Vex Robotics

The Vex Robotics Design System, is a build-it-yourself robot creation kit. Like an electric erector set, you need some batteries, some imagination, and a desire to build. The results will be a functional robot you can control with a wireless radio transmitter (like a remote-controlled car). With upgrades to the basic kit, you can add more features, parts, abilities, and even the ability to program the robot, allowing it to interact with the world on its own.

The excellent Vex manual provides you with instructions on how to build a basic robot, capable of movement and collision detection. The three shots below are a slightly-modified version of that robot.
The battery pack is the blue box on top of the unit. The radio receiver is the smaller yellow box beside the battery pack. The red and gray buttons on the front and back ends are collision detectors: If the robot bumps into something, it stops the wheels from turning (preventing your from stripping the gears or wearing out the axle mounts or motors). The large gray unit below the battery pack and radio receiver is the brain of your robot: The Vex Micro Controller. Plugging motors, sensors and other things into this unit allows your robot to move and interact with the world.

The Vex is intended for use by children and adults able to not only understand basic mechanics, but those able to work with small parts (like screws and motor components) and understand basic electronics concepts (you'll need to do a bit of tweaking to adjust trim levels on the radio transmitter, and motors and batteries and radio receivers need to be connected correctly for everything to function. The manuals do an excellent job of describing how everything works, but you still need the patience and delicate handing such components require