Kiwi's XPS test results are up.

[Daemon]

	Quote: Originally Posted by zoomer260
	"Might as well send current stick position" makes a whole lot of sense. Why it would wait for a reply would only makes sense if it intended to do something about it if it did not get a reply. Which if it did Jim would be all over these threads. Which he isn't. So since a laymen such as myself can only make use of information at hand would decide XPS just is not the way to go 2.4. I have no intention to bash anyone but the proof is in the pudding. He would settle this matter quickly if it was possible. Since for me XPS is a dead horse I am WAY more interested in how they all stack up to interferance before "lockout". Very patiently waiting on those results should the testing get that far. Thanks KIWI

It's a module based system with PPM signal as the input.
PPM frames are 20ms long. XPS can not send updated stick positions until the next
PPM frame comes along. However, if it fails to receive an ACK for the first packet it sends
(which could mean the Rx can't hear the Tx, or the Tx can't hear the Rx), it has 3 more
opportunities to re-transmit that same packet (can see it all in my screencaps posted above),
before the next PPM frame comes along with updated stick positions.

There's nothing illogical about how it works, and it can't really work any other way.
Packets are occasionally lost, and need to be retransmitted to avoid loss of responsiveness.

If it were tied directly to the Tx CPU then it could send updated stick positions much more frequently.

ian

[XJet]

	Quote: Originally Posted by Daemon
	It's a module based system with PPM signal as the input. PPM frames are 20ms long. XPS can not send updated stick positions until the next PPM frame comes along. There's nothing illogical about how it works, and it can't really work any other way. If it were tied directly to the Tx CPU then it could send updated stick positions much more frequently.

This is why I chuckle when I hear people gushing over how much more responsive their models feel with XPS (or any other module-based system).

The *fastest* way to get the stick positions to the servos is actually to use a good old FM/PPM receiver.

There are no processing or packetization delays -- the pulse is simply used to modulate the transmitter which produces a corresponding change in the receiver which is passed straight onto the servo.

All *any* module-based 2.4GHz system can do is add extra delays to the basic FM/PPM model.

Yes, a good module-based 2.4GHz system might just be better than a PCM system but I've never heard anyone using PCM saying "I feel more disconnected than when I used FM" so I still wonder if the difference is actually perceptible.

Ain't the placebo effect a wonderful thing :-)

The reality is that on 2.4GHz we have bandwidth to burn so the next step will doubtless be a doubling or tripling of the frame-rate -- but that won't be of much use until we have servos that can also cope with a much faster pulse-rate than the current 50Hz.

Exciting things ahead for RC :-)

[Simpleton]

	Quote: Originally Posted by XJet
	This is why I chuckle when I hear people gushing over how much more responsive their models feel with XPS (or any other module-based system). The *fastest* way to get the stick positions to the servos is actually to use a good old FM/PPM receiver.

Call it placebo if you will, but I can tell a difference between a Futaba PPM RX and a DSP filter RX such as a Berg. Both are FM PPM, both use the same TX module. So I suppose it's conceivable that if one went from a PPM FM DSP Berg to an XPS system, one could indeed perceive a difference?

[RTK]

	Quote: Originally Posted by XJet
	All *any* module-based 2.4GHz system can do is add extra delays to the basic FM/PPM model. Exciting things ahead for RC :-)

Not according to Futaba on their modular based systems, or at least on the high end ones.

[Flyfast1]

	Quote: Originally Posted by XJet
	This is why I chuckle when I hear people gushing over how much more responsive their models feel with XPS (or any other module-based system). The *fastest* way to get the stick positions to the servos is actually to use a good old FM/PPM receiver. There are no processing or packetization delays -- the pulse is simply used to modulate the transmitter which produces a corresponding change in the receiver which is passed straight onto the servo. All *any* module-based 2.4GHz system can do is add extra delays to the basic FM/PPM model. Yes, a good module-based 2.4GHz system might just be better than a PCM system but I've never heard anyone using PCM saying "I feel more disconnected than when I used FM" so I still wonder if the difference is actually perceptible. Ain't the placebo effect a wonderful thing :-) The reality is that on 2.4GHz we have bandwidth to burn so the next step will doubtless be a doubling or tripling of the frame-rate -- but that won't be of much use until we have servos that can also cope with a much faster pulse-rate than the current 50Hz. Exciting things ahead for RC :-)

XJet,

It would seem that the retransmission capability might prevent lost packets. Suppose that interference prevented a particular packet from being received by the receiver. With XPS, if the transmitter does not receive an ACK, then it retransmits the data (with the same values). If the retransmitted data is received by the receiver, then the data is successfully transmitted within one frame time period. With a convention PPM system, my understanding is that each frame is only sent once. So if interference prevents the receiver from receiving the frame, then that frame is lost and you have to wait until the next frame. It would appear that the XPS retransmission capability reduces the likliehood of lost frames. So, although the XPS system can't increase the speed at which updated stick position information is received, it would appear that it can increase the liklihood that each frame is received. Perhaps this is what users are experiencing.

-Ed B.

