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My S8R's ch6 has gone AWOL


Allan Bennett
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Ever since I switched to FrSky radios three years ago my TwinStar has been equipped with an S8R receiver -- not that it needed stabilisation, but I thought it would be a good platform to try out the system.  After two years or so successful flying I upgraded my equipment to FrSky v2 firmware, and shortly afterwards I crashed my TwinStar.  Thinking it was the receiver's fault (it later proved to be a trannie problem), when I'd repaired the aircraft I reinstalled the v2 S8R after reprogramming it to disable the stabilisation features.  It's flown like that for several months without mishap (after a new RF board in my trannie), so I decided to re-anable the stabilisation features last week.  That was simply a matter of going through the whole setup process again using FrSky's FreeLink program, and ticking the 'SXR enable' box.  After self-calibration, self-levelling was seen to be working in the correct direction (ailerons, elevator, and rudder), so I didn't check anything else.

 

When I took the model to the field last weekend for its first test flight in v2 stabilisation mode, my starboard engine wouldn't run.  I run it off ch6 so that I can have throttle differential for ground manouvering.  Back home I found that the problem was simply that my S8R's channel 6 was no longer working, and reprogramming my Taranis to use channel 8 for the second throttle has cured the problem.  Anyone had a similar experience, or thoughts about how it might have happened?  There's nothing in the FreeLink programming process that affects channel 6 so far as I can see.  If there's no obvious answer, should I continue to trust a receiver that's seemingly had one channel fail all by itself?

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Checks I would do in order Allan...

  1. Check TX outputs - is it outputting to channel 6? If yes....
  2. Rebind a new RX to that model, plug in a servo on channel 6, and check it is receiving the signal from the TX correctly. If that works...
  3. Start reading! This thread from Scott Page has a lot of resources to look at, as does this one on RCGroups. This post might help, looks like you may need to go into the config and tick Aux 1 and 2... The Frsky instructions are here too. 

One obvious point looking at the manual... Frsky do not recommend using channel 6 for anything other than the second elevator, as it is a stabilised output. Having your second throttle on channel 8 therefore probably makes sense anyway, but I agree you still need to troubleshoot the missing Ch6 before flying...

 

image.png.ed017a5a6bf8de68e425551842230b0c.png

 

Edited by MattyB
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Yes MattyB, binding another receiver to that model setting in my trannie was going to be my next step, to see how channel 6 behaves.  In fact, rather than playing with another receiver, reprogramming the S8R as non-stabilised again could determine whether the receiver's channel 6 is working.

 

I've always been a bit confused about the Aux 1 and 2 settings in the SxR setup, and can't remember whether I ticked them this time.  But since FrSky designate CH6 for ELE2, that's probably something everything to do with my issue since it's only started when I reprogrammed the receiver.

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1 hour ago, Denis Watkins said:

It is clear in the chart Allan, and I know you have seen it.

CH7 and CH8 can be and are User Defined

CH6 is already assigned as you know

The receiver is doing what it can do

 

Not really. The instructions show that is the default setup out of the box, but they can be removed from the set of stabilised channels through configuration. Unfortunately that config process is notoriously tricky with the S series RXs, though these days it is supposed to be somewhat easier with the mobile apps and bluetooth capability. 

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9 hours ago, Denis Watkins said:

It is clear in the chart Allan, and I know you have seen it.

CH7 and CH8 can be and are User Defined

CH6 is already assigned as you know

The receiver is doing what it can do

It's as clear as mud to me!  Well, not quite, now that MattyB has refreshed my memory with his snapshot of the instructions, I can see the info about Ch6.  It's significance was abviously missed by me in the past because with v1 firmware it was running in stabilised mode for a couple of years with the second throttle on Ch6.  Anyway, I'll be keeping Thr2 on Ch8 from now on, but I'll check in unstabilised mode first to ensure that Ch6 is still working, and then pay more attention to my stabilised programming to make sure I've dealt with Aux1 and Aux2 correctly.

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14 hours ago, MattyB said:

 

Not really. The instructions show that is the default setup out of the box, but they can be removed from the set of stabilised channels through configuration. Unfortunately that config process is notoriously tricky with the S series RXs, though these days it is supposed to be somewhat easier with the mobile apps and bluetooth capability. 

I use the SXR tools in both OpenTX and Ethos to configure S series receivers and don't find it that hard to do.  Bind the receiver, keep it at arms length from the tx, run the LUA script from the Tools menu and give the receiver time to save each step of the configuration.  Ch 5 and 6 can be set to Ail2/Ele2 or Aux5/6 in which case, as Matty points out, they are not affected by the gyros.

