S-Bus cable length for Redundant RX

[leowagen]

Hello all.

I haven't seen any "limitation" regarding the cable length for the redundant Rx's S-bus cable. Makes sense to have the recievers as apart as possible? maybe installing the slave Rx closer to the tail, with the antennas in different orientation than the master Rx? Airframe will be a full woodden quarter scale, gas powered Decathlon, controlled by an ISRM- Updated X10.

 

[Wayne]

Yes, depending on the model it is a good idea to locate them in different areas. There is a limit though as too long a wire length to the slave can cause issues, but honestly not sure I have heard of any reported issues with a slave being to far away..? Anyone?

 

[Flying Dutchman]

I have used a combination of a GR8 with an M+ slave in the rudder in a couple of gliders. Different Rx's than you're planning to use, but same concept. They were connected with a 36" braided cable, chosen to minimize noise pick up on that long line. It worked fine with regard to fail-safe operation in situations where the master lost reception, i.e. the M+ took over and provided seamless control. I never saw signs of noise on my controls. This arrangement should work fine for your Decathlon.

My problem (described in detail elsewhere on this forum) was that the M+ would not give control back to the master when it regained reception, so I lost the GR8's telemetry info (altitude, battery) for the remainder of the flight. Annoying when you're trying to make a 1 hour flight thermalling your glider, but not a problem if your only motivation for setting up redundancy is to save your large power plane during a glitch. I assume you typically won't fly it at a great distance, as we often do with gliders, so you probably have less chance of losing signal anyway.

 

[leowagen]

Thanks a lot Dutchman... you cleared out pretty nicely my concern.
This M+ behavior is usual? I mean, is just a thing from the M+ or it is how redundancy works? I mean, master Rx only recovers control if the slave actually looses signal, so control is regained by each only if the other one looses it.... This will be my first redundancy system as well as my first quarter scale model, so I'm bringing up all these doubts in order to have the best understanding possible of the system, and of course, to try to have the most safe system, for others, myself and the model itself.

 

[Flying Dutchman]

As far as I know this behavior is not unique to the M+, but I don't know for sure that all FrSky Rx's behave this way. A couple of guys on RCG did pretty in-depth analyses of it on the GR8/M+ combo as well as the ACCST equivalents, and determined that this is indeed how they work, i.e my experience was not a fluke. It certainly surprised me, as I simply assumed that the master would always regain control when it could. The 'manual' states that "the GR8 will automatically use the receiver with the best signal", but that is clearly not true.

All that aside, redundancy does work and will provide the safety you're looking for on your large Decathlon. I would choose a more capable Rx than the M+ for the slave, perhaps use two R10's or similar.

 

[leowagen]

As far as I know this behavior is not unique to the M+, but I don't know for sure that all FrSky Rx's behave this way. A couple of guys on RCG did pretty in-depth analyses of it on the GR8/M+ combo as well as the ACCST equivalents, and determined that this is indeed how they work, i.e my experience was not a fluke. It certainly surprised me, as I simply assumed that the master would always regain control when it could. The 'manual' states that "the GR8 will automatically use the receiver with the best signal", but that is clearly not true.

All that aside, redundancy does work and will provide the safety you're looking for on your large Decathlon. I would choose a more capable Rx than the M+ for the slave, perhaps use two R10's or similar.

Thanks again Dutchman.

I intend to use an R10pro as Master and an R8pro as slave. I need the 10 pwm channels from the R10pro, as well as its battery redundancy, and though I could use something much simpler as slave, I'd rather use the R8pro to make sure both are safe against ignition module noise.

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