I have been setting up helicopters and radios for a long time
now, but it has become apparent recently that more and more new
pilots are jumping in at the deep end with Computerised radios
such as the Spektrum Dx6i and DX7, although many still use the
stock Esky Radio system initially.
The problems with all these radios vary, but
there are some very important things that you need to understand
BEFORE YOU EVER SWITCH A TRANSMITTER ON.
I want to cover the 3 most common radios here
in this article in order Esky stock radio, Spektrum DX6i and
First of all we need need to digress a bit to
explain about what throttle curves are, and what they do.
The first thing to realise is that as soon as
the motor starts to turn, the main rotor blades will start to
turn as well (on all electric helicopters anyway). There is no
clutch system on electric helicopters. Having these spin up
unexpectedly is dangerous for obvious reasons, so you do not
want this to happen until you really want them to spin up (when
ready to fly)
For normal flight, most throttles use a fairly
linear increase from 0% up to 100%. This means that when you
have the throttle stick fully down, the motor does not turn at
all, but at 50% throttle stick setting, the motor will be
spinning at around 50%-60% of its maximum speed.
THEREFORE, SO WILL THE MAIN
ROTOR HEAD AND BLADES BE SPINNING AT 50% OF MAXIMUM REVS.
At 100% throttle stick setting, the motor will
be running at it's maximum rpm, and so will the rotor head and
From this we can see that while we have the
throttle stick FULLY DOWN, all is well, and the head will not
start to spool up on us. As soon as we start to move the
throttle stick, the motor starts and the head starts.
This arrangement is basically OK for those
learning to hover helicopters initially, as the more throttle
you apply, the faster the head rotates, and the more lift that
is created until the helicopter takes off. (Well, actually the
collective pitch on the blades also increase and decrease as you
adjust the throttle, but we will cover that elsewhere)
However, if you turn the IDLE UP SWITCH ON,
the throttle curve is very different indeed, as can be seen
clearly in the diagram below..
You can see
that when the throttle stick is fully DOWN for STUNT mode (Idle
Up), the Motor, and Head, are at FULL SPEED, as they are at full
throttle stick. Only at mid throttle does it reduce
slightly to 80% motor rpm.
THIS MEANS THAT IF YOU HAPPEN TO SWITCH THE IDLE
UP SWITCH ON WHEN THE THROTTLE STICK IS AT ZERO, YOUR HELICOPTER
WILL STILL SPIN UP TO MAXIMUM SPEED IMMEDIATELY.
Probably seems crazy to you, but it is provided
to allow you to fly the helicopter inverted as well as the right
The ONLY WAY TO USE THIS SAFELY is to bring the
throttle stick up to 50% in NORMAL MODE, and ONLY THEN, switch
to Idle Up mode, for as you can see in the diagram, the two
throttle settings are only the same at that one point.
One other thing also changes when you switch to
Idle Up mode with the stock Esky Tx, and that is the amount of
pitch on the rotor blades, and if you change modes at 50%
throttle, you will see the main blades suddenly pulling the
helicopter DOWNWARDS due to the additional negative pitch.
The diagram below illustrates this nicely. The
normal pitch curve doesn't start at bottom stick, but rather at
40%, whereas the Idle Up curve goes from 0% to 100% totally
linearly. This means that the normal curve gives you a
pitch range of approximately -4 to +8 degrees, but the Idle Up
curve gives -9 to +9 or thereabouts. They only cross at
50% throttle setting.
So, the moral here is to understand what the
Idle Up switch does
and to ensure that you never switch it on unless you have the
throttle at 50% stick setting
If you do
happen to get into Idle Up mode, DO NOT SWITCH BACK TO NORMAL
MODE until the helicopter is back on the ground, as the sudden
change in Throttle and Pitch settings are almost sure to cause
you to crash the helicopter.
OK, lets move
on to individual radios now.
ESKY 6 channel radio
This is the most basic of radios, and is
supplied as part of the RTF kits supplied by Esky, and in
particular the Belt CP, which is the helicopter chosen by many
new prospective helicopter fliers.
