M+ as a redundant receiver.

[Woodstock1]

I am currently flying SR8 pro access receiver and have been flying that for several months using A current sensor to count milliamps. I decided to use an M plus access receiver as redundant to SR 8. While flying it today somehow the telemetry reporting switched to the M plus and I lost the telemetry from the SR8 receiver causing a loss in the count of milliamps consumed ,which killed a battery. while using an M+ as a back up receiver to the SR8. Should I have disabled the telemetry and will that illuminate the loss of the sr8 telemetry. Or am I missing something else. Kiwi4

 

[Wayne]

Hmm, good question on the telemetry side, I'll have to do a little research on this subject..

For monitoring batteries is it always best to use volts IMHO as there are many things that can alter the amp hour output of a battery, ie. state of charge, temperature, condition of cells.

 

[Flying Dutchman]

My experience using an M+ as backup to a GR8 is that when the M+ takes over, it doesn't let go (i.e. switch back to the GR8). If you keep flying and encounter a condition that causes the M+ to lose signal, that will make it switch back to your primary Rx. I originally assumed that the primary Rx would take over again whenever it regains a good signal, but that is not the case.

 

[Wayne]

Odd, the main receiver should control the switch back.

 

[Joe Garfield]

As I'm shopping for receivers and researching redundancy, I can only offer information from what I've read in the manuals:

Note that the manual lists the operating range of the M+ as >1.2km, but the Sr8 as >2km. One could assume the SR8 would be the stronger connection. The SR8 manual doesn't give much detail about receiver redundancy, but the GR8 manual says "the GR8 will automatically use the receiver with the best signal" in regards to redundancy. In the GR8 manual it does say to disable the telemetry of the redundant receiver. Do these two receivers work the same in that regard?

And also note that the M+ has a very much reduced telemetry transmitting range.

Basically, when using the M+ as a redundant receiver, you can think of it as not much more than an additional antenna. In other words, if the SR8 loses radio control connection with the transmitter, it can still connect through the M+, but in that case, all control and functions are still done by the master SR8, so it would make sense to maintain telemetry features with that receiver.

 

[Flying Dutchman]

Joe, the notion of redundancy depends very much on what you're trying to accomplish. As I pointed out in my post above, using a GR8/M+ combo you won't know whether the primary or redundant Rx is running the show after a signal loss event, and this can have consequences for telemetry and possibly other issues. Like many others, I had made assumptions about redundancy operation (e.g. primary will regain control after the event, telemetry continues), which turned out to be incorrect. A few months ago there was a long discussion about this on RCGroups, where a couple of guys had done very in-depth analysis and experiments on GR8/M+ and similar combo's. If you're interested, look here https://www.rcgroups.com/forums/showthread.php?3602049-Activate-F-Port-on-RX6R-(ACCESS)#post47368009 (around posts 40-50).

If you're flying big power planes close to the ground (e.g. 3D) where a signal dropout could cause quick and disastrous consequences, an M+ backup Rx could save the day. Your primary consideration will be continuous control, and things like loss of telemetry are generally not significant. I would definitely use an M+ (or better), with something like an R8 Pro as the primary. And perhaps an RB to tie them all together.

But I mainly fly full house gliders with GR8's, and want to maintain telemetry (alt, vario, Vbatt, RSSI, etc.) at all times. I'm at an altitude where signal loss of a second or so has limited consequences - it just triggers a Failsafe condition until signal recovery. Startling, but no long term loss of control or associated damage, just bring the plane down and closer. However, if I use an M+ for redundancy, after it has taken over it will NOT let go. Now I'm at "400 ft" without telemetry, getting constant alarms, so I really need to come down to do a power cycle / reset. Annoying.

For my situation (gliders) I've come to the conclusion that proper antenna orientation and placement is critical, and a redundant Rx is more trouble than it's worth. So yes, you can indeed think of an M+ as just an additional antenna, but a very jealous one. I also have a few power planes with S8R's and an SR8, but they're relatively low value foamy ARF's for which I don't feel the need to set up Rx redundancy. My FrSky gear has been rock solid, and so far any control issues generally originated between my ears rather than in the radio link.

 

[Joe Garfield]

Hi,

It says in the second paragraph of the GR8 (and G-RX8) it says: "In addition, any SBUS equipped ACCESS receiver can be connected to the SBUS IN port turning it into a redundant receiver, the GR8 will automatically use the receiver with the best signal." I guess there's the chance that the M+ can always have better signal, which means loss of telemetry. Otherwise, if the receiver isn't automatically switching and then still transmitting the telemetry data that's being recorded, either something is broken or Frsky is completely wrong in their manual.

I think Frsky is confusing with how they write the manuals. In the G-RX8 manual it specifically says redundancy is a "Master-Slave" system, and the slave is just used for redundant control input signal and not full function. In each subsequent manual it gives less and less detail about what the redundancy actually is or does, but it does always say to use SBus for redundancy. I'm sure I also read somewhere that telemetry needed to be disabled in the Slave, but they definitely don't say that in the SR8 or GR8 manuals. Anyway, in a "Master - Slave" setup with no S-port link between the two receivers, there's no way the slave could transmit telemetry data back since that doesn't go through S-bus.

