Help me brainstorm - T8SG-v2 and LemonRX

[FrankFly]

I've been crashing planes and need to find where the issue is. Here is my setup.

I have 2 Jumper T8SG, v2 because my grandson and I fly together. Just to keep track, one is yellow, the other the "carbon" color. Both have been running great for nearly a year.

I have 6 currently operational airframes, all Flite Test or derivatives of their designs, all containing LemonRX stabilizer-plus with diversity antennae. I have 'failsafe' set on each to cut motor, go to autolevel mode with slight nose up and a fair amount of rudder.

I had been losing control at times. I determined that it was when using the carbon controller on any aircraft. I found the SMA connector loose so I opened the controller and found the ground pins had broken so I soldered the connector shell to the ground plane. I also noticed the antenna was loose at the flex joint so I replaced it with another antenna. All this under the assumption that I was losing output power, therefore, range.

I did a range test having the wife walk up the street while I walked down. She was holding one of the planes and I was carrying the controller pushing back and forth rhythmically on the aileron stick. She told me over cell phone when the control began to skip. I did the test with both the 'repaired' carbon controller and the yellow one. The skipping started at almost the same distance (within 20 feet.) I'm assuming problem is solved.

Here's where it gets strange. I take the controllers and some planes out to fly. My first three short flights with the carbon controller resulted in the motor stopping within a minute. I still had all other control to turn back and glide it to landing. On the fourth flight, flying fine when suddenly the aircraft rolled inverted, nosed down and continued rolling - corkscrewing to a vertical impact.

On all those flights, I never got more than 120 feet away, if that. I'm thinking it's not a reduced range issue, as the LemonRX never went to failsafe behavior. It seems like I lost some channels but not others. Another data point: I connected the carbon controller to a flight simulator using PPM and it controls fine.

I'm not sure where to go next. I don't really understand the transmitted protocols, so I can't envision where the controls can get selectively lost.

Ideas?

 

[BATTLEAXE]

In your failsafe mode why do you induce hard rudder with a nose up? That put you straight into the tip stall and corkscrew with a heavy impact at the end, like what happened. Although it is a very noticeable failsafe I would think getting it down softly would be the objective. But that's just me

 

[FrankFly]

In your failsafe mode why do you induce hard rudder with a nose up? That put you straight into the tip stall and corkscrew with a heavy impact at the end, like what happened. Although it is a very noticeable failsafe I would think getting it down softly would be the objective. But that's just me

Thanks for your reply. Good question. I used to set failsafe to autolevel, motor off and neutral controls. When I tested it a few times by turning off the transmitter in flight, the plane glided down fairly steeply. I played with dropping throttle while up high and found that a touch of nose up gave me a nice, gentle, slow glide, although a long one. So I tried to emulate that amount of nose up and some (not hard) rudder to keep the plane from leaving the area, when setting the failsafe mode.

 

[LitterBug]

I recently had the coax break at the bend on my DX8. It was sometimes erratic but never had any fail safes leading up to the final rip in two. After it split, it was obvious there was a range issue. I would double and triple check the antenna, especially at the bend.

I tend to hold my radio different during range checks than when flying. This can set the antenna bend into a different angle and possibly make it behave fine during a test, but fail when in a different bend. Maybe range test with the antenna at different angles to see if it gets different results.

Cheers!
LitterBug

 

[FrankFly]

I recently had the coax break at the bend on my DX8. It was sometimes erratic but never had any fail safes leading up to the final rip in two. After it split, it was obvious there was a range issue. I would double and triple check the antenna, especially at the bend.

I tend to hold my radio different during range checks than when flying. This can set the antenna bend into a different angle and possibly make it behave fine during a test, but fail when in a different bend. Maybe range test with the antenna at different angles to see if it gets different results.

Cheers!
LitterBug

Very good points. Yes, my antenna definitely broke and I replaced it with another. I actually tried 2, 2.4 Ghz antennae, one twice as long as the other. Both seemed to give the same range.

I was facing away for a while doing the range tests, but finally started walking backwards down the street. I'm sure a strange sight for the neighbors. Walking backward, flipping the controls and a cell phone on my ear.

I would like to find a way to measure RF power output without an expensive frequency analyzer. The T8SG does have a scanner mode, but most places there is so much wifi and other 2.4 Ghz going on, I can't discern the other transmitter. I still think I have a range issue and the receivers get flaky with a fringe-y signal.

 

[PsyBorg]

Just like video transmitters burning up with out antennas connected under power I am leaning towards the fact you may have damaged the transmitter at the out put amplifier stage. My guess is it will be intermittent due to heat build up. So on hotter or more humid days you will see more adverse issues.

The fact that it happens AFTER the amount of time it took to do range testing leads me further down this path as it works fine until it starts hitting a heat range that effects it.

 

[LitterBug]

If this is a removable antenna, Double check that the right polarity socket is on the antenna. Either the radio or the antenna should have a pin in the connector. If neither side does, that is probably the problem. On mine, the pin is on the TX side, not the antenna.

So my TX has an RP-SMA Female, and my antenna has a RP-SMA Maile.

LB

 

[FrankFly]

Just like video transmitters burning up with out antennas connected under power I am leaning towards the fact you may have damaged the transmitter at the out put amplifier stage. My guess is it will be intermittent due to heat build up. So on hotter or more humid days you will see more adverse issues.

