Independent tests prove lack of frequency hopping with XPS

[wrightme]

	Quote: Originally Posted by Wojcigitty
	To be fair, if I bought XPS and lost an airplane to it, I'd probably have a vendetta as well. These threads have been very enlightening, but at a hundred pages, it's getting redundant (except for Toumal's "In first approximation, a cow is a spherical object that emits equal amounts of milk in all directions.")

To be fair, if I bought a plane and placed any radio system in it, and it crashed, I would attempt to recreate the events and actually try and figure out what went wrong.

In fact, I crashed an XPS-equipped plane this morning!

I had full control all the way to destruction, when the wing disintegrated. I even had control to go to minimum throttle before the lack of a wing caused premature landing, in a non-optimal manner.

You place it in the air, it will land, whether you cause the landing, or not. We always hope nothing will go wrong. Today's crash was my first. I have used 72mhz Berg, Futaba, Hitec, and 2.4 Ghz Spektrum and XPS. With either Spektrum or XPS, I simply have no unintended control movements, and I do not worry when others are at the flightline with their TX. With 72, I had frequent unintended control movements.

Bottom line? If you don't like XPS, fine, but choose your alternative and move on. Vendettas and obsessions aren't healthy.

[BZFrank]

	Quote:
	The issue here is that XPS DOES NOT HOP IN A USEFUL FASHION

Well, thats not what is bothering me in the first place. Its this: XPS seems to work most of the time well, but tends to fail in some locations horribly. See e.g. one case here in Germany - during a Pylon racing contest in Leipzig last month. Eleven pilots with FASST, two with XPS (iFS). Both XPS flyers lost all their planes - two per pilot - due to radio lockouts. In two cases not even the failsafe kicked in - mandatory for pylon competitions - and the models flew away at high speed. These pilots did do their training at home with XPS (iFS), without troubles. Only when they came to the competitions location the lockouts started. Oh, and no radio issues with the other 2.4er radios at all at the same spot.

http://www.3d-pilot.de/bildergalerie.../P1010166.html

This seems to be consistent with other reported crashes using XPS. I don't know if it is caused by the lack of hopping, voodoo spells, phase of the moon or a race condition in the firmware. But lockouts seems to happen occasionally, none in some locations while more in others.

And yes, I have also seen XPS (as IFS) perform well.

But I for myself prefer a radio that has a more consistent record of credibleness.

wrightme: sorry for your loss! Hope it can be repaired.

Frank

[XJet]

	Quote: Originally Posted by wrightme
	Xjet himself spoke in the XPS forum noting the "less than warm welcome" (to paraphrase) that those who use XPS receive here.

Come on, *don't* do a JD and subtly twist what I actually said to suit your purposes...

I said the XPS FBs (fanboys) got less than a warm welcome -- not XPS *users*.

I have no problems with people using XPS and enjoying it -- it's when they step up to defend the indefensible or cite the word of JD as *proof* that they start falling into the FB category and *then* they receive a chilly reception anywhere there's a gathering of people with more objective perspectives and who'd rather rely on facts than blind faith gather to discuss such things.

	Quote:
	According to several here, reports of XPS can't be anything except a post from Paid Shills!

Unlike the XPS forum on RCG where JD and the FBs talk about how some (like myself) are in the paid employ of his competitors -- which is an utter lie -- but JD doesn't need evidence, he "just knows" and his league of FBs just take his word for it.

Then there is the FB who claimed that I'd stepped in to defend Spektrum in another thread on RCG. When I challenged him to cite the passage in which I did -- my request was deleted and he's refused to answer my PMs asking for similar proof. It seems that FB's aren't big on proof - unless it comes in the form of hearsay from some anonymous Boeing engineers who can't be named because they effectively defrauded their employers by doing the tests on company time and with company gear (and this makes them a trustworthy source of information???).

	Quote:
	Plenty of those here have done nothing to engender any feeling of attempting to FIND an actual problem with XPS. Instead it almost always degenerates to "Hops/doesn't hop,"

Could that be because whether XPS hops or not is important for a great number of reasons:

1. It determines whether the gear is suitable for large/fast/expensive models.
2. It speaks to JD's credibility and therefore every other claim he makes.

	Quote:
	Those of you who hammer on about how bad XPS is are really transparent in your vendetta. You all should really consider giving it a rest. Frankly, you give FG a bad name.

