Independent tests prove lack of frequency hopping with XPS

[sweetpea]

	Quote: Originally Posted by Toumal
	@sweetpea: You fly what you want, it's your good right. Saying that 72MHz had no frequency hopping either, and that thus it is unnecessary is, forgive me for putting it this way, rather ignorant. Jet is right when he says that 2.4 is used for a wide range of things, all of which interfering with a single-channel non-hopping system. I'm not so sure about 72, but at least 25MHz is not, it takes another RC modeler to shoot you down. The frequency band is in use exclusively for RC models.

What I said or meant to say is that freq hopping wasn't the reason I bought XPS in the first place. I was very skeptical of how it could work since when I asked the response was it was a 2-way communication so they can tell each other where to go when it happens. Well I thought about that and by the time it happens it would be too late. Too me that was just common sense. I bought it for the real-time telemetry that might tell me I'm losing data packets real time.....and satellites that would enhance the ability of any system to recieve the signal in any attitude (plus a little redundancy).

So sorry to burst everyone's bubble but my only real concern at the time was
how XPS would react to Wi-fi in Vegas (since the homes were so close) and cellphones at the flightline (even though they should be on a different freq). My home range checks were fine and my field range checks were fine. My first flight was ok (not stellar) as well. Subsequent flights I encountered possible problems (not lockout) and then finally lockout on approach.

I admit that I knew the limitations of a single antenna with no diversification and that in my case I don't feel 2.4 interference was to blame but I did feel that shadowing was most likely the cause but I couldn't prove it and I wasn't about to risk another GS plane. (hence the reason I wanted to wait on satellites for future GS flights along with telemetry).


I admit that these things never came about to my satisfaction and not in my time line that I was willing to wait. I also admit that JD has been less than honest with his life story, he's had bad press from previous business's and I felt that the advertising was overhyped. Most of you call it flat out lying. Its easy to see it that way. I took it just like I do every info commercial on TV that tells you that you have to have product X now becuase its the best or only option to you. Lying over adverstising, making false claims or unrealistic claims......call it what you want.


I also find it very problamatic about the XPS systems not going into Failsafe but the pilot has no control. For me that is more worry some than "hopping". This sounds more like shadowing where only limited data is getting through, just enough to keep it out of lockout but not enough to trigger it. Yes, very scary. I hope all of those units went back to XPS so they can trouble shoot that issue (maybe we will find out the reason and maybe we won't)

I also admit the system has numerous limitations. Some are the same as Spektrum/Fasst and some are different.

Is the system the best choice for you? That is upto you to decide.

Remember I bought XPS when back when Futaba hadn't announced they were even going to do FASST (or at least not a module for JR). I went to the Spektrum booth and flat out asked the guys there........"I've used your module in R/C cars and loved it. Will a version be coming out for JR radios in the future (I didn't ask for a date). I was told there were no plans to do that.

So XPS was my only option to keep my 10X in the air and go 2.4 Since then my options have opened up. I now have choices. I've made it clear that for me telemetry and satellites are what I want in 2.4 along with the encoding that 2.4 has that it FCC biding R/C radios won't shoot each other down. Toumal if "hopping" was all I cared about than I'd be flying a FASST module since it is the only system that does hop. Spektrum is going to crash if a signal is brought up close enough to the 2 freqs it uses and since its random (or so far that is what it appears to be) the freqs could sit quite close to one another so my odds of being shotdown from non friendly FCC 2.4 is a crapshoot. Everytime I fly I know that. Just like everytime I flew 72mhz someone could turn on or the neighbors behind my field in Vegas could've used a "dial a crash" to get rid of any plane flying since they hate the noise so much.


So again Toumal.......I'm currently flying Spektrum modules and they don't hop. I didn't buy Spektrum because it hopped or because it had 2 freqs. I bought it because I've used it in the past on R/C cars and for telemetry and satellites.

So far the telemetry has enabled me to fine tune my antenna placement at several fields. Also anytime I think I got hit......a quick check to the logger tells me whether it was just me or an actual hit.



I don't make myself nuetral/pro/against XPS. I simply wrote exactly what happened when I used it and why I switched.


So what's next........is everyone going to condemn me because I fly an Aerotech 35% Edge 540 and 42% Extra 300? I mean they are just airplanes and the owner has proven to be less than desirable (no arguement here on that either) Oh by the way I fly 3W and deal with Cactus so don't forget those either.

Lets not just stop on the fact I use(d) XPS.

I'm not in the buisness to tell FG or RCG users not to use a particular motor, plane, servo or radio system.