The fact that it happens AFTER the amount of time it took to do range testing leads me further down this path as it works fine until it starts hitting a heat range that effects it.

Thank you for that observation. You might have hit on it. I know that the antenna was broken , and that the ground pins of the sma connector were broken. So while each of those conditions existed, the RF amplifier might have been trying to work into no load. And living in South Texas where the temperatures this time of year run near or over 100F, temperature could certainly be an issue.

It appears that the (US) RF transmitter is on a daughter-card which also contains the antenna connector. I'll see if that part is available from the manufacturer (Jumper). I'm not sure if the virus is a factor, but I've not had them return my email.

 

[FrankFly]

If this is a removable antenna, Double check that the right polarity socket is on the antenna. Either the radio or the antenna should have a pin in the connector. If neither side does, that is probably the problem. On mine, the pin is on the TX side, not the antenna.
View attachment 174312

So my TX has an RP-SMA Female, and my antenna has a RP-SMA Maile.

LB

Thanks for that detail, and the photos. It's hard to believe that anyone would make two different reversed versions of the same connector.
I had checked that when I ordered the replacement antennae. The controller is normal SMA -- male threads and female pin. The antenna had female threads and male pin.

 

[FrankFly]

More of the same. Took the carbon T8SGv2 with the original antenna from the yellow T8SGv2 out with my oldest tiny trainer to eliminate the replacement antennae as the source of the issues. First flight the motor throttled down at 1:10 into the flight. Next flight, it flew about 3 minutes then lost power. I flicked the throttle control to minimum and right back and the power came back. But in another 20 seconds or so, the power dropped and did not come back when cycling the control. While it was gliding in to a runway landing, I lost all control about 5 feet above the ground and it settled into the weeds.

I suspect the 'Built in 4 in 1 RF Module' which is the small circuit board the sma connector is attached to, or the connection between that board and the sma connector. The board is $29.00 plus almost $10.00 shipping on Ali Express. that's approaching nearly half the price of a new controller, and not guaranteed to be the fix.

I ordered some solder-mount right-angle sma connectors (10 for about $7) and will try to replace the antenna connector. Very small work on a multi-layer PCB board, so no guarantee I can successfully replace it. If that doesn't work, it seems best to go straight for another T8SGv2 plus rather than spend half its cost on a board that may fix it or not. The finicky controller can be a dedicated simulator controller in that case.

 

[FrankFly]

Final on this thread probably.
I replaced the connector on the transmitter board and took it out with the original antenna from the other T8SG. I still had problems with it so I ordered another transmitter and relegated the problematic one to use with Phoenix RC Simulator, where it works fine. I was told on another forum that the RadioMaster transmitter is identical to the Jumper, so I could have saved $30. Good information a day late.

Thanks for everyone's help.

 

[bbyrne]

More of the same. Took the carbon T8SGv2 with the original antenna from the yellow T8SGv2 out with my oldest tiny trainer to eliminate the replacement antennae as the source of the issues. First flight the motor throttled down at 1:10 into the flight. Next flight, it flew about 3 minutes then lost power. I flicked the throttle control to minimum and right back and the power came back. But in another 20 seconds or so, the power dropped and did not come back when cycling the control. While it was gliding in to a runway landing, I lost all control about 5 feet above the ground and it settled into the weeds.

I suspect the 'Built in 4 in 1 RF Module' which is the small circuit board the sma connector is attached to, or the connection between that board and the sma connector. The board is $29.00 plus almost $10.00 shipping on Ali Express. that's approaching nearly half the price of a new controller, and not guaranteed to be the fix.

I ordered some solder-mount right-angle sma connectors (10 for about $7) and will try to replace the antenna connector. Very small work on a multi-layer PCB board, so no guarantee I can successfully replace it. If that doesn't work, it seems best to go straight for another T8SGv2 plus rather than spend half its cost on a board that may fix it or not. The finicky controller can be a dedicated simulator controller in that case.

Great that the problem was solved! Could you please share where you ordered the right-angle SMA connectors from? I'm having a similar issue and having some difficulty finding those connectors. Thanks in advance!

 

[FrankFly]

Great that the problem was solved! Could you please share where you ordered the right-angle SMA connectors from? I'm having a similar issue and having some difficulty finding those connectors. Thanks in advance!

Great that the problem was solved! Could you please share where you ordered the right-angle SMA connectors from? I'm having a similar issue and having some difficulty finding those connectors. Thanks in advance!

PM me and I'll send you some. I have 9 left over.

 

[danskis]

Does your T8 use Deviation firmware? If so it is different from the Radiomaster which uses OpenTX - a much more user friendly firmware.

 

[FrankFly]

Does your T8 use Deviation firmware? If so it is different from the Radiomaster which uses OpenTX - a much more user friendly firmware.

My T8SG has deviation firmware. I'm pretty satisfied after investing some time on it, I haven't found anything I can't do.

I haven't played with OpenTX, but have read from some that it's less intuitive. Apparently you don't agree with them.

Have you used both? What are your observations?

I'm not sure if Deviation will be supported much longer.

 

[danskis]

The main difference I've found is the lack of support - both online (youtube, threads) and at the field. OpenTX has been much more widely accepted so there is more support. After my Jumper T8 sent 2 planes into the ground I gave up on it.