CCEA A-Level Technology and Design AS 1 Mechanical and Pneumatic Systems: a complete overview of motion, levers, gears, pulleys, cams and pneumatics

What this option demands

The AS Mechanical and Pneumatic Systems option is the systems-and-control half of the AS year for students who choose mechanical control over electronics. It teaches you to analyse mechanisms that transmit and modify motion and force, and to control motion with compressed air. The examiners test the vocabulary of motion and mechanisms and a set of standard calculations: moments and mechanical advantage, gear and velocity ratios, and cylinder thrust.

This guide walks through the dot points of the option, then sets out the exam patterns CCEA repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

Motion, levers and rotary drives

There are four types of motion - linear, rotary, reciprocating and oscillating - and a mechanism changes the type, direction or magnitude of motion or force. Levers (first, second and third class) obey the principle of moments (effort times effort arm = load times load arm) and give a mechanical advantage of load over effort, trading force for movement. Gears change speed, torque and direction: the gear ratio is driven over driver teeth, and a reduction trades speed for torque, with compound trains multiplying the stages. Belt, pulley and chain drives transmit rotary motion with a velocity ratio of driven over driver diameter, the belt able to slip and the chain giving a positive drive.

Cams and pneumatics

Cams and followers convert rotary motion into reciprocating or oscillating motion, described by rise, fall and dwell, with profiles (pear, eccentric, heart-shaped) chosen for the motion required; the crank and slider converts rotary to reciprocating motion. Pneumatic systems use single- and double-acting cylinders controlled by 3/2 and 5/2 valves, with the output thrust given by $F = pA$.

How this option is examined

A typical CCEA profile for the mechanical option:

• Calculation. Moments and mechanical advantage, gear and velocity ratios, compound trains, pulley lifting systems, and cylinder thrust.
• Motion analysis. Identifying input and output motions, and reading a cam profile for rise, fall and dwell.
• Selection. Choosing a mechanism, gear arrangement, drive or cylinder/valve for a job.
• Reasoning. The speed-torque trade-off and the force-for-distance trade-off.

Check your knowledge

A mix of calculation and recall questions covering the option. Attempt them, then check against the solutions.

1. Name the four types of motion. (2 marks)
2. State the principle of moments. (2 marks)
3. A lever lifts an 800 N load with a 200 N effort. Find the mechanical advantage. (1 mark)
4. A driver gear of 20 teeth meshes with a 80-tooth driven gear at 400 rev/min. Find the output speed. (2 marks)
5. A 40 mm driver pulley drives a 120 mm pulley. State the velocity ratio. (1 mark)
6. Define dwell in a cam mechanism. (1 mark)
7. A cylinder piston of area $0.002\ \text{m}^2$ runs at 700 kPa. Find the thrust. (2 marks)
8. Which control valve operates a double-acting cylinder? (1 mark)