I'd say exactly the opposite. It shows that FG is an open forum where adults can engage in a reasoned, rational discussion focused on the facts, the evidence and the important issues -- without fear that any dissenting posts will be deleted in a keypress for fear they may reveal the truth.

[BaldEagel]

These froums are for the exchange of idea's and experiences if someone has an unfortuant experience than informing others is a way of communicating a possible problem.

When considering a prospective purchase I always trawl the net to see what experiences others have had with this item, a current and up to date forum will give you the most recent information on any product.

What I don't understand is those who wish to close a thread that does not correspond with there own experience, this does not serve any useful purpose other than to hide what could be up to date information.

Its a strange world, we are all convinced that our experience is a diffinitive statement, this is not the case, and I for one are grateful to those that have posted on here to highlight a possible problem with this equipment.

Thank you chaps I am most gratefull.

Mike

[wrightme]

	Quote: Originally Posted by XJet
	I'd say exactly the opposite. It shows that FG is an open forum where adults can engage in a reasoned, rational discussion focused on the facts, the evidence and the important issues -- without fear that any dissenting posts will be deleted in a keypress for fear they may reveal the truth.

Most of this "discussion" has been anything but "reasoned, rational." Too much of it is ranting about the system, and ranting AT those who choose to use it. Neither qualifies as fitting your "reasoned, rational" label.

[Dustflyer]

	Quote: Originally Posted by wrightme
	Most of this "discussion" has been anything but "reasoned, rational." Too much of it is ranting about the system, and ranting AT those who choose to use it. Neither qualifies as fitting your "reasoned, rational" label.

Not true.

In my case I bought XPS, found it to be unreliable and unpredictable and decided to make that information available to others. Knowing what I did, I could not in good conscience keep that information to myself. I went through a great deal of time and trouble to make my videos and post them.

In other cases crashes occurred using XPS. The cause of those crashes were, through process of elimination, narrowed down to a very high likelihood of an XPS problem. Hundreds of thousands of dollars worth of crashed giant scale and jets. Some would say "forget about it, stop whining, you can crash ofn72." But why should anyone forget about it? If I crashed my jet and narrowed the cause down to a bad 72mhz radio you can bet I'd tell others about it. I am very grateful to everyone for taking the time to report their crashes involving XPS guidance.

Other individuals took a great deal of time and effort to show, through tests, that XPS does not live up to its advertised claims. None of these people had to do any of it. They did it to help their fellow modelers. I strongly doubt they are being paid by Spektrum or Futaba. Why would they be? Spektrum and Futaba already dominate the field. Neither of those companies needs to defend their systems against XPS.

Once again thanks to all for getting the word out to your fellow modelers. It is precisely through word of mouth and forums like this that we get the crucial information we need to make our hobby safer and more fun.

[Toumal]

	Quote: Originally Posted by wrightme
	Most of this "discussion" has been anything but "reasoned, rational." Too much of it is ranting about the system, and ranting AT those who choose to use it. Neither qualifies as fitting your "reasoned, rational" label.

Quite the contrary. In fact, XJet and Kiwi have been the most diplomatic guys in these threads IMO. Besides, what is it that you call a rant? Kiwi stating the fact that he couldn't get XPS to hop? Skuba's response that he has to give XPS a special test that is geared towards making it hop? Kiwi and XPS stating that XPS should hop on interference, special circumstances or not?

A lot of the facts surrounding XPS are enshrouded in doubt by people who say that XPS-doubters call XPS-users names, and that it's all just an obsession to make XPS look bad. That's not true. The thing is that, for example, FASST's issues are well-known and acknowledged by the manufacturer, and they are issues for which there are workarounds. Still it's important to discuss these issues. You don't see me going in there and saying that all these discussions are crap because I never had a heat problem with my 614's. On the other hand, XPS's issues are neither acknowledged by the manufacturer nor is there a workaround.

I saw people fly XPS with no problems whatsoever. That's good! But it doesn't change a thing about the fact that XPS' hopping is vulnerable to very real interference scenarios, essentially making it as good or as bad as a single-channel non-hopping system with no antenna diversity. Can you fly with antenna diversity? Yes you can, but there are circumstances under which antenna diversity will keep you in the air vs. experiencing a lockout. Can you fly without frequency hopping (or rather: hopping that only occurs under very special circumstances)? Yes you can, ASSAN is selling a system that doesn't hop at all.

