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General notes on freely programmable mixers
The previous pages have described a wealth of
ready-to-use built-in coupling functions, in the context
of the two menus »Wing mixers« and »Helicopter
mixers«. The fundamental signifi cance of mixers and
the principle by which they work are described on
page 159. The following section provides information
about the so-called "free mixers".
In addition to the pre-programmed mixers mentioned
mc-20
above, the
HoTT also offers a number of
freely programmable mixers in every model memory
location, whose inputs, outputs and mixer ratios can
be defi ned to meet one's own requirements. These
include:
•
8 linear mixers, numbered 1 through 8
•
4 curve mixers, numbered 9 through 12
These 12 mixers are certainly adequate for most
applications and are certainly suffi cient when the
potential of the pre-programmed coupling functions
are utilized. In the »Mix active/phase« menu (see
page 204), each of these 12 mixers can be activated
or deactivated separately for each fl ight phase.
For the "free mixers", the signal present at any control
function (1 to 16) can be assigned as the input signal
or,for a so-called "switch channel" (see further below),
the signal from any switch can be utilized. The signal
that is present at the control channel and passed
to the mixer input is always infl uenced by its own
transmitter control and by any control characteristic
that may have been set, e. g. those specifi ed by
the »Dual Rate / Expo«, »Channel 1 curve« and
»Control adjust« menus.
The mixer output acts on a control channel (1
to – depending on receiver type – a maximum of 16)
that can also be assigned freely. Before this channel
routes the signal to the servo, it can only still be
infl uenced by the »Servo adjustments« menu, i.e.
by the the servo reverse, neutral point offset, servo
travel and servo travel limit functions, and possibly by
»Tx. output swap«.
192 General notes on freely programmable mixers
One control function can be used for any number of
mix inputs simultaneously: if, for example, several
mixers are to be switched to act in parallel.
Conversely, it is possible for any number of mixers to
affect one and the same control channel. Particularly
in the latter case, however, it is very important to
ensure that the servo concerned does not strike its
mechanical end-stops when several mixer signals
accumulate excessively. For safety's sake, it may
therefore be necessary to set an appropriate travel
limit in the »Servo adjustments« menu.
For more complex applications, mixers can be switched
in sequence. In this case, it is not the (transmitter)
signal at the "output" of a control function which forms
the input signal of the "series-wired" mixer, but the
(mixed) signal "further back" at the "input" of a control
channel. The following description of the free mixers
includes several examples of this type.
In the software, one "free mixer" is always initially
activated. Optionally the mixer can also be assigned to
an ON/OFF switch. Since there are so many functions
to which switches can be assigned, be careful to avoid
(undesired) multiple assignments to a single switch.
The two key mixer parameters are:
•
... the
mixer ratio, which defi nes the extent to
which the input signal acts on the output of the
control channel connected to the mixer output.
The mixer ratio for linear mixers can be set as
symmetrical or asymmetric. Curve mixers can also
be confi gured with up to 8 points to suit one's own
application and even implement extremely non-
linear curves.
•
...
the neutral point of a mixer, which is also
referred to as the "offset".
The offset is that specifi c point along the
movement of a transmitter control (joystick,
proportional control or switch) at which the
mixer no longer infl uences the control channel
connected to its output. Normally, the neutral
point is the center point of the transmitter control.
However, the offset can also be set at any other
point along the control travel. Since there are no
restrictions on the design of the curve mixers,
setting a mixer neutral point only makes sense for
the 8 linear mixers.
Switch channel "S" as a mixer input
Occasionally, however, only a constant control signal
is required at the mixer output, e.g. for a slightly
increased "up-elevator" trim when the aero-tow
release is closed – fully independently of its normal
trim setting.
In this case a switch is assigned both to the aero-
tow release and the mixer; it is then used not only
to open and close the release, but also to pass the
desired trim signal to the elevator via the mixer ratio.
To identify this special arrangement, this mixer input
control function in the program is designated "S" for
"Switch channel".
In addition, if the corresponding "target channel"
should now no longer be infl uenced by its "normal"
transmitter control, isolate the latter from the function
input of the affected control channel by way of the
»MIX-only channel« menu (page 205). Here too, for
clarifi cation of this there is an example of the function
provided in the following menu description.
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