger is ready to weld. "Rotten" Lisa Rogers describes the contraption as a bit like the game
Mousetrap, and she's not a million miles away from the truth. Their late idea is to mount wheels along the front of the taxi, so that they can steer the device left and right.

The Atoms have mounted their drive shaft, and reckon it's a very good fit indeed. They should be able to drive it at the equivalent of 100mph. But with minutes to go, they realise they've not built a feed mechanism. Some corrugated
iron comes to the rescue. And they're yet to mount the second axle, which has to be exactly the right distance apart - too close and the fireballs are going nowhere, too distant and it'll fall short.

Eventually, time expires. The Anoraks reckon their work is complete, but the Atoms look like they could have done with a little longer. Indeed, in tinkering time, they add a dolly wheel to drive both sets of wheels. The Anoraks add the
rather essential firing pin.

Each team will have six shots to burn four targets at increasing distances. The Atoms go first, and their opening shot - at the 10m target - bursts into flame. Shot two, at 20m, goes a fraction to the left - literally inches, and that'll be the wind. Easily corrected for shot three, which bounces its way to the target.

At the 30m target, shot four lands about 5m short. They don't have the legs. Up the revs for shot five, which just rolls into the target. That's a strike! Shot six is a literal go for broke effort - rev the engine up to the max, but it goes about two metres to the right, and some way short.

The Anoraks' first shot bounces short, and rolls left, It turns out that the trigger isn't working properly, and released a little late. Shot two is a direct hit, caught by the target on the fly. Shot three, for 20m, has a very loud bang and crash, the ball falls out of the trigger, and there's a hairy moment when it lands on the fuel tank.

A bit of gaffa tape, a slower rotation, and shot four lands bang on target. Have they got the hang of this? Shot five needs to land on target - it lands about 5m short, then rolls to the target.

A hit with shot 6 is a win; a miss will throw the contest to the judge. It launches, it rolls, but it lands about 3m short. The judge calls it based on the final shot, and - probably correctly, though there are arguments to the contrary - gives it to the Anoraks.