Unit 3
Topic 5: Mechanical systems and control Represent gear systems graphically: use circular templates and/or pair of compasses to draw gear systems
with: • The driven gear rotating in the opposite direction to the driver (counter rotation). • The driven gear rotating in the same direction to the driver (include an idler gear). • The driven gear rotating faster than the driver (with and without an idler). • The driven gear rotating slower than the driver (with and without an idler).
Design brief: learners write a design brief with specifications for a device that will use a combination of gears to
achieve: • A mechanical advantage with force multiplication of three times. • An increase in output velocity of four times.
Draw: use an isometric projection using simple instruments (as in Maths Set) to draw sketches showing gear systems that meet each of the two above specifications.
Sketches (2-D) showing gear systems that: • Provide an output force four times greater than the input force (MA = 4:1). • Provide double the rotation rate on a driven axle at 90o to the driver axle.
System analysis – bicycle gear system Analysis of the gears used on modern bicycles – terminology: master/slave or driver/driven; chain wheel; cogs. Systems diagrams Analyse a mechanical system by breaking it into input-process-output. Draw a systems diagram for a gear system with a mechanical advantage of 4 : 1. Plan a mechanical system to produce a specific output. Systems diagram for a gear train with the driven gear rotating faster than the driver.
4
Learners working in teams investigate and report on one of the following: •
• •
119–122
Investigate: The impact on the environment as a result of mining of: acid mine drainage OR investigate: The impact on the environment as a result of mining of dust pollution from mine dumps on residential areas. OR
investigate: Iron age technology: Indigenous mining of iron in South Africa before the modern era OR investigate: Bias in technology: Gender bias in career choice / opportunities related to mining.
20 2 2
Learner’s Book page
113–118
Time
allocation (2 hours)
2
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