MICROMOUSE

Robin Bradbeer has been involved with Micromouse since its inception in the late 1970s. At City University of Hong Kong he has successfully helped students build 50 mice - so far - in the past seven years.

In 1991 Hong Kong organised the World Micromouse Championships. 30 people entered from 13 countries. Each year City University hosts a competition for all universities and colleges in Hong Kong. Usually around 12 teams take part. This year's contest is planned for october.

This page is still under construction, so not all the links may be here. Please be patient if you get stuck!

The micromouse contest ... in the beginning

What is a micromouse?....Design hints

Competition rules (Hong Kong version)

Bibliography


THE MICROMOUSE CONTEST ....IN THE BEGINNING

The very first record of a 'mouse versus maze' problem can be traced as far back as 1950 when Dr Claude Shannon, widely acknowledged as the 'Father of Information Theory' and Professor Emeritus at the Massachusetts Institute of Technology, built the first maze- solving machine containing a sensing finger that was moved by two motors.

Two years later Dr Shannon built an electric mouse that could find its way through a maze, guided bv information "remembered" in a relay circuity underneath the maze. Experiments with the mouse helped stimulate researchers to think of new ways to use the logical powers of computers for operations other than numerical calculations - a key reason, probably, for the sustained interests in the exploits of the mouse.

In 1972, "Machine Design" magazine sponsored a "Le Mouse 5000" contest in which mechanical mice, powered only by springs from mousetraps, pitted their stamina against one another to see which could travel the longest distance down the racetrack. The first-place "Mousemobile" was one which travelled 825.3 feet.

In 1977, Machine Design sponsored yet another mouse contest, "The great Clock Climbing Contest", coupled with the rediscovered information of the 1972 "Le Mouse 5000" contest that spurred on the editors of the IEEE Spectrum magazine in their search for a truly electronic mouse. After much brain-racking and consultations with major manufacturers of microprocessors, they finally came up with the concept of a micromouse - a small microprocessor-controlled vehicle imbued with intelligence and capability to decipher and navigate a complicated maze. In May 1977, the first US contest, called the "Amazing Micromouse Maze Contest" was announced by Spectrum.

New York, June 5-7, 1979. A highlight at the National Computer Conference has 15 micromouse gathered, all poised for a go at the grand prize, of US$1000, and other prizes including an oscilloscope donated by Tektronix and a video computer system donated by Atari. It was the finals of the "Amazing Micromouse MazeContest", a fitting culmination since its first announcement in the May 1977 IEEE Spectrum magazine and four preliminary time trials later.

The final 15 pesky mice were part of the 6000 entries received, some from as far as Italy. Apparently, many failed to turn up - some reported "brain failure" while others claimed mouse "blow-up" and a variety of other reasons. While interest was high, evidently, the design and construction of an intelligent mouse was to be much tougher than most cared to think. Many contestants reported having spent 500 to 1000 hours, many of them off-work and up US$500 on materials and components. Obviously money was not the main reason for entering the contest.

Of the 15 mice, only 4 managed to solve the 8x8-foot maze during their first run and 2 more at their third attempts. The eventual winner was "Moonlight Flash", a mechanical non- intelligent mouse employing a wall- hugging strategy, romping home in a time of 30.04seconds. That a "dumb" mouse could outwit its electronically more sophisticated and supposedly more intelligent opponents then led to the rules being amended for subsequent contests. Instead of being along the perimeter, the goal was placed at the centre of the maze.

In 1980, the European version of the contest was launched at Euromicro '80 in London. Among the spectators were five delegates from the Japan New Science Foundation who took the rules back to Tokyo and subsequently organised the first All- Japan Micromouse Contest in November that same year. At the first All-Japan Micromouse Contest, none of the 18 mice entered managed to solve the maze but five years later

August 1985, Tsukuba, Japan, the site of the First World Micromouse Contest. Mice came from all over Europe and the US, of all shapes and sizes, employing sensors ranging from infra red to ultrasonic to CCD sensors, driving mechanism from stepper motors to dc-servo motors, all vying for the top honours. All the top prizes were clinched by Japanese. First was Noriko-1, named after the wife of the President of the Fukuyama Computer Club, returning a time of 19.83 seconds.

