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A Minimalistic Approach to Behavioural Robotics

David L Buckley - August 1995

Over the years considerable research has been undertaken attempting to solve the problems involved in designing programs for the control of mobile robots, especially those robots intended to operate in unstructured and possibly hazardous environments, ie natural as opposed to laboratory set-ups.

Various methodologies have been tried, including but not limited to Blackboard Systems,Fuzzy Logic Controllers, Neural Nets, Synthetic Neural Strands, Production Systems, Competing Behavioural Control, Subsumption Behavioural Control etc..

If the resulting program is to run in real time many of these techniques require a combination of special hardware and powerful processors, both of which push up the cost, size and complexity of the control equipment and hence the cost size and complexity of the finished robot. However in my experience the relationship between the complexity of the control hardware and that of the finished robot is certainly non-linear, complexity seems to have a fractal dimension of between two and three.

Many inspection tasks for reasons of size , safety etc (eg nuclear power plants) can only be carried out by mobile robots. When the installation to be inspected costs millions of pounds then a few hundred thousand pounds for an inspection robot is not a prohibitive amount. Should the robot become stuck, break down, or otherwise become unusable then not much comparatively is lost. However for any installation costing a few thousand pounds such a loss would be unthinkable.

Given the availability of small rugged and virtually expendable mobile robots, a vast number of tasks would then become suitable for them.

Out of the methodologies mentioned above as being used to design programs for mobile robots that using a subsumption type of behavioural control is capable of producing probably the most compact and readable program code.

Parallax Inc have recently launched their BASIC Stamp chipset comprising a PIC16C56 microcontroller with an onboard BASIC interpreter and a 256 byte serial EEPROM. Pretokenised BASIC is downloaded via an host PC's printer port to two pins on the PIC16C56. The whole computer comprising microcontroller, RAM, I/O connecctors, etc., using convention dual in line integrated circuits, takes less area than an ordinary postage stamp.

The availability of the Stamp processor, and the ease with which programs can be developed and tested, prompted the development of 'Tiny Tim' an autonomous mobile robot based on the Stamp chipset.

Tiny Tim weighs in at about 50g (2oz), and measures 3.8cm * 4.8cm * 3.3cm, it has a five layer behavioural control program, interacting with two motors, six sensors and a sounder.