POPBUGS - A Simulation Environment for Track-driven Robots

\X Chris Thornton \X

The simulation provided by the package is relatively realistic. Robots have inertia and proper tank-track dynamics. This means, for example, that locking one of the tracks causes the robot to pivot about the central point of that track rather than about the robot's centre. Sensors and motors can be arbitrarily noisy. At present, however, there is no way of introducing track-slippage; i.e., the tracks are assumed to have perfect grip.

The simplest way to familiarize yourself with the package is to watch some of the canned simulations. These show simulated robots, or `bugs' as they are called, interacting with a variety of worlds. Try one of the following (or an item from the list lower down).

• Obstacle-avoidance (short) This is the standard, entry-level bug-behaviour. A single bug with two proximity sensors roams a world containing a variety of objects. Each time the sensors return a high proximity value, the bug turns to the right.

• Pursuit (short) Another popular behaviour. Here the pursuing bug tries to stay on the tail of the leading bug.

• The POPBUGS user interface
• The POPBUGS program interface , or
• POPBUGS simulations of Braitenberg `vehicles' .

Sussex/POPLOG users can find out more about popbugs via HELP POPBUGS. See also TEACH VEHICLES, a teaching package for Braitenberg vehicles.

Other videos are as follows.

• Nesting A single bug moves around a world containing a number of movable, circular objects. If the bug encounters an object while heading (roughly) towards the centre of the world, it continues to move forwards pushing the object in front of it. The net result should be that all the objects are moved to the centre of the space.

• Centering (short) A bug with a single proximity sensor moves around a circular space. By changing direction each time there is a change in the sign of the sensed proximity changes, the bug effectively manages to keep moving towards the centre of the space.

• `Interactive' Braitenberg vehicles Braitenberg has shown how bugs with sensor/wheel pairs are attracted to sensed objects if their sensor-wheel connections are crossed and repelled if the connections are straight. Here we have three Braitenberg bugs arranged in a love/hate triangle. Each bug is attracted to the bug on the `left' and repelled from the bug on the `right'.

• Braitenberg's vehicle 3 This is mock-up of Braitenberg's vehicle 3 which is repelled by high temperature (red object), attracted by light (yellow object), attracted (and inhibted by) oxygen (blue object) and repelled (and inhibited by) organic matter (brown object).

• Fish wars This shows a very primitive sort of territoriality behaviour. The `fish' (circular objects) move around the world `eating' the brown objects until they get to feel very `aggressive' (this makes them go dark in colour) upon which they go off and try to attack one of the other fish.

• Getting through a saloon door Here the single bug has to get through the swinging saloon doors. Writing a stateless controller for this behaviour is a challenge. (The controller in this simulation uses a single state variable.)

• Asteroid avoidance Here the single bug must avoid the moving objects. It uses the standard `knee-jerk' avoidance routine and so cannot really cope. As the objects move faster, collisions become more frequent.

• Escaping from the smoke-filled room Here the bug must find the gap in the wall and move through it.

• Interactive Braitenberg blobs Another version of the love/hate triangle. Here the vehicles are large blobs with identical colour and trail-colour. Can be quite pretty.

• Trap-robbing Here the bug must move down the throat of the trap (i.e., keep equal distance from its two jaws) so as to get to the cheese situated at the apex. Gets harder when the traps begin to revolve...