Futaba 2.4 GHz FASST Service Advisory

I play by ear, which might have something to do with it. But don't al musicians, even when reading from a score, listen to what they'r playing so they can create the tone and emotional context they're tryin for?

One of the weird things I discovered from that experiment was tha there was a delay setting where the guitar strings felt like they wer covered in grease. I don't mean sounded like they were covered in greas

- they actually felt sort of sticky/slippery to the fingers of my lef hand. I think my brain was struggling to understand the delay betwee touching the string and hearing the note, and chose to interpret it i this way. Weird, a bit like one of those optical illusions we've al seen, only this one was an auditory illusion with a crossover to a th tactile sense!

I don't remember exactly what delay setting caused the "greasy" feelin (it's been few years), but I think it was around 30 mS or so.

-Flieslikeabeagl

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I don't get the Windows choice either. With Linux and Qtopia available why would anyone pay for a buggy OS like Windows CE? (Nice acronym "wince" !)

A bit off topic, but in Dec 2007 I was shopping for portable GPS uni for my car. I was surprised at the number of GPS units I found in stor displays that had locked up and were showing the Windows "blue screen o death", sometimes accompanied by the usual Windows error messages: "xyz.dll cannot be found", "zaerer.exe has committed an illega operation", and so on.

-Flieslikeabeagl

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In article , flieslikeabeagl wrote: | Doug McLaren Wrote: | > | > You'd be surprised how much damage an out-of-control R/C car can do. | > Consider an 1/8th scale car running into your shins at 60 mph -- or | > worse, hitting something and going airborne, flying at your face ... | > | I'll take your word for it. :) I have little personal experience with | RC cars.

As do I. But I have seen some crashes that could have really hurt somebody had somebody been in the wrong place ... ...

-- let me re-insert some text that was trimmed --

| > > Also when the Tx frequency hops, the Rx has to do likewise, which | > > means the two have to sync up again after every hop. And what | > > happens when something goes wrong and the sync up doesn't happen | > > immediately as intended?

--- re-introduction complete ---

| > This sync-up thing is pretty well worked out. People have been doing | > spread spectrum like this for what, 50 years? They know how to make | > it work, and it works. Basically, this is just FHSS FUD. | > | I'm not so sure...most 2.4 GHz FHSS RF links we use have the odd short | dropout that simply isn't of much consequence. Anyone who's used a | cordless phone or a Wi Fi ethernet card has probably experienced these | little glitches. They simply don't matter in the applications mentioned | above. But even a very short glitch causes loss of pilot confidence when | flying an RC model, and a slightly longer glitch can cause a crash.

I was talking specifically to the idea of FHSS `losing sync' when it hops. The only time that this will generally happen is if the TX or RX loses power, or gains/loses some time somehow (going through a wormhole or something similar might do it, let's hope your flying field doesn't have many.)

As for WiFi, it doesn't use FHSS at all, so it's a poor example of FHSS glitching. And cordless phones could use either form of spread spectrum -- or perhaps no spread spectrum at all.

As for glitches not causing problems, even a 1% packet loss in a TCP/IP link, over whatever medium, will really mess things up. The system can recover, yes, but throughput will drop by a very large margin. TCP does handle lost packets, yes, but not very well.

Losing 1% of your R/C frames probably wouldn't even be noticeable by most flyers, because once the next valid frame arrived, all would be well again. With PPM, frames usually aren't lost but are instead corrupted, so you might have a visible `glitch' in the controls where the servos do something you didn't tell them to, but with PCM and SS usually invalid frames are quietly dropped and you probably won't even notice.

| From memory, John Adams said that the FHSS systems had more short | dropouts in the RF link, and the problem was never overcome. There was | also reduced range and S/N ratio with FHSS due to the increased | processing gain of a DSSS system over an FHSS system.

In any event, it sounds like Futaba worked out whatever the problem was. They have been doing spread spectrum in their industrial R/C stuff for well over a decade now, so they probably do know what they're doing -- they just moved slowly in getting it packaged for us. This problem with the zero GUID has nothing to do with FHSS vs DSSS -- it's either a manufacturing process glitch, or overlooking a `weakness' in the components they use (and forgetting to add some sort of failsafe to detect that. They could certainly make their firmware throw an error if a 0 GUID is detected or an invalid CRC in the flash memory, had they considered it.)

(And which is more dangerous? An out of control R/C plane, or crane? Could probably go either way ...)

In any event, Futaba's system does sound like it has one big advantage over Spektrum's system -- how it handles _bad_ interference. Suppose somebody brings their 2.4 GHz camera to the field, and it's using the usual six MHz of bandwidth. Suppose that both 1 MHz channels that your Spektrum system are using are within this 6 MHz (and if Spektrum keeps them far apart, suppose that two people bring their 2.4 GHz cameras ...)

Spread spectrum can cut through interference to some degree, but the range will be greatly reduced. Since Spektrum can't hop channels at all, you'll crash once you get out of the greatly reduced range.

In the Futaba case, OK, less than 10% of the band is `ruined' -- but the rest is fine. So maybe you'll lose 10% of your frames -- the plane might seem slightly `jerky' (or maybe you'd need to lose a lot more than 10% for it to be noticeable) but it's still completely flyable. In fact, you could probably lose 95% of your frames and still fly the plane.

Of course, this is all guesses, because I don't have any Futaba spread-spectrum gear and have not tested any of it.

| That was one of the reasons I attended John Adam's talk back in Jan | 2006. This guy is an engineer and RC pilot

To be fair, if you get a job designing R/C equipment, people will take you a lot more seriously if you actually do R/C. Even if he knew nothing about R/C before getting hired, I'll bet his job/boss probably

*required* that he pick up the hobby if he wasn't already into it.

(It would be nice to be able to deduct R/C stuff on your taxes!)

| Exact title notwithstanding, after his talk and the flood of | questions he answered from the very interested audience

Being first is neat like that!

| I came away with a quite positive impression of the Spektrum | engineering teams work.

Futaba's team probably would have put on a similar performance, had they been first. They could do it now, but people wouldn't be quite so interested anymore -- now there's several R/C spread spectrum vendors, lots of people are using it, ho-hum.

Bit unfail, my WinCE PDA has performed without any issues, I guess it's the little darlings in the stores trying to break them and either trying to load or just deleting things they should not. Not what you'd do if it was your own.

However I thought it was an odd choice, but it gave Futaba the photo and MP3 ability they use for the display. I dare say they use it in industrial machines too,

That's gotta be tough.

Most of the people I know either use their fingers or a pick ;-)

Natural, you have it exactly correct.

Non-volatile memory, like Flash and EEPROM, does NOT mean non- corruptible. There are other technologies, some quite old like fusible link memory, hardware program cards/chips/plugs, etc., that are truly permanent memory. However, those methods could add significantly to production cost. The question is: "What price safety and reliability?"

To points brought up by others: As for re-using older transmitter technology and adapting it to the new 2.4GHz RF link instead of designing new circuitry throughout: that is a far more common practice than most people realize. Most new and complex systems build upon older, proven (read as "reliable") technology. The fact that the FASST system only allows three digit naming indicates that Futaba re-used much of its older encoder sub- system. So what? It works. I always thought that the main reason for going to 2.4 was to improve the RF link. Keep in mind that if you go with an XPS system, that is exactly what you're doing.

Finally, I haven't seen it mentioned anywhere, but I hope that Futaba has a handle on exactly what group of radios has the 0000 ID problem. Surely they can nail it down to serial numbers or production dates?

DougSter

Coffee/keyboard alert! Bastard ;-)