Sensing plants and weeds

Tertill detects objects the same way most touch screens sense your finger.  Both detect small changes in capacitance when a conductive object is near.  

Sensor plates mounted just inside Tertill’s shell on the front left and front right detect tall plants and conductive boundaries.  A smaller plate mounted on the bottom front of the robot is used to detect weeds short enough to slide under the robot.  When Tertill detects an object with its side-mounted sensors it spins right or left to avoid the object.  But if the bottom mounted sensor detects an object Tertill turns on its weed whacker.  In this way the robot avoids tall crops but attacks short weeds.