Lab Session #2
Investigate the working of Slotted-Link or Scotch-Yoke Mechanism
Apparatus
Slotted-Link or Scotch-Yoke Mechanism (based on availability)
Measurement tools: Scale, Vernier calipers and Protractor
Introduction
Working principle of Slotted-Link or Scotch-Yoke Mechanism
The scotch yoke mechanism (also known as slotted link mechanism) is a reciprocating motion
mechanism, converting the linear motion of slider into a rotational motion or vice versa.
The piston or other reciprocating part is coupled to a sliding yoke with a slot that engages a pin on
the rotating part. The location of the piston versus time is a sine wave of constant amplitude and
constant frequency given a constant rotational speed.
Expressions for Analytical analysis:
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The crank is rotating with the angular speed of ω = 200 rad/sec (CW) and angular acceleration of
α = 1500 rad/sec2
Displacement of plunger = OA’- OA’’
x = R (1- cos ϴ)
= R – Rcosϴ
where, ϴ = ω t
Differentiating the expression of displacement with respect to time, we will get velocity.
Velocity of plunger = R ω sin ϴ
Differentiating the expression of velocity with respect to time, we will get acceleration.
Acceleration of plunger = R α sin ϴ + R ω 2 cos ϴ
1) What are the different ways a Slotted-Link or Scotch-Yoke Mechanism can
manifest? Provide practical examples alongside merits and demerits of the
mechanism.
Example 1:
Reciprocating Pumps
Application: The Scotch-Yoke mechanism is commonly used in reciprocating pumps, where it
is employed to convert rotational motion from a motor or crank into linear motion to drive the
piston in the pump.
Merits:
1-Smooth Motion
2-Compact Design
3-High Force Output
Demerits:
1-High Wear and Tear.
2-Less Efficient at High Speeds
Example 2:
Piston water pumps.
Application:The mechanism converts the rotational motion of a motor into the linear
motion needed to drive the pump piston.
Merits:
1.Simple Construction
2.High Efficiency
3.Smooth Operation
Demerits:
1.Rapid Wear
2.Heat Loss:
3.Side Loading
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2) Is it an inversion of slider crank mechanism? If yes than explain and draw figure as
well.
Yes, the Scotch-Yoke mechanism is indeed an inversion of the slider-crank
mechanism. In mechanical engineering, an inversion refers to a different configuration of
the same basic mechanism, achieved by fixing a different link in the mechanism.
Explanation:
In a typical slider-crank mechanism:
• The crank rotates, and the connecting rod transmits this motion to the slider, which moves
linearly.
In the Scotch-Yoke mechanism:
• The crank is fixed, and the slider (or yoke) moves linearly, while the connecting rod
transmits this motion to the slot in the yoke, causing it to oscillate.
Diagram:
No. of Links:
There are 4 number of links(Crank,Yoke,Frame and Connecting link).
· Crank (Rotating Link): Rotary motion input.
Type of Links:
· Yoke (Slider): Sliding link that moves in a straight path.
· Frame (Fixed Link): Provides structure and support.
· Slotted Link: Connects and controls the relative motion between the crank and yoke.
No. of Joints:
There are 4 number of joints in the group.
· Revolute Joint: Provides rotational movement (Crank-Fixed Frame and Crank-Pin).
Type of Joints:
· Prismatic Joint (Slider Joint): Provides linear sliding motion (Slotted Link-Yoke).
DOF/Mobility:
Degree of Freedom (DOF) = 1. This means the mechanism has one input (the crank’s rotation),
and all other motions are dependent on this input.
M = 3(L-1) – 2J
M = 3(4-1) – 2(4) = 3(3)-8 =1
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Observations and Calculations:
Use Grubler’s Equation to compute the mechanism’s mobility Grubler
Equation: M = 3(L-1) – 2J
Crank
Rotation Experimental Analytical
Displacement
(deg) [cmm]
Velocity Acceleration Displacement Velocity Acceleration
[cm/s] [cm/s^2] [cm] [cm/s] [cm/s^2]
0 0 0 0.0 0 0
0
0.3 0.05 0.005 0.30154 0.08675 0.004635
20
0.8 0.09 0.003 1.16978 0.1331 0.003008
40
1.7 0.12 0.001 2.5 0.16318 0.001046
60
2.9 0.13 -0.002 4.13176 0.17364 -0.001046
80
4.2 0.11 -0.001 5.86824 0.16318 -0.003018
100
5.3 0.1 -0.005 7.5 0.133 -0.00462
120
6.3 0.05 -0.003 8.83022 0.0868 -0.00566
140
6.8 0.02 -0.004 9.69846 0.0302 -0.00604
160
7 -0.02 -0.003 10.0 -0.0302 -0.00566
180
6.8 -0.05 -0.005 9.69846 -0.0868 -0.00462
200
6.3 -0.1 -0.001 8.83022 -0.133 -0.00302
220
5.3 -0.11 -0.002 7.5 -0.1632 -0.001042
240
4.2 -0.13 0.001 5.86824 -0.17362 0.001044
260
2.9 -0.12 0.003 4.13176 -0.16318 0.003015
280
1.7 -0.09 0.004 2.5 -0.13303 0.004621
300
0.8 -0.05 0.002 1.16978 -0.08682 0.005667
320
0.3 -0.03 0.002 0.30154 -0.03015 0.00566
340
0 0.03 0.004 0.0 0.03015 0.004635
360
Length of links: 5.5cm
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Procedure
You have been asked to fill a table by recording displacement of slider as a result of incrementally
rotating the crank. You will then compare the results with those of analytical solution as per the
equations mentioned above.