At the 1987 Micromouse Championships, hosted by IEE at Savoy Place UK, 13 micromouse were set for a showdown. David Otten, from MIT captured both the first and second prize with his two entries, Mitee Mouse I and Mitee Mouse 11. A new but slightly complicated system of scoring, was also adopted. If the mouse could run from start to finish completer unaided, without having to rescued or re-started, a bonus of 10 seconds was deducted from the run time. Once the mouse had been touched, no bonus would be given. On top of this score was added 2 seconds each minute elapsed since the mouse too its turn. With this new system, the championship score of Mitee 11 which spent 2.48 minutes on the maze with a fastest run time of 15.7 seconds was 10.6 seconds.

The next major competition held in Singapore in July 1991 saw speed increase ever more. The first prize went to David Otten of MIT wit MITEE 6 in a handicapped time of 10.19 seconds. The first runner-up, Noriko X of Japan, took 10.23 seconds.

The World Championships held that year in Hong Kong, was the largest international gathering of mice since Tsukuba in 1985 - 21 contestants with 30 mice came from 13 countries. New comers to the micromouse scene from Ngee Ann Polytechnic in Signapore stole the honours from Niriko of Japan and Mitee Mouse from USA. The rules were changed at this contest to the ones which are in general use today. The change was made to encourage reliability over speed. The bonus of 10seconds for not being touched was replaced by a penalty. The Hong Kong contest saw the 45 degree running pioneered by Dave Otten at MIT now used by a number of mice.

Since 1991 the number of contests worlwide has increased dramatically. From 5 or 6 a year there are now over 100. Speeds have also increased, to such an extent that maze designers now reward "intelligence" over raw power.


WHAT IS A MICROMOUSE - DESIGN HINTS

The mouse is essentially composed of three main components: the drive, sensing and control sections. It has its own power supply, usually consisting of primary or rechargeable batteries. The rules forbid the use of energy sources employing a combustion process.

The mouse shall not be larger, either in length or width, than 25 centimetres. There is no restriction on the height. (It is interesting to note that the rules allow for the mouse to change its geometry while it is in the maze, provided the restrictions on the length and width are not exceeded at any time.)

DRIVE SECTION

Perhaps the simplest drive system is one that uses stepper motors which operate on current pulses. In a stepper motor, the rotor turns a fixed angle for each pulse applied to the stator coils, and this angle is independent of the load on the motor, provided this load is within its operating limits. This property is usually used to keep track of the distance travelled. Since each pulse turns the rotor by a fixed angle, this can be converted to a fixed distance on the ground by taking into account gear ratio and drive wheel diameter. For example, each pulse on the motor can cause the mouse to move approximately I millimetre.

Another popular drive system employs direct current (dc) motors. In dc motors, the angle turned by the rotor is a function of the current through the motor as well as the load on the motor. Thus it is not possible to determine the distance travelled from the current supplied to the motor (even if that was easy to measure or calculate). Tachometer feedback techniques must be used. Usually, the drive wheels are also geared to a tachometer or optically encoded wheel which provides pulses at a rate proportional to the speed of the rotor. The distance can now be determined by counting these pulses.

Stepper motors are retatively easily interfaced to the digital output ports of a microprocessor (control section) while dc motors required some form of digital to analogue converters to convert the digital speed setting from the microprocessor to an analogue voltage (or current) to be applied to the motor. Steppers, besides being heavier and bigger than dc motors with the same torque characteristics, suffer from anachronistic problems when driven at high speeds. Suppose that a fixed supply voltage with current switches is used to supply the pulses to the motor. As the speed increases, the pulses get smaller in duration, thereby decreasing the maximum current developed in the coils. As a result, the torque developed drops rapidly. One solution to overcome this problem consists of providing a larger voltage, including current limiting circuitry (chopper amplifier), to limit the current, particularly at low speeds.

Another limitation in stepper motor drives is that the rate at which pulses are applied (speed at which the motor is driven) cannot be changed very quickly. The mistiming of a single pulse .often causes sufficient instability to completely stop the rotor. This instability can be avoided if the pulses that drive the motor are derived from a voltage controlled oscillator with sufficient damping so that its frequency cannot change suddenly.

