Some may argue that a robot is not really a robot if it isnt autonomous. Maybe it is or maybe it isn't. Point being, those some are morons. Learning how to implement remote control features into a robot is a very important skill in robot making. To justify it, I will quickly go over robot intelligent control methods . . . Introductory to Robot Intelligence There is actually a spectrum for robot intelligence. Fully remote control and fully autonomous are not your only options. Instead you should decide what level of intelligence you wish your robot to have. Generally assume the more intelligent, the more difficult to build. Here are the main categories: 
Automaton 'Intelligence' The lowest level of robot 'intelligence' is a simple automaton device. My definition of an automaton is a device where there is absolutely zero decisions made no matter the given environment. They are simple devices where the action it does is repetitive and automatic. A simple circuit with a motor or a combination of gears and a spring could easily be an automaton. Ever hear of those 'robots' from the 1800's that apparently can write names and poems and other useless stuff? They were very well designed gear integrations. However these 'robots' would keep writing even if the ink well ran out of ink . . . The device simply has no fault tolerance, and will continue attempting the action. They did not even have a method to sense the environment - a requirement of decision making. BEAM 'robots' basically fall into the same category, except they are made from very well designed electronics instead of gears. Remote Control 'Intelligence' Remote control is the next level of robot 'intelligence.' Our current technology is capable of building so many machines physically capable of so much more than any lifeform on our planet. Our planes fly many times the speed of sound, our everyday cars can cross the Sahara Desert in days, but our best computers cannot even match a roach brain in terms of autonomy. Solution? Put the human brain in the driving seat of our machines. This allows for the best of both worlds. Strength and expendability of a machine, brain of a human. Battlebots is a perfect example. 
Teleoperation Teleoperation is one step above remote control. The advantage a computer has over the human brain is speed. A typical home computer today can crunch more numbers in a few seconds than a human can in an entire lifetime. But despite that speed, the computer does not have a good understanding of the situation. Added to that, our most advanced electronic sensors cannot match our human eyes and ears for observing the situation. Solution? Let the human make the decisions, but have the computer carry them out. A perfect use for this would be a robot spider. A human operator in no way can control 8 legs with 3 joints each. Instead, the human would give commands like 'go forward' or 'rotate' and the computer will handle the rest. This method is also very common with space robots because of the long transmission delay. Full Autonomy Fully autonomous robots are still a dream. It is a huge area in current state-of-the-art robotics research. It concerns artificial intelligence, consciousness, advanced sensory percerption . . . the list goes on. Huge philosphical implications as well. But all this is out of the scope of this tutorial. If you make a robot that can intentionally navigate from your couch to your kitchen and back without any collisions all by itself, you have built an autonomous robot. But if it fails to bring a beer back you are still a beginner in my eyes . . . How to Build a Remote Control Robot The remote control robot is probably the easiest of all robots you can make. A complete beginner can probably make a basic remote control robot in under an hour. The electronics part is plug-n-play, the robot chassis being what will take a little time. Remote control robotics is great for those who want to build a robot - yet does not have enough time, skill, and/or patience to so see a large project through to completion. Have a look at an example of a wall climbing robot with an arm. First, a video to help you get started: All you need is a few cheap commercially available items: 
Remote Control Transmitter The remote control transmitter is the handheld thingy with knobs and buttons and a long intenna sticking out of it. This will be the most expensive part you need to buy, around $40-$200. It will require it's own battery and battery charger. The remote control transmitter usually has very good range. Once as a test, I put my robot in the basement of a building, climbed to floor 10, then operated it without any issues. If you plan to ever do USAR (Urban Search and Rescue), this is a useful feature. The most important feature you need to be concerned with is number of channels it can operate on. Each channel allows you to control one more item on your robot. I recommend at least three, but I have often used up to six on a single robot in the past. 
