Warning X8R RX - do not use with CDI on IC powered 'planes

[Andy J]

Ron

I to had a very similar failure as described on your first post with a brand new X10S LBT and a RX8R Pro on its first use in a mid size 4 stroke plane. Just as I was coming into land at a range of about 20 yards the transmitter announced loss of telemetry followed by the model doing a bunt dive form a height of about 5ft. Luckily damage was minimal so was able to verify the Rx was still functional which was not what I expected to find.

After playing around with the model at home I could repeat the loss of telemetry fault at very close ranges but not the loss of control so tried re-positioning the antennas to ensure they where at 90 deg to each other but this did not help. Whilst doing further checks I put the transmitter into moving all servos mode and I immediately got a string of telemetry warnings, loss of control and voltage warnings.

As I then suspected that the Battery could be the cause I put a DVM on one Rx channel and noted the odd voltage dip so believe the issue was caused by the UBEC as the supply to the device was at least 11.2V. Changing to a 15A UBEC seemed to cure the problem so interested to know Ron if you had a UBEC as the regulated supply to the Rx.

Rather than fly with the 15A UBEC have now changed the Rx power set up to a 6V nimH battery which so far appears not to have the issues of voltage warnings or loss of telemetry, but have yet to test this in the air.

Andy

[Ron Gray]

@Andy - no regulator control as all of my models run with 2s LiFe batteries powering the RX and a separate one for the CDI. On the Sbach I also had an Optipower Ultra Guard RX backup.

Anyway, I’ve now done some more testing and could not reproduce the problem on 3 different X8Rs! So, using the X8R that was in the crashed Sbach I tried changing the aerials from the flat pub type, to the fat and then to the wire type, still no problem. I then recalled that one guy had reported some internal arching within a spark cap which he thought caused a problem so I ran the test again, this time pulling the plug out of the cap in increments until, bingo, I got the telemetry lost warning followed by the RX locking out. If this is the cause then it explains why the fault can vary between installations with the same setup. The next test will be to see which of my RXs this effects - I have X4R, X6R, D8, and the R9 to try out.

Maybe there is some light at the end of the tunnel..........

[Paul Marsh]

Another point, I use one of these on all petrol models, so making sure the power is isolated from the rx. also gives you the option of shutting the engine down, should the servo fail.

Were you using one of these on the Sbach? Be interesting to know if the opto switch did or did not make a difference in this case...

layout of most of my petrol models. Dual switch, opto and rx placed as far away as possible...

[Ron Gray]

Yep, opto switches used on all of my gassers.

[Andy J]

Is anyone having issues with glow motor set-ups?

Not particularly happy with FRSky having just spent £600 on a set up that clearly has issues with electrical noise. Very reluctant to fly my larger models with this gear until the issue is resolved.

When I get into work tomorrow will take a look at the UBEC I had in the model to see if the voltage out is clean or not or if the issue was just that the load caused the voltage to drop.

[Andy J]

Is anyone having issues with glow motor set-ups?

Not particularly happy with FRSky having just spent £600 on a set up that clearly has issues with electrical noise. Very reluctant to fly my larger models with this gear until the issue is resolved.

When I get into work tomorrow will take a look at the UBEC I had in the model to see if the voltage out is clean or not or if the issue was just that the load caused the voltage to drop.

[Peter Christy]

I've been using FrSky gear for 7 or 8 years now, without issue. I started out using D8 and a "hack" module in a "cuddle-box" transmitter. It proved 100% reliable, so I splashed out on a Taranis and started buying "X" series receivers. Recently I bought an X10S.

So far, everything has behaved impeccably on both glow and electric models. The range is excellent. I had one receiver that was DOA, and it was changed immediately and without quibble by T9.

My experience so far has been that it is every bit as reliable as the JR systems that preceded it, but at a fraction of the cost.

That is not to say that I'm doubting that there may be an issue under specific circumstances, as outlined by Ron. But as I pointed out earlier, unless you can reliably replicate the issue on the ground, it is very difficult to produce a fix.

FrSky have previously shown themselves very responsive to customer input - much more so than many established manufacturers. This is why I believe it is important to get to the bottom of this, and why I've been asking Ron to carry out some bench tests to try and establish exactly what it is that triggers the fault condition.

In my experience, there is no issue with either glow or electric operation.

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Pete

[Ron Gray]

In either electric or glow setups I haven’t had a single FrSky issue, it’s only with some of my CDI installations and I’ve been flying with FrSky for approximately 180 hours.

I’ve now carried out further tests with X4R, X6R and L9R RXs and I can make them all lockout although I had to actually touch the L9R with the spark plug to get that one to fail. In all cases the RXs were locked out and did not come back on line until I carried out a power off/on. I haven’t yet been able to check the new R9 RXs but that will be the next test followed by a D series test as I’ve got a couple of those kicking about!.

[Peter Christy]

This is good info, Ron. When you have finished your tests, tell us exactly what it is you did, and the conditions under which the failure occurred.

One other thing that might be worth trying: although conventional wisdom is that it is best to keep the ignition system and radio gear completely isolated from each other, does the fault still occur if you connect the ground (negative) leads of the two systems together?

Ignition interference is funny stuff - like earth loops in audio equipment - and sometimes doing the opposite to what common sense tells you can fix a problem.

Worth checking.

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Pete

[Ron Gray]

Tried the combined ground but it had no effect. Then went back to your previous post and tried the shielding of the RX with foil, or in my case some litho sheet. This worked and I couldn’t get the RX to lock out unless I moved the spark plug to the end of the aerials when it would cause a lockout. So if I shielded everything with the litho plate, no lockout but how practical that would be in an airframe? As a bonus I also got one huge shock as I let the plug touch the litho plate which I was holding! Still haven’t tested the R9 as for some reason I can’t get it to bind.