SENSOR SECTION

The top walls and the floor of the maze are painted so that infrared emitters and detectors can be easily used to sense the absence or presence of walls by simply "looking" at them from the top. Usually, a number of emitters and detectors are used to sense the position of the walls relative to the mouse so as to enable the mouse to travel in between the walls. In the simplest design, (MAPPY kit from NAMCO, Japan), three emitter- detector pairs are used to track the walls on either side. The three sensors indicate if the mouse is too far away, too close or just the right distance from the walls. To allow for finer resolution, some designs (e.g. MITEE 11 and MITEE 111) use up to 12 miniature sensors on each side. The more sensors one uses, the more information the control unit has to process in order to determine its position for motion control. The front walls are usually detected by one or two sensors and are used to decelerate and stop before colliding with the wall in front of the mouse.

An alternative method of detecting the proximity to walls uses ultra- sound ranging techniques. Although this method can be used to detect walls that are much further away, it is usually less reliable owing to standing wave effects. For some particular distances, the reflected echo from two different paths of different distances destructively interfere so as to cause the returned echo to be missed altogether.

CONTROL SECTION

A microprocessor is usually required to solve the maze so as to find the optimal path to the centre, having remembered the maze configuration from the sensor information during the exploration runs through the maze. Other functions performed by the microprocessor include providing control signals to drive the motors (e.g. pulsing stepper motors).

A general purpose microprocessor provides the environment to run programs for the exploration. However, to control the motor, get information from sensors, drive indicator lights, etc., additional peripheral chips are required. This adds to the complexity of the mouse electronics thereby reducing its reliability.

Special purpose microcontroller chips are sometimes very useful in reducing circuit complexity as these usually incorporate input and output peripheralfunctionson-chip. MITEE 11 and MITEE Ill use controller chips which have RAM, EPROM, timers, serial IO ports, parallel 10 ports, pulse width modulation drivers, bi- directional up/down counters and an analogue to digital converter all in the single package.

The capacity of RAM and ROM in micro-controller chips is usually limited to a few kilobytes. Furthermore, support is usually provided only for program development using cross- assemblers, some even without macro-facilities. Even if higher level language support is provided, squeezing the code into the limited capacity memory may be a problem. This then is the main (and perhaps the only) disadvantage of using a microcontroller chip over a general purpose micro rocessor.

MOVEMENT CONTROL

A common method of steering the mouse through the maze employs two independently connected motors driving wheels on either side of the mouse, with another two idle castor wheels or roller bearings in front and at the back, in a rhombic trolley configuration. The mouse is made to turn by spinning the two drive wheels at different speeds. On- the-spot turns can be achieved by spinning the wheels in opposite directions.

Another technique uses a three wheel configuration. The front wheel is connected to a steering mechanism while the two rear wheels are driven by the same or independent motor drives. This technique appears to provide greater stability in keeping the mouse on the straight track at high speeds. However on-the-spot turns are usually not possible. Three point turns are required, which are relativelv more difficult to implement and slower in execution In the case of ENTERPRISE, the two rear wheels are independently driven, and turning is achieved by turning the front steering wheel to point to the right direction while at the same time driving the rear wheels at different rates corresponding to the turning curve.

MAZE SOLVING

It turns out that the shortest path from the start to finish is usually not the fastest path. It is generally true that turns are slower to execute compared to straight runs. Thus, in solving the maze, the algorithm must take into account different "cost factors" for paths with turns compared to paths without turns. It isalso generally true that two straight paths of lengths I and 19 squares can be run in a shorter time than two lengths of 10 squares each (assuming that the acceleration profile is linear). Taking account of this advantage is a bit more difficult.

While techniques for solving the maze problem, using a representation of a quaternary tree are quite well established, the use of these techniques with cost factors mentioned above for straight runs versus turns, or different length combinations of straight runs, can make the search algorithm very complicated. Another problem that is even more difficult to incorporate is to sort the unknown maze areas according to proximity and determine an optimal (fastest) route to visit them.

OVERALL CONSIDERATIONS

It appears that with the current rules, where one minute of exploration is equivalent to two seconds of the run time, it is relatively cheap to explore the maze. Thus the crucial factor deciding victory is usually the speed at which the final run is made. Thus more attention is focused on the drive section. The sensor section also plays an important part in drive control. If the sensors can measure the position of the walls to a finer resolution, then proportionate control may be used to increase the stability of the drive control loop.

One of the challenges in designing the sensor circuitry is to work out a configuration which will allow the mouse to determine its deviation distance and direction from the ideal path through the maze. For example, a mouse whose heading is tilted at an angle away from the centre line between walls on either side of a straight path is more prone to crash than one which is heading in the same direction as the centre line but with an offset.


