Telemetry problem

[barryt]

I have a normal Taranis Tx (v2.2 international software) and an S6R + MLVSS + 40A Current Sensor installed in my Tiger Moth. The radio is setup to provide low flight battery (14.0v for 2 seconds) and low flight battery cell (3,5v for 2 seconds) voice warnings.

During a gentle flight, using a constant throttle input, I occasionally receive two or three low battery or low cell warnings.

The telemetry data shows a steady decline of flight battery voltage from full charge 16.8v,down to 15v at the end of the flight. Current draw is a steady 16A at cruising speed. At no time during the flight does the flight battery voltage drop or dip below 15v.. At the end of the flight the battery capacity is 50%.

Any idea what is causing these seemingly spurious messages?

Could it have anything to do with the Rx antenna installation. (RSSI never drops below 56)

Is there a site which explains in detail how this telemetry system works?

Thanks for your assistance. Much appreciated.

 

Edited By barryt on 23/07/2020 14:17:30

[Denis Watkins]

Was this model always fitted with an S6R Barry?

Was the model trimmed with stabilisation off?

[barryt]

Hi Dennis. The model was originally fitted with a X8R last year.The CG and trim were sorted using that Rx. The S6R was fitted as an experiment last December. No trimming was required with.stabilisation off and the trim does not change with stabilisation on.

I upgraded my Tx and Rx software during lockdown, We have only recently been allowed to return to flying and this issue is now showing up..

[Bob Cotsford]

I've used the MLVSS for a few years and only get warnings when I whack the throttle open on a battery that's getting near the end of it's life. Do you have another sensor you could try?

[barryt]

Hi Bob, yes, I'll try another sensor tomorrow.

[Denis Watkins]

Posted by barryt on 23/07/2020 15:03:33:

Hi Dennis. The model was originally fitted with a X8R last year.The CG and trim were sorted using that Rx. The S6R was fitted as an experiment last December. No trimming was required with.stabilisation off and the trim does not change with stabilisation on.

I upgraded my Tx and Rx software during lockdown, We have only recently been allowed to return to flying and this issue is now showing up..

Have had this low voltage warning Barry, and even if hardly perceptible, all three axis servos are moving at one time.

Even at 50 feet up, a slight gust will operate 3 servos before you detect any movement and the voltage surely drops

momentarilly. All your descriptions are concise and your margin of 1 volt is very close to give a warning.

I would accept your gear is giving you the set low voltage warning correctly.

Bear in mind it is just a voltage warning that does not take into account capacity, which in your case is 50% left in the pack, which is ample

[Tim Kearsley]

Just a thought Barry, how often does the Taranis log the telemetry data, e.g. every second, every two seconds? I just wonder if a burst of throttle is causing the Voltage to momentarily sag between logging writes. Unlikely I would have thought but, as I say, worth a mention.

Tim.

Having now re-read your original post, I see you mention flying at constant throttle.  Forget I spoke!!

Tim.

 

Edited By Tim Kearsley on 23/07/2020 15:21:16

[Bob Cotsford]

Posted by barryt on 23/07/2020 15:03:33:

....

I upgraded my Tx and Rx software during lockdown, We have only recently been allowed to return to flying and this issue is now showing up..

Was that to RF v2.1? I think there were reports of spurious telemetry warnings with SxRs with the original 2.1 firmware, you might want to check for the latest firmware version as it was re-issued for various receivers.

[Attilio Rausse]

Telemetry warnings reported are 'Telemetry lost' warnings, I have had the same experience as yourself without updating the firmware which I think is due to the ageing of the battery during lockdown even though my batteries were kept at storage voltage. You have a lot of leeway with your settings, maybe increase the 3.5V for 2 secs to 3 or 4 secs you are still within safety margins.

[Bob Cotsford]

Thanks for setting that straight Attilio, I'm still not updating either so have no direct experience. For electric models I tend to set the low cell warnings even lower, usually 3.3v, to reduce the impact of short term voltage drops under load. I still wouldn't expect to see an intermittent drop of 2 seconds duration under a steady throttle state unless the pack was well out of  balance.

