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Throttle arming switch on Futaba 8FG

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I've been setting up a throttle arming switch on my Futaba 8FGS for a model which didn't have it.


For previous models, I have used a switchable throttle curve:


  • curve #1 (default) has all outputs set to 0

  • curve #2 (activated by switch) has all outputs set to the same as the input



With this model, this didn't seem to work. Curve #1 (all zero) was never activated, no matter what the position of the switch.


After much experimentation (and cursing), I have discovered that there seems to be a bug in the 8FGS software. If none of the receiver channels are set to VPP (variable pitch propeller) function (in the FUNCTION screen), then the throttle curve switch is ignored even though it is set and can be seen on the THR CURVE screen! I can't find any mention of this in a web search though.


The manual *does* document that not having anything set to VPP function means that the PIT(ch) CURVE screen doesn't appear, which makes perfect sense and doesn't bother me. However, the THR CURVE screen does appear, does allow me to configure switchable curves, but the switch never actually works to select them! Grrr!


I also tried configuring this via a mix instead ("mix throttle to throttle, 100% -> -100%" being the advice I've heard). Actually getting this to work on the 8FGS has also proved something of a strain.


The best I seem to be able to do is to mix -100% -100%, with offset Y also set to -100%, which does have mostly the correct effect: with the switch in safety position, the throttle stick is (mostly) ignored and the output is low. However, due to the way the throttle trim works, I have to choose between either correct idle at throttle stick low but slightly higher idle at the other end, or the slightly higher idle all the way through the throttle stick movement! This does appear to be a trim thing, as if I set the mix to take account of trims then the whole range of the throttle is this slightly higher idle!


All a bit frustrating!


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Martin -


Surprised at this as I've used the throttle curve on the 8FG as a kill many times, however... try using a pair of mixes as below. I'm sure it goes without saying, but test their effect using the 'servo monitor' function rather than chop yourself up with a spinning prop ;)


Mix 1:

thr -> thr

Offset: -100

Rate A: -100

Rate B: 0


Mix 2:

thr -> thr

Offset: 0

Rate A: 0

Rate B: -100


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Thanks for the tip. I'll try it out.


I have used the throttle curve many times before. The issue with this plane though was that I happened to not have VPP assigned to any channel. I think it's normally assigned to one of the higher channels, and since I wasn't using them on other models I never bothered to change it. With this model I'm using channel 5 for AIL2, and I think maybe this is where VPP was originally assigned.


Assigning a random unused channel to VPP does allow throttle curve to work, but is only an option if there are unused channels to waste in this way! That is the case for this plane, but won't always be.


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If you have version 5 of the software there is an item on page 2 of the model button called motor.


I use this to invoke an arming switch, which will even beep at you when you select the model if it is not in the armed position when you switch on.


Hope this helps




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I've seen the MOTOR function - how do you use this to implement an arming switch? All the examples I've seen using that have been for powered gliders, with the motor on a switch - either full power or off.

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Ah... I found this:



Sounds like they provide the throttle arming function as a specific feature for electric planes, provided you use the MOTOR function rather than THROTTLE for the throttle channel. I'm not sure if that will work for this (IC) plane though, as it sounds like that functionality might replace the throttle cut functionality (which obviously I do need on an IC plane).


However, that is an interesting option... I might test this out and consider moving my electric planes over to MOTOR rather than THROTTLE (though I was also considering moving them to Taranis anyway to get battery voltage telemetry).


Thanks for all the tips!


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