Robotics brings together several very different engineering areas and skills. There is metalworking for the body. There is mechanics for mounting the wheels on the axles, connecting them to the motors and keeping the body in balance. You need electronics to power the motors and connect the sensors to the controllers. At last you need the software to understand the sensors and drive the robot around.
This book tries to cover all the key areas of robotics as a hobby. When possible examples from industrial robots will be addressed too.
You'll notice very few "exact" values in these texts. Instead, vague terms like "small", "heavy" and "light" will be used. This is because most of the time you'll have a lot of freedom in picking these values, and all robot projects are unique in available materials.
Design Basics 
Note to potential contributors: this section could be used to discuss the basics of robot design/construction.
- What you should know
- Physical Design
- Design software
- Tools and Equipment
- Electronic Components
- Mechanical Components
- Building materials
- Basic Programming
Physical Construction 
This section could be used to discuss various means through which robots are constructed.
This section could be used to discuss components used in robotics or the making of robots.
- Power Sources
- Actuation Devices
Computer Control 
This section could be used to discuss the things involved with controlling robots via computers.
- Control Architectures
- The Interface
Sensors that a robot uses generally fall into three different categories:
- Environment sensors tell the robot what is happening around it
- Feedback sensors tell the robot what it is actually doing, and
- Communication sensors allow a human or computer to provide a robot other information.
Sensors aren't perfect. When you use a sensor on your robot there will be a lot of times where the sensors acts funny. It could miss an obstacle, or see one where none is. Key to successfully using sensors is knowing how they function and what they really measure.
Exotic Robots 
This section could be used to cover "special" robots.
- Special Robot brains
- Cooperating Robots
- Hazardous Environment Robots
- Types of Robots
- Modular and fractal Robots
- The LEGO World