Growing up I tinkered with BEAM robotics. It's a philosophy of design that begins with these types of very simple reactive circuits usually from scavenged parts. It's nice to see someone break down the effect of different variables in the design.
https://en.wikipedia.org/wiki/BEAM_robotics
Reminds me of BIO bugs from when I was a kid
http://solarbotics.net/BIOBugs/default.htm
Reminds me of BIO bugs from when I was a kid
http://solarbotics.net/BIOBugs/default.htm