ENGIN2303
ENGIN2303 – Mechanism and Machine Theory
Assignment 3 – Design task (25% of the course mark)
Due: Week 12 (Friday 13/10/2023)
Part A: Mechanism analysis
The crank in the mechanism shown below rotates with an angular speed of 𝑁 𝑟𝑝𝑚. 𝑁 depends on the last 2
digits of your student ID as shown in the table below:
Last 2 digits of your
student ID between
00-20
21-40
41-60
61-80
81-99
𝑵 (𝒓𝒑𝒎)
110
120
140
150
160
The direction of rotation of the crank (link 2) is of your choice; this can be in the counter-clockwise direction
(ccw), as shown in the figure, or clockwise (cw) direction. The length of the crank is 𝑥; the value of 𝑥 is of
your choice within the range 180 ≤ 𝑥 ≤ 280 𝑚𝑚. The 0.4 𝑘𝑔 cylindrical slider (link 6) of diameter 100 𝑚𝑚,
attached to one end of link 5, pushes against a pressure equivalent to a head of 12 𝑚. The power stroke of
the slider is along the negative direction (−𝑣𝑒) of the 𝑥 − axis, as shown in the figure.
Consider all other links are massless. Design links 4 (𝑂4 𝐵) and 5 (BC), and the distances 𝑶𝟐 𝑶𝟒 and 𝑶𝟐 𝑪
so that the motion of link 6 fulfils the conditions set out by yourself. Some examples of the conditions
are:
-
the maximum velocities of the slider during the power and/or return strokes,
the maximum acceleration of the slider during the power and/or return strokes,
quick return or quick action (power) stroke
the maximum torque delivered by the crank
the maximum power delivered by the slider
Describe the conditions that you decided to set and briefly explain them with your justifications. Note that the
lengths of links 4 and 5 don’t have to be in proportion with the length of link 2 as shown in the figure.
Power stroke
6
𝑦
There is a revolute
join and a slider at
this location
𝜔2
𝑥
You are required to perform the following analysis for this part in your report: (85 marks). Note: present
all these tasks in a report format.
1. Animate the linkage on both Linkage and Matlab.
2. Plot the path of the mid-point of link 5 using Matlab.
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(20 marks)
(5 marks)
ENGIN2303
3. Plot a graph showing how the transmission angles vary with the crank angle. Note the maximum and
minimum values of these transmission angles. Is this an ideal mechanism to perform this task based on
the conditions set out by yourself? If it is not, then what are the changes to this mechanism that you want
to propose? Is there a better approach (a better or simpler mechanism) to perform this task? (15 marks)
4. Perform the velocity and acceleration analysis for the mechanism. Graph the velocities and accelerations
of links 3, 4, 5, and 6 against the crank angle.
(15 marks)
5. Use the virtual work method to calculate the crank torque, 𝑇, as a function of the crank angle, 𝜃2 . Plot
the 𝑇 − 𝜃2 diagram of the crank.
(10 marks)
6. Design a flywheel for this system such that the speed fluctuation is not to exceed 5% of the crank speed.
What's the power of the motor needed to drive the mechanism?
(10 marks)
7. For suitable pin diameters and a coefficient of friction 𝜇 = 0.12, estimate the energy lost at pins 𝐴, 𝐵, 𝐶,
𝑂2 and 𝑂4 in every cycle.
(10 marks)
Part B: Mechanism synthesis
Design of a windshield wiper system
Windshield (windscreen) wiper system is an important safety component of a car. Wipers help provide clear
vision for the drivers of the road ahead of them by clearing the water droplets off the windshield. A typical
windshield wiper system is shown in the figure below where the two wipers are synchronised with one
another. This system utilises only one motor to drive both wipers.
You are tasked to design a new wiper system for a car manufacturer. However, the manufacturer does not
want to disclose the exact size of the windshield just yet. You will need to base your calculations and design
on a windshield size of your choice. Note that the figure shows the wiper blade cover areas from the point of
view of the driver; the RHS is shown as the dark-blue-shaded area while the LHS is shown as the greenshaded area. Some system requirements are:
• The windshield shape must be similar to the light blue area shown in the figure. The windshield surface
is relatively flat.
• The RHS wiper blade, which covers the dark blue area, is longer than that of the LHS blade, which
covers the green area.
• The motor, which is attached to a crank, has to be placed vertically below the pivot points of the wiper
frame, shown as 2 circles in the figure; and horizontally between the two pivot points.
• The angle swept by the green wiper has to be larger than that of the blue wiper.
There are some aspects that you need to investigate yourself and predetermine the values for:
• Windshield dimensions.
• The spring force pushes the wipers against the windshield and the friction factor between the blade
and windshield material in both dry and wet conditions in order to size an appropriate motor for this
system.
• Other conditions set out by yourself.
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ENGIN2303
Note that reasonable assumptions for data required for your calculation are acceptable. You must properly
cite the source of information or show the calculations that support your estimation.
Hint: Apply the graphical linkage synthesis method and utilise AutoCAD in the design phase. Then simulate
in Linkage before carrying out further calculations. Use fourbar linkage, adding a twobar chain to a fourbar
linkake, or Watt sixbar linkage.
You are required to perform the following tasks for this part in your report: (65 marks). Note: present
all these tasks in a report format.
1. Use AutoCAD (or SolidWorks or Inventor) to perform the linkage synthesis task. Submit your CAD file
with appropriate notations and colours to show the steps taken. Include some screenshots of your work
in your report and provide more details of the approach; link the figure to your writing.
(20 marks)
2. Animate your design in Linkage
(5 marks)
3. Animate your design in Matlab
(15 marks)
4. Choose an angular velocity for the motor used to drive the wiper system and perform the velocity and
acceleration analysis. Plot velocities and accelerations of various links against the crank angle. Estimate
the power required by the motor to drive this system.
(15 marks)
Task submission requirements
Submit a neatly and professionally typed PDF, Word, or .mlx report with all calculations, steps taken to derive
the mathematical models (typed up using equation editor or latex), how the model is implemented in Matlab,
and all necessary illustrations. The report must also include:
- An abstract
- An introduction section that provides the theory, some background information, and requirements of this
task.
- Figures and graphs produced using Linkage or Matlab. Figures must have figure numbers and captions.
Only provide figures when absolutely necessary; avoid having figures as space-filling.
- Screenshots or printouts of the Matlab code(s). If the codes are too long, then put them in an appendix
and refer to them in the report body.
- References and citations where necessary.
At least one Matlab file and one Linkage file must be included in your submission. CAD drawing that clearly
shows the step taken to solve the problem, use colour or notations where necessary.
Mark deductions
- No or not enough detail is provided for the problem formulation and calculation, the assumptions made
and their reliable source of information.
Up to -10 marks
- Format and structure of the report, equations are professionally presented using either equation editor
or Latex.
Up to -5 marks
- Numbering and captions for figures and tables.
Up to -5 marks
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