This is my first mini Sumobot. Police has six sensors in total, four of which are edge detection sensors and two opponent detectors. For those who are new to Mini Sumo:
Mini-Sumo robots fight in a circular ring which has a drop at the edge. The ring is black with a 1 inch white border, this allows for the use of optical sensors to sense where the edge is. The object of the game is pretty simple - push the opponent out of the ring!
Police runs from 6 AA batteries, and uses GM3 geared motors. Its basic function is... turn on, move foward unless a sensor is activated. If a side sensor is activated, it will reverse and turn to face the direction in which the contact was made, it will the drive forward towards it.
If either front edge sensor is activate (one on each corner), then the robot will reverse and turn away from the edge. If at any time the robot is reversing towards the edge, the rear edge sensor will activate and cause the robot to stop reversing and move forward again.
On the top of the robot you can see some two capacitors and two resistors plugged into an IC holder. These control the reverse time of the robot, for this reason I have left them accessible allowing me to change the time.
All of the sensors on this robot were built using guitar string. The methods will be covered in the Tips and Tricks Section.
The sumo circuit, using two DPDT (Double Pole Double Throw) relays, two NPN transistors, two resistors, two capacitors, two motors, and six LEDs. Really there are two LEDs and two Bi-Color LEDs, however I just used six LEDs.
The circuit operation is pretty simple. When switched on the motors are powered through the relay, at this point the relay is not active and so the motors are connected to the normally closed (NC) pins of the relay. If a side sensor is triggered, the respective capacitor charges and feeds a current to the respective transistor. The transistor then allows current to flow
and hence completes the circuit for the magnetic relay coil. The coil in the relay now activates causing the motor connected to that coil to recieve an inverted supply (ie, its posotive becomes its negative, and negative becomes posotive), therefore causing the motor to spin in the opposite direction. This will continue until the capacitor fully discharges, at which point the transistor will turn off, and the relay will reset to its
previous state. If a front edge sensor is triggered, both capacitors will charge, however one will not charge as much due to the LED setup, this cause the robot to reverse and then turn at the end of its reverse because one motor remains in reverse for longer. If at any time the robot reverses towards the edge the capacitor will be shorted, causing it to go forwards again.