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RX8R pro with Uni-FW: sporadic servo twitching on channel 8

C

Christoph_D

New User
Hello,
After the hurdles of binding and activating the RX8R pro at a colleague's have been overcome, a new "phenomenon" has come to light.
On channel 8 (slot 8) a connected servo twitches sporadically. The twitching (very short, a few degrees of deflection) sometimes occurs after 10 minutes, sometimes 3 times in 5 minutes.
With a motor controller (YGE 65) connected to channel 8, the motor even starts up very briefly (turns a few degrees).
The behaviour could be tested/ seen with 2 different RX8R pro receivers.

System:
Horus X12S (latest V2LBT FW)
Receiver RX8R pro with UniSW Vers. 57
Power supply with 7 Volt BEC or 2S LiIo with >7,5 Volt
The transmitter was also tested with a completely new model memory with only switch SE mixed to channel 8 with 100%.

If you "map" channel 8 to slot 6 in the RX using mapping, the "appearance" moves with it. A second servo on slot 8, to which channel 6 is assigned, is quiet. No twitching. All other channel outputs are also quiet. This phenomenon did not exist with the original FrSky FW, or could not be observed before.

During testing, the number of CRC errors was also observed using LUA script. The counter sometimes showed an increase in the value after the servo twitch. But not every increase of the counter leads to a servo twitch. The value of the counter was only between 20 and 30 after about 10 minutes.

Unfortunately, we have no way of logging the "pulse output".

Can someone check this with their system and an RX8R pro?

With an X6R (don't have another receiver at the moment) the problem does not exist (channel 8 mapped to slot 6).

sorry for the long text

Regards
Christoph

Translated with www.DeepL.com/Translator (free version)
 
I've run a test for a few minutes, first with a X9Lite with ISRM module in ACCST mode, then with a RM TX16S with multiprotocol module using FrSky V2 LBT.
The X9Lite was solid with no CRC errors and no twitching.
The TX16S ended with 722 CRC errors but still no twitching of the servo.
I only have the one RX8R-PRO to use for testing.

This does seem to be a radio transmission problem given the twitch is on a channel not a servo output.

Can you test with a different transmitter?

Anyone else able to test for this problem?

Mike
 
I've tried several transmitters and now have my prototype X9D+ where I see channel 8 with the symptom you describe. I've captured a bad pulse on my oscilloscope several times.
Just running a test on a X8R, not seen a problem there so far, so I may be able to debug this on the RX8R-PRO.

Mike
 
I've just posted a version 59 for the RX8R-PRO. This should fix the servo twitch problem (which is specific to the RX8R-PRO).

For the technical, the processor on the RX8R-PRO has a 32-bit timer, rather than a 16-bit timer, which is the one I use to generate the servo pulses. The timer is set to only count 16-bits. There was an occasional time when a compare value was written to the timer that exceeds 16-bits, although this value was subsequently written corrected. This caused an (undocumented) compare interrupt immediately, resulting in the shortest pulse of the 4 pulses on servo outputs 6,7,8 and SBUS to start about 940uS earlier than it should start.
The fix is to make sure only 16-bit compare values are written.

I had been testing and seen several occasions in ten minutes where a servo pulse was too long. With V59, I tested for over 20 minutes and there were no errors.

Mike
 
Problem now fixed on my RX on CH7 by flashing with V59.
Thanks for the superb diagnostic work and fix Mike!
Steve.
 
Just now trying my first UNI installed RX8R Pro and having the twitching on several channels. Tx is X10S Express. I guess I need to do some reading on how to flash? I'm all too familiar with flashing the FrSky firmare, I thought UNI was supposed to be easier? ;)
I have video of the issue but don't see a way to upload here. Is it of any use? I could upload to Vimeo, etc. if helpful.
 
Last edited:
johnfv said:
Just now trying my first UNI installed RX8R Pro and having the twitching on several channels. Tx is X10S Express. I guess I need to do some reading on how to flash? I'm all to familiar with flashing the FrSky firmare, I thought UNI was supposed to be easier? ;)
I have video of the issue but don't see a way to upload here. Is it of any use? I could upload to Vimeo, etc. if helpful.
Click to expand...
Not sure if my twitching is only channels 6/7/8. I believe I saw it on both my elevator channels (3/7) but I may be confused about which. I also had it on aileron but that could have been 6. The video I captured IS channel 7 (left elevator).

I was planning to maiden this plane (78" Extra NG from Extreme Flight) today, Saturday. As best I can tell, if I update the firmware it must be activated via email (which won't be answered until Monday)? Not clear to me if an already activated (installed by Aloft) Rx can be updated without another activation.

Fortunately I have another (non UNI) RX8R Pro that I can use, I've spent quite a bit of time on this issue already. I do appreciate being able to find clear documentation about the issue I'm experiencing relatively easily; THANKS all for that.
 
Last edited:
The twitching was fixed in V59 so if you have an earlier version you do need to update.
Flashing is performed exactly the same way as with FrSky firmware.
If the Rx is already activated, then you simply flash the update, it will remain activated.

Mike
 
MikeB said:
The twitching was fixed in V59 so if you have an earlier version you do need to update.
Flashing is performed exactly the same way as with FrSky firmware.
If the Rx is already activated, then you simply flash the update, it will remain activated.

Mike
Click to expand...
Thanks for the reply. I already swapped out the Rx with another but good to know that I can simply update the one with issue. Again, thanks!
 
I finally got around to flashing my RX8R Pro., thanks again.
One question: I'm guessing that a new RX8R Pro from Aloft will ship with V59?
Also, just double checking: any caveats about using a UNI Rx with a redundant NON-UNI Rx (XM+, RXSR, etc>). From searching here it seems it's OK?
 
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