COMPETITION RULES

INTRODUCTION

A Micromouse is a small microprocessor-controlled robot vehicle that is able to navigate its way through an unknown maze. It is a typical product of "mechatronics" embodying within itself an integration of computer and electronic technology and mechanics. The main challenge for the contestant is to impart to the micromouse an adaptive intelligence to explore different maze configurations and to work out the optimum route for the shortest travel time from start to finish.

1.1 The maze shall comprise l6 x l6 multiples of an 18 cm x 18 cm unit square. The walls constituting the maze shall be 5 cm high and 1.2 cm thick. Passageways between the walls shall be 16.8 cm wide. The outside wall shall enclose the entire maze.

1.2 The side of the maze walls shall be white, and the top of the walls shall be red. The floor of the maze shall be made of wood and finished with a non-gloss black paint. The coating on the top and side of the wall shall be selected to reflect infra- red light and the coating on the floor shall absorb it.

1.3 The start of the maze shall be located at one of the four corners. The starting square shall have walls on three sides. The starting square orientation shall be such that when the open wall is to the "north ', outside maze walls are on the "west" and "south". At the centre of the maze shall be a large opening which is composed of 4 unit squares. This central square shall be destination. A red post 20 cm high and 2.5 cm on each side, may be placed at the centre of the large destination square if requested by the handler.

1.4 Small square posts, each 1.2 cm x 1.2 cm x 5 cm high, at the four corners of each unit square are called lattice points. The maze shall be constituted such that there is at least one wall touching each lattice point, except for the destination square.

1.5 The dimensions of the maze shall be accurate to within 5% or 2 cm, whichever is less. Assembly joints on the maze floor shall not involve steps of greater than 0.5 mm. The change of slope at an assembly joint shall not be greater than 4 degrees. Gaps between the walls of adjacent squares shall not be greater than l mm.

1.6 A start sensor will be placed at the boundary between the starting unit square and the next unit square. A destination sensor will be placed at the entrance to the destination square. The infrared beam of each sensor is horizontal and positioned lcm above the floor.

MOUSE RESTRICTIONS

2.1 Although the superstructure of the mice may "bulge" above the top of the maze walls, mice must be subject to the following size constraints - width 25 cm, length 25 cm. There is no height limit. Mice must be completely self-contained and must receive no outside assistance. The method of wall sensing is at the discretion of the builder; however, the mouse must not exert a force on any wall likely to cause damage. The method of propulsion is at the discretion of the builder, provide that the power source is non-polluting - internal combustion engines would probably be disqualified on this coun! If the judges consider that a mouse has a high risk of damaging or sullying the maze they will not be permit it to run. Nothing may be deposited in the maze. The mouse must negotiate the maze; it must not jump over, climb, scratch, damage or destroy the walls of the maze.

RULES OF THE CONTEST

3.1 The time taken to travel from the start square to the destination square is called the run time. Travelling from the destination square back to the start square is not considered a run. The total time taken from the first activation of the micromouse until the start of each run is also measured. This is called the maze or search time. If the micromouse requires any manual assistance at any time during the contest, it is considered touched. Scoring is based on these three parameters.

3.2 Each mouse is allowed a maximum of 10 minutes to perform. This may have to be reduced to 6 minutes if there are many good mice. The judges have the discretion to request a mouse to retire early if by it lack of progress it has become boring, or if by erratic behaviour it is endangering the state of the maze.

3.3 The scoring of a micromouse shall be obtained by computing a handicapped time for each run as follows:

Handicapped Time Score = Run Time + Search Penalty + Touch Penalty

Where,

Search Penalty = 1 /30 of the maze or search time, in seconds, associated with that run, and

Touch Penalty = 3 seconds plus I /10 of the run time, in seconds, if the mouse has been touched at any time prior to the run.

For example, if a mouse, after being on the maze for 4 minutes without being touched, starts a run which takes 20 seconds, the run will have a handicapped time score of 20 + 1/ 30(4X60) = 28 seconds. However, if the mouse had been touched prior to the run, an additional touch penalty of (3+(1/l0X20)) seconds is added giving a handicapped time score of 33 seconds.