I'm not calling anyone an idiot for flying XPS. Heck I bought FASST without really having seen it hop beforehand. But now we not only know that it does, but also that it works pretty damn good.

What does get me riled up personally (and I know that I should control my temper about that) is when people "advise" potential buyers about XPS and tell them that a) XPS is as safe as the other systems, or b) antenna diversity doesn't really matter all that much. I personally think it's not advisable to use XPS in a heavy aircraft, and the reasons are based on facts and experience - yet it's still only my opinion.
I don't care about JDs background really, for all I know he could've built a great and reliably system without having a degree himself. I also wouldn't judge him entirely based on his past projects - we all learn and make mistakes, besides I don't know what was really going on back then.

However, telling someone that flying his 38% Extra with XPS is as safe as using FASST or Spektrum is akin to telling young drivers that it's okay to drive without a seatbelt, and that the cushioning on the steering wheel will work just like an airbag on a collisions.

You can say that you don't share mine or XJet's opinion, and that you drove 10.000 miles without a seatbelt and had no problem, and you can say that you don't believe that the tests involving seatbelts are representative or that rubber can work just as well as an air-inflated bag. It's your right to uphold whatever opinion you fancy. And I thank FG for making it possible for people of either opinion to share and discuss them.


EDIT: Just to get this out of the way, I wear a Futaba shirt and a Futaba hat when flying. That doesn't mean my voice is bought though, in fact I bought that and a lot of other apparel at towerhobbies. My Futaba TX rests in a genuine Graupner Varioprop case, that doesn't mean I'm bought by Graupner either.

[wrightme]

Dustflyer,
Did you ever test anything more than one TX and one RX module in your "twitching" videos? If not, you used a sample size quite a bit too small to determine usability. With my 3 TX modules, and about 5 in-use RX modules, I have never experienced the symptoms your videos show. It is quite likely that:
1) one of your modules was faulty
2) the TX to module connection was faulty

Toumal, XJet has become more diplomatic, and Kiwi is definitely diplomatic. The others, not so diplomatic. Reading this thread can easily show which posters fit which mold. Several posters really denigrate anyone who chooses to fly with XPS, and many of them likely have never TRIED XPS themselves. Some of those have tried it.

As for the mfr claims, I am on the fence on that issue. I will state that I do see that no bench-test has caused an XPS "hop," but I also see that all bench tests I have viewed have presented methods that are VERY unlikely to be experienced in the real world of flight. Most crash reports also do not address the actuals of the RF environment at the time, and only allege that a "no-hop" scenario is to blame. The crash reports that do allege a "no-hop" cause also (for the most part) assume that no other cause could have been a factor.
Several crashes (or near-crashes) that HAVE been troubleshot to a failure cause HAVE shown that power delivery to the RX must be "bulletproof."

A failing that is a recurring theme in this discussion (and the 6014 discussion) is the assumption that "since my Brand X #49.62 RX worked, this Brand Y #339.q RX should work in exactly the same manner, with no alterations necessary." Such an assumption is a good way to have a failure.

[Toumal]

	Quote: Originally Posted by wrightme
	Dustflyer, Did you ever test anything more than one TX and one RX module in your "twitching" videos? If not, you used a sample size quite a bit too small to determine usability. With my 3 TX modules, and about 5 in-use RX modules, I have never experienced the symptoms your videos show. It is quite likely that: 1) one of your modules was faulty 2) the TX to module connection was faulty

Actually, this weird flapping has been recorded several times by different people. Browse through the XPS threads to get the relevant video links. Oh it could be a faulty RX, or TX module - and even though we can't rule out a systemic problem or some kind of local interference, all possible reasons should be considered. But hey, if several people saw this happening on their Spektrum systems, boy would there be a storm of complaints in the forums. Furthermore, two people in my club returned their IFS gear here in Austria, citing the very same problems (unprovoked servo movements, no link, loss of link). I know these people personally and they are long-time Graupner users with no reason to "bash" IFS/XPS.

Then again, you only have my word that I'm not making all this up as I go along...

	Quote: Originally Posted by wrightme
	As for the mfr claims, I am on the fence on that issue. I will state that I do see that no bench-test has caused an XPS "hop," but I also see that all bench tests I have viewed have presented methods that are VERY unlikely to be experienced in the real world of flight.