Sketch
Steps:
1. Measurement of link lengths and dimensions:
2. Initial position setup:
3. Incremental rotation of crank (10°):
4. Resulting displacement of slider
5. Repeat to fill the table
6. Compute the corresponding positions using analytical method
Additional Observations
The velocity and acceleration graphs show smooth, sinusoidal motion typical of the
Scotch Yoke mechanism. Velocity peaks at 90 and 270 degrees, with zero velocity at 0,
180, and 360 degrees, indicating direction reversal. Acceleration is highest at the stroke's
start and end, suggesting increased forces and potential wear at these points. The
mechanism provides gentle, continuous motion, making it ideal for low-to-moderate load
applications. However,high accelerations at the extremes could lead to frictional wear over
time
Conclusions
The experiment confirms that the Scotch Yoke mechanism provides smooth, continuous
motion, ideal for low to moderate loads. High acceleration at stroke extremes indicates
potential wear and stress on components. This makes the mechanism suitable for
applications requiring precise motion but may require maintenance under high-load
conditions. Overall, it efficiently converts rotary motion to linear but with limitations under
heavy usage
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Plots:
Experimental analysis:
Analytical analysis:
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a) Comparison between Slider crank mechanism and Scotch yoke mechanism (after
going through the case study shared in class). Both linkages must be compared
graphically as well as apparently (based on resulting motion, number of links and
joints)
Criteria Slider Crank Mechanism Scoth Yoke Mechanism
Resulting Motion Converts rotational motion into Converts rotational motion into
reciprocating linear motion. reciprocating linear motion.
Motion Path The stroke follows a sinusoidal The stroke follows a true
path with non-uniform sinusoidal path with uniform
velocity. velocity.
Velocity Profile Non-uniform velocity (faster in Uniform velocity throughout
the middle, slower at ends). the stroke.
Number of Links 4 links: Crank, Connecting 4 links: Crank, Yoke, and
Rod, Slider, and Fixed Frame. Fixed Frame,Slotted link.
Number of Joints 2 Revolute Joints, 2 Prismatic 2 Revolute Joint, 2 Prismatic
Joint (slider path). Joint (crank pin through yoke
slot).
Stroke Length Non-uniform, depends on the Uniform and directly
crank rotation and connecting proportional to crank rotation.
rod length.
Application Examples Internal combustion engines, Compressors, engines requiring
pumps, mechanical presses. smoother motion, some linear
actuators.
Advantages Commonly used, reliable for Smoother, uniform linear
non-uniform motion, easy to motion; less mechanical stress.
maintain.
Disadvantages Non-uniform motion may be The yoke experiences wear due
undesirable in certain to sliding motion.
applications
Motion Efficiency Less efficient in achieving Highly efficient in producing
smooth, uniform motion. uniform linear motion.
Graphical Representation Motion curve is approximately Motion curve is a pure sine
sinusoidal but with velocity wave, representing uniform
variations. movement.
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Lab Assessment Evaluation Rubrics
CLO1 (P2) Execute the working of various mechanisms by experimentation.
The Lab task will be evaluated based on the mentioned cognitive assessment criteria.
Inadequate Fair Good Excellent
Proceeds with Proceeds with
Sequence of the correct Proceeds with the correct
Steps Fails to proceed sequence of the correct sequence of
with the correct steps, but with sequence of steps,
The student sequence of some steps, accurately demonstrating
proceeds with the steps, leading to inaccuracies or following precision and
correct sequence incorrect results. omissions that necessary competence in
of steps affect the procedures. following
outcomes. procedures.
Handles the
Mishandles the Handles the apparatus with
Apparatus Handles the
apparatus, apparatus precision and
Handling apparatus
showing a lack of correctly, competence,
correctly, but
understanding showing a good demonstrating
The student with some
and leading to understanding excellent
handles the minor mistakes
potential damage and control understanding
apparatus in the or lack of
or incorrect during and control
correct manner confidence.
execution. execution. during
execution..
Records
Readings and Records
Records readings and
Observations Fails to record readings and
readings and observations
readings and observations
observations with precision
The student observations correctly,
correctly, but and competence,
displays the correctly, leading accurately
with some accurately
readings and to inaccurate or documenting
inaccuracies or documenting
observations incomplete data. the necessary
omissions. and presenting
correctly data.
data with clarity.
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