I have a JR 10x transmitter, which came with the JR R1000DS (dual conversion) PCM receiver.

I lost a beautiful patternship that I built from scratch, approximately 3 years ago, when it went into failsafe, just as it came into land. Of course, after the crash, everything worked. Didn't even break a prop, but totally killed the 'plane, after only 15 flights.

So I have been flying an Aresti III, with a Hitec receiver. A few of the local "pattern boys" suggested that I should go back to a PCM receiver.
After some further discussion on their part, we asertained, that when I had crashed 3 years ago, I was using a crystal that was a NON genuine JR crystal, as at that time in Australia, the particular channel I wanted, wasn't available, and that some crystals had been cut locally. The crystal in question, definitely DIDN'T have the usual JR "printed info" on the side of the crystal, but was stamped on the side of the case. I have a different channel, which I know for sure is a genuine JR, as it does have the printed info on the crystal.
Another reason put down to cause the crash, was I had the receiver antenna inside the fuselage. Now, remember, this is an ALL WOOD plane, with NO carbon fibre, with the elevator servo wires as far as possible from the Rx antenna.

Step forward to 2 months ago. Armed with the info about the no genuine/versus genuine JR crystal, I put the R1000DS, complete with the GENUINE JR crystal, on frequency 36.390, (which is what I fly EVERYTHING I have on) into my trainer. ALL my other plane's have Hitec PPM receivers. I flew it to for probably 30 flights no problems, no hint of a shut down.

Step forward to last week. I finally finished another beautiful all wood patternship. I did the JR range test, I was able to get over 85 paces from the plane, as per what is on JR's site on pcm range testing.

And just for added insurance, I had the Rx antenna OUTSIDE the plane.
I put the R1000DS, with it's genuine crystal, and off I went.

All went well.

For nine flights.

Then today, without warning, into failsafe. Of course totally destroying the plane, and as the ground is so hard (nearly summer here) even though the engine was at idle, broke the crank, bent the hatori header, destroyed the pipe (ALL NEW!!!), crumpled the intake manifold, bent the wing tube, and basically destroyed everything forward of the trailing edge of the wing. Strangely, just to add insult, one wing is almost untouched, just enough to make you think twice before jumping on it and hurling it into the dumpster.

AND of course, plug it all back together, everything works.

So why use PCM? I know I will send the receiver back, and will then be politley told there is nothing wrong with it.
Somebody is sure to say, batteries, or switch harness, but all good quality, and all test out ok.

The only thing to fix is to put a 10 pound sledge hammer through the RX. BUT I have 2 649s single conversion PCM's? Do I dare trust them?

Needless to say, it's put a very bad feeling about building another patternship. It's just about taken everything out that I have left for pattern, and certainly will take a long time to get over, let alone save up to buy the bits necessary.

So all you experienced guys, convince me why I should EVER use a JR PCM receiver again. And WHAT to do with my649s rx's (my feeling is, use the SLEDGE HAMMER).

Thoughts appreciated, but keep it practical please.

.
.
.
Sounds like you have some serious radio interference at your field. Lockout wasn't the cause of your crashes, it was the symptom. If you had a PPM system, who knows what would have happened - but you still would have lost control.
.
.
.
Perhaps you need to look at the DX7 system that is on 2.4 GHz. . . . Another option for 72Mhz is the Berg or FMA receivers with digital signal processing. I know the FMA system has IR sensors that will level your wings and nose if it loses signal and goes into failsafe.
.
.
.

You could still suspect the crystal. If it ran OK in the trainer there may certian vibrations or hamonics coming from the pattern type of setup your running. Causing either reciever or crystal failure. Since its going into PCM lockup I would suspect the crystal or radio inerference. You might even have a battery cell going bad on the receiver end or a transmitter issue.

Gosh... the more I think about it the more things COULD have gone wrong.

Dont yah just luv this hobby?


Hope you find the problem... good luck.

Wayne G.

I know I'll prolly get flamed for this ,but a good flying friend lost his H-9 260 this summer due to a hit,coming in on final.We had talked about going to PCM before this and I explained to him he needed to test the plane out with a PPM first then switch to a PCM . His idea was, if the failsafe is set correctly you may not loose the plane !WRONG! I did my best to tell him a plane can go into failsafe mode at any time and in any position if hit with enough interference. Some people say a PCM won't mask interference while others say it will.
If you maybe would have used a PPM to ground check with,you may have found out there was a problem before hand and would have saved your plane .
Sorry for your loss of what sounds like 2 nice planes and some spendy equipment.

