(SEM VI) THEORY EXAMINATION 2018-19 THEORY OF MACHINES

Theory of Machines (RME-602)

Complete Section-Wise Explanation – B.Tech Semester VI

 Introduction to the Subject

Theory of Machines is one of the most important mechanical engineering subjects because it explains how machines actually work in motion, not just how they are designed. This subject connects kinematics, dynamics, and real mechanical systems such as engines, gear trains, governors, cams, brakes, flywheels, and balancing systems.

The exam focuses on:

Understanding mechanisms and motion                      Analyzing velocity, acceleration, and forces

Solving numerical problems                                          Explaining practical mechanical systems

The paper is divided into three sections: A, B, and C, and all sections must be attempted as per instructions.

SECTION A – Conceptual Fundamentals

Pattern:
Attempt all questions
7 questions × 2 marks = 14 marks

Nature of Section A

Section A checks whether your basic concepts are crystal clear. These questions are short, but they come from core definitions that appear repeatedly throughout the syllabus. Answers must be brief, correct, and precise.

Explanation of Section A Topics

Lower Pair and Higher Pair:
A lower pair is a pair of elements having surface contact, such as piston and cylinder. A higher pair has point or line contact, such as cam and follower. Lower pairs are smoother and more durable, while higher pairs allow complex motion.

Redundant Degree of Freedom:
Redundant degree of freedom exists when a mechanism has more constraints than required, making some motions unnecessary or restricted without affecting the overall motion.

Law of Gearing:
The law of gearing states that the common normal at the point of contact of two gear teeth must always pass through a fixed point on the line of centers, ensuring constant velocity ratio.

Turning Moment Diagram:
A turning moment diagram represents the variation of torque produced by an engine during one cycle. It is drawn to analyze speed fluctuation and design flywheels.

D’Alembert’s Principle:
This principle converts a dynamic system into a static one by introducing inertia forces opposite to acceleration, making analysis easier.

Primary and Secondary Unbalance:
Primary unbalance is due to the main rotating mass, while secondary unbalance occurs due to the angularity of the connecting rod in reciprocating engines.

Transmission Dynamometers:
These are devices used to measure power transmitted by a shaft, such as belt transmission, torsion, and epicyclic dynamometers.

SECTION B – Analytical & Numerical Understanding

Pattern:
Attempt any three questions
3 × 7 marks = 21 marks

Nature of Section B

This section tests your ability to apply concepts, solve numericals, and explain relationships with clarity. Proper steps, diagrams, and formulas are essential here.

Explanation of Major Questions

Kinematic Chain Analysis (Question 2a)

This question tests your understanding of mechanism structure. You are required to identify binary, ternary, and quaternary links, calculate degrees of freedom using Gruebler’s equation, and understand loops and joints.

Gear Tooth Geometry (Question 2b)

This problem is based on involute gear theory. It involves calculating addendum using module, pressure angle, arc of contact, and circular pitch. This tests precision and formula application.

Porter Governor Numerical (Question 2c)

This question focuses on governor mechanics. You calculate equilibrium speed based on centrifugal force, ball mass, sleeve load, and geometry. The friction part tests understanding of speed range.

Flywheel Energy Relation (Question 2d)

Here, you derive the relationship between coefficient of fluctuation of speed and maximum fluctuation of energy. This concept is directly linked to turning moment diagrams and flywheel design.

Band Brake Numerical (Question 2e)

This problem applies friction theory to braking systems. You calculate operating force for clockwise and anticlockwise rotation, showing how direction affects braking torque.

 SECTION C – Advanced Analysis & Design

Pattern:
Attempt one part from each question
5 questions × 7 marks = 35 marks

This is the most important section. Performance here decides distinction or average grades.

Question 3 – Kinematics of Machines

Four-Bar Mechanism Analysis

This problem requires drawing velocity and acceleration diagrams for a four-bar chain. It tests graphical skills, understanding of relative velocity, and angular acceleration calculation.

Coriolis Acceleration

This is a theory-derivation question. You derive the magnitude and direction of Coriolis acceleration, which occurs when a body slides over a rotating link.

Question 4 – Cam & Gear Theory

Cam with SHM Motion

This question involves cam profile construction, displacement diagram, and calculation of maximum velocity and acceleration. It checks both drawing skill and theory application.

Gear Terminology

A theory question testing understanding of fundamental gear terms like pitch circle diameter, module, backlash, pressure angle, and addendum.

Question 5 – Dynamics of Engines & Flywheel

Slider-Crank Mechanism Numerical

This problem is based on forces in a reciprocating engine. You calculate piston force, gudgeon pin load, side thrust, and reversal speed. It tests combined kinematics and dynamics.

Flywheel Function & Energy Expression

You explain why flywheels are used and derive the expression for maximum fluctuation of energy from turning moment variation.

Question 6 – Balancing & Governors

Balancing of Rotating Masses

This is a classic numerical involving vector resolution both analytically and graphically. It checks understanding of static balancing.

Porter Governor Working

This theory question requires a neat sketch, explanation, and derivation of speed equation. Presentation is key here.

Question 7 – Brakes & Dynamometers

Self-Expanding Shoe Brake

This question explains why self-expanding brakes require less effort and derives friction torque expression.

Brake vs Dynamometer

You differentiate between braking and power-measuring devices and explain rope brake dynamometer with sketch.