RC Radios - Transmitter and Receiver
You hold the transmitter in your hand and the
receiver is installed in your SOZBOT. By manipulating the control sticks,
knobs and buttons, you are controlling the robot. If you are new to RC, this
guide will help you figure out what is important for an antweight and will
serve you if you are trying to purchase a radio for your antweight.
The radio wave transmission of data between the
transmitter (Tx) and Receiver (Rx) can have the following characteristics:
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Transmitter Radio Characteristics
- Modulation - method
used to encode the control information from your sticks, knobs and
switches into radio waves.
- AM - Amplitude Modulation,
the amplitude of the radio wave changes when you move your controls.
Generally regarded as cheaper, having less range and also less features.
Also, they are known for radio interference problems. For antweights,
range is not an issue, but these radios are generally regarded as low
end and used in toys.
- FM - Frequency Modulation,
the frequency of the radio wave changes when you move your controls. The
amplitude is kept constant. Two common types of FM are PPM and PCM
- PPM - Pulse Position
Modulation - the data is encoded in frequency pulses in which the
position of the frequency changes. The most common type used, some of
the cheaper ones are comparable in cost to AM.
- PCM - Pulse Code
Modulation - Proprietary data encoding where the data is transmitted
in a series of 0 and 1s, just like a computer communications protocol
with error checking. Each manufacturer has their own protocol and you
cannot interchange PCM gear from different manufacturers. These radios
cost more than regular FM without PCM, but typically have a PCM/PPM
selection to allow you to use non-PCM receivers to save weight.
- For more info:
http://www.rcfaq.com/answers/radio/
- Frequency - radio
frequency/channels used to transmit the control signal. Radio channels are
assigned to frequencies and there are different frequency bands available
to use. This applies to both AM and FM.
- Aircraft only bands 72MHz
Band, Channel 11-60.
- Ground only bands 75MHz
Band, Channels 61-90
- All uses 27MHz Band,
Channels A1-A6
- All uses but must have an
FCC Amateur license 50MHz Band, Channels RC0 - RC9
- Shift - Applies to the
radio signal decoding that different manufacturers use. You only care
about this when you are mixing Tx and Rx from different manufacturers.
- Positive Shift - Method used
by JR and Airtronics
- Negative Shift - Method used
by Futaba and Hitec
- Other Info on Transmitters
- Narrow Band- In 1991, the
FCC mandated that RC had to use a smaller band so they could fit more
channels into the frequency bands. Before 1991, the width of a band was
40kHz, now its 10kHz.
- Crystals – Channels are
selected by a crystal and by simply swapping out matching crystals on
both your transmitter and receiver, you can change the channel you are
using.
- Control Channels – Not to be
confused with the radio channel (frequency), each radio can control only
so many outputs. These are referred to channels. Typically you will find
2-channel, 3 channel, 4-channel, 6-channel, 8-channel and 9-channel. You
need to select a radio that has enough channels to drive your robot.
More channels cost more. For example, if you have a robot that only has
2 motors and no weapon, a 2-channel radio would work, one each wheel. If
you have a weapon, now you need 3 channels. Usually its better to have
more channels in case you want to add more things later. For an
antweight, 4 channels would be enough for 95% of the robots.
- Mixing – Typically used for
drivetrain. You want to mix your single control stick so it drives your
right and left motors. When you push forward, you want both motors to
drive forward. Same with reverse. When you push the stick left, you want
your left wheel to turn in reverse and your right wheel to turn forward
so your robot spins. Radios don’t typically do this and require mixing.
Cheaper radios don’t allow you to mix in the radio while the computer
radios will let you set it up that way. If your radio doesn’t do mixing,
you can obtain mixers that you can install on your robot.
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Receivers Radio Characteristics
Receivers are very important to antweights, with 16 oz
of weight to work with, you want the smallest and lightest receiver you can use.
Typically the receiver that comes with your transmitter will be bigger and
heavier than what is available.
- Conversion – Receivers come in 2 flavors, single
conversion and dual conversion. Dual conversion filters the incoming signal in
2 steps rather than one (as with Single Conversion) thereby eliminating more
interference and glitches. The conversion type has nothing to do with the
radio signal being transmitted, just how the receiver decodes or converts it.
Single conversion receivers tend to be cheaper and lighter and ideal for
antweights and can be used with any transmitter as long as they are on the
same channel and same modulation type. Single conversion receivers typically
come with 4 channels maximum.
Never use dual conversion crystals in a single
conversion receiver or vice-versa. It won’t work.
- Products – Below is a list of various small and
lightweight receivers. You will notice that the lightest receivers are
aircraft frequency. This is because they are typically used in
super-lightweight indoor aircraft. As antweights take off in popularity, I’d
expect to see some lighter ground frequency receivers.
I also added a list
of aircraft receivers to show how much lighter they can be!
The list is incomplete, but represents the lightest receivers I have found.
E-Mail us if you know of any others we should add to the list.
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