#maze solvers

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MAD (2001) by Duncan Louttit, Swallow Systems, UK. MAD is a simple wall following robot designed for schools to build and enhance.

"The whole thing is as simple as I can make it and uses a small number of low-cost parts. How fast it can be made to go remains to be seen, but they can be made to follow the simple course. … You should note the funny shapes of the microswitch actuators. These need quite a lot of fiddling with to stop the mouse from getting hung up in corners. It would be better to mount the microswitches vertically and fit balsa actuators on them. The wood can be easily sanded to change the shape to the best one. As the actuators then move without rotation the shape is less tricky to arrive at. You should also note that the battery position is also critical. Moving it around will affect the traction available on each tyre." – Duncan Louttit.

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Mini-Mouse (2003) by Martin Barratt, UK. "The Wall Follower design presented here is based on a mouse designed in early 2003 as a result of running out of time during the development of a full maze solver. Mini-Mouse (it is conventional to give your mouse a name) was entered into the 2003 competition and gave a creditable performance. It did not win its class but was the fastest of the non-contact entrants. As a fully paid-up member of the `quart out of a pint pot' club, the author decided that Mini-Mouse should be a single-chip design using the smallest PIC possible, the choice being the 16C71, which offers little in the way of hardware features except a four channel 8-bit ADC. This approach was obviously going to lead to design compromises and place somewhat greater demands on the intricacies of the software (which was to be written in assembler) but that is the author's preferred design strategy." – Martin Barratt, Micromouse wall follower, Electronics World, Part I (June 2004), Part II (July 2004).

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Isambard I (2006) by Martin Barratt, UK. The first excerpt above combines video from UK Micromouse 2006 and MINOS'07 at the Royal Holloway, University of London, where Isambard I took part. It also participated in MINOS 2009 (see second video) coming in ninth.

"Many of you know that I have an unhealthy interest in Stepper Motors and doggedly persist in using them to drive my Mice. Stepper driven Mice generally have large and heavy batteries but does this have to be? Stepping Motors seemed to be a good choice, particularly as they were easily available and not particularly expensive. As an electronics engineer, I felt that I might be able to design a drive system that was both small in size and low in power requirements … which is incorporated into Isambard I." – Martin Barratt, Stepping Motors - they must be good for something, MINOS'07.

"At the 2007 Minos micromouse conference, Martin Barratt gave a talk about his stepper motor driving scheme. For best performance, steppers really need to be driven by a high voltage. However, the current will need to be limited to prevent the motor overheating. Normally this is done with dropper resistors which waste all the energy or with chopper drives that can be relatively complex. Martin has an alternative approach that provides the high voltage needed to produce fast step rates and the low current needed to reduce dissipation and keep the battery size under control. The essence of the method is quite simple. Stepper motors look like inductors to the driver circuit. The torque available depends upon the current flow through the coils but the rate at which the current can increase is proportional to the applied voltage. If you drive a stepper at low voltage and low frequency, it is perfectly happy. You will get adequate torque as the rise-time of the current will be a small part of the total step time. As you increase the step rate, there is less and less time for the current to rise and the torque suffers greatly. Simply using a higher voltage will result in the coils being over-driven severely. This will require a large battery and will make the motor overheat significantly. Martin’s solution is to have a two level power supply and a switch. At low speeds, or when the stepper is holding, the coils are supplied from a lower voltage. When a step is made, the switch connects a high voltage to the motors for a short period – long enough to get the current up to a respectable value quickly enough to ensure the motor responds quickly." – Peter Harrison, Bi level stepper driver.

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Kitty (2007) by Martin Barratt, UK. Kitty was placed fifth in the wall-following category at the MINOS'07 micromouse competition, with a time of 69.8 seconds — and with a little bit of help.

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Isambard II (2009) by Martin Barratt, UK. Isambard II came fifth at RoboTIC 2009 with a time of 28.81 seconds. The first video excerpt above is taken from the RoboTIC 2011 UK micromouse competition.

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FatCat (2010) by Tim Foden, UK. FatCat came eighth at RoboTic 2010 with a time of 76.57 seconds, and won a prize for the best new mouse. RoboTic is the winter micromouse event in the UK; the video is an excerpt from RoboTic 2011.

"Star of the show this year was probably Tim Foden with FatCat. Tim is a relative newcomer to the micromouse contest but, at his current rate of progress, it won’t be long before he starts to challenge for the top spot. The encoders are pretty remarkable. Note that the mouse has very inexpensive motors which do not have encoders. Tim has build very simple encoder discs which give an approximately sinusoidal response to the reflective sensors mounted on the encoder boards. The small PIC24 processor on each of these, reads two such channels for each encoder. These are arranged in quadrature so that it is possible, by simple trigonometry, to determine the absolute angle of the shaft holding the encoder discs. This is exactly the technique used by the AS5040 magnetic encoders but this is a (very effective) DIY solution. The job of the PIC is to turn the reading into counting signals for the main processor. In this way, the main processor can treat the encoders exactly the same as any other digital encoder. Should Tim change to AS5040 encoders or the vastly more expensive Faulhaber/Maxon motors with integrated encoders, the basic software in the mouse will remain the same. This arrangement, while still needing some tuning, manages sub millimetre accuracy and allows the mouse to calculate its position and heading wherever it is in the maze. Thus far, FatCat can only turn in place but, as soon as Tim has implemented smooth turns, I expect he will be able to put in very fast times with quite inexpensive hardware. This year, he was awarded a prize for best new mouse." – Peter Harrison, RoboTIC 2010.

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Kaasjager "Cheese Hunter" (2008) by Coen Roos, Netherlands. Kaasjager, or "Cheese Hunter" in English, came seventh in the 2008 UK Micromouse competition with a best time of 40.46 seconds. Kassjager was a stalwart of the UK micromouse scene, and the video excerpt is from RoboTic 2011.

"Kaasjager was designed and built by Coen Roos, a retired employee since 2001 of the ‘Netherlands Organization of Applied Scientific Research’ TNO in Delft where he was involved in electronics design and instrumentation since 1970. He says he started the project in “2006 with little or no knowledge of the critical areas of the envisaged project”. The high level maze solving functions of his entry are performed in an Atmel Atmega32 microprocessor programmed in C++ while the low level motor control functions in a PIC16F870 are programmed in assembly. Low cost motors are used with a single 400 mAh cell for power. Part of the external gear reduction is a 1 quadrant encoder (no turn direction) using a slotted opto and a gear with increased tooth depth providing a resolution of ~ 1 mm. Three infra-red sensors are used to measure the relative distance to the left, right, and front walls. The mouse measures 105 mm(L) x 66 mm(W) x and 88 mm(H) with a mass of 280 grams."– Green Ye, APEC 2013 Mice.

[stevebattle]

Raccoon4W (2012) by Chen-Yu Huan, Lunghwa University of Science and Technology, Taiwan. Raccoon4W came first at the APEC 2012 Micromouse competition.