Discussion - Micro receivers in fixed wing models

[Bob Cotsford]

I want to hear opinions and especially experiences about using 'full range' micro receivers normally marketed for multirotors in fixed wing models. I'm thinking of the type that only have Sbus or similar bus system outputs, many smaller than a small postage stamp. Used with suitable decoders or Sbus servos these can provide (in the case of the FrSky gear that I use)up to 16 independant channels plus telemetry.

The type of use I'm thinking of is as follows:

10 independant channels: 2 ailerons, elevator, rudder, 3 retract units, flaps, nosewheel steering, linked throttles.

Only digital servos, ESCs and electric retract units.

Receiver redundancy.

Receivers and decoder to be mounted in the wing (where most control functions are)

Why micro receivers? I don't need standard servo outputs on the receivers and it's a lot easier fitting 2 micro receivers in than 2 standard ones.

Cons that I can see -

plugs and wiring between receivers and decoder is a much lighter guage than the usual servo wiring (but it's in an electric model and servo power comes from the decoder board).

they just don't look right.

erm - what if anything, am I missing?,

Edited By Bob Cotsford on 03/01/2020 11:38:37

[Ron Gray]

👍for the FrSky RX and ARCHER series.

[Andy Hat]

Go for it but range-check, range-check, range-check (and check under power and all angles too, those tiny aerials...).

Stick to -official- FrSky receivers - I have learned this from experience...

You can remove the receiver casing from a standard RX to save space and weight.

[Andy Hat]

One tip - put nice blob of hot glue over the connection of the aerial to the board.

[Bob Cotsford]

The receivers are an R-XSR and an XM+ which have the IPEX aerial fittings and come ready glued Andy. My camera flash is a bit limited so apologies for the poor picture quality. This is one receiver, one 10 channel decoder/redundancy board, a power splitter to feed the retracts from one ESC while the other ESC feeds the remaining electronics, all tucked into what was the space for spring/air retract control servo and valve. The second rx is velcroed to the wing and connections to the fuselage are via an Ashlock connector. I suppose I could have given up on redundancy and fitted the second receiver instead in the fuselage to drive rudder and elevator with it's own pack but as I had the Ashlock in stock... I still need to solder a plug on the Sport connection hence the green wire pushed into the plug at the top.

Edited By Bob Cotsford on 03/01/2020 16:20:56

[Bob Cotsford]

I should say will be R-XSR and XM+, the second rx is currently an old vanilla XM for testing.

[Ron Gray]

Looking good for the Deuces Bob 👍

[Bob Cotsford]

Ron, it's coming along. I've just ordered some Irvine spinners as I don't trust the balance on anything marked E-flite after the Carbon-Z Cub! It certainly makes for more pleasant fettling if you take the wing outer panels off. Although the model looks to be unflown the covering isn't brilliant with some delamination that I need to patch over. Plenty of time for that though, I don't plan on any trips to the field before the new tax year. The field might have drained a bit by then.

[Andy48]

Posted by Andy Hat on 03/01/2020 13:55:51:

Go for it but range-check, range-check, range-check (and check under power and all angles too, those tiny aerials...).

Perhaps, but you are not getting the best out of OpenTX. Far better is after the initial range test, ensure logging is enabled for the RSSI, and make a short flight or two not going too far away. Then examine the RSSI over the course of these flights, and then extend the range. That way you know where the safe range boundaries are.

Traditional range tests are always a compromise.

[Bob Cotsford]

I agree Andy, with RSSI announced through audible warnings ground range checks only really show up major issues such as intermittent connections. It sounds as though no-one has tried a setup like this yet!

[Devon Slopes]

Its not quite what you are trying to do, Bob, but I'm in the middle of doing something similar on a 9 channel e-glider I'm building. My thought processes were started by the fact its a six servo wing, which for a conventional setup means at least 6 signal wires and two power wires into the wing. I thought SBUS might be the answer, giving me just one signal wire into the wing, but then discovered that a RX was lighter than a decoder! So, it was a simple step of logic to end up with an RX6R in the wing, and an G-RX8 in the fuselage. In principle I don't even have to connect the RXs together, but in practice will probably do so as it gives me the possibility of having some redundancy between them. Of course the big difference between this and what you are doing is that I am not using the truly micro RXs, which is a downside, but do avoid the need for decoders.

So, could I ask what is the decoder/redundancy board you are using?

[Bob Cotsford]

Hi DS, I've used FrSky 4 channel Sbus decoders in each wing half on several models to reduce the number of plugs and sockets, and I also have a few XPS X10+ boards that predate the FrSky redundancy stuff. From the other RC forum. I've used them in 40cc petrol and .90-1.20 4 stroke glow models with complete success. The only drawback is that they put out a 9ms pulse rate so digital servos are essential. I did think about two receivers, one in the wing and one in the fuselage but that needs either a power lead between the two or a second power supply. As I have some Ashlock harnesses going spare I went for a redundant setup in the wing.

There's an Sbus thread around somewhere that lists a variety of alternate brand decoders.

Looking back, I've been using these for around 4 years!