The DHT module and antenna are installed in the
Controlaire Mule transmitter. A balsa block is also
attached with servo tape to mount the single-channel emulator and LED/button circuit board.
An FrSky DHT transmitter module is shown
with all of its preassembled components.
Some of you will remember when we flew single-channel radios and only controlled the rudder on
our airplanes. Our transmitters either
had a button on the end of a cable
or, as the transmitters got smaller and
could be handheld, the button was on
the transmitter. The introduction of
transistors allowed RC manufacturers to
build smaller and smaller single-channel
transmitters, but the button still existed.
As I wrote in the past, there were many
gadgets designed to replace the button
to actuate the escapement or servo.
I have enjoyed reading about the
“button-pushers” gathering in the
United Kingdom, which has been going
on for several years. A trip to Phil &
Shaun’s Single Channel & Vintage R/C
Page website is an enjoyable one, and
you can see and read about what Phil
Green and Shaun Garrity have been
doing in the United Kingdom.
Although some choose to restore old,
single-channel radios, there is another
way to obtain reliable operation while
using your single-channel, handheld
transmitter. Why not convert it to 2. 4
GHz? With the help of some FrSky
electronics and Phil Green, I will explain
to you how I converted a popular
Controlaire Mule transmitter.
I converted an FM single-channel
transmitter to 2. 4 GHz several years
ago and I use it to fly a Mini Mambo.
For this how-to column, I decided to
convert a Controlaire Mule—a single-channel transmitter that was sold by the
thousands. To emulate the action of a
compound escapement using modern
servos, I am using the single-channel
emulation encoder produced by
The first thing to do is discard all of
the inner workings of the transmitter
except the switch, including the button.
While flying my Mini Mambo, I found
that the button on that transmitter did
not allow me to fly well, so I decided to
purchase a button with a micro switch,
which provides a crisp click when I
push it. I found mine online, although
I don’t remember where I bought it. It
was inexpensive, so I bought several.
The primary item for this conversion
is an FrSky DHT module that is
available from several sources. The
module uses Advanced Continuous
Channel Shifting Technology and has
telemetry capability, which is not used
in this application. There is also a cable
with an attached three-position switch
that can be unplugged and discarded.
The DHT module comes with an
antenna and a small circuit board with
an LED and a button.
Because the Mule does not have any
internal mounting brackets, I mounted
the DHT module at the top of the case
using servo tape. I made a mount for
the button/LED board and the single-channel encoder from hard balsa wood.
I attached both items with servo screws,
which can be seen in one of the photos.
87 Model Aviation JULY 2017 www.ModelAviation.com sponsored by HOW-TO issue
How-to for button pushers