Thanks guys for replys,
Toymaker,
different crystals on each crash.

Of course, I don't know whether the Transmitter is at fault, except to say I use on all my other sport planes, on PPM.

klhoard
We are on 36 mhz here. But the new spectrums are on their way. I have used a 649 pcm in my spark ignition plane with no probs,... so not sure about interference at our field. Too many guys fly there without problems.

So, if I ever get motivated to build another pattership, it will have a PPM receiver.

There was ABSOLUTELY no warning. working perfectly, then into fail safe.
Ground range test, with the engine running, was well over 85 large paces.

The only thing I have thought of, this receiver has only ever been in these two patternships (apart from the trainer test). It's possible it was always faulty. I bet I won't get any satisfaction from the local importer though.

I would have rather seen the glitching, if there was a real problem. I might have seen it and been able to find out what the problem was. With just being locked out on PCM, I got no warrning, just a lovely pile of bits and a severely damaged engine.

I really am wondering what the good of PCM is?
Surely to see a glitch is better than to just go into failsafe and crash!!!!!.

I don't think PCM is your problem. Have you had the TX checked out? Is it possible that the battery is dislodging from the back of the 10X? This has been known to happen with 10X transmitters. I had it happen once but luckily the plane was still on the ground. Open the battery door and push the battery in and see if slides in further.

Keith Black

Were you getting any glitches when using the PPM Hitec reciever?

If Yes, then it probably was an interference related problem.

If No, then I would say it was a reciever problem.

Remember, PCM is there to make it safe for people, not to save RC aeroplanes from crashing.

I fly in Brisbane on 36Mhz. I have had countless thousands of flights on PCM without a problem in pattern models. The PCM technology has been around for a long time and is sound its probably your equipment which isnt. I would definetly put the sledge hammer to that reciever. I am sure that the cost of a replacemnt reciever is minimal compare to your loss across 2 models.

Peter

.
.
.
Now that I've re-read your posts closer. . . I agree with applying the sledgehammer to this receiver. . . .
.
.
.

Hi Peter,
no glitches with the PPM.
The pain is, I only went back to the PCM because the "pattern experts" all told me I should "really be using pcm", for what ever reason.

Yes, the receiver will be reduced to less than 1mm high shortly, unless I can get some help from the importer.
But you know the story, send it back, and always it comes back, with a "no problems found report" I've $3000 worth of dead planes to say otherwise.

It's actually really tarnished my view of JR products. Seems silly to spend all that money on a JR system, and then use a Hitec PPM receiver, because that is the only thing you feel confident in.

Thanks for help.

No problem

I wont get into a debate about JR /Futaba and whatever.

I personally use Futaba and can honestly say that I have not had a problem with glitches and lockout with my ZAP WC2 for the time I have owned it (6 years).

I work in the electronics game and I dont worry about servicing my own equipment. I dont have access to all the tech notes and schematics that is needed to service this equipment properly. I have seen many instances were faulty equipment was returned to australian importers only to have it returned in the same state. Depending which tech and how he feels on the day can determine how well they can diagnose a fault.

The only repair I would carry out on any reciever is replace the aerial if I broke it. Other than that I throw it away and buy a new one. You mentioned you had some 649 JR recievers as well. I would be a little nervous about those as well. I have seen at least 2 of them fail, both on the ground thankfully.

Good luck with it all.


Peter

Actually, a PCM receiver, when in fail-safe mode, demonstrates the prsense of interference or a low battery situation. For the latter, I was able to detect a dead cell in a receiver pack while performing a ground test.

Probably it is not a good idea to use non-standard crystals? Personally, I only use new or professionally-checked crystals/receivers.

The clear advantage of PCM receivers (at least Futaba brand) is better noise (interference) handling, and longer range of reception. So why not use PCM receivers on high$$$ pattern ship for a mild amount of extra $$$?

--qc

You are missing the point on the crystals.
Firstly, I was unaware the original crystal was locally cut. It was supplied buy importer.
Secondly, the latest crash was with the Genuine crystal (I new my original post was too long and would get read in completion). The rationale was, the original crash WAS caused by a non genuine crystal, hence the idiotic confidence I had to retry with a GENUINE JR CRYSTAL. And of course, all ground checks, and indeed, 9 perfect flights. AND of course, after the crash, everything still works well.
Battery was new, recycled, tested, before and after. No Dead cells. AND it was a 5 cell anyway.


