Throttle cut only works on one motor of twin

[Allan Bennett]

My transmitter is a Futaba 10CG, but I'm posting here because I think my question is a generic one about mixes.

On all my electric models I've programmed a switch to kill the throttle, using a THR -> THR mix. No problems so far.

But I decided to add throttle differential to the two motors on my TwinStar (which has undercarriage), to improve taxiing. To achieve that I've connected one ESC to the throttle channel (channel 3 with Futaba) and the other to channel 6. I've then programmed the following mixes:-

Mix 1: THR -> THR as before, to disable the throttle;

Mix 2: THR -> FLAP (i.e. channel 6) so that the other throttle mimics the one in channel 3;

Mix 3: RUDDER -> THR so that right rudder slows down the starboard motor (the one in channel 3), activated by a switch;

Mix 4: RUDDER -> FLAP so that left rudder slows down the port motor, activated by the same switch.

The motor differential responds as I want it to, subject to some field trials to gauge how much differential I need, but the problem I have is that my throttle-cut function only disables the throttle channel (starboard motor), not the flap channel (port motor).

I've tried programming a FLAP -> FLAP mix in a similar manner to my THR -> THR mix, using the same switch, but it has no effect.

Any suggestions, please, about how I can program a throttle-cut that will affect both motors?

[Denis Watkins]

Just a note Allan, on all my Tx, Futaba, Spectrum and JR, THR cut only works on the Throttle channel. My only twin did THR cut successfully, but I slaved the Aux channel to the THR, with no other mixes, so effectly controlling 2 motors from one channel, unlike your recipe

[Allan Bennett]

It's not the THR CUT function I'm using (which reduces the throttle below zero by a user-defined percentage), but a mix which simply disables the throttle altogether.

My Mix 2 is slaving channel 6 (defined as FLAP by Futaba) to the throttle channel, which is the same as you say you do. I'll try the THR CUT function -- presumably it needs to be set to -100% to shut down the motor irrespective of the throttle stick position.

Edit:  Nope, THR CUT only works on the THR channel, not the one that's slaved to it.  It can't reduce the throttle by more than 40% (more than enough to shut down a glow engine on tickover) so doesn't prevent an electric motor starting up if you open the throttle beyond a certain point, which is presumably why people use the THR -> THR mix for electrics.

Edited By Allan Bennett on 28/09/2016 20:34:06

[Jon H]

I would not recommend mixing throttles to rudder. It sounds like a good idea but does more harm than good in practice. I have never needed it on any of the multi engine models I have flown.

[MattyB]

Apologies Allan, but my Futaba knowledge is very rusty - the last set from them that I used was ~25 years ago, a two channel 27Mhz Attack as I remember; not much mixing on that!

This is a great example of why I don't like the canned mixer style approach as used by Futaba, JR, Spek et al. They are fine if all you want to do is a commonplace setup, but throw anything remotely unusual at them and you're scrabbling around trying to work out how the programmers mind works and concoct workarounds which frequently compromise other areas of the setup.

Yes, open source offerings like OpenTX do approach some of the simpler tasks in a different way that can initially be hard to grasp coming from a big brand set. The payoff though is that almost anything is possible - you can setup a throttle cut for 1, 2 or 22 motors in seconds. Even better by using logical switches can create a sticky throttle cut where accidental immediate throttle ups are impossible even if you disengage the cut with the throttle raised. I will never go back to a canned mixer set for anything other than the simplest BNF micros.

Edited By MattyB on 28/09/2016 22:27:15

[cymaz]

I have a Seagull Dual Ace. I put an 8 channel Rx into it and used different channels for each engine. This was so that the idle end points could be adjusted independently. I use an FrSky 8 ch Rx and a Futaba 9 Cap with a 2.4 module. Now whilst not the same set up as yours this might give you a couple of ideas....BTW, this also includes high/low idle switching. Switch H is throttle cut. Switch G is idle control.

Edited By cymaz on 29/09/2016 06:07:20

Edited By cymaz on 29/09/2016 06:11:18

[Allan Bennett]

Posted by MattyB on 28/09/2016 22:26:32:

.... This is a great example of why I don't like the canned mixer style approach as used by Futaba, JR, Spek et al. They are fine if all you want to do is a commonplace setup, but throw anything remotely unusual at them and you're scrabbling around trying to work out how the programmers mind works and concoct workarounds which frequently compromise other areas of the setup. ...

I agree with you on that, but I've got too much invested in Futaba Tx and Rxs to consider changing to Taranis! If I remember correctly, my old 35Mhz Futaba used to refer simply to channel numbers, rather than giving them names, which I found much easier to figure. Will a Taranis accept a Futaba FASST module? I'll pay more attention to yours when we next meet!

But you got me thinking; I've just tried channel 7 for the second motor, since Futaba calls that AUX1, but the result is the same, my switch still only cuts the channel 3 throttle.

John, apart from my programming problem, I don't see any harm in using motor differential. As I said in my original post, I've made it switchable so I will only use it when taxiing. Without it my Twinstar simply goes wherever the wind steers it, usually in the opposite direction, when I try to taxi back to me after landing.

Cymaz, your THR -> AUX1 mix differs from mine only in your switch setting being STK-THR. I've changed mine to that (I had a switch assigned since it won't let me assign nothing), but it makes no difference. Since you're talking about end points though, I presume your model uses glow motors. That being the case, the THR CUT function probably works for you -- it doesn't work for electric since it can only be programmed to cut a certain percentage (up to 40% on my trannie) off the throttle position, enough to cut the throttle when at idle, but not enough to prevent an electric motor re-starting if the throttle stick is moved beyond 40%.

