Topic 6

Cranks

Cranks are similar to a simple cam. They convert circular movement into a reciprocal one (up and down motion) or vice verse. However there are some fundamental differences. Firstly cranks only ever work in a circular motion and they only have one drive action per revolution. That said when it comes to mechanical toys you can make some amazing machines based on the crank.

The crank has many uses. Firstly it is often the driving mechanism for hand-operated mechanical toys. It is important to support the crank with some type of bearing. In this case, it is the sides of the box that provide the support. Although the crank only works in a circular motion, its drive can be made to go from side to side as well as up and down. Another big advantage with the crank is having power on both the upward and return strokes. This means you don't have to rely on gravity, which can be a problem with cams.

The amount of up and down movement is called the throw of a crank and is measured by the size of the circle it scribes when turning, which will be twice the diameter.

This crank will have a throw of 4cm. (2+2=4)

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