Mechanotechnics N6

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Mechanotechnics N6

This document includes important informa on about the revised curriculum for Mechanotechnics N6, scheduled for implementa on in 2021.

Main changes to the curriculum New content General aims

• No longer concerned about the Chris an na onal norms.

Evalua on

• Weigh ng of Knowledge and Understanding has decreased from 10–40 to 10–25; Applica on has gone from 30 to 30–40 and Analysis, Synthesis and

Evalua on has gone from 20 to 20–35.

Module 1: Clutches (10%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles on plate, cone and centrifugal clutches, including axial forces, torque and power. • Overview of new content: – Includes content on the func ons, applica ons and theories that students will be required to recall, defi ne, describe and explain. – Students will be required to draw labelled diagrams. – Many new calcula ons have been prescribed. • Iden fy the primary func ons of clutches. • Draw and label mul -plate clutches. • Explain theories of plate and cone clutches, such as uniform wear theory and uniform pressure theory. • Defi ne conical clutches and explain their applica ons. • Describe and explain the applica ons of centrifugal clutches. • Perform numerous advanced calcula ons from basic principles: force required to press the plates together, the number of contact pairs required in a plate clutch to apply the required pressure, the combined speed between the engine and sha s at the moment no slip occurs, total me of slip, total me of sha to reach certain speed, torque, retarda on torque of engine or sha , combined speed, fric onal force, axial force to transmit given torque, total axial force to engage the clutch, moment of iner a, angular velocity, angular accelera on, me, maximum pressure, pressure at outer diameters, centrifugal force, force on spring, fric onal force, angular velocity, mass of shoe, power.

Module 2: Brakes (10%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles on band and block brakes, including tensions, torque and braking me. General introduc on • Explain the basic principles of brakes. • List the elements that are applied in brake design.

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Mechanotechnics N6

Main changes to the curriculum New content

• Overview of new content: – Now specifi cally broken up into the separate sec ons of band brakes, block brakes, and band and block brakes. – Includes theory of basic principles and applica ons that students will be required to list, defi ne, describe and explain. – Students will be required to draw labelled diagrams to assist in their explana ons. – Many new calcula ons have been prescribed. Band brakes • List and explain two types of band brakes. • Draw a labelled diagram that shows the theory applicable to fl at belt drives and centrifugal force. • Calculate tension ra o, torque, moments, power, ver cal components, number of revolu ons, me, angular velocity, work done and minimum coeffi cient of fric on. Block brakes • Defi ne and explain the applica on of block brakes. • Calculate coeffi cient of fric on, force, normal reac on force, power, diameter of disc, torque, me, number of revolu ons, drum diameter, number of turns and maximum braking torque. Band and block brakes • Describe band and block brakes. • Explain the structure of a fl exible steel band with the aid of a labelled diagram. • Calculate ght side band tension and slack side band tension. • Calculate normal reac on force of a brake drum on the block, fric onal force tangen al to the fric on circle of the drum and the semi-angle subtended at the drum centre by each brake block, minimum force, moments, power, distance, me, and resolve forces of the brake lever.

Module 3: Line sha s (10%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles on: – combined reac ons on solid sha bearings, torque and power – moments of gears, pulleys and fl ywheels on a sha – calcula ons of simultaneous reac ons on solid sha bearings (including torque and power on solid sha bearings), moments of gears, pulleys and fl ywheels on the sha s. General introduc on • List the basic principles and func ons of line sha s. • List the factors that should be considered when selec ng line sha s for specifi c func ons. Line sha calcula ons • Calculate torque, power, principal stress, sha diameter and sha speed, reac ons on the horizontal and ver cal plane, and ght side and slack side belt tensions. • Draw diagrams to illustrate the calcula ons.

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Mechanotechnics N6

Main changes to the curriculum New content

• Overview of new content: – Now split into three specifi c sec ons: ○  General introduc on, which covers basic principles, func ons and important factors of line sha s. ○  Line sha calcula ons, which also includes a specifi ca on for students to be able to draw diagrams to illustrate calcula ons. ○  Gear drive calcula ons, which includes specifi ca ons for students to be able to list and explain theory, with the aid of labelled diagrams. – Many new calcula ons have been prescribed for both line sha calcula ons and gear drive calcula ons. Gear drive calcula ons • List types of gears and applica ons. • List the forces that must be considered when two gears mesh. • Draw a labelled diagram to illustrate the direc on of forces when gears mesh. • Draw a diagram and explain the pressure angle between two gears in mesh. • Calculate ver cal and horizontal reac ons in bearings, torque transmi ed, power transmi ed, tangen al force between gears, radial force and belt tension.

Module 4: Flywheels (10%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles on: moments of iner a, and angular velocity and accelera on, including fl uctua on of speed and energy. • Overview of new content: – Includes content on the basic principles and func ons of fl ywheels that students will be required to list. – Many new calcula ons have been added.

