Poll XPS - User Opinions

[MikeF]

I agree that looking at the box won't be possible. I think the best use for flying will be verbal warnings of things like voltage, temp and RF link issues. I believe it will have a memory card to save flight info for later review.

Mike

[woketman]

I someday want telemetry to give me audible warnings about battery voltage (if it dips below a user set thresh hold) and signal strength received or packets that needed re-send (in other words a warning when the receiver's ability to receive is getting compromised, with a BIG safety factor). There are other parameters that you might not need to be informed, in real time, about very often. In those cases, a buddy can stand there and tell you what he sees on the screen or you can take a look at the recorded data later.

[pmackenzie]

AFAIK, the telemetry is planned to have both storage capability via a memory card (SDRAM?) and can be set to make audible cues as required.
Also includes an MP3 player for practising sequences

Now all we need is for Jim to get it on the market

Pat MacKenzie

[CLovell]

I have a module for my Futaba 9C and the 10ch RX. Jammed it into a Sig Kougar as a test bed. The installation is intentionally awful... I wanted to see what would if I just got it in there with no consideration other than the 2 inch rule. This installation was particularly ugly in this airframe because the RX needs to sit in the rear of the radio compartment and with the pushrods running through the middle of the fuselage, the RX is mounted a 45 degrees with the antenna off in the left corner of the fuse.

Range tested per the instructions… with the worst case being on the right side of the airplane because most of the signal has to go through the bottom of the RX. Everything checked out per the instructions. Put three flights on about 8-10 minutes per and really wrung the thing out, mainly so I could tell if something was either slow or unresponsive. Also flew out to distances/altitudes I would see with large warbird and jets. Worked fine.

Finally, I took the thing out about 1000 feet and up to who knows how high altitude, it was a dot, a small x really, barely able to make out wings level. I figure mostly in a climb too far away to really see to control (can’t fly what you can’t see), but I still had control. Made a pass left to right so that the RX antenna was at it’s worst position, meaning the circuit board was between the RX ant and me. Worked fine. Only thing I could safely do at that point was spin it down until it was close enough to see to maintain controlled flight.

So, this isn’t extensive flight testing. Certainly a suboptimal installation and yet I had no issues. I’m confident enough to install it in my Jets or Warbirds.

I'll let keep ya posted.

[Kou]

CLovell:

Make sure you get good power to the RX. I think direct battery connection is the best.

MK

[P-Diddy]

Clovell, keep the reports coming, that was exactly what I wanted to read!!!

-Pat

[P-Diddy]

So, now I feel comfortable voting on this since I have the XPS system installed in a T-Rex 600N and a 29% Giles G202 with a 40cc gas engine. I have had absolutely no problems with the XPS system.

Additionally, I found it to be very simple to bind and program the Rx's, including the failsafe. I'm not sure why it has been said to be so difficult, but I was successful on all of my programming on the first try on three Rx's so far. The 3rd Rx is in a 33% Yak 54 that had an engine problem when I went to test the XPS in it, so it has not flown yet.

[longhair]

Good info to have, especially that there were no issues in the heli.

[XJet]

As someone with two XPS systems, a strong background in digital electronics/RF and some concern over the outrageous claims being made by Jim Drew in respect to the technology behind this system I've been doing some testing.

XPS works well enough for most people when operated in a stable 2.4GHz environment. This is witnessed by the many users who claim to have hundreds of trouble-free flights.

However, I have discovered (by testing) that the XPS has no way of coping with the sudden appearance of high noise (interference) levels when it's in use.

If you're flying XPS, and some source of 2.4GHz noise appears on the frequency your XPS system has chosen to use, it *WILL NOT HOP* to another frequency. All control will be lost.

This is contrary to JD's earlier claims for these units in which he stated that if the noise is too high they will frequency hop.

When challenged over this, JD has (somewhat reluctantly) admitted that the sudden appearance of a large amount of noise or other interference on the frequency XPS has chosen at boot-time to use will cause it to fail.

Now, with all those successful flights to its credit, this may seem inconsequential -- but it is something that other manufacturers have clearly though important enough to provide contingency for.

Futaba constantly hops and will therefore be such "moving target" that a single-frequency noise/intereference source will have virtually no effect on it.

Spektrum uses frequency redundancy to ensure that if one of its chosen operating frequencies is hit, the other will likely provide sustained connectivity so the user retains control.

So the frequency diversity touted by JD for XPS is (just like that mythical eight-element spherical antenna) just hype.

With this in mind, I would consider XPS to be significantly less robust (interference-wise) than either Spektrum or Futaba.

This lack of reliable frequency diversity may also go someway to explaining those "it worked fine for 200 flights then locked out on me" scenarios that have popped up from time to time with XPS. Chances are that the system was hit by a sudden increase in noise or other strong signal on the frequency it was using. With no ability to change to another frequency and no backup frequency in operation -- the results will be unpleasant.

