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Quick questions on Linkages explained: O-Level Design and Technology
4short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is reverse-motion linkage?Show answer
A reverse-motion linkage makes the output move in the opposite direction to the input. A rigid link has a fixed pivot at its centre; the input connects to one end and the output to the other. Pushing the input end up rotates the link about the central pivot, so the other end moves down. Input up gives output down.
What is push-pull (parallel) linkage?Show answer
A push-pull linkage transfers motion in the same direction from input to output, often to move a control at a distance. Links connected in line pass a push or pull along, so pushing the input pushes the output the same way. It changes the position of a motion rather than its direction. Used for remote controls and connecting rods.
What is bell-crank linkage?Show answer
A bell-crank linkage changes the direction of motion through about a right angle. A bent (L-shaped) link is pivoted at the corner, so a horizontal input produces a vertical output, or vice versa. Bicycle brakes use a bell crank to turn the pull of a cable into a sideways squeeze on the wheel; the old bell-pull systems that rang servants' bells are the origin of the name.
What is parallel-motion linkage?Show answer
A parallel-motion (parallelogram) linkage keeps a part moving parallel to its original position as it moves. Two equal links pivoted in a parallelogram arrangement let a platform rise and fall while staying level. Used in angle-poise lamps, toolboxes that open with trays staying level, and parallel rules. It changes position while keeping orientation.
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