The Micromouse contest has been running internationally for over fifteen years now. There are a number of powerful reasons for its continuing appeal. The objectives are very easy to understand, even if the scoring rules may at times seem complicated. The contestants can improve their performance, year by year, because the contest is ongoing. This year's effort is not lost the day after the contest.
The contest final is a spectator-friendly event which takes around two hours to complete. The mice are often imbued with personalities by their builders, so that the personal involvement is intense.
The mice are faced with the problem of a maze to solve and the need to find the fastest path to its centre. They must find the solution completely unaided by human handlers, while performing tasks of position and steering control, navigation, mapping and strategy. These same tasks will confront the Bilbies.
I should explain that in Australia, mice are a pest which ravage crops in their tens of millions. After a recent poisoning campaign, the local newspaper ran a jubilant headline, "MILLIONS DEAD". The Bilby, on the other hand, is a long-eared marsupial which looks like a rather soppy cross between a mouse and a rabbit. While rabbits are regarded as an even greater menace than mice, the bilby is rather scarce and is therefore cherished.
So why is there a need for a new contest with such a close resemblance to Micromouse?
An essential feature of Micromouse is that the mice are totally self-contained, with all their processing power on board. This makes the pre-university entry level of expertise too high for all but a very few contestants. By allowing the rodent to be attached to a PC (or similar) computer, the computing and software problems become universally accessible. Now there only remains the problem of constructing a mobile robot and a maze to run it on!
Old computers are dying in droves. With each discarded XT, one or two five-and-a- quarter inch disk drives hit the scrap heap. In each of these drives is a stepper motor ideal for becoming half the motive power of a mouse - or Bilby. They may not give the fastest performance, but the stepper motors give a quick and easy start. Plastic wheels can be connected directly to their shafts - no need for gearing. A small sheet of aluminium can be bent to form a chassis with the wheels side by side and 'skids' fore and aft, wheelchair style. A single Darlington driver chip can be driven via the printer port to control both motors.
So what of the maze? A Micromouse maze has a lot of walls, over two hundred and fifty, each precisely made and painted and with precision pins or slots for mounting. That is only the start. The maze base is three metres square and (as I know to my cost) can involve the drilling of over a thousand precision holes. This is a strong deterrent to a new group!
The Bilby maze is based on the same size matrix, but instead of 'alleyways' it is based on 'stepping stones'. Eighteen-centimetre squares are cut from wooden composite sheet. This is the white-plastic coated board which is often used for shelving or kitchen cupboards. The squares are butted together on the floor to form a layout which looks a bit like a crossword puzzle. The squares can be fixed together by holes and dowels, or be merely stuck together on the underside with adhesive tape.
There is of course no need to start off with a complete sixteen-by-sixteen maze. Indeed the 'starter' contests might only require the bilbies to race side by side on identical layouts of a dozen squares or so, negotiating a few turns to reach the finish.
Even this simple level requires sensing, exploring and steering control. Photoelectric sensors very similar to those of micromice can detect the edge of the track. For the electronic novice, however, there is the simpler solution of feeling for the edge. Four lines in the printer port provide input lines to the computer. Switches which connect these lines to ground can be read by a simple line of software. The switches need not even be microswitches - a very effective sensor can be made from a couple of paperclips!
Once these first stages have been successfully accomplished, progress to the solution of a full-size maze will be rapid. At the same time, the contestants will probably become dissatisfied with the performance of the simple steppers and will experiment with faster motors and better sensors.
The next challenge is to build the processing power into the Bilby. With no worry about size limits and wall clearance, all sorts of solutions can be tried - even to the extremes of laptop computers wobbling through the maze. The enhancements can lead towards the eventual evolution of the Bilby into a Micromouse which will fit inside that maze.
Scavenger squads are already amassing a heap of parts at the University of Southern Queensland. Circuit boards, wheels and chassis are added to the kits which will be presented to the many schools which are joining in the contest. With perseverance and luck, Bilbymania will soon be convincing schoolchildren that interfacing computers to problems in the real world is really not all that difficult - and that mechatronics is fun.
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