A remote control robot is very easy to build, and allow you to have great fun with your robot quickly. It's very useful to have a remote control to test soccer moves or fighting hits.
I found it is very popular in Japan to have competition of soccer robots or fighting robot controlled by people. Mecha have always been popular in Japanese mangas and animations, and a remote control robot is not so far from that.
But remember that you don't want to just build your RC car. The fun is to give orders from the remote, and let the robot process them.
In Japan, they have multiple competitions that use RC robots instead of autonoumous ones. I went to a small soccer robot competition and could ask the participants the dreaded question: it's RC, so is it a real robot?
In fact, all they do is give order to the robot about the directions, and to shoot or catch the ball. The robot usually applies previously designed sequence of movements to control the motors and perform the action.
The robots also have a few sensors. For example, an accelerometer is used to let the robot know if it fell on the back or the front. It will then use this information to choose which way it should stand up.
So the goal here is clearly to focus on the mechanical design of the robot. If you have a soccer robot that is faster and more stable, you are more likely to win. But you can still make the job easier for the operator by making much of the processing on-board.
Remote control robots are also a great way to test new designs. If you want to check if your robot can climb slopes, go through a pipe or pick up a ball, it's a lot easier to test by hand than programming it.
Finally, I find it's a lot faster to create an RC robot, and playing with it is really fun. You can even combine both, so that you're robot can go around by itself, but if you start the remote it listens to you: double the fun.
Let the fight begin!
There are many ways to make your robot wireless. A very cheap way to do it is to use an IR receiver and a remote control (any remote at home will do the trick). The main problems are that it can only be used for short distance, and if you have the right direction. Plus the commands can be quite limited.
A way to do it right, is to use radio system. You can buy some RC radio from a RC store. If you want to connect your robot to your PC, this very complete Xbee Wireless Kit gives you everything to connect your Arduino board to a computer. You can then use your keyboard, mouse or Kinect as a remote. You can even program the whole artificial intelligence on the PC and create a remote brain for your robot.
Other pages that may interest you:
How to choose your first robot?. Need help sorting the options for your first robot? This is the best guide to choose it.
Learn the basics of robot programming. What's the difference between a PC and microcontroller? How can you structure the AI of your robot like a pro? The answer is here.
A list of useful robotic sensors for your projects. You'll also learn some ideas on how to use them for your projects. Sometimes, you just need to know what sensors exist to inspire new projects.