Receiver The receiver is a small little box thingy that you put on your robot. It accepts the signal from your transmitter, processes it, then outputs a servo ready signal. This will be the second most expensive part, usually around $30-$60. It will require around ~5V to power it. Receivers can get really small: 
Operating Frequency Crystal Both your transmitter and your receiver will each require a crystal. These are necessary to ensure both of your devices are operating under the same frequency (so purchase both crystals with the same channel!!!). For RC, there are two frequencies you need to be aware of. One is for air and one is for surface. Remember, its illegal and bad practice to control a remote control car with an air frequency. You could accidently cause someone's remote control aircraft to crash and kill some poor cute innocent squirrel! But you already knew that . . . When you purchase your receiver/transmitter, they will specify whether it should be used for air or surface RC. Another note, the crystal is fragile. If your remote control vehicle crashes a lot, the crystal could get damaged. I once made a robot for a USAR competition that was designed to handle 7 foot drops. But apparently the crystal was not. It broke. Sadness. The solution? Receivers often come with a foam pad thingy to wrap it in for shock absorption. If not, find some foam padding and use it. The crystals usually come as part of your transmitter and receiver, but if not, or if you break one, they cost like $8 plus shipping to replace.
HDPE and/or aluminum should be used for the frame. Want to build it in 5 minutes? A simple square sheet of HDPE with all parts velcroed on will actually work! But you should attach everything more permanantly for a well designed robot. 
Optional: Servos Servos, although not required, are designed to be used with remote control vehicles. All you do is literally plug it straight into your receiver and it instantly works. Get two servos - one for each side of your robot - so that you have differential drive. Put a castor in back for balance. You can also use additional servos for other things such rotating a camera, lifting a shovel, or operating a robot arm. If you are on a strict budget, I highly recommend the Hitec HS-311 servos. They only cost about $8 and work really well for what you need. But of course, the $30 servos work even better . . . And here is how to mount servos onto a robot chassis. 
Optional: Teleoperation Now you do not need a microcontroller for any basic remote controlled robot. But if you want it teleoperational, you must have something to process your commands. So how does this work? The basic concept is - send a command with the transmitter to the receiver - the receiver then outputs a servo square wave - a simple resistor capacitor circuit changes this square wave to an analog value - and then an analog port on your microcontroller interprets this analog value into a particular command, based upon your written program. The servo signal to analog signal converter circuit: 
Optional: High Power Motor Driver / Speed Controller If you want a high powered robot that uses something much more powerful than hobby servos, you would instead want a motor driver. Most on the market should directly accept a signal made for a servo, and convert that to what you would need for DC motors. Just hook this device up to your receiver, and attach your motors and battery to it, and by happy squirrels you have an instant Battlebot. Be aware that these can get a little expensive, and many are only capable of handling a single motor - meaning you would need to buy two. 
Optional: Speed Controller The speed controller is basically an H-bridge that operates by a remote control signal. Plug one wire into the receiver, two onto the battery leads, and two on the motor leads - and wallah its controllable by your transmitter. If you wanted to build a fast dc motor driven remote control vehicle, or perhaps need a motor to drive the weapon of your battle bot, this is the way to go. Last Step: Assembly of your Remote Control Robot I figure the best way to explain this is to show an example. This particular robot was made by me and a friend in less than 5 hours back in early 2003. It uses somewhat expensive lexan plates, a lego castor, and super glue, double sided sticky tape, and velcro to connect everything together. Ghetto, yes. But it held together really well and was easy/quick to make. 
It was designed to play soccer, but since I lived in Pittsburgh at the time there was also plenty of snow to shovel . . . Here is a video of it in action: The remote control that I used was the Laser 6  .
And here are two teams of remote controlled soccer robots all made in the same fasion: 
Radio Frequency Reference Chart On rare occasions you may want to know what frequency you are broadcasting on, and not just which channel it is. For example, if your remote control robot is for an underwater environment, you would want the lowest frequency possible to minimize attenuation (interference). 72 megahertz, Channels 11 - 60: This is the most popular choice for flying models. Most radios designed for model aircraft and helicopters will be available on these channels. DO NOT use this frequency for anything other than aircraft, as you could unintentionally cause a crash of someone else's remote control aircraft nearby. Big deal? Not so big when they lose hundreds in $$ from damage, or even worse, a death or injury results from the crash . . . 75 megahertz, Channels 61-90: Cars, boats, and other non-flying models must use one of these channels. Pistol grip radios are available on 27 MHz as well as 75. 27 megahertz, Channels A1-A6 and 50 megahertz, Channels 00-09: While legal for air or surface use, we recommend that 27MHz be used only for surface models. A pilot and driver broadcasting on the same 27MHz frequency would cause interference and could cause a crash. 50MHz channels can be used for R/C, but require the user to attain a Technician-class Amateur Radio License from the FCC.
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Remote Control Robot
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