[Peter Christy]

Now we're getting somewhere, thanks to Ron! It looks as if its a shielding problem, and that should be easy to sort out.

I would suggest trying wrapping some cooking foil around the receiver (making sure the aerials are outside the foil, of course!) or maybe sandwiching the receiver between a couple of sheets of thin carbon fibre. I suspect both will prove effective.

Then do a careful range check to ensure that this has not been affected. It shouldn't affect the range, but it pays to be cautious!

If this fix provides the desired results, we can forward the info to FrSky.

I always said receivers should be in metal cases.......!

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Pete

[Ron Gray]

In summary, none of the X series RXs passed the ignition interference test, but the R series, both 868Mhz R9 and the RX8R PRO plus the D series all passed the tests. Here are some videos I took of the testing:

[Masher]

Thank you very much Ron, excellent work which is much appreciated, shame you had to go through so much grief to get to this point!

I must say that as someone who has spent 40 years in the design of Rx and Tx equipment, I am amazed how resilient these systems are! I am used to screening to the hilt and maximum physical separation so even the X8R is very good in real terms.

Thanks

[Ron Gray]

@Peter - as you will see in my videos, to be 100% sure, the aerials need screening as well, which is not a good idea!

@ Masher - thanks, I actually quite enjoyed the testing but am still amazed that the X series RXs are so intolerant to external interference. Having said that, they are still excellent value for money and I will continue to use them, just not in CDI equipped 'planes!

Edited By Ron Gray on 06/05/2019 17:58:23

[Peter Christy]

Hi Ron,

I won't have time to view all the videos tonight - or even maybe tomorrow - but I will have a good look at what you have done.

All my X8s and 6s are currently buried deep in fuselages, and not very accessible, but I'll see if I can get one out over the next day or two. I don't have a CDI lying around (again, mine is in a model!), but I do have a piezo gas lighter that might do the trick.

Thanks for your excellent work on this, and also for publicising it. I was considering removing the DSM-2 Rx from my scale heli (Rxcel ignition) and replacing it with a FrSky, but I think I'll wait pending further investigations.

After all, if it ain't broke, don't fix it!

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Pete

[Andy J]

Ron when you made a litho plate screen for the Rx, did you connect it to the 0V of the Rx as would have thought that should have improved its screening properties?

Also I was advised by RCGroups guys to upgrade my FrSky SW on both the Tx and Rx. Did that for the Tx but was completely lost on what item to purchase to do this on the Rx.

Andy

[Ron Gray]

I only used the litho plate to test to see if it made a difference, which it did, but I didn’t take it any further as I’ve no plans to use it.

Regarding upgrading firmware on the RX, I find it easier to do this via the TX and the pins inside the module housing. I am on the latest firmware.

[Andy J]

So how you check the Rx SW standard Ron?

[Ron Gray]

@Andy - if you mean the RX firmware, then this is no way to check it. Best bet is to download the latest version, copy it to the Firmware folder on your TX, connect the RX to the bottom 3 pins in the module bay (the cable connections to the pins in the bay are in a different order to those on the RX) then use the TX to flash the RX with the firmware.

[Peter Robinson 9]

I have just read through the forum regarding 8xr rx problems. just a few thoughts I am flying various petrol aircraft using dle engines. On my setups I always use two Rxs bound together and seperated inside the aircraft to give me more diversity with regard to antenna's and reception. I used last year two x8r and never missed a beat ? I had maybe once a day a telementry losed but carried on asuming that I had rx switched over and never worried about it.

But from now on I will be purchasing the pro just to make sure but still run two rx maybe x8r pro and a 6xr together. Just a thought that with the size and cost of models it may be well worth having two rx's.

My other setup is 8xr (old) with x6r running sbus into the redudancy bus uinit to give me 16ch and a ch for each surface on giant u-can do 3D and have no problems except the ocassional telementry loss.

[Peter Christy]

Hi Ron,

I've now had chance to review your tests, and thanks for a very thorough and effective demonstration of the problem!

Could I ask you to try one more thing? Can you repeat the test on the most susceptible receiver (the X8R that crashed, from your videos), but using a standard 4-cell NiMh pack as a supply, instead of the LiPo / regulator setup?

Again, I'm trying to establish just how the interference is breaking through - whether it is pick up in the power supply rails or directly into the processor. This test may (or may not!) give a different result.

Cheers,

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Pete

[Ron Gray]

@PeterR - as I see it, the signal is not getting lost therefore I don't think that having a redundancy RX in place would help, but I will test that too.

@PeterC - I will test that setup tomorrow when I'm back home.

[Peter Robinson 9]

Hi Ron that would be interesting, all i'm doing is making sure I get a good rx connection. When I flew last week I got telementry loss I did not check the rx (8 pro with X6r) for lockout, but will do this weekend and see the led status on both rx's on the ground. A quick question what should you set the telementry values and rssi values on frsky tx menu as a default for warnings?

Peter R

[Peter Christy]

Ron: Should have added - use a decent 4-cell pack, and plug it straight in to the receiver, not via a switch.

I'm trying to eliminate as many variables as possible!

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Pete

[Ron Gray]

@PeterR - I think I get RSSI warnings when less than 35 or 40, I will have to check. I didn't use to be too concerned about 'telemetry lost' warnings as it used to be followed within a split second by 'telemetry recovered' and this mainly happened when the TX was too close to the RX. Having now experienced RX lockout after 'telemetry lost' warnings I am now listening out for it all the time I'm flying!

@PeterC - no problem, switches can be a pain (and a cause of crashes!) so will test without on in the setup.

I've also got Orange and Lemon RXs which I used to use on basic foamies with a DSM module in the TX so plan to see if they are susceptible to the RF noise too.