The Box2D Joint Toy demonstrates revolute, gear, prismatic, wheel, distance, and pulley joints. It is divided into 7 levels. The enter key advances to the next level and the backspace key restarts the current level. The effect of hitting the space bar varies from level to level. This code demo has no sound.

The Levels

1. The Windmill

A windmill with a revolute joint connecting the vanes to the body. The revolute joint has a motor. The space bar reverses the motor's direction of rotation.

2. Gears

A system of 9 interlocked gears constructed using revolute and gear joints.The largest gear has a motor and the others are driven by their gear joints. The space bar reverses the motor's direction of rotation. The 4 square gears mesh perfectly the same way that round gears do.

3. Nautilus Gears

A system of 5 nautilus gears, which are gears in the shape of a nautilus shell. The center gear has a revolute joint with a motor. The other gears have variable speed, so they cannot be animated by Box2D. We have to animate them ourselves which means doing a little math.
The space bar reverses the motor's direction of rotation.

4. Rack-and-Pinion

A rack-and-pinion consists of a round gear called a pinion connected to a toothed rod called a rack. When the pinion rotates, the rack moves horizontally. The pinion has a revolute joint with a motor. The rack is connected to the pinion using a gear joint and a prismatic joint. The space bar reverses the motor's direction of rotation.

5. Car

A car drives autonomously back and forth over a pair of ramps. The car is constructed using a pair of wheel joints that have motors. The space bar reverses the motors' directions of rotation.

6. Newton's Cradle

Distance joints are used to construct a Newton's Cradle with 6 balls. When the balls are stopped, hitting the space bar will lift and release from 1 to 5 balls in sequence. After that it should behave like a real Newton's Cradle. When the balls are in motion, the space bar stops them.

7. Elephant Drop

A pulley joint is used to lift a safe when an elephant is dropped into a wooden cradle. The pulley wheels and ropes are animated in code.

Keyboard Controls

The LARC Engine

This code uses the LARC Engine and is part of the LARC Code Base.