I honestly think it is better to see the glitch (PPM) than not, and at least have a chance to rectify the problem. With both my PCM failures, I never got a chance to, as it never came out of the lockout.

Sorry I missed your post regarding the 2nd crash.

Maybe it is not too late to ask: are those two JR PCM receivers dual conversion? Was the receiver battery voltage normal? What about tx's? Is there any significant difference between the pattern plane and the testing trainer: such as carbon-fiber parts?

--qc

One thing he mentioned is "single Conversion". Frankly I won't use any reciever anywhere that is not of the dual conversion type.
Every time I have used single conversion I have had minor to major hits.

My only other comment, is that I never use a failsafe. Frankly I have gotten all my planes back that got hit, with one exception. personally I don't want the receiver making any decisions. I really can't recall very many if any stories about how "failsafe" saved the day.

do you?

Yeah, single convesion is not a way to go.

At least to Futaba brand, PCM receivers have a better chance to fight against interference. In that sense, PCM is a plus.

Guys, don't confuse pure single conversion (no filtering) with what JR calls "single conversion". Dual Conversion is a filtering technique used to clean the signal. JR opted for a different filtering technique they refer to as ABC&W that they believe is superior to dual conversion. Therefore when you read "single conversion" on the JR RX it doesn't mean they have no filtering.

This begs the question of why does JR have dual conversion RX's. From what I hear it's because some people simply won't buy an RX that isn't dual conversion so JR provides that as an option so as not to loose market share (remember this is coming from someone that has no connection with JR so it's conjecture, but probably not far from the truth).

Most JR users swear by ABC&W filtering and are adamant that it makes no sense to fly the JR dual conversion RX's. However, on two occasions I have gotten minor glitches (lockouts) using the JR ABC&W PCM and solved the problem changing to the JR Dual Conversion PCM RX. The latest case was with the JR 770 slim line RX in my electric pattern plane (electric is know for causing interference). I got numerous short lockouts on turn around maneuvers. When I changed to the JR 945 Dual Conversion PCM RX the problem went away. However, later to make weight I tried the JR 790 slim line Synth RX (also ABC&W) and I've been glitch free for well over 100 flights. So maybe the problem was with the JR 770 design, that particular 770 or even the crystal, who knows.

Ozzieflier, am I understanding correctly that you used the same physical RX in both pattern planes that crashed?

Keith Black

Hi QC,
I am fairly certain the 649's are single conversion PCM receivers (I'll have to check). One of these I have used considerably in my petrol powered model, no probs touch wood. I have the fail safe to completely kill the engine.
But the one that killed my patterniship, was the dual conversion. Top of the line. I have had many conflicting stories about single versus dual conversion, I ALWAYS use the dual Hitec for PPM, but have been often told the single conversion in PCM is good. I guess my petrol engine confirms that.
Battery voltage is good, TX battery is good.

I have actually gritted my teeth and just been out flying with the same Tx, but of course a PPM Hitec receiver, no probs.
There was no carbon fibre in the pattern ship, it was all nice and tight, nylon clevis on engine etc, hyde mount. I might add, I was using the same engine in an older pattern plane, but I was using the Hitec 7 channel PPM receiver.

But I go back to, I guess I will never know, except I now have a VERY FLAT R1000DS RX (there was some satisfaction in achieving that) that is now a NO conversion (something it was good at).

But the question still remains.

Why use PCM????????????????????????????????????????????

Sure, I've seen some guys go into fail safe and recover. But if it doesn't even give a glitch, how do you know what is wrong.
Do I know it went into failsafe? Yes!!!!. The engine dropped to idle (which I had set), and everything else was on hold, in this case, I was inverted with a little down elevator, so it basically outside looped (about 3 times) into the ground.
I must say, they were probably the most perfect loops I have NOT performed.

Hi Keith
Yes you are correct.
Same physical receiver, but in second case, genuine (for sure) JR crystal, on different channel to first crash. As I said, the reason was, lots of conjecture that the original crash was caused by non genuine crystal.

Obviously, after yesterday's experience, it would have to point squarely at the RX.


So, probably my 649's are basically ok. I think there are quite a few guys in Australia that use the 649's .

But for me, I am so gun shy now, I think I will just go with my gut, and fly with the Hitec Rx's. At least if it glitches, I will see it.


I am no longer convinced on PCM. I really do believe, as the old say goes, PCM= Programmed Crashed Model.

