Honestly I know more people with the T8J that have switched them over to UHF since it was lower cost to start with since going UHF takes over anyways.
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Yeah there are many factors that could change the reason and require an increase or decrease in the Pitch/Roll basic gains.
I'm luck there are 2 adjustment knobs on my 8FGs so basic's are on the left, Atti's are on the right
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Wobbly as in "twitchy" or wondering around?
And in both Atti & GPS modes?
If it's twitchy and wobbling the gains might be too high (Basic gains for Pitch/Roll)
If it's wandering like a bad lock it could be low gains or if in GPS the compass might need to be recalibrated and repositioned for...
When plugged into the Assistant via the USB it should disable the motors/functions and allow you to see the control inputs & programmed functions to verify all is correct such as fail safes, flight modes, stick input...
That would indicate a problem with the S.bus port on the Rx and would see if you can swap it right there infront of the shop to see if that's the case. Using S.bus is a thing of beauty over traditional if you have the option
Good to hear they are going to further investigate as I have been looking over options but without trying another Rx it can't be ruled out.
Anyone in your area have a spare you can test?