Programming twin motors for differential thrust

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I was thinking about twin engines and linking the rudder stick to the throttle to get differential thrust. This is especially useful on something like a 'Goolie' but I'll definitely try it on the NemoTwin.

On rcgroups.com I saw long discussion on programming for the Goolie and it became apparent that many people never read the manual for their radios. This is crazy, you have paid so much for it, why not get the best out of it by doing a bit of homework?

DX6i

Sadly, this radio will not do any mixes that involve the throttle. I have tried a bunch of stuff and have been unable to get any mix using the throttle as a source or target to work.

DSX9

This proved to be very easy to set up since it has built in facility for twin motors.

Before doing this procedure, make sure that your rudder reversing is correct.
  1. Hold ENT and turn on the radio,
    select a new model and reset it.
    Set the name of the model
  2. In [Device select] set the GEAR channel to INH (or whatever channel you want the second motor on, I will refer to it as the 'gear' channel, you replace it with whatever you are using)
  3. In [Wing Type] set the 'gear' channel as the Twin engine mate. Set the trim link to ACT.
  4. Click 'LST'
  5. Exit to the function menu via INFO-DISP
  6. If you check in 'Monitor' now, you will see that throttle will move the throt and the 'gear' channel together. Since you have activated the trim function, the throttle trim will affect both equally.
    In the image below you can see that the throttle is partially raised and both channels have moved tot he red dots.
  7. Set 'Mix 1' as RUDD->RTHR, set rates to +50 and -50. In Monitor you will see that Left Rudder stick increases the RTHROT channel. (More power on right engine to turn left)
  8. Set 'Mix 2' as RUDD->LTHR, set rates to -50 and +50. In Monitor you will see that Right Rudder stick increases the LTHRT channel, and decreases RTHRT. (More power on left engine to turn right).

    PS: If you are running IC motors then you do not want the inner engine to reduce throttle because at low throttle settings using rudder may then kill the motor, so in this case set the mix values so that only the increase half of the rudder motion affects the throttle levels.

OK, that is the basic setup. Since I run electric I believe it is a good idea to program in a throttle kill so that bumping the throttle cannot run the motors unexpectedly. I use the 'Throttle Curve' for this, even on my Vapor.

  1. Since we have 2 throttles and 2 curves per throttle, there are 4 throttle curve mixes to set up. The 0 position is with the switch 'down' and the '1' position is with the switch 'up'. Both LTH.0 and RTH.0 curves must be set up for zero throttle travel, and both LTH.1 and RTH.1 curves must be set for normal throttle operation.
  2. Go to Throttle Curve setup and set the 'Mix' switch as the selector. This is the switch at top left rear on a mode2 DSX9 and is the one I've found to be bumped on or off the least when handling the radio (remember I use a tray so YMMV).
  3. For position 0 (down or back) we want the throttle stick to have no effect, so set the curve to 0 for RTH.0 and LTH.0. In the background of the above image you can see that the point L, 3 and H have been set to 0% so that the graph shows no curve at all, it being flat along the bottom, indicating that no matter waht the throttle stick position is, there will be no throttle output.
  4. For position 1 (switch up or forward) leave the curves as is, or set them to the desired shape so throttle works as normal.
  5. Hang on, we have mixes set that can give 50% throttle despite the throttle being inactive!
  6. Go to Mix1 and Mix2 and set the switch to 'Mix' under [SW SELECT]. Now both throttle curves and the rudd->throt mixes come alive when the Mix switch is in the up position.

Of course the 50% mixes set above are only an example. Some planes will need less, some more. I'd advise starting conservatively and then increasing in 10% steps till it becomes scary, then back off 5% (-:


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Last modified: February 18 2013 16:08:04.