Braitenberg vehicles

Simple rules can appear to be smart

Braitenberg vehicles are simple vehicles that show how the interaction between simple rules can lead to complex behaviour. Although these vehicles have no ability to make decisions or even to remember the past, a Braitenberg vehicle may show flexible behaviour and appear to be goal-directed. The script on this page (open script in separate tab) allows you to experiment with Braitenberg vehicles and see how these vehicles act and interact in a simple environment. The controls for this script are described at the bottom of the page.
The JavaScript on this page makes use of HTML5.

Braitenberg vehicles are simple autonomous agents that move around based on sensor input. On this page, we consider vehicles that have two wheels, each controlled by its own motor. Sensors that measure the light intensity can affect the output of these motors, either positively or negatively. Depending on how where the sensors are located and how these sensors are connected to the motors, the behaviour displayed by the vehicle can differ greatly.


Fear	Aggression	Love	Exploration
Figure 1: Four simple Braitenberg vehicles.

Figure 1 shows an example of four simple Braitenberg vehicles. These four vehicles are also preprogrammed in the script. Although these vehicles are quite similar and have the same light-sensitive sensors at the same locations, the way these sensors are attached to the motors causes strong differences in their behaviour.

The first vehicle, called Fear, connects the leftmost sensor to the left wheel motor and the rightmost sensor to the right wheel motor. In both cases, the forward speed of the motor is increased when the sensor detects more light. This means that when this vehicle detects light to the left, the left motor increases speed and the vehicle veers to the right. That is, Fear tries to move away from the light.

The second vehicle, Aggression, is similar to Fear, except that the sensors are wired to motor at the opposite end of the vehicle. That is, the leftmost sensor is connected to the right wheel motor while the rightmost sensor connects to the left wheel motor. Like Fear, the sensor connections of Aggression are positive. This means that if the vehicle detects light to the left, the right motor increases speed and the vehicle veers to the left. That is, Aggression moves towards the light. The closer the vehicle gets to the light, the stronger the increase in speed of the motors, until the vehicle speeds through the light.

Love is a vehicle that is similar to Fear, except that the sensors decrease the forward speed of the motor to which they are connected. This means that when the vehicle detects light to the left, the left motor decreases speed or even reverses, and the vehicle moves to the left. Like Aggression, Love moves towards the light. Unlike Aggression, however, the closer Love gets to the light, the slower it moves. As a result, Love moves towards the light until it reaches the perfect distance.

The final example is Exploration. Exploration has the same crossed wiring of Aggression, except that the sensors decrease the speed of the motors to which they are attached. This means that if the vehicle detects light to the left, the right motor decreases speed or even reverses, and the vehicle veers to the right. Like Fear, Exploration avoids the light. However, Exploration slows down in light areas, almost as if it is cautiously exploring the light.

In the script above, you can test out the different basic Braitenberg vehicles by loading them into the selected vehicle. By varying the number of lightbulbs and dragging and dropping them to different locations, you can experiment with the way they react to different environments.

More complex vehicles

In addition to the basic vehicles, the script above allows you to construct your own vehicle design. Each vehicle has a base speed for each motor, which means that vehicles can move forward, backward, or in circles when left in the dark. In addition to the lightbulbs in the environment, each Braitenberg vehicle is also equipped with a lightbulb of its own. This addition of light onto vehicles themselves can result in surprising new behaviour.

The lower part of the script shows a larger Braitenberg vehicle in a black box, which allows you to customize a vehicle. Each vehicle has up to eight sensors, which are depicted as coloured dots. By dragging and dropping these sensors, you can place them anywhere you want along the exterior of the vehicle. Sensors are colour coded to indicate that they are connected to the left wheel (white sensors), the right wheel (black sensors), or the lightbulb (yellow sensors). Note that a vehicle’s sensors are never affected by its own lightbulb.

Even though Braitenberg vehicles are purely mechanical, you may notice that it is easier to describe these vehicles as if they had intentions and goals. This shows that in some cases, it is easier to understand these vehicles through theory of mind, by pretending that they have unobservable mental content.

Controls

Arena: In the arena, vehicles and lightbulbs can be moved by dragging and dropping them in their desired location.
Lightbulb slider: This determines the number of lightbulbs in the arena. For performance reasons, the number of lightbulbs has been limited to four.
Vehicle slider: This determines the number of Braitenberg vehicles in the arena. For performance reasons, the number of vehicles has been limited to four.
Load a basic vehicle select box and button: These controls allow a user to load one of the four basic Braitenberg vehicles shown in Figure 1 into the vehicle selected from the arena. In addition, it also allows a user to load a custom Braitenberg vehicle. These controls can also be used to save a Braitenberg vehicle design for later use.
Default speed of left/right motor slider: This slider determines the speed of the left and right wheels for a vehicle in the dark.
Default illumination slider: This slider determines the brightness of a lightbulb of the vehicle when left in the dark.
Braitenberg vehicle bay: This control shows the selected Braitenberg vehicle, and allows the user to move around sensors through dragging and dropping.
Number of sensors on vehicle slider: This slider determines the number of sensors on the vehicle.
Selected sensor slider and select boxes: This determines what the selected sensor is connected to (left motor, right motor, or lightbulb), the input of the sensor (light or distance) and the strength of this connection.
Pause/Continue simulation button: Allows a user to pause and continue execution of the simulation.
Save simulation setup button: Downloads the current Braitenberg arena state as a text file. This can be loaded into the current arena state with the Load simulation setup button.
Load simulation setup button: Allows a user to change the code of the Braitenberg arena. This can be used to load a previously saved arena state.