Edited By Bob Cotsford on 23/07/2020 16:46:47

[barryt]

Hi all, and thank you for your helpful correspondence. I flew again this morning in quite gusty conditions. I used a different voltage sensor as recommended. My batteries are only a year old, always balance charged and stored at 50%.

All seemed well and I even opened the throttle to complete a loop. No warnings, so I thought the problem was solved. Then just before landing, a low battery warning.

The battery showed 45% capacity on landing. I have just checked the telemetry and while the drop in voltage during the loop is obvious, it again shows a steady decline in voltage level to the lowest point at the end. There are no significant dips anywhere. The data is recorded at 0.2s intervals. At the moment, I can find no evidence that these warnings are real. The flights seem normal and I am landing with plenty of reserve capacity, however the warnings are making me nervous.

This model is very draggy and really only enjoys flying at one (slow) speed. If I open the throttle, the prop noise and whistling in the rigging increases, but not much else. Using a 13x5 prop, I need to loose some altitude to get around a loop!

I guess my next move would be to change the battery and if no improvement, I'll change the Rx. An approaching cold front will delay a retest for a few days. Watch this space.

[Andy J]

Barryt, I had a similar issue regarding of occasional low voltage warnings on my Cularus glider fitted with a FRSky Rx and battery sensor. Found the issue to be the electrical load presented by the motor pulling down the battery voltage for very short duration's when throttle inputs were applied and the motor has to do more work increasing the rpm.

[barryt]

Sorry for the long wait. It's winter in this neck of the woods and opportunities for flying the tiger moth have been few.. It really doesn't like crosswind landings. (perhaps that should read 'I'm not good enough to execute crosswind landings'!)

I'm glad to report that the problem is resolved but not without some intense head scratching. I'll try to keep the explanation short and I hope it might help someone in future.

One additional clue showed up on a subsequent test flight, i.e.'Rx voltage low'. This time it was apparent as a couple of spikes on the telemetry log. This was the first time that the logs actually showed a defect.and, for me, a confirmation that something was actually wrong. The Rx voltage is measured by the S6R and not the MLVSS. I don't have an explanation as to why these spikes showed up in the logs, but the flight battery warnings did not.

My Rx and Servo power comes from the flight battery, via a 6v 5A switch mode regulator.

Having already swapped out the flight battery and receiver, I made up a new wiring harness (in case there was a poor solder joint) and fitted a new regulator. I made up a test lead for my digital multimeter and measured the rx voltage by removing an aileron servo lead and putting the test lead in its place. Unwittingly, I had made thing much harder for myself with this random choice of test point, as you will see.

So much twiddling of Tx sticks and looking for Rx voltage dips on a DMM is not the best setup. An oscilloscope would be more appropriate. The Rx voltage looked rock solid. Eventually, I thought there was a slight dip (only millivolts) while wiggling the aileron stick. (only one aileron servo plugged in). I unplugged that servo and plugged in the other aileron servo to make a comparison. Well it looked the same so I concluded that all was well.

So I disconnected my test lead, inserted both aileron servo leads and powered up the model, (no prop fitted). Lots of Tx stick wiggling clearly showed dips in the Rx voltage shown on the Tx display and accompanying verbal warnings. I pulled out all the servo leads and retested, plugging them in one by one. All was fine until I plugged in an aileron servo which clearly spiked the Rx voltage down. Ah ha, is this it? I disconnected that aileron servo and plugged in the other aileron servo. Same problem!

I still couldn't believe I had a simultaneous failure of both aileron servos so I took them out and checked the linkages and ailerons for free movement. They were fine and there are little air loads to contend with on a tiger moth.

So two new servos fitted and following a successful test flight with no telemetry warnings, and another test flight with all of my original equipment (flight battery, Rx,and Regulator) fitted, I conclude that my problems were caused by early stage failure of both aileron servos.

Both the original servos still function using a servo tester but it is quite clear that they are causing electrical noise when running and they are getting worse.

I can only presume that the electrical noise triggered the early telemetry warnings even though the the warnings themselves did not directly pinpoint the cause of the problem.

Thanks everyone for your assistance, much appreciated.