[dick hanson]

	Quote: Originally Posted by XJet
	This is why I chuckle when I hear people gushing over how much more responsive their models feel with XPS (or any other module-based system). The *fastest* way to get the stick positions to the servos is actually to use a good old FM/PPM receiver. There are no processing or packetization delays -- the pulse is simply used to modulate the transmitter which produces a corresponding change in the receiver which is passed straight onto the servo. All *any* module-based 2.4GHz system can do is add extra delays to the basic FM/PPM model. Yes, a good module-based 2.4GHz system might just be better than a PCM system but I've never heard anyone using PCM saying "I feel more disconnected than when I used FM" so I still wonder if the difference is actually perceptible. Ain't the placebo effect a wonderful thing :-) The reality is that on 2.4GHz we have bandwidth to burn so the next step will doubtless be a doubling or tripling of the frame-rate -- but that won't be of much use until we have servos that can also cope with a much faster pulse-rate than the current 50Hz. Exciting things ahead for RC :-)

The difference in actual flying --between a PCM and a purpose built 2.4 DSM2 -is noticable -(as example a DX7-9 etc..)
the servos we originally ALL used before PCM hit the market --were NOT really happy with the 512 systems (early PCM made them steppy -notchy) -
PPM signal was smoother --no mistake - the new digital servos took incoming info and increased smoothness to erase the steps- and an added benifit --was that there was more info ( inputs of power to motor) on the new digital servos this smoothed out the PCM 512/1024 plus made holding power better
So----- if you take a DX7 -and good servos - you will see a definite improvement .
Hardly anyone (no one I know) ever flies /flew IMAC ' TOC with PPM-- I can't really comment on 2.4 vs PPM -except for my little foam models and there - the servos are almost all pretty lousy around center The new little JR's are VERY good -but then I threw away all my PPM little rx stuff as it was also so friggen glitchy I couldn't wait to get rid of it.
My present 9303 on 2048 -on 2.4 --is without a doubt - smoother more positive than ANY system I ever flew prior to it - no Placebo effect -I can (as could others who tried the same setup tell the difference. This on a fairly std 33% EDGE digitals on all surfaces - A123 batteries

[Kiwi]

OK gents.

I´m stuck here away from most of my tools but I found enough to keep some more information coming your way.

Today I sat a SPEKTRUM 7 radio and an XPS module in a 8UAPS transmitter one meter (thats a yard guys) from the scanner. Both antennas were attached and in clear veiw of the scanner receiver antenna.

What was I looking for this time?? Power. It seems that there is a conception that XPS can wade through more noise or interference because it is more powerful.

http://www.flyinggiants.com/gallery/...=40924&cat=500

My test with both radios fully charged, exactly the same distance from the scanner show otherwise.

I will let the more technical savvy guys explain the difference as its something I do not proffess to know.

I hope you guys can lay it down in easy to understand terminology.

If you click on the link it will take you too a better image. Double click that image to expand it.

SPEKTRUM is on the two outer channels and XPS is the one in the middle. The Dbm reading appears to be significantly stronger for the SPEKTRUM setup as opposed to XPS.

If this is the case then XPS does not appear to hop frequencies and delivers less power than SPEKTRUM system.

Given that SPEKTRUM is more powerful and twice as resilient then it appears to me that SPEKTRUM has an obvious advantage when it comes to being beaten around by noisy flying sites or interference.

[Julez]

	Quote:
	Not according to Futaba on their modular based systems, or at least on the high end ones.

Definitely crap for the modules that use the PPM pulsetrain. Try to beat 0.5ms for a purely analogue transmission. Many "dedicated" systems (T6) also use a PPM pulsetrain inside, they are also slower than the MHZ versions.

[Kiwi]

OK here´s another one for the gallery.

This time I had SPEKTRUM 7, XPS and FASST (TM14) all running side by side.

Again some interesting results but not so easy to see as last time.

The outer two channels are SP7 and again they show a higher performance than XPS so it was no fluke. Then if you expand the data logger file you will a very large amount of blue dots with the upper level also above the XPS transmission power levels.

So my assumption is that FASST and SPEKTRUM have superior transmitter output than XPS.

If I am wrong I am willing to listen to reason so anyone with knowledge on what I have here is totally welcome to pull it to peices for us.

http://www.flyinggiants.com/gallery/...hp?photo=40925

[gareth.ky]

Interesting. I see something peculiar in the FASST plot there. Seems like every once in a while it hopes sequentially producing streaks or smears in the time plot. Like its doing a simple cycle through the channels. Then it goes back to pseudorandom hopping untill about a 30 seconds later when it produces the smears again the the exact same places.

I wonder what its doing there? Maybe its nothing. Maybe its doing something cool.

[ConRadical]

Kiwi,

what power output was the XPS system set on? It is adjustable and i believe it's set on one of the lower ones from the factory to conform to international FCC like organizations.

	Quote: Originally Posted by Kiwi
	OK gents. I´m stuck here away from most of my tools but I found enough to keep some more information coming your way. Today I sat a SPEKTRUM 7 radio and an XPS module in a 8UAPS transmitter one meter (thats a yard guys) from the scanner. Both antennas were attached and in clear veiw of the scanner receiver antenna. What was I looking for this time?? Power. It seems that there is a conception that XPS can wade through more noise or interference because it is more powerful. http://www.flyinggiants.com/gallery/...=40924&cat=500 My test with both radios fully charged, exactly the same distance from the scanner show otherwise. I will let the more technical savvy guys explain the difference as its something I do not proffess to know. I hope you guys can lay it down in easy to understand terminology. If you click on the link it will take you too a better image. Double click that image to expand it. SPEKTRUM is on the two outer channels and XPS is the one in the middle. The Dbm reading appears to be significantly stronger for the SPEKTRUM setup as opposed to XPS. If this is the case then XPS does not appear to hop frequencies and delivers less power than SPEKTRUM system. Given that SPEKTRUM is more powerful and twice as resilient then it appears to me that SPEKTRUM has an obvious advantage when it comes to being beaten around by noisy flying sites or interference.

[Kiwi]

Conrad,

Unless I need to pop the case open and move some switches then I cant say. I tested it as it arrived and assumed it would need no more.

Four screws and you can get inside it but its not mine to do that with mate.