Frsky receiver redundancy

[David P Williams]

I have been using Spektrum kit for my models since it first became available, but have also been using OpenTX on a Taranis X9D+ for a couple of years with a couple of models. I've now decided to change over to OpenTX for all my models over time, and have just bought a Horus X10Express which I like a lot, with a Jumper 4in1 module to run my Spektrum equipped models until I replace their receivers.

 

I am currently building a large and heavy I/C powered model that will represent a significant investment in building time and money, and I'm trying to work out the best radio setup to use. It is only a simple 4 channel (well 5 with two aileron servos) model, but I would like some redundancy in power supply and receivers.

 

I have an RX8R PRO ACCST receiver which states that it can act as a redundancy receiver when connected to another, and I have a spare X8R ACCST.

I have an Archer R8 PRO ACCESS receiver which also states that it can act as a redundancy receiver when connected to another ACCESS receiver.

I have a Powerbox sensor switch bought for another project but not used, to give a redundant power supply (I would use two LiFes).

I have a second hand Frsky RB10 redundancy bus, but I don't really like trusting second hand stuff for this model.

I don't mind spending more to obtain a robust setup.

 

I have spent hours googling various forum threads, Youtube videos, etc but can't seem to find any useful info on the pros and cons (or even much detail on how to setup and test) using two interlinked receivers versus one of the Frsky Redundancy Buses. Most of the info seems to be quadcopter/FPV based and I haven't been able to find very much at all relating to 'traditional' model airoplanes, particularly large ones.

 

Do any of you have experience in this area and could help with suggesting a suitable setup?

(I could always stick with Spektrum and use a Powersafe receiver with multiple satellites of course?)

[Chris Bott - Moderator]

Following.

It will be interesting to see the latest state of play. 

I guess you need to decide whether you wish redundancy of power supply, redundancy of receivers or both. 

 

One question to try to find the answer to:-

I think I've seen that at least some of FrSky's redundancy system relies on detection of lost frames in the S.Bus signal to decide whether to change over, but that the latest ACCST version 'beautifies' the lost frame figures to such an extent that no lost frames are ever reported. Sorry to be vague, but it is an area to be careful in. 

 

 

[Bob Cotsford]

I think the beautifying only affects some 3rd party flght controllers from what I can make of the RCG discussions, those using linked receivers seem happy enough.  If you want real redundancy then I'd go for a redundancy bus such as your RB10 as it gives battery redundancy and drives the servos direct from the batteries rather than loading up the receiver bus.  I've not used an FrSky one but I used to use Jim Drew's XPS XP10 unit when I owned petrol powered models.

[Ron Gray]

I've used the RB10 and RB20 that latter supporting HV plus Telemetry on either Rx. Both are very good but if you don't need HV then the RB10 is ideal.

[MattyB]

I would check the RB10 with some simple tests to prove it's RX and power redundancy features, then use that. Two RXs, two battery packs, a few servos connected and a servo test setup on your TX... just unplug stuff one by one and check the servos keep moving. Give it a few hours of operation at home driving (say) 8 servos simultaneously; if it can handle that and still pass the redundancy tests I say it is good to go.

 

PS - Does your model petrol or glow? Remember the X series RXs are not rated for spark ignition, there have been problems with them in the past despite Frsky denying that initially. There are now petrol specific models in their lineup though such as the RX8R pro.

[Ron Gray]

Good point about the gassers MattyB, I did a range of YouTube vids a couple of years ago showing the problem, from memory I also tested the RB10 at the same time.

[David P Williams]

Thanks chaps. The model has a big glow engine, so no ignition problems. I'm leaning towards buying an RB20 as ACCESS compatible firmware is available for it whereas the latest firmware update for the RB10 is from 2017. It can also do telemetry switching between the two RXs and has proper battery connectors rather than just solder pads.

 

I've done a fair bit more reading this afternoon, wading through huge threads on other forums. The RB20 seems pretty solid after some glitches with early ones. I can even daisy chain additional RXs, like tiny M+ ones into each attached RX to act as extra 'satellites'. There seem to be plenty of people using them in big petrol engined models and jets with no problems.

 

I think I'll test out the RB10 with a couple of my ACCST RXs and use it in my WotsWotXL to replace the Spektrum AR8000 it currently has.

[Chris Bott - Moderator]

That sounds like a very good plan. It's a very long time since I looked but doesn't the RB20 have more telemetry such as current drawn from each servo output etc?

[flight1]

hi         i have used  redundancy  on my large dh82 , very good no issues . i first had a rx8r and xm  no issues but if main rx failed you will loose telemetry (no big deal really), but i wanted battery redundancy as well. so i upped the game and now have rx8r pro and R-XSR all plugged into a RB20 with two batteries (+2 switches)all works very well no issues.

when using a rb20etc  you don't actually need any  rx's with pwm servo ports, as all the servos are plugged into the redundancy bus and the rx's use the s bus.

 

In both redundancy methods I tested by screen wrapped each rx aerials in tun and moving  my tx away to trigger lost signal and all worked as it should. (i have a large 70cc petrol never any issues)

 

How large is this model and are you using large servo's? If you are the rb20 is best and has redundant telemetry as well over the rb10.

 

i am happy it all works as it should

[Ron Gray]

From memory on the RB10 one of the RXs has telemetry disabled. For even better redundancy I used an R9 RX as the secondary RX thus giving me either 2.4 or 868 bands.

Edited February 18, 2021 by Ron Gray

[David P Williams]

Flight 1- thanks for the encouraging info. I appreciate that receivers with PWM ports are not needed, but I have this irrational thing about 'proper' hard cased receivers vs tiny bare circuit boards smaller than a postage stamp for 'proper' large models, although I know that the RB20 would be handling all the servo power. They just don't look as if they're up to the job even though the specs say they are. The model is this one and the servos are good old fashioned Hitec 645MGs. It should end up around 25lb AUW.

 

Chris - As I understand the manual, the RB20 telemetry per channel is just a warning of low voltge (less than 4V) or that the overload has tripped (>10A).

 

Ron - Yes thanks, I'm aware that the second receiver on the RB10 must have telemetry disabled. As for dual band - I think I'll be sticking with all 2.4.

[flight1]

Those little tiny  rx are the same as the bigger ones minus the bulk of the pwm conversion circuitry and connector pins, full range and just as capable/reliable so no worries there, but the one with the large case do feel like you got something in hand?.

NO need for the redundancy bus I would just go for one of your pro rx's and a x4r/x6r,( just make sure they are either both accst or both archer types) and use  2 good switches with 2 life (6.6v)batteries to keep to the kiss principle as much as possible. that one switch voltage regulated powerbox is only rated a 4a and is a sing point failure( no need to regulate for the rx and servos)

 

as for the engine ignition what are you going to do for power, My preferred method is to come of the two batteries using a tech-aero ultra ibec (via a y lead), very reliable and constant voltage to ignition

[David P Williams]

Thanks Flight. Yes I know the tiny RX are OK. People have range checked them out to 2.5km+, so circuits at my club patch should be fine. I might use one tucked down the back of the fuselage with the main RX up front

 

I'll go with the redundancy bus as it will give telemetry on the battery states just for additional comfort. It will be fed by two LiFes with two good switches, not the Powerbox one.

 

No engine ignition as it's a glow engine, but it does have a glow driver with it's own (NiMh) battery