• Reasons for Building the Machine
• Programming and Software Design
• The Superstructure
• The Processing Architecture
• The Sensors
• The Actuators
• Power Systems

Reasons for Building the Machine

The Sheep have been built to investigate co-operative and emergent behaviour in large collections of autonomous agents. They are small and relitivly cheap machines built in a modular fashion so that adding capabilites to them is a fairly simple task.

Programming and Software Design

Unfortunatly the Sheep have to be programmed in assembler, that said the specially written Z80 ZUES assembler has given excellent service, it generates Motorola S1, S2 and S3 files which are then down-loaded into each sheep using a serial interface (see Processing Architecture).

Each sheep will implement all of Matarics Basis behaviours, using Subsumption implemented in assembler. Currently this has only been done for the avoid behaviour, which has been an interesting learning curve.

The Superstructure

The superstructure is constructed from Technic Lego, though the machine has fallen from a few table-tops it has proved surpisingly resiliant. Perhaps slightly on the heavy side but very easy to build and connect boards and sensors to, Technic Lego is an excellent and cost effective soloution for an experimental vehicle. It is possible however, that later versions of the Sheep will be custom manufactured in aluminium if properly geared motors can be found. My current fashion in placing cooling fins on the back of a machine can clearly be seen in the design of each sheep.

Processing Architecture

All the Sheep use the same processing architecture, which is a mixture of four different board types:

• Flexible Architecture boards
• Processing boards
• Generic Digital IO boards
• Generic Analog IO boards

• Generic IO boards
• Lightweight IO boards

The Sensors

The Sheep are heavily laden with sensors, there are several reasons for this including:

• Sensor redundancy
• Making sense of multiple incompatible sensor readings

• Ultrasonics
• Switch sensors
• Temperature Sensors
• Microphones
• Magnetic Sensors
• Light Sensors
• Infrared Trancievers

The Actuators

• The motor actuators are from Technic Lego - 4.5V, there are two of them, actually driven at 6V. The motors are very highly geared and so use around 0.1A when driven constantly. It can move at around walking pace but can fairly easily avoid a persons hands attempting to catch it. The power transistors are rated at 10A but current limited to around 6A
• Each Sheep will also incorporate a small speaker for generating sounds and signals both to other Sheep and other vehicles/systems.

Power Systems

The battery systems carried by each Sheep are nowhere near as complex as Prestons power systems and simply consist of a 6V sealed lead-acid battery. As described in the Sensor section a Sheep can monitor the current drain and the voltage level of its battery. The battery is to the rear of the machine and is designed to be swapped out with ease so that Sheep downtime is reduced to a minimum.

At some-time in the future it is hoped that each Sheep will have an onboard recharging system so that the Sheep can replenish its power supply itself.

A large switch on the rear enables each Sheep to be switched off when not in use. An electronic fuse rated at 7.0A protects the machine from overloads, though this may be reduced to nearer 2A in future designs.