Thanks.

ozzieflier,

In your last post you made a very important comment that to me sheds a great deal of light on this issue. You stated that the plane "outside looped (about 3 times) into the ground". To begin with I don't see how a plane with the throttle cut could outside loop three, or even two times. Secondly the fact that it stayed in what we're all assuming is "lock out" for that long is EXTREMELY unlikely with out either MASSIVE interference or another problem like low (or no) voltage going to the RX.

I'm sure you checked things, but i would seriously have to call into question whether or not the RX was even receiving power (or adequate voltage).

Did you check the battery voltage after the crash?
Did you try wiggling all wires to check for shorts?
Did you do thorough checks on the power switch?
Was it the same switch on both planes?
Were you using a regulator?
When testing on the ground after the crash did you have to re-plug anything in?
Are you sure the switch was still in the on position after the crash (Don Szczur had his first Brio turn itself off in flight from vibration).

Keith Black

I understand your emotional response against PCM, but PCM absolutely IS the way to go, no questions about it. There have been lengthy discussions here about this and I think the evidence is clear. What you experienced is either A) a bad RX (no fault of the PCM technology) or B) some other factor such as low voltage.

I admit that I have re-used an RX after a crash (actually after a mid-air) but considering the cost of our planes it's probably not worth it. I know someone that says they take a hammer to an RX that's in a crash when they get home just so they're not tempted to use it again (actually this is smart with high dollar planes). In your case you had a crash that you knew was due to loss of control, this is an extra good reason never to use the RX again (hind sight eh).

I’ll look for some of those old PCM threads.

Hi Keith
I had/have done all that you itemised above. I am an electonic techo by trade, so I think I have god fault finding logic.

It is possible though, if the rx is faulty, for it to just stop working.
The battery voltage is good
I run 5 cells, no voltage regulator. I have always done that, with all my planes, rx's.

regarding the outside loops, the plane had bit of speed on, so it was easy to achieve. And let's face it, was it 2 or 3 times. The main point is, it was holding the elevator at the last know input, AND I heard the engine cut back to idle.

Yes, Hindsight.

That said, lesson learned. Hammer used.

BUT not convinced on PCM

Maybe I might look at the new 2.4 ghz technology. The idea sounds smart. But would like to know how the tranny feels/how smart etc before being the guinea pig, and if it's good for pattern.

A buddy of mine lost a Patriot 2 weeks ago in a similar incident. Same thing... JR radio. Ended up being moisture in the transmitter that caused the problem, it had nothing to do with the flight pack. Turns out the JR transmitter is extremely sensitive to moisture, and the light rain we had been having on and off took it's toll. My setup with Futaba never had a glitch.

ozzieflyer,

Here's a link to an excellent post from the NSRCA mailing list. It's a detailed description of testing done by an RC Club on PPM vs. PCM. One of the best post I've seen on the subject: [link=http://lists.nsrca.org/mailman/htdig/nsrca-discussion/2006-September/044780.html]PCM vs. PPM tests[/link]

Keith Black

So back to your original question "Why use PCM?", the main reason in my view is safety. I have changed all my glow (and electrics other than foamies) over to PCM because I would rather lose a plane than kill/injure someone. I did this after reading about a young person killed in the UK by a runaway aircraft - yes a freak accident but one that would have been avoided if the owner of the plane were using a PCM Rx set to idle on failsafe.

I was at a pattern contest earlier in the year when an Rx in a 5kg model went off line (crystal fell out) and it was terrifying. Sad thing was that the Rx was PCM but the failsafe position for throttle had not been set or didn't work for some reason. The model was in the middle of a loop when the Rx failed and continued to loop between 200 and 500 or so feet in the air for about 10 minutes before it ran out of fuel, by that time it had flown over the town before landing in the grounds of the town's university (amazingly landing upright with no damage). No problem in the end but that was pure luck. It could just have easily crashed into a home, sporting field, town street, etc - or worse a person. If this had of occured that would have been the end of that flying field and incredibly bad publicity for our hobby nationally were a death to result.

Of course PCM does not stop unfortunate incidents happening but it does reduce the risk significantly and I reckon that's a good thing.

All my PCM Rx are set to throttle to idle and hold the control surfaces. All my Rx are JR, I have 2 x RS10DS (dual conversion synthesised), 2 x NES649 (single conversion), 1 x RS77S (synthesised), 1 x R770S. All seem to work ok.

I reckon you just had a bad R1000DS, this could have occurred with a PCM or PPM Rx so it's really nothing to do with the modulation of the Rx.

I hope this helps to answer your question,

Twoturnspin

PS. I'll bet the re-scuplting you did with a hammer felt good!