🚀 go-pugleaf

In article <C1F9Lq.1t9@hpchase.rose.hp.com>, jahr@hprnd.rose.hp.com (Steve Jahr) writes:
> Doug Braun (dbraun@cad636.intel.com) wrote:
> : 
> : --
> : 
> : I have a 4-channel Futaba FM system, and I was thinking of getting
> : a plane (Sig Samuri glider) that needs elevon mixing.
> : 
> : Does anyone make a little black box that goes in the plane
> : to do the mixing electronically?  Otherwise, has anyone ever
> : heard of a modifiecation to the transmitter to hard-wire
> : it to do the mixing?  How about a mod to add more channels?
> : I would assume the chip in the transmitter that does all the work
> : has the capability of doing more than 4 channels, and you
> : could wire in pots or switches to some unused inputs to
> : get more channels.
> 
> As has been posted...
> 
>     You could use the ACE Christy electronic mixer.
>     You could use a mechanical mixer (sliding tray or DuBro).
>     You could use the RCD "MOM" (Master Onboard Mixer).

Scratch that mechanical mixer... the Samuri is a 2-channel model
that uses wingerons, i.e. both whole wings rotate independently to
provide roll control and together to give pitch control (requires
strong ball-raced servos...). There isn't enough room in the fuse
to add a mechanical mixer (unless you're extremely clever), and
with the wing twist setup you don't want ***ANY*** slop in the
linkages.

> As to mixing... it is probably possible.  The biggest difficulty
> would be creating two "inverse" signals to drive the alternate
> ailerons.  Once this is accomplished, then mixing the elevator
> signal onto these signals is probably fairly simple.  To provide
> fuel for thought... I'll repost something I wrote up a while back
> on adding channels to a Tx.  The main relevance to this discussion
> is basic control stick circuitry.

   ... good stuff on adding channels deleted ...

The way to do this in the Tx is to add the aileron and elevator
channels together for one servo, and subtract them for the other
- then use servo reversing if necessary to get the right actions.
Building an "adder" and "sutracter" is not hard if you have some
basic electronic knowledge. The subtractor is the trickier of the
two as you need to set up a reference voltage equal to that of
the control stick when it's at neutral. Somebody posted a Tx V-tail
mixer quite a while ago that used this principle (same circuit, just
different channels mixed). If that person is still on the net perhaps
they could repost the circuit. Failing that, and if there is interest,
I could post my circuit. However I must point out that I didn't get
around to building it (not because I didn't think it would it work,
but because I ended up using my computer radio for that model instead).


Chris Kaiser

Postgrad, Elec. Eng. Dept.
University of Canterbury
Christchurch, NEW ZEALAND