I will tell them my experience with what I have used and if I know about some issue I'll tell them to research up on it before buying. Again.....I'm no Mark Leesburg or 5 yr old Justin prodigy. No one is going to NOT buy XPS because I said not to and no one is GOING to buy because I didn't say not to buy it. My cranium is a little smaller than that thinking.

[dirtybird]

Boy there is a lot of BS on this thread.
Call me a fanboy. I have had my systems (XPS)a year an a half with narry a glitch that was not my fault.
I don't bother to range check anymore.

[XJet]

Just to balance the ledger, today I received an email from an Australian XPS user who related his tale of woe. He and another flier were in the air using XPS when they both got shot down at the same time.

XPS gave the usual lame excuse about "the whole band being saturated" etc, etc.

It's second tier. It'll work just fine when conditions are favorable but doesn't have the extra levels of resilience to interference that Spektrum/JR or Futaba have.

[Mike Busutil]

I too have put my trust in XPS and am flying it in my 50% Edge 540.............I have

seen no problems from day one. A few guys at my field also fly XPS with the same

results. For me XPS works, hopping or not..........

[XJet]

	Quote: Originally Posted by Mike Busutil
	I too have put my trust in XPS and am flying it in my 50% Edge 540.............I have seen no problems from day one. A few guys at my field also fly XPS with the same results. For me XPS works, hopping or not..........

It's great that you've had such success, but to quote from the email I received today:

	Quote:
	Today is the 27th July 2008 weather conditions 12 deg C with a few showers. Myself and a Mate both have 40 size aircraft with XPS 2.4GHz 8 channel receivers and modules. Both radios are JR 3810's. Both aircraft have been flying for over 12 months on XPS 2.4GHz with no issues. This morning I range checked with no problems and had 1 flight with no issues. My mate also range checked a took his aircraft up for its first flight of the day and I also went up at the same time. Approx 8 minutes into the flights he was flying straight and level when he called that he had lost all signal with the aircraft and it rolled onto its back and came in from approx 100 feet and around 120 metres from him. I immediately flew around to land and also flying straight and level over the top of his downed plane I started to receive glitches in my aircraft. As I turned on final approach at approx 90 to 100 metres out and 30 to 40 feet of the ground I also lost all signal to the aircraft. Both aircraft destroyed.

So I'd say that right up until a couple of days ago, both these guys would have had the same good-news story to tell about XPS.

That's the trouble with a system like this - you don't miss what it doesn't have (frequency agility or redundancy) until it's way too late.

[JEFFRO503]

I'm not going to call the XPS user's fanboys......

But the guys who "do" defend it on here are the few who hasn't had any problems yet ( i said yet )

You guys that still use it and it works for you, that's great. But again , like i stated in the past , i took like 3-4 nights and read through this entire thread. And what i found we're guys in the Start of all this that we're defending XPS , sooner or later , they got bit.....and bit extremely hard!


One question : You guys that still fly XPS , do you do any competing or go to big fun fly events? I have been to quite a few , and have not found ONE PERSON who flies with XPS.

Mike...you have a 50% edge.....that's a huge friggin' airplane! BTW...i commend you for being that serious into the hobby. Do you compete with this aircraft? usually when someone puts that chunk of change down on an aircraft , they have to be pretty serious into it.

I'm just wondering , because around here in the NW , and all the fields i fly at , not ONE person that i know of , or have spoke to , uses XPS.

God forbid , you don't find out the hard way , just to prove a point that XPS works. if you do fly XPS at any events......and i'm there , i'll make sure i stand on the other side of the protection barrier.

[sweetpea]

according to the explanation...........they were not shot down at the same time.

Clearly one plane lost control while the other was still flying. Then later the other plane lost control. Over the same point. Possible interfernce from that specific angle? Who knows without the dang telemetry unit that I wish they had up and running already!!!!!

They both lost control true.....but at different times. Though very close to the same spot from the sound of things.

Also is there mention of any failsafe?

Next 2.4 doesn't glitch like 72mhz, so I would suspect something else was going on with at least one of the aircraft or the person isn't relaying the information correctly.

Of course it still could be an XPS problem or it might not be anything related to XPS

There have been reports of loss of control of XPS aircraft with no failsafe envoked, could this be that? (this worries me more than a no hopping situation).

Xjet-
Is this a different account of what has been on RCgroups for the past week or so (before 27 July)? I know there was a thread there about a couple of guys who reported they locked out at the same time (unlike what your quote says).

http://www.rcgroups.com/forums/showt...&highlight=xps

[XJet]

	Quote: Originally Posted by sweetpea
	according to the explanation...........they were not shot down at the same time.

