Something very important to any robot is the sensing system. Whether it be a robot to spray-paint cars, a Martian lander, or our humble little RickBot... it is absolutely essential that sensing is both responsive and accurate.
It would be somewhat crazy of you to muffle your ears, cover your eyes, and start running down the middle of your local town centre. The same goes for a robot. You don't want to let it loose if it is likely to charge off and smack itself into a solid stone wall. Well, not unless that sort of thing passes for "fun" in your mind... :-)

Within RickBot are fourteen sensors:

This is, by no means, fixed. You can add more complex things. Ideas here.

Of course... there are schematics!