Scotch Yoke Mechanism

OBJECTIVE 1. To demonstrate the action of a simple crank-driven Scotch Yoke mechanism. 2. To determine graphically the relationship between the linear displacement of the scotch yoke and the angular displacement of the crank. PROCEDURE

1. The slider block and crank is lined up so that the block is read zero and the crank is at 0°. 2. The displacement is measured once the slider block is jotted down for every 10° clockwise of the crank indicator by using the outer scale of the crank. 3. When the above method is done with a full rotation, the same method but with a counter clockwise motion is repeated. 4. The acquired measurements are then tabulated in a proper table, and a graph of the slider displacement versus the crank angle is drawn.

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DATA AND ANALYSIS

Graph of length versus angle

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Clockwise Angle (°) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360

Displacement (mm) 0 1 2 3 6 9 13 17 21 25 30 34 37 41 44 47 49 50 50 50 49 47 44 41 37 34 30 25 21 17 14 9 6 3 2 1 0

Counterclockwise Angle (°) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360

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Displacement (mm) 0 1 2 3 6 9 13 17 21 25 30 34 37 41 44 47 49 50 50 50 49 47 44 41 37 34 30 25 21 17 14 9 6 3 2 1 0

Average Displacem ent (mm) 0 1 2 3 6 9 13 17 21 25 30 34 37 41 44 47 49 50 50 50 49 47 44 41 37 34 30 25 21 17 14 9 6 3 2 1 0

DISCUSSION 1. From the graph acquired, we can see that as the angle displacement increases, the slider displacement increases until about 180° whereby the maximum length of the slider is reached. 2. The slider’s displacement will then decrease once again until zero as the angle continues increase and reach 360° 3. One interesting observation of the graph is that the initial slope is the same as the returning slope. 4. From this, we can see that the slider travels forward and returns at the same speed. 5. Another observation made is that the beginning and the top of the graph shows a very similar curve but the end of the graph shows a less steep and much gentler slope compared to the earlier. 6. This is due to the lower velocity and smaller displacement of the slider at the end as compared to rest of the graph. 7. If we were to observe the slider, we will see that as the slider moves to the left, it starts off slowly but begins to pick up speed and slows down again before coming to a halt. 8. It then starts off in the opposite direction slowly, and on the way back, the Scotch Yoke mechanism pulls the slider at the same speed and then slows down a lot before halting again.

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CONCLUSION From the graph attained, we can determine graphically the relationship between the linear displacement of the sliding block and angular displacement of the input crank for a Scotch Yoke mechanism. This setup is most commonly used in control valve actuators in high pressure oil and gas pipelines. It has been used in various internal combustion engines, such as the Bourke engine, Syn Tech engine, and many hot air engines and steam engines. We are also able to demonstrate the action of a Scotch Yoke mechanism. REFERENCE 1.

MECHANICS OF MATERIALS - Fourth Edition in SI Units Ferdinand P. Beer E. Russell Johnston, Jr. John T. DeWolf McGraw-Hill

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