MECHANISMS DNT 7059/01 2023 V/2

Design and Technology Notes for 7059/1 and 7055/1 Topic on Mechanisms Foreword; This is a collaborative effort due to the pertinent lack of DnT notes in the online space, headed by Tino (+65 8933 9390) and Wei En (+65 9752 6078) of Beatty Secondary, whom is contactable if necessary. 1) Input – movement into system - Process – conversion of INPUT to OUTPUT - Output – resultant converted moment 2) Feedback; The output is fed back to the input, on which depending on the output, the input is adjusted to achieve a desired result. - Open-loop Control System - An open-loop system has no feedback, so it cannot respond to environmental changes. - Closed-loop Control System - A closed loop system is able to respond to environmental changes using feedback from within the system. 3) Types of motion

4) Functions of mechanisms Conversion of motion; Changing of one type of motion to another. Transmission of motion; Changing the place of movement. Control of motion; Controlling the speed, amount of force, direction, and distance of movement. 5) Mechanical Advantage - Mechanisms are often used to allow a small effort to move a large load. - Mechanical advantage is the ratio between the output force and the input force - Calculated as 𝑀𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙 𝐴𝑑𝑣𝑎𝑛𝑡𝑎𝑔𝑒 = 𝑂𝑢𝑡𝑝𝑢𝑡 𝐹𝑜𝑟𝑐𝑒 𝐼𝑛𝑝𝑢𝑡 𝐹𝑜𝑟𝑐𝑒 - If the mechanical advantage > 1, output force will be larger than the input force. 6) Types of mechanisms 6a) Levers • First class lever – the fulcrum is in the middle of the effort and the load. • Second class lever – the load is in the middle between the fulcrum and the effort. • • Third class lever – the effort is in the middle between the fulcrum and the load. 6b) Linkages - Made by connected levers together. - Able to turn a small force into a large pushing force Four-bar linkage Consists of 4 connected links. Different movements can be achieved by changing the lengths of the links. Can be used to convert motion from: - One type to another; one speed to another - One size to another; and

- One axis to another 6c) Pulleys A pulley is a wheel on a axis or shaft. Pulleys are used to lift loads, transmit motion, and transmit power. - There are 2 types of pulleys; simple and compound pulley system. A simple pulley uses only one pulley; The fixed pulley is attached to a stationary object like a wall or ceiling. A movable pulley moves up or down with the effort. A compound pulley is a combination of fixed and movable pulleys. The pulleys are mounted on the fixed and moving axles. Pulleys are connected with rubber belts to transmit power from a motor to other working parts. They can be connected in either open drive or closed drive.

Advantage; Belts are simple and inexpensive. They run smoothly with little noise and vibration. They need no lubrication and require minimal maintenance. Disadvantage; Belts may slip and stretch, resulting in lowered efficiency. Application; Washing m