Module 5: Reduc on gear boxes (10%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles on: – calcula ons of torque and power (including accelera on of diff erent gearbox components) General introduc on • List the basic principles and func ons of fl ywheels. Flywheel calcula ons • Calculate the moments of iner a, mass, radius of gyra on, angular accelera on, linear accelera on, number of revolu ons, pulley or fl ywheel diameter, me, pulley radius, kine c energy, poten al energy, displacement, linear velocity, tangen al accelera on, centripetal accelera on, angle, average angular decelera on, fric on torque, power, mass percentage of error, rota onal speed and loss in kine c energy. • Calculate mass moment of iner a of a compound system. • Calculate the percentage of error in mass moment of iner a if only the ream is considered. • Calculate coeffi cient of speed. General introduc on • List the basic principles and func ons of reduc on gearboxes. • Draw a diagram to illustrate wheel and pinion in a gear train.

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Mechanotechnics N6

Main changes to the curriculum New content

– calcula ons on worm gear drives, including helix angle of worm screw thread and axial forces on worms and worm wheels. • Overview of new content: – Includes theory of basic principles and func ons for gear trains and worm gear drives that students will be required to list, defi ne, describe, and explain. – Students will be required to draw labelled diagrams to assist in their explana ons. – Many new calcula ons have been prescribed for both gear trains and worm gear drives. Gear trains (simple and compound gear trains) • Defi ne the term gear train and give examples of gear trains and applica ons thereof. • Accelera on of gear trains (simple and compound) – Calculate torque required for accelera on, effi ciency of gears, equivalent moment of iner a, input and output torque, resis ng torque, and total kine c energy. • Worm gear drives – Explain the working principle of worm gear drive. – Draw diagrams to show single start worm gear and double threaded worm gear. • Worm gear drive calcula ons – List the formulas, quan es, symbols and basic SI units for units of measurements used on worm gear drive calcula ons. – Calculate worm helix angle, angle of fric on, effi ciency of worm drive, power output and input. – Calculate pitch circle diameter, peripheral velocity, end thrust, number of teeth on worm wheel, gear ra o, centre distance, reduc on gear effi ciency and fric onal torque. – Calculate number of threads on worm, eff ort, distance moved and velocity ra o.

Module 6: Rail trac on and vehicle dynamics (15%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles on: – calcula ons of accelera on and decelera on of trains on level tracks and inclines, including locomo ve trac ve eff orts, resistances and super-eleva on – calcula ons on the eff ect of centrifugal force around curves, maximum safe speeds, side thrust on rails, and condi ons for no side thrust with banking. Rail trac on • List the basic principles and func ons of rail trac on and vehicle dynamics. • Explain the eff ect of centrifugal forces on vehicles travelling around a curve. Rail resistance terms • Explain the meaning of the following terms: rolling resistance, inclined resistance, and accelera on force. Locomo ve trac ve eff ort • Defi ne locomo ve trac ve eff ort and drawbar pull.

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Mechanotechnics N6

Main changes to the curriculum New content

• Overview of new content: – Expanded to include six separate units. – Includes theory that students will be required to list, defi ne and explain. – Includes formulas, quan es, symbols and basic SI units that students will need to list for calcula ons on skidding and overturning on curved tracks and vehicle dynamics. – Many new calcula ons have been prescribed for rail trac on calcula ons, skidding and overturning on curved tracks, and vehicle dynamics. Rail trac on calcula ons • Calculate speed on level tracks, accelera on, decelera on, upward movement and downward movement, constant accelera on and decelera on, total locomo ve force, wheel speed, locomo ve trac ve eff ort, locomo ve power, trac ve resistance, accelera on force, me, average power developed, drawbar pull, grade resistance, distance, braking force, energy dissipa on, retarding force, axle torque, velocity ra o, number of drive axles, mass, transmission losses and maximum speed. Skidding and overturning on curved tracks • List the formulas, quan es, symbols and basic SI units for units of measurements used on skidding and overturning on curve calcula ons. • Defi ne the following terms: unbanked and banked tracks, and unbanked curves and banked curves. • Calculate maximum speed without skidding and overturning, coeffi cient of fric on, moments, super-eleva on, maximum speed, side thrust, minimum radius of unbanked curves, banking angles. • Calculate mass, centrifugal force, centre of gravity, height of centre of gravity above the track and fric onal resistance. Vehicle dynamics • List the basic principles and func ons of vehicle dynamics. • List three opposing forces that aff ect trac ve eff ort at constant speed. • List the quan es, symbols and basic SI units for units of measurements used on vehicle dynamics. • Defi ne the following terms: power, trac ve eff ort and engine torque.

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Mechanotechnics N6

Main changes to the curriculum New content

• Calculate the following: input and output power, axle torque, trac ve eff ort, engine torque, gear ra o, transmission effi ciency, braking torque, decelera on, ini al angular velocity, engine power on level road, engine power on incline, angular and linear accelera on, angular velocity, angular retarda on, magnitude of the balancing couple, load transfer, normal reac ons, weight, front rear axle reac ons, load transfer, minimum distance before stopping, and maximum possible accelera on.

