Large Model Association Forum

I'm thinking of putting twin receivers in a large spitfire I'm thinking of this set up -

Receiver 1
Left aileron
Right elevator
Throttle
Rudder

Receiver 2
Right aileron
Left elevator
Flaps
Gear

Anyone any thoughts on this?

Terry, what's wrong with that? Nothing at all! Go for it. It complies with the requirements for over 20kG models (if your model is going to exceed that then it is mandatory) other than that it's fine. Feed a separate battery to each Rx & if you can control your engine choke on the opposite Rx should the other Rx fail for any reason you can stop the motor by switching in the choke!
Cary

There are Rx's out there now where two receivers are piggy backed together so that if one fails then Fairies in the back up receiver take over from the Pixies who have down tools, the idea being that control is retained over ALL channels not just one aileron / elevator etc.

Is there anyone out who fully understands these sets and can comment on the pro's and cons??

I would say that the pro s are that its a very neat and tidy installation with a promise of flawless performance - the cons are that as you are sifting through the wreckage, you've only got their word for it . . . ?

An excellent point Mr Masters ;-)

And if you power both receivers from each of the two batteries (with a sprinkling of switches and diodes to taste), a single battery or switch failure won't put you in a partial failure mode you'll retain full control.

Rob Buckley wrote:And if you power both receivers from each of the two batteries (with a sprinkling of switches and diodes to taste), a single battery or switch failure won't put you in a partial failure mode you'll retain full control.

Ah yes Rob but a servo failure (and I have seen 2 last year) will take down both battery packs so no radio. I used to do as you suggested but after a big scare that was only identified due to onboard telemetry monitoring battery voltage I now power the receivers separately. I was amazed at how fast the voltage was dropping from a pair of 3800mha batteries due to a servo internal short. I literally had less than a minute to land before the voltage went below 3.6v which is the point my receivers stop working.

John

Just a thought, but if you do as Rob says with the batteries you may not even realise there is a problem. (until the crash) With separate systems you are given a stern warning and a good chance of a safe recovery.

John, that's interesting, what type of batteries were you using? To suck two 3.8Ah batteries from full to flat in under a minute would be drawing over 100A, which you'd expect to melt the cause of the problem or a cable (especially servo wire) somewhere before it could flatten the batteries.

I've gone over to using A123 batteries now, that can supply many an amp (I fly one model using the same batteries to power the motor and they can give a good 30A continuous with not much voltage drop) and they work well on receivers.

Bob, using an arrangement like I suggest depends on a rigorous check before every flight that everything is working properly, switching each battery on and off in sequence to check it. If you just turn it all on and fly, there could as you say be a hidden failure that puts you one step closer to a crash.

There is still only one transmitter

Indeed true, but the transmitter generally has a far easier time and hasn't got a petrol engine strapped to it in general use!

Modern transmitters beep at you a lot if their battery is getting low, which until telemetry existed was a great advantage over the airborne equipment that was traditionally thrown into the sky on the hope it would all be ok until you landed, or at least fault-tolerant.

The overall safety argument is still that models are controlled by simplex control systems, so when it fails and they crash, the flying area is safe so nobody is hurt & nothing valuable damaged.

Totally independent power supplies to each receiver is the dish of the day . . that servo failure cant get to 'em all then ! Unless you get two servos failing - one on each receiver !! In the same flight !! - Doh !

One of these bad boys is the way to go...each individual servo output fused!

http://www.rc.emiter.hu/rc-miskolc/index.php/pb1-power-board-english

Maybe . . but my money would, not only be still in my pocket, but would be on Terrys original wiring set up. Its a KISS job !


PS. For what its worth, I did once carry out some flight experiments (with a hack) and I noticed that cross surface connection actually made no difference in partial flight control. Throttle and choke control on each receiver is a top tip though

Thanks for the input everyone. I intend to go on separate batteries and no switches (plug in/unplug)

It's going to be electric so hopefully not too much Vibration but no choke on the second receiver

Rob Buckley wrote:John, that's interesting, what type of batteries were you using? To suck two 3.8Ah batteries from full to flat in under a minute would be drawing over 100A, which you'd expect to melt the cause of the problem or a cable (especially servo wire) somewhere before it could flatten the batteries.

I've gone over to using A123 batteries now, that can supply many an amp (I fly one model using the same batteries to power the motor and they can give a good 30A continuous with not much voltage drop) and they work well on receivers.

Bob, using an arrangement like I suggest depends on a rigorous check before every flight that everything is working properly, switching each battery on and off in sequence to check it. If you just turn it all on and fly, there could as you say be a hidden failure that puts you one step closer to a crash.

Rob
First instance had twin 4500 mha Nims and the second case had twin 3800 mha lifs's. In both cases the model was only saved by very quick action by the pilot after the telemetry started counting down the voltage. Without the telemetry both models would have crashed. In both cases very experienced electronics engineers were in attendance an confirmed the voltage drop. We were all astounded at how fast the voltage dropped whilst trying to get a plane back on the ground quickly. In one case there were some melted wires but in the other case no visible heating of any of the wiring but a melted servo case.
I have just heard of another model that was lost this time by a short in the fuselage to wing wiring (possibly as a result of wing flex ?) Twin batteries through a Powerbox. The short was enough not only to melt the wires together but also melted the circuit inside the powerbox so that failed.

Stick with seperate power supplies to each receiver.

John

Totally agree with you John, keep both Rx systems completely separate, in fact keep it simple. If you have two engines make sure that the loss of power on a Rx still means you have control over both engines. Fitting one of my loss of battery volts failsafes means the afflicted Rx will cause the relevant engine (if a petrol engine) to shut down, the pre programmed failsafe from your Tx will not because the Rx is dead. Rob mentions that "the flying area is safe so nobody gets hurt", this is not so if your engine is still at full bore and you have no control over it.
(Sorry about the Failsafe 'plug' but with models being powered by ever larger petrol engines I think anything that can be done to limit disasters is worth doing!) Dave

As an update of this thread...
A club mate and I are building this Giant Mannock. I’ve decided to install a twin Rx system using a pair of FrSky TFR8s FASST RXs.

I’ve gone down this route for a couple of reasons...

I’ve never tried a dual RX set up before
With all the time and money spent on it an extra £s on a receiver seems good redundancy

RX 1

1 port aileron
2 strb elevator
3 throttle
4 rudder
5x
6x
7 power input
8x

RX 2
1x
2x
3x
4x
5 opto isolator for ignition
6 strb aileron
7 power input
8 port elevtor
The RXs run on separate batteries and switches. We’ve set it up and it still all running fine.....anyone have issues or see a potential problem

Peter , I would add an ignition on/off servo/switch to the second receiver so that if RX1 fails then you can stop the engine via RX2
If it has an electric motor you can set up your TX so that you need both the throttle stick and a switch to operate the motor
(" And logic ")
Also have twin batteries such that each RX has 2 power inputs/leads to provide redundancy . Regards Ian Turney-White

Thanks Ian. Each Rx has its own battery and switch. It’s a petrol motor so there is also a throttle cut off using the Tx kill switch. Also the failsafe for the ignition is always set.

Would I just add a Y lead for the ignition opto isolation?