Make a Simple RC (Remote Controlled) Robot Car

Whether you are an engineering student building a multi terrain vehicle or an electronics hobbyist trying to impress people with your skills, Making a RC robot car (wireless)  is much better than the wired robot which you will have to tail while driving.
Here is a simple, yet informative post for beginners in the field of robotics. Mind you, this not robotics. This is just a toy with which you can play around and still get a hold of the basic concepts in building robots. You can check out some our archives for more tutorials on robotics.
To sum it up, there is one hell lot to do before going around telling people ‘I build robots’ but hey you got to start somewhere right?

Objectives

We will discuss a basic ‘Land Rover’ with nothing. Well not exactly nothing, but nothing complex. As I mentioned earlier this is a really simple project, so simple that not even an embedded computer (microcontroller) is used.
The emphasis is just on the mechanical design and some basic circuitry. We learn the interface of the commercially available RF transmitter and receiver module coupled with HT12E/D pair (Encoder/Decoder) to transfer data over the air to the motor driver L293D.

Things you will need:

These are the things that you will need. Most of them are really common and can be bought in local stores. If you can’t find something, you can always get it form online vendors.
Just be extra cautious when buying the RF Rx-Tx module. They are really fragile and can be rendered unusable before even you had seen them properly.

1. DC Geared motors
2. Wheels
3. Metallic chassis
4. L293D motor driver IC
5. DPDT switch
6. HT12E encoder IC
7. HT12D decoder IC
8. RF Rx-Tx Module
9. 12V Battery pack
10. Some basic tools and soldering iron.

Working Logic for the RC Robot Car

Understanding Datasheets

The next step is to learn how to access the data sheet for the components that you are using. Its actually not that big a deal, just Google the component name and you are provided with numerous links to the datasheet. The real tricky part is to find what you are looking for in the PDF file that you just downloaded.
The data sheet is the only sole documentation that the manufacturer provides for his product so it will contain all the electrical parameters such as the max-min current rating for that device and its V-I characteristics.
Most of the time, such in-depth knowledge about these parameter are not really a must. Although you need to know the VI-ratting and pin description. So finding what you really need form the data sheet comes over practice. You, almost every time will have to look for the,

1. Input Voltage and Current
2. Operating temperature
3. Logic Level
4. Pin description
5. Timing diagram
6. Application Circuit

Hardware

Now that the basic requirements are made, let’s get into the hardware. Mounting the motors on the chassis and the wheels to the motors is something that you should be able to do with little or no difficulty at all. So I will leave it for a self study. Beyond this step you should be more care full.
Now solder some wires on to the motors (if they are not already there) and excite them with power supply and mark which direction they spin for a given polarity. Do the same for the same for all the other motors. Once the marking is done. Short the terminals of the motors on the same side of the bot.
The idea is that the motors on one side of the robot should spin in one direction if excited with a particular polarity. So the motors should be wired something like this,

In this way you have 2 wires from 2 motors instead of 4 wires (2 from each motor). Repeat the same process for another pair of motors and get two more wires. Now you will have 2 + 2 = 4 motors, and 4 wires from entire set.
Once all the four motors are paired and only four terminals are available for excitation you can get started with the actual circuitry. Now go ahead and read about L293D. It is a dual H-bridge motor driver to be short. It is used to drive the motor in both forward and back ward direction.

Direction Control

For the direction control section we are going to be using what is called the Differential Drive algorithm. I know it sound fancy but that’s no big deal. Since we have paired one set of motors to the left of the remote car, we will call this pair the left or right pair based on side of the car they are present.

Left Motor Pair	Right Motor Pair	Direction
Front	Front	Front
Front	Back	Right
Back	Front	Left
Back	Back	Back

As you should have guessed, the car will go front or back if both  the pair of motors operate in one direction and left or right if they operate in different directions.

RF Transmitter Receiver Pair

Now here is what the RF transmitter and receiver modules will look like. There are a verity of manufacturers so don’t panic if your modules are looking different. Even the frequency in which they communicate should not be a problem as long as both the receiver and the transmitter are of the same frequency. All modules are Pin and Pad compatible in case you are planning to design a PCB.

Power Supply

This is the power supply schematic. It has a 7805 to regulate the input 12V to 5V. There is a DC power jack to which the power supply has to be plugged in. The switch is used to turn ON and OFF the power supply.

The receiver Schematic for the RC Robot Car:

This is the circuit diagram for the receiver. It has the RF Receiver module connected to e decoder to decode the data that is being sent from the transmitter. The decoded 4 bit data is then given to the motor diver L293D as input logic to drive the motor.

Preparing the remote control

The remote control will have two DPDT switched like the one shown below. They are to be used for direction control of the remote car. The connection is simple, take a wire and short the opposite extreme pins of the DPDT switch as shown in the right side image. So far you should have used up 4 pins of the switch and 2 more pins left for connections.
In the image below I have labelled them as A, B, C, and D corresponding to the two switches. These 4 pins should be connected to the 4 pins in the transmitter circuit (yet to be discussed) with the same names.

The Transmitter Schematic for RC Robot Car:

Now for the transmitter circuit, you will have to bear in mind that this is your remote (this along with the DPDT switch). So try to make it as handy as possible. Trust me the last thing what is a remote that is too big/heavy to carry around. Make a good closure for this circuit.
Unlike the receiver, this does not need to have a beefy battery. You could power this circuit with a 9V battery. Again here there is a connection box labelled To DPDT switch. Here you have to connect the terminals form the switch following the appropriate names. The last two pins +5v and GND terminals in this circuit is for the power supply to the DPDT switch and can be ignored if you have already given power by some other means.

That’s all for a getting started to robotics (well it is not exactly robotics) There is a lot more to learn beyond this point. This should have cleared some of the basics up for beginners and a total waste of time for the advanced readers  anyway, since its all done lets feel happy about it in either cases.
This is the car that I made. But this is slightly different form the one explained. It uses a TSOP 1738 receiver to receive IR data from a typical TV remote to control the bots movement. Other than fact that it uses Infra red communication instead of a radio frequency they are the same. It is more complicated in terms of code than the one described above (it is a post for another day).
This is the a small video that I made when I made this bot. It shows the parts quiet clearly (or slowly I should say) Please ignore my sense of music if you didn’t like it and if you did leave a comment.

Testing your Circuit

Since this post was published, readers have have run into various kinds of problems while trying to make the remote controlled robot car. This is a very simple circuit and yet you will be surprised if I told your there are more then a dozen place where you could go wrong. I took the trouble of going through all the comments in this post and compiled a list of all the problems that my readers have run into and the solutions that I have given them into a separate post with tips, tricks and techniques that will help you debug the circuit once you have made it.
I strongly suggest you to read the post Circuit Debugging – Tips Trick and Techniques before attempting to make your own rc robot car. If you are still having any doubts, post your comment in that article and I will try my best to help you out.
In the mean time you might want to read about some more advanced robots that we have in our Robotics Archives. For making any robot you should have a reasonably good knowledge on embedded systems and basic electronics and mechanics.