I've never perceived this to be "full receiver" redundancy especially since I started with the G-RX8, but I could see how the manual is misleading people to think you're getting 'full receiver redundancy' if you only looked at the GR8 book.

I also think they REALLY could have been more clear about the fact telemetry is lost in the event of a signal loss between the Master, even though you can still control it through the slave. I now agree that I'd rather not have a redundant receiver - especially with Access telling me when my signal is starting to get low.

 

[2MUCH2DO]

Odd, the main receiver should control the switch back.

Not true acccording to the rdundancy posts for the x20 and my own experience, it will not switch back in access unless the M+ hits an rf alarm. There is also no way to send a recievers native telemetry as an s.port out to another rx (like altimeter or A2 from a gr8). Its an unfortunate hole in frsky redundancy. I actually posted in github describing it, hopeing notes will get back to rf team.

 

[Wayne]

Recent testing of the RB series shows that FrSky does a couple of odd things with the telemetry feed. Not sure why they do this just yet.

 

[Joe Garfield]

I noticed in some receiver manuals, such as R-XSR, it says to "Make sure telemetry is disabled on the slave receiver when the receiver is FrSky X series receiver.," I don't know why this wasn't included in the M+ instructions.

Also, the 'switching to best signal' is not only written in manuals, but also on many product pages across multiple websites/dealers. Hopefully someone is in touch with FrSky if they're finding this not to be true. Either something isn't working right, or maybe the test setup is faulty, tricking the receiver, or maybe data is misinterpreted. For example, if telemetry is NOT turned off on the slave receiver, and the test is using slave telemetry to discern when the switch happens, then it's not really an accurate test if the telemetry is not supposed to be on.

 

[Txmustangflyer]

Huh???

 

[Joe Garfield]

What I’ve learned is that transmit and telemetry are handled separately. When the term "redundancy" is used, traditionally it means transmit signal redundancy, a fail safe that maintains flight control in case the main receiver loses the signal transmitted by the radio.

Telemetry is sent from the receiver to the radio, and since handled separately, does not necessarily stop when the receiver loses the transmitted signal from the radio.

Think of communication like two separate lanes on a highway.

Redundancy is basically like a second antenna, or a detour around a blocked lane on the way to grandma’s. A second receiver is used and connected only via sbus as its only job is to send control information to the master receiver - to go around the road block to grandmas, via sbus. In this case telemetry (the lane back home) is still maintained by the master rx. If there’s a total drop in communication - both lanes blocked - the slave hopefully picks up control, and telemetry from master resumes when signal is regained.

Access can control several receivers at once. This is different from redundancy, because it’s not master-slave but simultaneous control. However I think can be used for ‘redundant telemetry." In this case the second RX is connected by s.port, both are bound and setup as rx 1 and rx 2. Channels 1-8 are assigned to rx 1, and unused channels assigned to rx 2. When telemetry signal from rx 1 fails, it switches to rx 2. So receiver 2 is the detour on the way home, via s.port.

@Flying Dutchman Here is why people are saying the receiver is not automatically choosing the best signal in redundancy:
Redundant control signal receivers, via sbus, should be picking the strongest signal, this is done by the master Rx. Telemetry data via s.port, on the other hand, only changes receivers when the signal is broken. The evidence people are using to determine which receiver is acting as "master receiver" is from telemetry data, which is invalid, because the control signal can constantly be changing between receivers, while telemetry signal stays with the last working receiver. It’s very possible the R8 was receiving and controlling while the M+ was transmitting telemetry.

In @Woodstock1 case, there should be no telemetry from the second receiver if your goal is redundant control signal (via sbus.) Because you had telemetry active on your slave, it grabbed control of the telemetry signal and never let go, as designed, because there was no subsequent loss of telemetry signal.

 

[Wayne]

FrSky's redundant receivers have always been redundant regardless of telemetry. With ACCESS the transmitter can now handle more than one source for the telemetry, thus no more need to kill the telemetry on redundant receivers.

The main receiver controls when it switches over to the redundant receiver for a cleaner signal, the transmitter has no part in this operation.

Hope this helps.

 

[Joe Garfield]

But in that case (leaving telemetry on) you'd have to daisy chain the sensors / s.port so that you get the same readings, but if you connect S.bus only for redundant receiver and leave it's telemetry on, you won't get telemetry data for any sensors other than what's built into the Rx. Correct? So OP either should have turned off telemetry on Rx#2, or connected it via S.port AND Sbus?

 

[Wayne]

No.

If you kick over the the backup receiver, it is used for RC control. sensor telemetry is not needed in this case, aircraft survival is the key. Chances are it will switch back to the main receiver in a second or two anyhow.

With telemetry for both receivers being logged you can compare RSSI.

 

[Txmustangflyer]

You still have to daisy chain the redundant recievers though correct? I'd be using two either M+ or the Archers..One at the tail, one rear mid fuse, then the RX towards front of fuselage.

 

[Wayne]

I don't think you will need 3 receivers, 2 is fine, just place the little guy as far back as possible. FrSky has a very good link quality as it is. Daisy chain - Sort of Sbus in and out connections need to be made between the receivers.

 

[Txmustangflyer]

Ok. When do you expect to have the RS back in?

 

[Wayne]

Hopefully next week.

 

[Txmustangflyer]

Okies