This video shows the KD01 (differential drive) robot testing out its new Moth sensor, which is composed of two tiny GA1A12S202 Log-scale Analog Light Sensors mounted on the front of the robot at about 45 degrees to port and starboard. The difference between the two sensors' outputs are used as a bias to steer the robot to port or starboard. Such a sensor permits the robot to have a "Moth Behaviour", or move towards a bright light.
Whereas a Moth Behaviour moves the robot towards a light, an Anti-Moth Behaviour (sometimes called a Cockroach Behaviour) moves it away from the light, into the darkness.
The KD01 robot is currently operating under what's called "open loop" control, meaning that there's no feedback from the Hall effect motor encoders (magnetic sensors on the motor shafts) telling it how far the port and starboard motors have traveled, so the robot cannot perform odometry and has no idea where it is. Absent any functional bumpers or infrared sensors, it's pretty blind too, all it can do is just move towards the light, much like a moth at night, whacking its head repeatedly against your bathroom window.