How Radio Controlled Toys Work

A typical radio controlled toy truck

You have probably seen the ads on Saturday morning television proclaiming the amazing abilities of the "Super Ultra Road-rippin' Devastator" or some other radio controlled (RC) car. And you may have seen people at the park flying a model airplane or blimp, or controlling a miniature boat sailing serenely across a pond.
In this article, you will learn all about radio control. You will find out what frequencies are used for RC toys, what the different components are and how they all work together. You will also learn what the difference between radio control and remote control is when talking about toys or models.

Types of RC Toys

RC toys come in a large variety of models, including:

• Cars
• Trucks
• Fantasy vehicles
• Airplanes
• Helicopters
• Blimps
• Sailboats
• Motor boats
• Submarines
• Robots
• Animals

While the mechanics of how they operate can differ greatly between different toys, the basic principle is the same. All radio controlled toys have four main parts:

• Transmitter - You hold the transmitter in your hands to control the toy. It sends Radio waves to the receiver.
• Receiver - An antenna and circuit board inside the toy receives signals from the transmitter and activates motors inside the toy as commanded by the transmitter.
• Motor(s) - Motors can turn wheels, steer the vehicle, operate propellers, etc.
• Power source

The transmitter sends a control signal to the receiver using radio waves (see How Radio Works for details), which then drives a motor, causing a specific action to occur. The motor in a car may cause the wheels to turn, while the motor in a plane may adjust the flaps. The power source is typically a rechargeable battery pack, but sometimes it's just normal batteries.
In many of the RC toys, the radio controlled motor provides guidance while another source of power provides the locomotion. Here are some examples:

• A model airplane often has a small gas-powered engine to turn the propeller; the RC motor controls the flaps.
• A sailboat uses the wind for propulsion; the RC motor controls the rudder.
• A blimp uses helium or hot air for lift; the RC motors control small propellers.

A typical RC car transmitter

RC Toy Transmitter

RC toys typically have a small handheld device that includes some type of controls and the radio transmitter. The transmitter sends a signal over a frequency to the receiver in the toy. The transmitter has a power source, usually a 9-volt battery, that provides the power for the controls and transmission of the signal. The key difference between radio controlled and remote controlled toys is that remote controlled toys have a wire connecting the controller and the toy, while radio control is always wireless.
Most RC toys operate at either 27 MHz or 49 MHz. This pair of frequencies has been allocated by the FCC for basic consumer items, such as garage door openers, walkie-talkies and RC toys. Advanced RC models, such as the more sophisticated RC airplanes, use 72-MHz or 75-MHz frequencies.
The majority of RC toys are labeled with the frequency range they operate in. For example, the RC truck below has a label designating it as a 27-MHz model.

This truck operates at 27 MHz.

Most RC toy manufacturers make versions of each model for both frequency ranges (27 MHz and 49 MHz). That way, you can operate two of the same model simultaneously, for racing or playing together, without having to deal with interference between the two transmitters. Some manufacturers also provide more specific information about the exact portion of the frequency band that the toy operates in. A good example is Nikko of America, who offers the option to create racing sets of up to six toys with each model tuned to a different part of the 27-MHz frequency range.
Transmitters range from single-function simple controllers to full-function controllers with a wide range of options. An example of a single-function controller is one that makes the toy go forward when the trigger is pressed and backward when it is released. To stop the toy, you have to actually turn it off.
Most full-function controllers have six controls:

• Forward
• Reverse
• Forward and Left
• Forward and Right
• Reverse and Left
• Reverse and Right

In most full-function controllers, not pressing any buttons or turning any knobs causes the toy to stop and await further commands. Controllers for more advanced RC systems often use dual joysticks with several levels of response for precise control.

A typical RC signal transmission

Radio Control

Let's take a closer look at the RC truck we saw on the last page. We will assume that the exact frequency used is 27.9 MHz. Here's the sequence of events that take place when you use the RC transmitter:

1. You press a trigger to make the truck go forward.
2. The trigger causes a pair of electrical contacts to touch, completing a circuit connected to a specific pin of an integrated circuit (IC).
3. The completed circuit causes the transmitter to transmit a set sequence of electrical pulses (see How Radio Works for details). Each sequence contains a short group of synchronization pulses, followed by the pulse sequence. For our truck, the synchronization segment -- which alerts the receiver to incoming information -- is four pulses that are 2.1 milliseconds (thousandths of a second) long, with 700-microsecond (millionths of a second) intervals. The pulse segment, which tells the antenna what the new information is, uses 700-microsecond pulses with 700-microsecond intervals.

A typical RC signal transmission

pulse sequences

• Forward: 16 pulses
• Reverse: 40 pulses
• Forward/Left: 28 pulses
• Forward/Right: 34 pulses
• Reverse/Left: 52 pulses
• Reverse/Right: 46 pulses

1. The transmitter sends bursts of radio waves that oscillate with a frequency of 27,900,000 cycles per second (27.9 MHz). If you have read How Radio Works, you will recognize this as pulse modulation.
2. The truck is constantly monitoring the assigned frequency (27.9 MHz) for a signal. When the receiver receives the radio bursts from the transmitter, it sends the signal to a filter that blocks out any signals picked up by the antenna other than 27.9 MHz. The remaining signal is converted back into an electrical pulse sequence.
3. The pulse sequence is sent to the IC in the truck, which decodes the sequence and starts the appropriate motor. For our example, the pulse sequence is 16 pulses (forward), which means that the IC sends positive current to the motor running the wheels. If the next pulse sequence were 40 pulses (reverse), the IC would invert the current to the same motor to make it spin in the opposite direction.
4. The motor's shaft actually has a gear on the end of it, instead of connecting directly to the axle. This decreases the motor's speed but increases the torque, giving the truck adequate power through the use of a small electric motor!
5. The truck moves forward.

If you look inside the RC truck, you will see that it is very simple.

A look at the inside of the truck

Inside an RC Truck

Inside our RC truck, we have two electric motors, an antenna, a battery pack and a circuit board.
One motor turns the front wheel right or left, while the other motor turns the rear wheels to go forward or backward. The circuit board contains the IC chip, amplifier and radio receiver. A few simple gears connect the motors to the wheels. It is really amazing how versatile the range of movement is with so few components.

• Inside the car, you will find a circuit board with several capacitors, resistors and diodes, as well as the IC that controls the motors. The radio receiver consists of a crystal that oscillates at a specific frequency, inductors and an antenna.
• The electric motors receive power from the batteries. The flow of the power is regulated by the IC.

For more information on RC toys, radio control and related topics, check out the links on the next page.