Question

A toy with reciprocating movement is shown. As the wheels of the toy rotate, the head is required to reciprocate. If given options are indicative of conversion of rotary to linear motion using a disc located at the centre of the wheel shaft, which option will result in the required movement when the toy is pushed forward? Assume a working spring loaded cam mechanism in the relevant option/s.

• A. Fig A
• B. Fig B
• C. Fig C
• D. Fig D

Hint:

Snail cams are the most common mechanism in animated toys because they store energy gradually over a full rotation and release it instantly, creating a lively and realistic animal motion.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question belongs to the topic of

Theory of Machines and Cam-Follower Systems.
We need to select the correct cam profile attached to the wheel axle of a toy turtle that will cause its head to move back and forth (reciprocate) smoothly as the toy rolls forward.

Step 2: Key Formula or Approach:

• A cam is a rotating machine element that gives a reciprocating or oscillating motion to another element called a follower.

• When the turtle is pushed forward, the wheels rotate in a specific direction.

• A smooth, continuous reciprocating motion of the head requires a cam profile with a gradually changing radial distance from the center of rotation to the follower contact point.


Step 3: Detailed Explanation:

• Let us analyze the cam profiles in each option:
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Option A: Shows a "snail cam" profile. Snail cams feature a radius that increases gradually over almost 360 degrees, ending in a sharp vertical step back to the minimum radius. This profile is designed to push the follower outward slowly and then let it drop suddenly under spring tension. This creates a highly distinct, rhythmic snapping reciprocating motion (ideal for a pecking or bobbing turtle head).
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Option B: Shows an eccentric circular cam with a flat notch. This would cause a jarred, discontinuous motion that is less effective.
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Option C: Shows a gear-like lobed cam. This would cause high-frequency, rapid vibration of the head rather than a visible reciprocating gesture.
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Option D: Shows a simple eccentric circle, which gives a simple harmonic motion but lacks the distinct forward-reach and quick-retract profile characteristic of animal-mimicking toys.


Step 4: Final Answer:
Option (A) is the correct cam design to achieve the desired head movement.