Design and Technology

Cams
 Drop/Snail
A snail/drop cam has a slow rise and then a sudden drop. This is a one-event-per-turn cam with a slow build up to the peak and a rapidly decreasing edge. This cam has one direction only, which is counter clockwise.  Pear
A pear shaped cam that is made from a circular disc of material, which is then elongated to create its shape. This cam will provide a steady rise and fall in the in the follower followed by a period where the follower does not move.  Eccentric
An eccentric cam is a disc with its centre of rotation positioned ‘off centre’. This means as the cam rotates the flat follower rises and falls at a constant rate. As it rotates it pushes the flat follower upwards and then allows it to drop downwards. The movement is smooth and at a constant speed.

Cranks
An arm attached at right angles to a rotating shaft. It is used to convert a circular motion into a reciprocating motion. Attached to the end of the crank by a pivot is a connecting rod. The end of the rod attached to the crank moves in a circular motion, while the other end is usually constrained to move in a linear sliding motion. Gears
 Bevel
It is used when the direction of a shaft's rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The teeth on bevel gears can be straight, spiral or hypoid.

 Spur
Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions.  Worm
The worm gear only has one tooth but it is like a screw thread. The worm wheel, coloured yellow, is like a normal gear wheel or spur gear. The worm always drives the worm wheel round, it is never the opposite way round as the system tends to lock and jam. Pulleys
A simple machine consisting essentially of a wheel with a grooved rim in which a pulled rope or