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Program description: transmitter control settings – model helicopter

By default the “lim” input is assigned to the rotary pro-

portional control CTRL 7, which is located at top left on

the transmitter:

+100%

trv

free

ctrl 8

ctrl 7

thr

gyr

lim

This pre-deﬁ ned assignment eliminates the need to

prog

ram two ﬂ ight phases - “with idle-up” and “without

idle-up” - as are often used by other radio control sys-

tems for this purpose, since the method of raising the

system rotational speed below the hover point is more

ﬂ exible with the mx-12 HoTT program, and can be

ﬁ ne-tuned more accurately than using the conventional

“idle-up” function. However, if you prefer to program your

helicopter “with idle-up”, then switch off the “throttle limit”

function, described below, by setting the “Lim” input to

“free”.

Meaning and application of “throttle limit”

As mentioned previously under “Throttle”, the power

output of the engine or motor of a model helicopter is

not controlled directly using the throttle (Ch 1) stick - in

contrast to ﬁ xed-wing model aircraft. Instead it is control-

led indirectly by the throttle curve settings which you set

up in the “Helicopter mixers” menu. Alternatively the

throttle is controlled by the speed controller if the unit

you are using is a governor or regulator.

Note:

Naturally it is possible to set up different throttle curves

to suit different stages of ﬂ ight using ﬂ ight phase pro-

Throttle limit function

“Lim” input

gramming.

By their very nature, both methods of controlling power

have the same result, i. e. that a helicopter’s motor never

gets anywhere near its idle speed during “normal” ﬂ ying,

so it is impossible to start or stop the motor easily unless

some other means is used.

The “Throttle limiter” function solves this problem in

an elegant manner: a separate transmitter control - as

standard this is the rotary proportional control CTRL 7

located at top left on the transmitter - is employed to limit

the setting of the throttle servo or the speed controller,

which means that you can throttle right back to the idle

position. At this setting the trim of the throttle / collective

pitch stick assumes control, and can be used to switch

off an electric motor directly. At the other extreme, the

throttle servo or speed controller can, of course, only

reach its full-throttle position if you release full servo

travel using the throttle limit control. That is why the

“lim” input is reserved in the Helicopter program for the

“Throttle limiter” function.

For this reason the right-hand positive value in the

“Travel” column must be large enough to ensure that it

does not limit the full-throttle setting available via the

throttle curve settings when the throttle limit control is at

its maximum position. Usually this means a value in the

range +100% to +125%. The left-hand negative value in

the “Travel” column should be set in such a way that the

throttle limit control reliably cuts the electric motor, or

closes the throttle to the point where you can cut the I.C.

motor using the (digital) Ch 1 trim. For this reason you

should leave this value at +100%, at least for the time

being.

This variable “limiting” of throttle travel provides a

convenient means of starting and stopping the motor.

However, it also gives an additional level of safety if, for

example, you have to carry your helicopter to the ﬂ ight

line with the motor running: you simply move the control

to its minimum position, and this prevents any accidental

movement of the Ch 1 stick affecting the throttle servo.

If the carburettor is too far open (or the speed controller

not at “stop”) when you switch the transmitter on, you

will hear an audible warning, and the screen displays

the message:

throttle

too

high !

Tip:

ou can call up the “Servo display” menu to check the

inﬂ uence of the throttle limit slider. This menu can be

accessed from virtually any menu points by simultane-

ously pressing the ef buttons of the left-hand four-way

button. Bear in mind that servo output 6 controls the

throttle servo on the mx-12 HoTT.

Basic idle setting

Start by turning the throttle limiter - by default the rotary

proportional knob CTRL 7 located at top left on the

transmitter - clockwise to its end-point. Move the throt-

tle / collective pitch stick to the maximum position, and

ensure that a standard throttle curve is active in the

“Channel 1 ¼ throttle” sub-menu of the …

“Heli mixer” (page 94 … 105)

… menu. If you have already altered the standard

throttle curve which is present when you ﬁ rst initialise a

model memory, then this should be reset to the values

“Point 1 = -100%”, “Point 3 = 0%” and “Point 5 = +100%”

- at least temporarily.

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