Mechanisms (work in progress)

Mechanisms (work in progress)

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Common problems


  1. Wherever things move, there must be small enough friction to allow the movement, but at the same time the part must be held in place. It is sometimes challenging to design a bearing that can do both. Don’t pretend this isn’t a problem!
  2. Be prepared to prototype many iterations. A common mistake is to try to fix a prototype you have become attached to when it is time to throw it out and build a new one.
  3. Make early prototypes out of cardboard and other non-precious material


  1. You must provide guides for the cam follower so that it stays in the right place but can move freely to follow the cam
  2. If the friction between the cam and the follower is too high, it will either jam or break.


  1. When linking to rotating components (servo motors, cranks) remember that moving parts might move in an arc and not a straight line. If you constrain links too much they will either jam or break.

Worked Example: Moving Eyeballs




  • Servo linkage basics
  • Animated linkage mechanisms
  • Short article on servo alignment
  • 507 Mechanical Movements, some animated
  • Library of kinematic models for design
  • Manipulate Four Bar Linkages in this live simulation and see how changing the lengths affects the way they work
  • How to select the right size motor

Books (PDF)



  • Physical Computing by Dan O’Sullivan and Tom Igoe
  • Making Things Move by Dustyn Roberts



Where to buy parts

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