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An Introduction to Mechanisms

1 Linkages

Learn It

  • Linkages are mechanisms which allow engineers to alter force and/or motion to perform useful functions.
  • We can use linkages to change:
    • The direction of motion
    • The type of motion
    • The size of a force
  • A linkage is made up of connected rods and pivots.
  • The motion and/or force that is input at one end of a mechanical linkages is different from the output.

Learn It - Reverse-motion linkage

  • A reverse-motion linkage changes the direction of motion.
  • The reverse-motion linkage in the video below, alters the direction of motion. Pushing as input, becomes pulling as output, and vice versa

Badge It - Silver

  1. Replicate the reverse-motion linkage shown above using Wacano
  2. Adjust the pivot, so that a small input displacement becomes a large output displacement.
  3. Adjust the pivot, so that a small input force becomes a large output force. Take a photo of this one and upload your work.

Learn It - Parallel-motion linkage

  • A parallel-motion linkage creates an identical parallel motion with regard to direction.

  • The setup above shows a parallel linkage that transfers identical motion.
  • By adjusting the pivot points, we can alter sizes of motion and/or forces.

Badge It - Gold

  • Set up a parallel linkage using Wacono, to give provide the largest possible force on the rubber band.
  • If an input force of 5N moving a distance of 10cm was used, what would be the output force if the output distance was 2cm?
  • Take a photo of your linkage and upload this with your explanation.

Learn It - Bell-crank linkage

  • A bell-crank linkage changes the direction of movement through 90°.
  • A bell-crank linkage looks a like an "L".
  • By pulling (or pushing) the linkage in one direction, it creates a similar motion at the other end of the linkage at 90°.

Learn It - Treadle linkage

  • A treadle linkage shows how linkages can be used to change one type of motion into another.
  • In this case, the rotary motion of the cam moves a parallel-motion linkage.
  • The parallel-motion linkage controls the identical side-to-side, or oscillating motion.

Badge It - Platinum

  1. Create a Bell-crank linkage and a Treadle linkage.
  2. Research and report on two uses for each of these types of linkage.
  3. Your report should include images of your linkages on one document, and explanation of how they work, and examples of their use, including diagram.

Extension - Here are some more linkages you could build

1 - Peg, slot and slider


2 - Rack and Pinion


3 - Crank, link and slider