Okay... within seconds of each other ;-)

	Quote:
	Clearly one plane lost control while the other was still flying. Then later the other plane lost control. Over the same point. Possible interfernce from that specific angle? Who knows without the dang telemetry unit that I wish they had up and running already!!!!!

If (as you suggest) this was a case of the models flying into a strong field it also reinforces my own claims that you simply don't get the " gradually rising noise floor" around which XPS was designed hop (on the basis of JD's extensive "real world testing"). Interference on 2.4GHz tends to appear very suddenly - which is why the XPS hopping algorithm (even if it works as claimed over a 15-second period) is totally useless.

	Quote:
	Also is there mention of any failsafe?

No mention of failsafe.

	Quote:
	There have been reports of loss of control of XPS aircraft with no failsafe envoked, could this be that? (this worries me more than a no hopping situation).

Yes, that problem does seem to be resurfacing with some frequency. Just as worrying as the problem is JD's Futaba-like attitude "I see nothing wrong here, what problem? My code has no bugs"

	Quote:
	Is this a different account of what has been on RCgroups for the past week or so (before 27 July)? I know there was a thread there about a couple of guys who reported they locked out at the same time (unlike what your quote says).

That was my first thought too -- but they appear to be 10-days apart and in different countries. The incident reported to me only happened last Sunday, the RC Groups one was reported back on the 18th.

I'm beginning to wonder if my theory (one XPS transmitter swamping the receiver in another nearby due to constant retries when ACKs are lost) may be even more likely given the similar circumstances and outcome of these two cases.

As soon as the weather clears here I'll run a test. I have two XPS systems so I'll set up a test scenario to check for that.

Until then, I'd advise XPS fliers to stand as far away from each other as possible when on the flightline -- just in case (and don't commit any large, dangerous or valuable models to XPS).

[Woketman]

XJet: ask these guys, via reply e-mail, about the failsafes please. Thanks.

[DesertHucker]

	Quote: Originally Posted by XJet
	I'm beginning to wonder if my theory (one XPS transmitter swamping the receiver in another nearby due to constant retries when ACKs are lost) may be even more likely given the similar circumstances and outcome of these two cases. .

XJet could it be the receiver swamping the signal with ACK's retries, since it is bi-directional and the plane lost control while passing over the crashed one.

Loza

[Gordito Volador]

	Quote: Originally Posted by dirtybird
	Boy there is a lot of BS on this thread. Call me a fanboy. I have had my systems (XPS)a year an a half with narry a glitch that was not my fault. I don't bother to range check anymore.

No more range checks? I'm glad that works for you. I'm very happy to hear when someone is truly enjoying the hobby! For me I'll stick with Spektrum/JR and Futaba. I am grateful that Kiwi and X-Jet have spent the time and energy to keep us informed about the technical aspects of 2.4 Gig radios. There is nothing better than being an informed buyer, I personally wouldn't refer to the content of this thread as BS.

[sweetpea]

Some of this thread is BS and some of it has value.

There are some issues with XPS and there are some theories (not proven truths) about XPS.

It is very strange though that there are 2 accounts of system lockout while 2 XPS units flew at or near the same time. Problem is both accounts have them flying for a period of time then suddenly they lose control. So its not a clear cut......you shot me down situation

Did they get close enough to have one RX swamped by the others ACK requests?

Are the systems on the same channel, which 2.4 can and does do since they timeshare the freq. Does this play into the equation?

Is it just coincidence and they all crashed from an outside source?

Xjets future test will be interesting

[dirtybird]

That is if Xjet ever gets around to putting tests where his mouth is.
Here is a test that most of you can perform if you have XPS.
Sit the receiver on the top of your microwave and get the system operating. Then trun on the microwave and see if it stops working.
I have done this test with two microwaves and can not find a time that the system stops working.
Since both are on 2.4 ghz XPS must do something to keep working.
I have even tried it with the MW door open and the cut off switch bypassed.
The output of my microwave is 150W

[Woketman]

That's nice. Now all you have to do is figure out a way to strap the microwave under your jet when you fly. Maybe THAT way XPS will function reliably, cause it sure ain't doing it now for a lot of guys!!!!

Let's face it: XPS is 2nd tier. A GREAT solution for $30 foamies ONLY!!!!

[Bob S]

	Quote: Originally Posted by dirtybird
	That is if Xjet ever gets around to putting tests where his mouth is. Here is a test that most of you can perform if you have XPS. Sit the receiver on the top of your microwave and get the system operating. Then trun on the microwave and see if it stops working. I have done this test with two microwaves and can not find a time that the system stops working. Since both are on 2.4 ghz XPS must do something to keep working. I have even tried it with the MW door open and the cut off switch bypassed. The output of my microwave is 150W

Actually a microwave is 2.45GHz.