3.4 When the mouse reaches the destination square, it may stop and remain at the maze centre, or it may continue to explore other parts of the maze, or make its own way back to the start. ff the mouse chooses to stop at the centre it may be lifted out, manually, and restarted by the handler. Manually lifting it out shall be considered touching the mouse and will cause a touch penalty to be added on all subsequent runs. If the mouse does not choose to remain in the destination square it may not be stopped manually and restarted.

3.5 The time for each run (run time) shall be measured from the moment the mouse leaves the start square until it enters the destination square. The total time on the maze (maze or search time) shall be measured from the time the mouse is first activated.

3.6 The time taken to negotiate the maze shall be measured either manually by the contest officials, or by infra-red sensors set at the start and destination. If infra-red sensors are used, the start sensor shall be positioned at the boundary between the start square and the next unit square. The infra-red beam of each sensors shall be horizontal and positioned approximately 1 cm above the floor.

3.7 The starting procedure of the mouse should be simple and must not offer a choice of strategies to the handler. The starting procedure shall be submitted to the judges when the mouse is registered on the day of the contest.

3.8 The mouse handler is given 1 minute, from the moment the mouse is taken out of the cage, to make adjustments, if any, to the mouse sensors. However, no selection of strategies must be made and no information on the maze configuration entered or captured into the memory.

The maze or search time clock will commence after the expiry of the I minute time limit even if the handler is still making adjustments to the sensors.

3.9 If a mouse "gets into trouble" the handlers can ask the judge for permission to abandon the run and restart the mouse at the beginning. A mouse may not be re-started merely because it has taken a wrong turning - the judges'decision is final. The judges may add a time penalty for a restart.

3.10 If any part of a mouse is replaced during its "performance" such as batteries or EPROMS, or if any significant adjustment is made, then the memory of the maze within the mouse must be erased before restarting. Slight manipulations of sensors will probably be condoned, but operation of speed or strategy controls expressly forbidden without a memory erasure. It is assumed that mice will have software stored in EPROMS. However, at the judge' discretion, but not in normal circumstances, mice with battery backed up RAM may be allowed to download control software if the memory is erased accidentally during a run. The handlers, in this instance, must convince the judges that the original software has been reloaded.

3.11 If no successful run has been made, the judge will make a qualitative assessment of the mouse's performance, based on distance achieved, "purposefulness" versus random behaviour and quality of control.

3.12 If a mouse elects to retire because of technical problems, the judges may, at their discretion, permit it to perform again later in the contest. The mouse will be deemed to have taken an extra three minutes search time (ie if a mouse retires after four minutes, then when restarting it is counted as having taken seven minutes and will have only three more minutes to run). This permission is likely to be withdrawn if the programme is full or behind schedule.

3.13 The judges will use their discretion to award the prizes, which in addition to the major prizes may include prizes for specific classes of mouse - perhaps lowest cost, most ingenious, best presented, etc.

3.14 Before the maze is unveiled the mice must be accepted and caged by the contest officials. The handlers will place the mice at the start under the officials' instructions.

3.15 The starting procedure of the mouse should be simple and must not offer a choice of strategies to the handler. For example, a decision to make a fast run to the centre as time runs out must be made by the mouse itself.

3.16 Under normal circumstances, no part of the mouse may be transferred to another mouse. However, the judges may allow a change of batteries or controller in exceptional cases, if due to accidental damage. Thus if one chassis is used with two alternative controllers then they are the same mouse and must perform within a single 10 minutes allocation. The memory must be cleared with the change of controller.


MICROMOUSE BIBLIOGRAPHY

This bibliography is not up to date! It is also esoteric reflecting my own interests. I would welcome new additions to this list. At the same time if someone has the patience to put it in alphabetical order please let me know!

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Cynar, S.J. : Micromouse, an interdisciplinary educational experience: CoED (Computers in Education Division of ASEE, USA), v9, n4, pp 78-80, Oct-Dec 1989

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Provo, B. : Micromouse: an intimation of engineering excellence: NEWelectronics (NZ), September 1990, pp 36-39

Otten, D.M. and Kassakian, J.G. : The micromouse: an electromechanical challenge: Powertechnics Magazine, December 1986, pp 21-24

Billingsley, J. : Micromice find ways to a maze: Sensor Review, April 1990, pp 89-90

Billingsley, J. : Alternative robotics: Practical Electronics, July 1986, n7, pp 26-27

