Society of Robots has a great video of a robot arm-clocks - The robot arm is probably the most mathematically complex robot you could ever build. As such, this tutorial cant tell you everything you need to know. Instead, I will take shortcuts and just talk about the bear minimum you need to know to build an effective robot arm. Please bear with the math . . . enjoy!
To get you started, here is a video of a robot arm assignment I had when I took Robotic Manipulation back in college. My group programmed it to type the current time into the keyboard . . . (lesson learned, dont crash robot arms into your keyboard at full speed while testing) HOW TO - Build a robot arm - [via] Link.
http://blog.makezine.com/archive/2008/01/how_to_build_a_robot_arm.html