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[ The challenge and teams | Result | Rebels' diary | Atoms' diary | Science | Related links ]
General science
The designs
Pros and cons
Kinetic energy transfer
Kinetic energy is energy caused by moving. A car running at 60mph has enough kinetic energy to coast along with its motor cut off for another half a mile or so. It slows when the energy is 'eaten-up' by drag and mechanical friction, or when the car hits an obstacle which causes it to stop.
Kinetic energy (KE) is shed faster at first (because it varies with the square of speed). After half the braking period, only a quarter of the kinetic energy will remain.
Momentum
Momentum was critical to this week's challenge because knocking pins down is all about a transfer of momentum from the team's machines to the pins.
Momentum can be defined as 'mass in motion'. All objects have mass, so if an object is moving, it also has momentum. The amount of momentum which an object has is dependent upon two variables: how much stuff is moving and how fast the stuff is moving. Momentum depends upon the variables mass and velocity. In terms of an equation, the momentum of an object is equal to the mass of the object times the velocity of the object: Momentum = mass * velocity
Friction
If you are in a coasting vehicle, friction provides a long braking distance and eventually you will stop. Friction force will vary depending on the material making contact with the ground and what the ground material is and how level it is. Our teams needed to have wheels which produced enough traction to grip the ground but not so much that the wheels were 'sticky', producing lots of friction. This is why a professional bowling alley will oil and shine their alleys because they want to ensure there is as little friction as possible so the ball loses less speed as it travels towards the pins.
Keeping rolling without an engine
Under very hard braking, the front wheels of a typical road car provide about 70% of the braking effort. This is because the grip of the tyres is proportional to the weight acting on them and because the vehicle's weight is thrown forwards by braking.
When you see a car doing an emergency stop, you see the nose of the car dive as the front suspension compresses under the extra weight. It is at this point our teams wanted their bowling banger to harness this kinetic energy transfer to let their respective 'balls' roll into the pins.
The Up 'n Atoms welded a massive weighty counterweight above the head of their driver and out to the front because they wanted to mess with the centre of gravity, encouraging forward momentum as the weight pulled down on the front of the arc in a roll.
When it didn't quite work, they filled the canister with water - adding more weight to encourage the forward roll to continue.
REME Rebels
The Rebels built a pivoting trolley with a seat and small engine from a scooter. The pivot point was at the rear of the trolley. At the front of the trolley there was a sprung catch operated by a foot pedal. Damper springs under compression pushed down on the circular drum when the catch was released. Before release, the vehicle was effectively in an 'armed' state.
Expert Pete wanted to build the drum or wheels from rims gas-axed or cut out of welded sheet steel and cross-bracing. On the outer circumference of the wheel, he wanted there to be a flat plate strip running surface for smooth running.
On reaching the foul line, the drum would drop to the ground under the force of the spring compression in the dampeners and the trolley would pivot into the wheel where it would lock in place, held by a ratchet catch.
Up 'n Atoms
The Up 'n Atoms plan was for a micro car with a huge roll cage surrounding it. The car's wheels protruded at the bottom for power and on hard braking the entire vehicle rolled on its cage and two pivoting sections completed the sphere to enable a full 360-degree roll.
The pivoting sections of the Up 'n Atoms' design dropped down through gravitational force and a catch activates upon connection being made to secure the two sections and complete the full circle.
The Atoms opted for a more labour-intensive process for the fabrication of their roll-cage segments. They used straight pieces of box which they cut at small regular intervals, then bent and welded them back together. This was a good system as it enabled them to manufacture the curve to their exact specifications - but it was hugely labour intensive.
REME Rebels
Pros