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LUA scripts are still a mystery to me, and I didn't realise that OTX was able to configure an SXR receiver.  The receiver is well embedded in the model, so I don't want to have to take it out again to do the 4-position calibration, so I think that using FreeLink and just modifying the present setup by ticking/unticking a couple of boxes might be the safest way.  I didn't have a chance today because of family.  Will try tomorrow.

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You should only need to do the 4-point calibration once (actually 6-point, IIRC). Once done it should be done for all time, unless (perhaps) you change the firmware. What does need to be re-done is the "in model" calibration, for each installation (which way up the receiver is mounted, etc). Once done, its best to disable the "calibration" switch on the Tx so you don't hit it accidentally.

 

I don't have any of these receivers, but I have helped a fellow club member set up his. Haven't done it for a while, so I stand to be corrected, but I'm pretty sure the above is correct.

 

And yes, its a LOT easier to do it from the scripts in the Tx!

 

--

Pete

 

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Sorted!

 

Yes, you're right Pete, it is a 6-point calibration.  As for the in-model calibration, the switch has to pass through its mid point 3 times to start the calibration, so accidental activation is unlikely.  As it happens I've programmed mine so it only works when my throttle-cut switch is cut.

 

Back to the original issue; I temporarily reprogrammed my trannie with Ch6 following the throttle channel, and then used FreeLink to alter the S8R configuration -- I ticked the Aux1 and Aux2 boxes, and unticked the Quick Mode box.  With that, a servo plugged into Ch6 then moved with my throttle stick.  Problem solved, but I'll be keeping Ch8 as my Thr2 channel from now on.

 

One thing is still confusing me though; with Aux1 and Aux2 unticked, Ch6 was not responding to trannie input, but with them ticked it does respond but, as has been pointed out earlier by MattyB, it should be in stabilisation mode.  If that's correct, it means that my starboard motor's rpm must have been varying slightly whenever I flew in stabilised or self-levelling mode, something I never noticed ?

 

 

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One final thought Allan: IIRC there are two relevant scripts. One does the initial (6-point) calibration. The other does the "in-model" set-up. Once you've done the 6-point one, you should not need to do it again, so it should be safe to just do the "In-model" setup.

 

The scripts lead you by the hand through the process, though my friends system uses Archer receivers rather than just the ACSST (D-16) mode, so there may be some differences.

 

On his system, it was also possible to re-assign the internal receiver channel allocation from the Tx. This was necessary on his system, as he was using all 10 channels on that model, and the stabiliser program was trying to use channels with physical sockets on the receiver. By re-programming the receiver we were able to get all 10 physical outputs for servos, and the stabiliser switching on channels that had no physical output (11-16).

 

Sounds complex, but once you've done it once, its quite easy!

 

I'm wondering if this had something to do with your odd behaviour with Ch6 and the Aux channels?

 

--

Pete

 

Edited by Peter Christy
Clarification
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It takes some getting used to, especially as it's only once in a blue moon that I need to go through this!  Anyway, it's working according to ground checks in my workshop.  I mis-wrote in my previous post (and can't seem to edit it once someone's read it) that I'd unchecked the Quick Mode box; I actually have Aux1, Aux2, and Quick Mode all checked, and I've saved it on my laptop so I should be able to remember next time.

 

Reading the instructions once again, my understanding now is that ticking Aux1 and Aux2 disconnects Ch5 and Ch6 from the SxR stabilisation system.  So, to my way of thinking, that doesn't explain why my Ch6 appeared to have no output at all -- I would have expected it to basically follow the throttle channel, with slight variations in response to stabilisation.

 

With my S8R, Peter, I have all 8 channels available as PWM outputs, and the stabilisation control is done through Ch9 to Ch12 by default.  Sounds like that't the same as your friend's Archer receiver, so it's good that he was able to reassign channels to get 1-10 for the model iteself.

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Yes, that's right! The re-assigning of the channels wasn't done as part of the stabilisation setup. As I recall, it involved going to the radio setup menu, scrolling down to the receiver, highlighting it and hitting enter. This brought up another menu, where one of the options allowed you to re-assign a physical output to a different channel. Its a bit like the way its possible to re-assign the channel order in the Tx, if you don't want to go with the default, except this is working in the receiver. This enables you to switch the stab channels up into the 11-16 region, out of harm's way!

 

Not sure why they didn't do that as a default, it would have made more sense...!

 

--

Pete

 

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