Friedman, B. : Using back emf for tacho to cut motion control servo costs: Electronics Engineer (HK), October 1991, pp 156-159

Provo, B. : Micromouse and Nelcon: an educational experience: Proceedings NELCON '90, (NZ), Sept 1990, pp 173-179 Christiansen, C. : Announcing the amazing micromouse maze contest: IEEE Spectrum, May 1977, v14, n5, p27

Stewart, I. : Mathematical recreations; The true story of how Theseus found his way out of the labyrinth: Scientific American, February 1991, pp118-121

Tarjan, R: Depth-first search and linear graph algorithms: Society for Industrial and Applied Mathematics' Journal on Computing, v1, n2, pp 146-160, June 1972

Hopcroft, J. and Tarjan, R. : Algorithm 447 - efficient algorithms for graph manipulation: Communications of the Association for Computing Machinery, v16, n6, pp 372-378, June 1973

Gould, R. : Graph Theory: Benjamin-Cummings, 1988

Schummy, H. and Billingsley, M-A. : Computers in the maze garden, Micromouse competition in Copenhagen: CHiP, (Germany), March 1985, n3, pp 243-4. (In German)

Waldschmidt, K. et al : Superlite; a self teaching maze solving robot: Elektronik, (Germany), v31, n25, pp 72-8, December 1982 (In German)

Rollins, D. : Polymaze! Solver: Creative Computing, v L9, n12, pp 294-311, 1983

Takeno, J. and Mukaidono, M. : The construction of maze solvong robot MS-2 with ultrasonic sensor system: Research Reports in Engineering. Meiji University, Japan, n44 pp 33-8, 1983 (In Japanese)

Takeno, J. and Mukaidono, M. : A maze solving algorithm and its programs using Z-80 assembler language for a robot: Research Reports in Engineering, Meiji University, Japan, n43, pp 33-47, 1982 (In Japanese)

Gerten, R. et al : Coupling two microprocessors to do the data processing in a micromouse: Euromicro Symposium on Microprocessing and Microprogramming, pp 153-9, Sept 1981

Nansel, Bob: LIMBO Part Three: Building the mobility base: Micro Cornucopia, pp22-31, n50, Nov-Dec 1989.

Japanese micromice take Bostson: The Institute (IEEE, USA), p1, March 1986 MIT micromice win in California: The Instutute (IEEE, USA), p2, May 1987

Otten, D. : Building MITEE Mouse III: Part 1: Circuit Cellular Ink (USA), pp32-39, June 1990 Otten, D. : Building MITEE Mouse III: Part 2: Circuit Cellular Ink (USA), pp40-51, August 1990

Provo, B. and Durham, J. : A dual processor mouse: Proceedings NELCON '90 (NZ), pp179-188, September 1990

Avila, E. F. :Of mice and machines: Robotics Age, October 1984 Heiserman, D. C. :How to design and build your own custom robot: TAB, 1981

Cynar, Sandy J, : Simulating the maze solving algorithm for the CSULB micromouse: Proceedings 1992 SCS, ASEE, IEEE Education Society International Conference on Simulation inEngineering Education.

Billingsley, J. :Micromice at Expo '85, Tsukuba: Electronic Systems News, Spring 1986, pp32-33

Bradbeer, R. :Educational uses of micromouse and robot ping pong in the teaching of mechatronics: Proceedings NELCON'92 Wellington New Zealand, August 1992, pp75-80

Zelinsky, A. :A mobile robot exploration algorithm: Robotics and Automation, v8, n06, December 1992, pp707-717

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Borgefors, G. :Distance transform in abritrary dimensions: Computer Vision, Graphics Image Processing, v27 1984 pp321-4,

Bradbeer, R: Using mechatronics projects, such as micromouse and robot ping pong, in teaching robotics: implications for Southern China": Robotics Techniques and Applications, May 1995, Beijing (In Chinese)

Bradbeer, R: Advances in mechatronic education using micromouse as a teaching tool: Mechatronics and Machine Vision in Practice, M2VIP, Queensland, Australia, 1994

Bradbeer, R: Teaching robotics can be fun, as well as educational! the experience of micromouse and robot ping pong for teaching mechatronics" 2nd Asian Conference on Robotics and its Applications, ACRA '94, Beijing, China

COPYRIGHT Robin Bradbeer, City University of Hong Kong

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