Module 7: Sta c and dynamic balancing (15%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles on sta c and dynamic balancing, focusing on: – balancing of masses rota ng in the same plane – balancing of masses rota ng in diff erent planes – dynamic forces on bearings. • Overview of new content: – Now also includes a unit on balancing of a single rota ng mass, with theory and calcula ons. – Includes theory that students will be required to explain with the aid of diagrams. – Students will now be required to construct couple and force polygons (diagrams). – Many new calcula ons have been prescribed for dynamic forces at bearings. Balancing a single rota ng mass • Explain the concept of balancing of a single rota ng mass with the aid of a labelled diagram. • Calculate the centripetal accelera on. • Calculate thrust on front bearings. • Calculate centrifugal force. • Calculate balancing of mass. Balancing of several masses rota ng in the same plane (rota ng coplanar masses) • With the aid of diagrams, explain the concepts of balancing of several masses rota ng in the same plane. • Explain the diff erence between sta c and dynamic balance. Balancing of masses rota ng in diff erent planes (Dalby’s Method) • Explain the concepts of balancing of several masses rota ng in diff erent planes. Dynamic forces at bearings • With the aid of diagrams, explain the concepts of dynamic forces at bearings. • Calculate axial distance between planes of revolu on, angles and mass. • Construct couple polygons and force polygons.

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Mechanotechnics N6

Main changes to the curriculum New content

• Calculate the value of couple, dynamical loads on bearings, rela ve angular posi on, distance, value of unbalanced couple, magnitude of bearing reac ons, direc on of reac ons, and minimum and maximum ver cal forces.

Module 8: Kinema cs (20%)

• Old syllabus only specifi ed ability to do advanced calcula ons from basic principles (with velocity and accelera on diagrams where necessary) for three sec ons: – Rela ve velocity diagrams, four-bar chain, and direc on of angular velocity inversion – Instantaneous centre of rota on, and three instantaneous centres in line – Slider crank mechanism (graphical determina on of velocity and accelera on of a slider or piston) • Overview of new content: – Now contains four separate units with new theory and calcula ons. – Students will be required to defi ne and explain concepts, terms and calcula ons with the aid of diagrams. – Many new calcula ons have been prescribed. Mo on • Defi ne the concept of relevant mo on. • Explain with the aid of diagrams the diff erence between linear mo on and angular mo on. • Defi ne the following terms with the aid of diagrams: machine, constrained kinema c pairs, kinema c chain, mechanism, four-bar chain, inversion, slider crank chain, rela ve velocity, and accelera on. Rela ve velocity and accelera on • Calculate velocity; add and subtract vectors. • Draw velocity diagrams for points on a link and

Instantaneous centre of a link. Centripetal and angular accelera on • Defi ne the terms centripetal and angular accelera on. • Draw diagrams and show the calcula ons for centripetal and angular accelera on. • Calculate tangen al accelera on. • Calculate centripetal and tangen al components. Accelera on of links • Defi ne the concept of accelera on of links. • Draw accelera on diagrams. • Calculate velocity, angular velocity and angular accelera on, and indicate direc on of rota on. • Calculate linear velocity and linear accelera on using diagrams. • Draw fully labelled space diagrams according to scale and fi nd the instantaneous centre. • Draw velocity and accelera on diagrams and show the angular accelera on of links and linear accelera on of the slider.

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Mechanotechnics N6

Important points

1. This version of the book contains all of the changes to the curriculum. 2. There is a Lecturer’s Guide with: • comprehensive answers • marking guidelines • links to online materials to support teaching.

Features of TVET First Mechanotechnics N6

• The book is fully updated and aligned with the new 2021 curriculum. • It is packed with fully explained, step-by-step examples. • Ac vi es are provided to help students apply their knowledge to real-life situa ons. • The book includes tables, bulleted lists and fully labelled diagrams to aid with explana on. • Starter ac vi es are included to help s mulate discussions for learning. • There are online links to help students understand real-life examples and mechanisms. • Exam ps are supplied to help students remember important methods for overcoming exam challenges. • Summaries and exam-type summa ve assessments, given at the end of each module, are indispensable tools for revision and exam prepara on. • Formula sheets with formula descrip ons, given at the end of each module, are excellent revision and consolida on tools for exam prepara on. • Important terminology is clearly explained and highlighted to help students understand diffi cult concepts and overcome language barriers. • Enrichment ac vi es are supplied for all eight modules to ensure full understanding of all concepts and further extend students. • Short answers for all module ac vi es are provided to allow students to self-assess. • There is an extensive Lecturer’s Guide with ac vity answers and background informa on (including marking guidelines). • Lesson and teaching plans have now incorporated via the 10-week plan.

TVET First author

Sparrow Consul ng