This radio offers very few control options
other than the obvious sticks and their respective trimmers, but
the later versions also changed the functionality of one of the
The earlier Esky radios had to adjustable
knobs on the top of the Transmitter (Tx), one either side of the
aerial. The left hand one has always allowed you to vary
the Hovering Pitch to an extent, while on the earlier TX's
the right hand knob allowed small variations to be made to the
Hovering Throttle. The later Esky Radio now use the right hand
knob to change the gain on the gyro to let you adjust HH gyros
There are also 2 switches on top of the radio,
behind the knobs. The right hand (spring) switch is only ever
used if you have another radio acting as a buddy box, with both
radios wired together.
The LEFT HAND
SWITCH is the REALLY IMPORTANT ONE TO KNOW ABOUT
- as shown by the red arrow above
This is the one called the IDLE UP switch by
Esky, but is also known as the STUNT switch, or even the
As you should by now know, this switch is
something that you really do need to treat with extreme care.
Always check BEFORE switching your Tx on that this switch is
pushed away from you (OFF) so it is in NORMAL MODE. There
is a safety system built in to the electronics that
"should" prevent the motor spooling up if the Tx is
turned on with the Idle Up switch ON - but then - why risk the
SPEKTRUM DX6i & DX7
These are possibly the most used Radio Systems
by RC helicopter pilots today
Both are fully computerised systems, and
provides a great many ways for you to adjust and setup your
helicopter to make it fly optimally to suit your particular
preferences. Because of that, they are also somewhat
complex at first glance, and have lots more switches on them, as
you can see from the pictures above.
The right hand picture shows you where the
Idle Up switch is located on a DX6i.
Many of the switches/functions on the Dx6i/DX7
are not used by helicopter pilots, such as MIX settings, and
indeed, many pilots do not use the DUAL RATE settings/switches
either, so we will ignore these and assume they are always left
UP (away from us)
The Idle Up switch can be as dangerous as on
the Esky radio, except for the fact that YOU CAN SET THE CURVE
UP YOURSELF. Unless you want to fly in Idle up mode, it is
a good idea to have both the Throttle and Pitch curves (called
STUNT by Spektrum) set up exactly the same as your NORMAL
curves, so that if you happen to switch the Idle UP switch on
accidently, IT WILL BE NO DIFFERENT to the NORMAL curve.
If you do have a true
Idle up curve set, then the same warnings apply as with the Esky
The other very useful switch (IF SETUP IN THE
RADIO CONFIGURATION) is the Throttle Hold switch, located at the
back right on top of the radio. Most people set this to be
0% or even a small negative value to ensure that when this
switch is ON, the motor WILL NOT START UP AT ALL, irrespective
of the throttle stick position. Clearly this is a very
useful safety measure.
The only other switch that helicopter pilots
use regularly is the Flaps/Gear switch, which is typically
setup in the configuration to let you switch the mode the gyro
operates in between Rate mode and HH mode (AVCS). Most
pilots choose to have the switch away from then (0) to be HH
mode, but it is a good idea to check this before you take off.
Before you switch on a DX6i, CHECK ALL
SWITCHES and ensure that they are ALL set correctly, but in
particular make sure that the IDLE UP/STUNT switch is AWAY FROM
The DX6i has various safety circuits built in
that warn you of incorrect switch settings on start up.
The two most common you will hear will be beeps indicating that
either the Idle Up switch is FORWARD (ON), or that the Throttle
Hold is forward (ON), or that the throttle stick or throttle
trimmer are not fully down.
In all cases, you need to reset these or
change switch settings before the Tx will initialise correctly.
To avoid this, it is always
best to get into the habit of ensuring that the throttle and
trimmer are fully down, and that both the Idle Up & Throttle
are in the OFF position before switching the Tx on.
If the radio continues to beep
and not initialize, check all other switches, but they should
not effect the Tx from initializing.
This is the bigger brother of the DX6i, with
more features and one additional channel.
It is again a fully computerised system, but
with with 7 channels, and provides a great many ways for you to
adjust and setup your helicopter.
It also moves the Idle Up switch for some
strange reason from the top left to the front left, replacing
the original Idle Up switch position with the rudder D/R.
The Idle up switch on the DX7 is now the
longer switch that is 2nd in from the left on the top front. It
is also a 3 way switch, as the DX7 offers you a full 3rd set of
curves. Also, the Dx7 does NOT have a switch marked
Throttle Hold, but most people configure it to still be top
right right switch that is labelled as Rudder DR.
Other than this, the Dx7 and the DX6i are
pretty well identical in terms of safety when powering them up.
I really do hope
that this tip helps
ALL pilots to avoid powering up their radio incorrectly.....