I disagree, with one exception: The only thing that's not entirely realistic in Kiwi's test is the distances between the RX and the two transmitters. That's why I propose that future tests be held with greater distances AND varying distances between the RC TX and the interfering TX. For each test the positions should be fixed. All these ranges should be measured and specified so the tests are repeatable.

Don't get me wrong, Kiwi's test is perfectly repeatable - one can see the distances between the module and the two transmitters. It's just that one could claim that if there's greater distance between the RX and the interfering TX, there might be no loss of control.


But again: I believe that for XPS to hop, it requires a working link between RX and TX. Loss of control happens because such a link is no longer present, and thus the way XPS hops does not give you a boon in reliability. As so many people have pointed out, it's up to the manufacturer to present evidence for the truthfulness of his claims, and JDs video only proves that the manufacturer either doesn't understand the difference between interference and saturation - or that he deliberately "misunderstands" what we're talking about. Considering that the manufacturer has made very "optimistic" statements regarding his antenna performance, statements which are being repeated like a sermon by devoted followers, I wouldn't get my hopes up.

At this point I hope JD is doing the right thing and coding a hopping scheme pre-negotiation into his modules, so that XPS can actually hop to a free channel on sudden interference.

[wrightme]

Toumal, my point IS that the distances of TX and RX matter. The bench test IS repeatable, but not relevant for real-world flight.

Your response and viewpoint is relevant and well-spoken. Your response has NOT been the "norm" in this (or in other) thread.

I agree that there have been more than one such report of uncontrolled servo movement, it hasn't been scrutinized to a reason, merely pointed out as a problem with XPS. If it WAS a "problem with XPS" as many like Dust allege, each owner of XPS would experience it. Since each owner doesn't experience it, the answer must be something other than a specific problem with all XPS units.

[Dustflyer]

	Quote: Originally Posted by wrightme
	Dustflyer, Did you ever test anything more than one TX and one RX module in your "twitching" videos? If not, you used a sample size quite a bit too small to determine usability. With my 3 TX modules, and about 5 in-use RX modules, I have never experienced the symptoms your videos show. It is quite likely that: 1) one of your modules was faulty 2) the TX to module connection was faulty

Yes I did.

I sent the first receiver and transmitter module back to XtremeLink for exchange. The new ones did the same thing.

Regarding the transmitter:

1) The transmitter was in perfect working order. The reason I bought XtremeLink in the first place was a crash I had on 72mhz. Spektrum modules were not yet available, XPS was the only game in town. After the crash I immediately sent the transmitter in for checkout. Hobby Services reported it in perfect working order but they changed a few parts anyway, mainly the pots. If you followed my threads on RC Groups you will recall JD telling me my problem was dirty pots. My pots were not only clean, but brand new.

2) I installed a Spektrum module in the transmitter and it worked perfectly. I successfully flew my H9 33% Cap with it. Never had a problem. Never a twitch, completely unlike my experience with XtremeLink.

3) Yes, you may recall JD offerring to "check out" my 9Z WCII transmitter or even buy it outright. That is true but I refused. Once I let that transmitter go he could have done what ever he wanted to it. To me it made no sense to give away my transmitter or have it "checked out" since I had already done that and it worked perfectly with Spektrum.


I have no problem with people using XPS but in good conscience I believe I have to at the very least warn them of the risks in doing so.

I strongly believe it is foolhardy to fly anything in the vicinity of spectators with XtremeLink. Why subject yourself to the liability considering all that is known about it?

There are people in the world who do risky things and use those activities to express their individuality and set them apart from everyone else. Standing by something like XPS is one of those things. It might not be the best judgement but it fullfills a need.

[Toumal]

	Quote: Originally Posted by wrightme
	I agree that there have been more than one such report of uncontrolled servo movement, it hasn't been scrutinized to a reason, merely pointed out as a problem with XPS. If it WAS a "problem with XPS" as many like Dust allege, each owner of XPS would experience it.

Not necessarily. It might be caused by local RF interference on the channel that XPS chose. That interference might not be present everywhere. I'd imagine that if those people were to check the band with a frequency analyzer or a WiFiSpy2, they'd see something out of the ordinary on the 2.4 band.