The only reason I post this here is because a post to this effect was quickly deleted from the XPS support forum.

It seems that even though he's admitted it, JD doesn't want the world to know that yet another bit of XPS hype has been debunked.

This is stupid really -- XPS is good enough for most of the people most of the time so why bother making outrageous claims for technology and functionality that just doesn't exist?

If you're finding your XPS system works flawlessly I'm very pleased for you. I just hope that sometime (perhaps when you're visiting another flying field) you don't encounter interference that knocks you out of the sky but leaves Spektrum and FAAST users untouched.

[longhair]

So, worst case it is the same as 72MHz?

[JimDrew]

We have the only system that communicates noise in the environment and in fact WILL hop to a cleaner frequency if the noise floor rises. That hop may not even be due to the aircraft experiencing a problem, it could also be from the transmitter side (like other 2.4GHz systems on the flight line).

XJet does not have an "extensive RF background". He does ride around on glowing pulse jet powered go carts and hides cruise missles though. I guess that makes him an expert on someone else's product.

[longhair]

How much noise will it tolerate before hopping and is there a scenario that would cause it to not hop and lose contact other than having the band blanketed? I personally think you have a product that is worth buying and fully intend to purchase one this year at Toledo (I learned a long time ago not to buy version 1.0 of anything)

I do have an RF and electronics background as I have been a broadcast engineer and IT geek for the past 15 years.

[bzfrank]

Hi,

I have done some testing too and was no able to get XPS to change the channel. I found out some other facts however using a portable Spectrum Analyser.

XPS uses 16 Channels in the 2.4 Ghz band, 5 Mhz wide. It allocates one channel for use. Center frequency for each channel can be calculated as F = (2405 + 5 * (k - 11)) MHz, where k = 11, 12, ... 26. (Exactly as Zigbee does)

This is the typical signature of a XPS (power level 5) system:




For the tests I tried to raise the noise floor first by using an analog video transceiver set to the same frequency range as the XPS system. That did not caused it to jump, it just stayed on the same channel.

I did a second test using a DX-7, which is know to output quite a hefty signal. I noticed that in my environment the XPS system always starts on Zigbee channel 12. So I let it allocate the channel, and put the system away to shield it. I then started a SpectrumRC DX-7 for as long as I got it to work on the same frequency range for its lower channel and put that away too.

I then pulled out the XPS system and checked its channel allocation - still 12. Then I added the DX-7. XPS stayed on 12, no jump.




As you see the channels of the XPS (Zigbee Ch 12) and DX-7 are now overlapping which must cause the noise floor to raise for both devices. Still XPS did not choose to jump. (The signal at 2472 Mhz is the second channel of the DX-7)

I am still trying to get it to do the channel change, next time I'll try with some othe analog 2.4 equipment.

Jim, can you tell us some details on when XPS is going to jump? What noise level must be reached to have it change its channel? It definitely does not just 'hop to a cleaner frequency if the noise floor rises'.

Best regards

Frank

[XJet]

Originally Posted by JimDrew

We have the only system that communicates noise in the environment and in fact WILL hop to a cleaner frequency if the noise floor rises. That hop may not even be due to the aircraft experiencing a problem, it could also be from the transmitter side (like other 2.4GHz systems on the flight line).

Backtracking on your earlier admission Jim?

XJet does not have an "extensive RF background".

My, now you've got a crystal ball eh?

Well I've been working professionally in RF since 1977 (that's over 3 decades) and am currently employed to develop RF and digital electronics for UAVs.

I guess JD doesn't know what "extensive" means.

And, if you can't defend your position, why not just attack the messenger as a last form of defense?

He does ride around on glowing pulse jet powered go carts and hides cruise missles though. I guess that makes him an expert on someone else's product.

Well Jim, I have to say that I seem to know a hell of a lot more about it than you do.

Can you please provide the name of the lab that did the radiation pattern testing for that magic PC logo you call an "eight element antenna" on the XPS PCB?

Testing RF radiation patterns requires quite specialist equipment so if you can support your claims in respect to this essential aspect of XPS, you must have used someone with that specialist gear. That means an established university or testing lab.

Which was it Jim?

And yes, for the record, RF isn't all I do -- but I'm not into paintball I'm afraid :-)

[Daemon]

Frank, did you try moving the XPS Tx and Rx away from each other while the
external noise source was close to either one? I'd think the analog video Tx
would be the worst (my 500mW 2.4Ghz video Tx on 3 of its 4 channels
takes out my home network completely).

If you monitor the current draw at the XPS Tx closely you'll know exactly
when it starts retransmitting packets (either due to the Rx not
hearing the Tx and not sending Acks, or the Tx being so overwhelmed
with noise that it can't hear the acks from the Rx.) because
the current draw will go up (On my Optic 6, it shows the voltage go
down immediately). I think if you move the Tx and Rx away from
each other and put the noise source very close to one or the other, you'll
see the Tx start retransmitting, and then negotiate a channel switch.

ian