What must have in robot?

Answer 1

In general, if you want it to move it will require some kind of actuator (like a motor, bimetallic strip or contractible wire like the Stiquito) which usually requires some kind of electronics to control it and batteries to make it run. This is one of the smallest and simplest autonomous ones I have found yet, thanks to FriPilot

http://members.tripod.com/robomaniac_2001/id120.htm

Otherwise, I have had pretty good luck with buying small remote control cars at the dollar store (or the stuff my nephews throw away) and taking them apart to reconfigure the motors into what I want, but that ends up with wires connecting the robot to the controller. Some of the people I work with have pieced together cheap radio control cars and other parts to get radio control robots.

If you prefer robot kits, some hobby stores sell a few inexpensive ones that are sometimes configurable like these

http://www.kitsusa.net/phpstore/html/Robot-Kits---Non-Soldering-1-1.html

Otherwise some of the less expensive construction kits like LEGO or K-NEX or Construx or a few others have motors and gears in the kits. If you have a larger budget, Lego Mindstorms, Bioloid and several others are more advanced kits that are programmable and autonomous. With some ingenuity and asking around, you can make a robot-looking thing out of just about anything (or almost nothing) and you probably will find some ingenious methods of making it move.