Rotary Motion
Rotary motion is motion in a circle. It is the starting point for many mechanisms.
ConversionsRotary motion to: 
Transformations 


Linear Motion  Wheels. Rack and pinion. 
Increase / Decrease  Gears. Chain. Worm gear. 

Reciprocating Motion  Piston. Geared mechanism. Cardan gear. 
Reflect  Gears.  
Oscillation  Crank. Quick return. 
Rotate  Bevel gear.  
Intermittent Motion  Geneva Stop.  
Irregular Motion  Cam. 
Worm Gear
A worm is used to reduce speed. For each complete turn of the worm shaft the gear shaft advances only one tooth of the gear. In this case, with a twelve tooth gear, the speed is reduced by a factor of twelve. Also, the axis of rotation is turned by 90 degrees. Unlike ordinary gears, the motion is not reversible, a worm can drive a gear to reduce speed but a gear cannot drive a worm to increase it. As the speed is reduced the power to the drive increases correspondingly. Worm gears are a compact, efficient means of substantially decreasing speed and increasing power. Ideal for use with small electric motors.
Make your own working worm gear model.
Turn the handle and the worm turns! The 24 tooth gear turns at 1/24 of the speed of the handle.
Quick Return
Download and make your own working quick return mechanism. Use it find out how the quick return mechanism works first hand or as the starting point for your own model. More details...
Geneva Stop
Gears
Rings of Gears and the Two Pound Coin
Reciprocating motion
Escapement
Chain and Sprocket
Chains are used to connect gears. They work in a similar way to pulleys but with a positive drive rather than a reliance on friction. Gears which are connected by chain turn in the same direction unlike gears which mesh against each other.
Check out the updated page here:
Cardan Gear
Invented by Girolamo Cardano in the 16th century the Cardan gear is a way of converting rotary motion into straight line motion. Watch how the red dot on the inner purple gear exactly follows the vertical dotted line. The outer gear has a diameter exactly twice as large as the inner gear. In the above example they have 40 and 20 teeth respectively. Cardano also invented a type of universal joint and investigated the mathematics of probability. Understanding the mathematics of risk helped him make a living from gambling until eventually he could find noone to gamble with and had to move onto new pastures...
Bevel Gear
The bevel gear is used to change the axis of rotational motion. By using gears of differing numbers of teeth the speed of rotation can also be changed.
You can download and make your own working bevel gear in the shop