Sumo Robot PCB and Circuit Explaination:
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The sumo robot circuit is one of the most simple you will find, it is also very robust.

The sensors, all sensors are mechanical switchs which are normally open (NO):

Left and Right Opponent Sensors - these can come in the form of guitar string or bump sensors, remembre that for official rules the robot must not exceed 10 by 10cm, this means that guitar string sensors cannot stick out past this before the game begins (you may wish to release them in someway as I did for Police V2).

Edge Sensors - Mount these in the front left and right corners.  The best method for these mechanical sensors will be covered soon on the site.  Basically you want a sensor which when it goes over an edge, a wire will be able to close a contact.

Rear Edge sensors - these are an addition which simply short out the capacitors.  The capacitors only become charged if an opponent sensor is activated, causing the robot to reverse in one direction to face the opponent.  When this happens we must stop the robot reversing blindly over the edge!  The sensors should be of the same form as the front edge sensors.


The resistor values used are only to protect the base of the NPN transistors, almost any NPN transistor can be used.  Check the datasheet of your transistor to check the acceptable base current allowed.  Most resistors from 1k to 10k will be fine.

The capacitor values set the reverse time when an opponent is detected.  The capacitors will snap charge on detection of an opponent, which will then keep the transistor on until the capacitor is drained.  One capacitor will always be charged less than the other due to the configuration of the diodes.... by doing this we see a reverse followed by a slight turn when one capacitor drains before the other.

The diodes shown can be normal diodes or LED's..... note that the colour of the LED will affect the turn time!  experiment to find the best for your motors.