Twin receivers

Post here for general queries or anything radio related.
Terry Jessop
Posts: 43
Joined: December 20th, 2008, 11:27 am
Contact:

Twin receivers

Postby Terry Jessop » February 6th, 2018, 8:54 pm

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?

Cary Bailey
Posts: 210
Joined: January 26th, 2011, 7:43 am
Location: Stoke On Trent
Contact:

Re: Twin receivers

Postby Cary Bailey » February 7th, 2018, 9:29 am

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

stuart knowles 1611
Posts: 146
Joined: December 27th, 2008, 11:46 am
Contact:

Re: Twin receivers

Postby stuart knowles 1611 » February 7th, 2018, 9:57 am

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??

Glenn Masters
Posts: 76
Joined: January 3rd, 2009, 12:02 am
Contact:

Re: Twin receivers

Postby Glenn Masters » February 7th, 2018, 12:42 pm

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 . . . ?

stuart knowles 1611
Posts: 146
Joined: December 27th, 2008, 11:46 am
Contact:

Re: Twin receivers

Postby stuart knowles 1611 » February 7th, 2018, 3:40 pm

An excellent point Mr Masters ;-)

User avatar
Rob Buckley
Posts: 459
Joined: March 14th, 2009, 12:08 pm
Location: Just Outside Bath
Contact:

Re: Twin receivers

Postby Rob Buckley » February 7th, 2018, 7:17 pm

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.
LMA Secretary - I've got a reasonable idea where you live!

John Greenfield
Posts: 330
Joined: December 5th, 2008, 2:08 pm
Contact:

Re: Twin receivers

Postby John Greenfield » February 8th, 2018, 8:11 am

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

Bob Thompson1894
Posts: 701
Joined: December 6th, 2008, 1:08 pm
Location: Notts
Contact:

Re: Twin receivers

Postby Bob Thompson1894 » February 8th, 2018, 8:39 am

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.

User avatar
Rob Buckley
Posts: 459
Joined: March 14th, 2009, 12:08 pm
Location: Just Outside Bath
Contact:

Re: Twin receivers

Postby Rob Buckley » February 8th, 2018, 1:17 pm

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.
LMA Secretary - I've got a reasonable idea where you live!

barrie burton
Posts: 115
Joined: December 4th, 2008, 12:54 pm
Contact:

Re: Twin receivers

Postby barrie burton » February 8th, 2018, 2:13 pm

There is still only one transmitter

User avatar
Rob Buckley
Posts: 459
Joined: March 14th, 2009, 12:08 pm
Location: Just Outside Bath
Contact:

Re: Twin receivers

Postby Rob Buckley » February 8th, 2018, 3:01 pm

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.
LMA Secretary - I've got a reasonable idea where you live!

Glenn Masters
Posts: 76
Joined: January 3rd, 2009, 12:02 am
Contact:

Re: Twin receivers

Postby Glenn Masters » February 8th, 2018, 3:58 pm

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 !

User avatar
Rob Buckley
Posts: 459
Joined: March 14th, 2009, 12:08 pm
Location: Just Outside Bath
Contact:

Re: Twin receivers

Postby Rob Buckley » February 8th, 2018, 7:46 pm

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
LMA Secretary - I've got a reasonable idea where you live!

Glenn Masters
Posts: 76
Joined: January 3rd, 2009, 12:02 am
Contact:

Re: Twin receivers

Postby Glenn Masters » February 8th, 2018, 8:37 pm

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

Terry Jessop
Posts: 43
Joined: December 20th, 2008, 11:27 am
Contact:

Re: Twin receivers

Postby Terry Jessop » February 8th, 2018, 9:51 pm

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

John Greenfield
Posts: 330
Joined: December 5th, 2008, 2:08 pm
Contact:

Re: Twin receivers

Postby John Greenfield » February 9th, 2018, 9:03 am

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

Dave Hayfield
Posts: 203
Joined: December 8th, 2008, 1:24 pm
Location: Isle of Thanet
Contact:

Re: Twin receivers

Postby Dave Hayfield » February 9th, 2018, 5:21 pm

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
Sandwich Bay Flying Club
LMA 520


Return to “Radio Equipment”

Who is online

Users browsing this forum: No registered users and 1 guest