SearchR/C Transmitters

Basics of R/C Transmitters and Receivers.

Transmitters and Receivers

Basically the transmitter (Tx) sends a radio signal to a receiver (Rx) and the receiver passes that information along to the devices in the R/C model (droid in our case).

Transmitters (Tx) are paired with their receiver (Rx). Often they are sold as a set. Many systems are similar and sometimes receivers can be used with different transmitters, but make sure you get a compatible receiver for your transmitter, especially if you have to replace it.

Anything with a transmitter and receiver can be used to control things (well, there may be laws about what frequencies can be used for what), and the terms "transmitter" and "receiver" aren't restricted to R/C cars. Your automatic garage door opening remote is a transmitter and the box in the garage has a receiver.

Transmitter types

I'm going to overgeneralize, but hobby transmitters come in two basic forms:

• Car transmitter.

Sort of a gun shape with a wheel on it and a trigger. The wheel steers the car and the trigger controls it's speed.

• Airplane transmitter.

This typically has two joysticks, one for the left hand and one for the right hand. Each stick can usually move forward, backward & left & right. They'll try to center themselves, except for one of the forward/backward sticks, which won't have the springs. This is the throttle of an airplane. Interestingly, the controls are different in the US from most of the rest of the world, known as "Mode 1" and "Mode 2". Make sure you're buying the expected kind of transmitter!

- Mode I transmitter right forward/back stick won't return to center.

- Most II transmitter's left forward/back stick won't return to center. Used by most US R/C pilots.

Some transmitters can have the springs removed/added if desired. More about Airplane R/C

Channels

A "Channel" is a discrete sets of information the transmitter can send to the receiver. Eg: "Go this speed." We probably also want to steer, so that's another channel.

One of the most interesting thing to droid builders about channels is "how many are there on my transmitter?" If I have 2, then I can probably move and steer. Another might be able to let me turn a dome. Another could launch a lightsaber or play a sound (usually people use other systems for the sounds).

Two things are pretty important to know about R/C channels: The transmitter and receiver kinda have to agree on them, and the channels might have different kinds of information.

The Tx & Rx have to agree. It doesn't do you any good to have a 9 channel transmitter if you only have a 4 channel receiver.

Some of the systems with higher numbers of channels need extra stuff to really make full use of them. Make sure you understand what you're buying.

The channels usually don't all have the same capabilities. Some might allow a range of values, like a dial, so that you can have a smooth variety of speed. Others might be a simple on/off toggle switch. Make sure that the transmitter you're considering has the right kinds of channels for the features you want.

Sometimes channels can provide special information that really doesn't even have a separate switch or knob on the transmitter.

Assignment

There are common standards for channel assignments that your transmitter is probably preset to. Many transmitters with more than a few channels allow reassigning some of the channels. That can help if you plug a servo into the wrong Rx port or have other special needs.

How many channels do I need?

Well, that's a good question. It depends on what you want to do, and what you might want to do in the future. Fortunately, it's pretty easy to upgrade a transmitter, so a cheap entry level one to get started, and then a fancy one later if you need it can be a great strategy.

Count the number of things you need to do and figure out how you're going to send those signals. Most droids need at least speed and steering, so that's two channels. Artoo's have a dome, so that's a third. Other channels can be used to open a door or spray a mist or throw a lightsaber. Typically each feature uses another channel.

If the droid has some sort of processor you might be able to get fancier. Lara's mouse droid has lighting, which uses one channel with a knob on the transmitter to select colors. Since there's a microcontroller onboard, she can make the knob do chasing lights in one direction, and a single light in the other direction.

Pairing

Modern transmitters share the same frequency, so you have to tell the receiver which transmitter to listen to. This is called pairing, like pairing a Bluetooth.

Check your manual, but to pair, usually you do something like plug a special jumper into the receiver (don't lose it!) and push a button on the transmitter.

Frequencies

R/C transmitters use frequencies assigned by government regulators. Some countries require operational licenses or restrictions that are beyond the scope of this page. Please make sure you follow the regulations for your location.

Toy R/C cars typically use the 29Mhz or 49Mhz frequencies and are relatively simple systems that can easily interfere with each other. So 2 kid's cars can steer eachother and cause all sorts of havoc. We tend to want to avoid that sort of thing when we might be hanging out with other droids.

Modern hobby R/C transmitters use the 2.4Ghz range and have special DSM software that prevents most interference. You really want to make sure you're using one of these newer radios.

Older transmitters had assignable frequencies, by changing the "crystal" used for the transmitter and receiver, but there can still be conflicts. Few newer hobby radios use this technology anymore.

Sound remotes

These aren't really R/C type remotes, but many droid builders use a 12 channel type system commonly found on Amazon or ebay.

Note that these additional 12 channel type sound transmitter many droid builders use can also interfere with each other. Often they can be assigned to different settings, so if you start hearing sound from your droid (or your neighbors), check if your sound remote can be reconfigured.

People have also written code for microcontrollers to select sounds based on a combination of inputs from a normal receiver.

Beginner mode

Many transmitters have a switch that reduces the other inputs by half or so. A common error is to bump the beginner mode switch and then wonder why your droid isn't moving :) If you have such a feature on your droid, make sure you understand it.

The beginner mode switch can also be very useful for beginners! If you go to a Children's Hospital and want to let a kid try driving your droid, you might want to consider turning on the beginner mode if you have one. (our mouse doesn't really steer well in that mode, so it may not always work.)

Mixing

Many transmitters have ways to combine the inputs for various behaviors. Most have ways of inverting the signals. Those features aren't usually strictly "necessary", however with modern electronics they're pretty easy for most manufacturers to add.

Adjustments

Most transmitters will have a way to "center" the signals for the joysticks. So if your droid is drifting to the right, there's probably a button to adjust "center" on your stick a little to the left, so that when you let go of the steering stick, your droid actually goes straight.

Cost

Transmitters and Receivers can go from $20 to hundreds of dollars.

The R/C industry has a few "big names" that have been in the business for years and have reliable equipment with lots of features that are compatible with tons of accessories. However, modern microcontrollers have allowed newer companies to provide functional Tx/Rx combinations that are fairly inexpensive.

The tradeoffs are similar to many other products. Cheaper ones is that they may not be as easy to service or have good customer support if there are problems. On the other hand, who cares if it's only a quarter of the price?

Several builders have had success with the inexpensive Turnigy and similar Chinese brands available from places such as hobbyking.

More Info

We have a page about the Turnigy9X transmitter

We also have a page about Airplane RC assignments.