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The 3D graphic below shows a model of a mechanism from the pull along toy car on the right - Leaving Cert DCG - Question C-4 - 2009
Question C-4
The 3D graphic below shows a model of a mechanism from the pull along toy car on the right. The rotating cam causes the rider to move up and down and the link mecha... show full transcript
Worked Solution & Example Answer:The 3D graphic below shows a model of a mechanism from the pull along toy car on the right - Leaving Cert DCG - Question C-4 - 2009
Step 1
Draw the displacement diagram for the cam given that it imparts the following motion to the follower:
Answer
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A to B (0° to 90°): The motion starts with uniform acceleration. Draw a curve that represents this rising action. The curve should be concave up, showing acceleration increasing until 90°.
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B to C (90° to 150°): During this phase, the follower rises with uniform velocity. Draw a straight line from point B to point C, indicating constant speed.
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C to D (150° to 180°): Here, the motion is a falling action governed by simple harmonic motion. This portion should be a smooth downward curve, resembling half a sine wave, signaling a decelerating descent.
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D to A (180° to 360°): Finally, the follower falls back to the starting position with simple harmonic motion. Similar to the previous segment, it should show a smooth downward curve back to the closing point of 0° around the displacement diagram, completing the cycle.
Step 2
On a separate diagram, draw the link mechanism as a line diagram.
Answer
- Start by establishing point O (fixed point) and point P (where the link slides).
- Draw the cam outline without displaying its detailed features.
- Extend the link EF from point E (the pin joint on the cam) to point F.
- For the representation of the trajectory, mark several positions of point F as the cam makes a full revolution.
- Connect the loci of point F with smooth curves showing the range it covers as the cam rotates, emphasizing its displacement due to the varying positions of the joint.