Edited By Allan Bennett on 29/09/2016 08:37:35

[Jon H]

i didnt see the part about only using it on the ground. Clearly too much haste there. For taxing it will be fine, in the air its likely to cause a spin!

[Allan Bennett]

Posted by Jon Harper - Laser Engines on 29/09/2016 10:25:01:

i didnt see the part about only using it on the ground. Clearly too much haste there. For taxing it will be fine, in the air its likely to cause a spin!

Wouldn't make any difference for me as I never use the rudder in the air But I will have to take care, for it's another switch to check in my pre-flight checks, just in case I ever feel the urge to move the rudder stick while flying..

[Dave Bran]

Posted by Jon Harper - Laser Engines on 29/09/2016 10:25:01:

For taxing it will be fine, in the air its likely to cause a spin!

Sorry John, but that is SO far from the truth. My use started in 2008 with a B25 profile "Mitchell" that did not have rudders and would have been very difficult to add. I used throttle to rudder mixing for differential thrust, and without too much difficulty came to settings that allowed me to fly smooth flat (and totally safe) circuits using the Throttle/Rudder stick ONLY, done one handed and much to the puzzlement of people watching.

I used a simpler mix (on a 6EX as it happens) and put throttle 2 direct to the rudder channel. I had throttle cut working on both motors but am unable at present to check how I did it, maybe just the simpler mix.

[Dave Bran]

Posted by Allan Bennett on 29/09/2016 08:36:58:

Will a Taranis accept a Futaba FASST module?

Hobbyco in the USA sold a FASST module for JR Transmitters.

The Taranis (and Horus) have JR module slots.

RipMax started selling the same module (with NO information at all on it!!), then wondered why so many JR owners suddenly wanted to fly FASST. (They didn't even know about the Taranis, out for many months by then...........Oh Dear!!) I found Hobbyco had a manual buried in their "obsolete/no longer stocked" website section.

Bottom Line:- I have a fully working FASST module on my Taranis and the Taranis RF setup selects this module when the correct model is chosen, best of both worlds. Have been using this for several years now with no issues.

[Dave Bran]

RipMax was sold as RM12-MX 2.4G FASST Module for JR

Hobbico JM912

Looks like both now obsolete though possibly stock somewhere.

[Dave Bran]

**LINK**

[Allan Bennett]

Thanks Dave for your info and research. Having thought about it a bit more, and seen the price of a new Taranis transmitter, it seems like the best route (if I can't find a solution to my programming problem) is to bite the bullet and go for Taranis. Then I can recover some of my cost by, hopefully, selling my Futaba receivers as I buy replacement Frsky ones.

[Jon H]

Posted by Dave Bran on 29/09/2016 11:05:05:

Posted by Jon Harper - Laser Engines on 29/09/2016 10:25:01:

For taxing it will be fine, in the air its likely to cause a spin!

Sorry John, but that is SO far from the truth. My use started in 2008 with a B25 profile "Mitchell" that did not have rudders and would have been very difficult to add. I used throttle to rudder mixing for differential thrust, and without too much difficulty came to settings that allowed me to fly smooth flat (and totally safe) circuits using the Throttle/Rudder stick ONLY, done one handed and much to the puzzlement of people watching.

I used a simpler mix (on a 6EX as it happens) and put throttle 2 direct to the rudder channel. I had throttle cut working on both motors but am unable at present to check how I did it, maybe just the simpler mix.

If you dont have rudders thats another story and differential thrust is your only choice. With full house control mixing throttles is not recommended as it leads very quickly to an overcontrol situation.

Allan, if you dont use the rudder in flight then thats fair enough but i must confess i couldnt get through a flight on any model without using mine. I find it very useful for keeping everything where i want it to be

[Allan Bennett]

Posted by Jon Harper - Laser Engines on 29/09/2016 12:43:30:

Allan, if you dont use the rudder in flight then thats fair enough but i must confess i couldnt get through a flight on any model without using mine. I find it very useful for keeping everything where i want it to be

Actually, (digressing a little) I took up heli flying a few years back because I was conscious that my left thumb wasn't getting enough exercise. Bank and yank normally works for me for fixed-wing, though I have been known to use rudder with my 1/5 Cub to demonstrate flat turns

[MattyB]

Posted by Allan Bennett on 29/09/2016 12:12:20:

Thanks Dave for your info and research. Having thought about it a bit more, and seen the price of a new Taranis transmitter, it seems like the best route (if I can't find a solution to my programming problem) is to bite the bullet and go for Taranis. Then I can recover some of my cost by, hopefully, selling my Futaba receivers as I buy replacement Frsky ones.

Yeah, you probably won't recover the TX cost (unless you sell your 10CG of course), but Futaba stuff is still worth a fair bit secondhand and FrSky comparatively cheap to buy, so when it comes to RXs it may well work out cost neutral. The other advantage is you get RX voltage and RSSI (received Signal strength indicator) telemetry built in as standard to every RX, not something that is on board with FASST RXs in the £20 range.

[Allan Bennett]

Problem solved! I've installed a FrSky receiver in the model now, and my Taranis can disable both motor channels with one switch. Just what I wanted.

[Andy48]

Welcome!