Linkages

Linkage is the term applied to the parts of a machine or mechanism that connect moving parts together.

Linkages can be made from a range of materials, but wood and metal are perhaps the strongest and most commonly used. It is important to note that where there is movement between materials there must be a bit of free movement otherwise the mechanism will jam.

Linkages are used to transfer motion, so they must be properly designed in order to function as intended.

Linkages can be adapted to make very simple yet effective automata. Using popsicle sticks or something similar, you can create a scissor-like action that extends when the ends are squeezed together and contracts when opened. This simple device is easy to make and is very effective. The more sticks you use, the greater the reach and more dramatic the action. The example below is made from popsicle sticks that have been drilled to allow split pins to join the sticks together. Two separate jaws are centrally hinged and taped on each end. This mechanism creates a snapping action and can be modified for different creatures.

REVERSE MOTION LINKAGE

As the top rod moves to the left the bottom rod moves to the right. The bars move in opposite directions. Another way of describing this linkage is the the direction of movement in one rod is reversed in the other rod. The fixed pivot is the centre of rotation.

PARALLEL MOTION LINKAGE

As the large rod at the top of the diagram moves to the left the two small rods at the bottom move to the right. All the rods are parallel to each other.

CRANK AND SLIDER LINKAGE

The rods move forwards and backwards in slider. The fixed pivot anchor the linkages to one place.

BELL CRANK LINKAGE

This linkage allows horizontal movement to be converted to vertical movement. It also works the opposite way round. A practical example of this is the brake mechanism on a bicycle.