Specifications

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For accurate manoeuvrability in this application it is necessary that the sensors have a
long enough range to avoid collision during turning. Figure 4.10 illustrates this need.
Figure 4.10 Sensor Distance Requirements
The above diagram illustrates that even after the robot has stopped to avoid an object,
the turning circle will result in the corner of the robot still proceeding forwards. It is
necessary for the sensor to be able to read further than this turning circle. The necessary
distance can be reduced significantly by turning the outside wheel backwards so it pulls
away from the wall, this however does pose the issue of being able to reverse into
objects, as there is no rear sensors.
Also, when in this illustrated position, it would be preferable if the sensors could judge
a long distance at the sides of the robot. If the robot where to turn left after stopping in
figure 4.10, it would turn directly into a wall and be interrupted by the side sensor half
way through a turn. This would make coding of the processor more difficult. Initial
experimentation has shown the ideal range of the sensors will be approximately
200mm-300mm but definitely no less than 100mm for the front sensor.
Furthermore, for household applications the obstacle to avoid may be the wall. If a
short range sensor is used and placed above the skirting board the wheels may impact
this before the sensor realises there is an obstacle. This will result in scratches on the
obstacles and possible breakage of the robot. Also, the robot will be jammed until loss
of power or failure of components.