Wallie by Harm Andries Kingma

Wallie is an attempt to make a very small and very simple robot which is still able to perform a
certain task. In this case that task is wall-following. As you can see on the picture, Wallie's body
is an old PC mouse. It uses differential steering to navigate across its world. Its two motors are
very small 5 volt gearbox motors. I have salvaged a tape pressing roll from an old cassette deck and
transformed it in a very small castor wheel. This works beatifully. 

Wallie uses three infrared obstacle detection sensors to locate and follow a wall. These are mounted
on the front of the bot as can be seen on the picture. One pointing a little bit to the left, one
pointing forward and one pointing a little to the right. These sensors either see or don't see an
obstacle. There is no distance measuring capability available. When an object comes within
approximately 7 cm of the sensor, it will trigger. 

The brain of wallie is an ATMEL AT90S2313 microcontroller. It is programmed with the AVR port of the
linux GCC C-compiler. 

The wall following procedure is as followes: First, Wallie waits until it gets offered a wall to
follow. In other words: You have to put him so close to the wall that the sensors of the bot see it.
Wallie will then start to drive forwards a little bit in the opposite direction of the wall. When
the distance to the wall gets to great, the sensor pointing to the wall will not see it anymore.
Wallie will then start to drive towards the wall again until he sees it again. Then he starts to
move away from the wall again etc. This way he will follow the wall without touching it. When it
does not find the wall within a short period, this means the wall has moved sharply away from the
bot. Wallie will then start to turn sharpy towards the direction he expects the wall to be until it
is found again. The second special situation is when the sensor facing the wall and the sensor
facing forwards see the wall. This means the wall has made a sharp turn towards the robot. Then
wallie will react by turning away from the wall until only the sensor facing the wall sees the wall.
The third special situation is when all three sensors see the wall. This means Wallie has driven up
a dead end or a very sharp edge in the wall. He will then start to turn on the spot until the sensor
pointing to the front does not see the wall any more. He then faces in the correct direction again. 

On my website: http://members.home.nl/hakingma/ you can also find a movie of wallie in action,
together with a description of my other three bots.



Email: hakingma@yahoo.com


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