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[Julez]

Hi!

The Spektrum lockouts are all about Spektrum, not 2.4GHz.
Spektrum recievers are very sensitive to load peaks. They tend to reset in this case, and need 2-10sec to re-establish a link.
FASST recievers do not show this behaviour.
I wrote about the background here:
http://www.rcgroups.com/forums/showt...6V#post7753366

	Quote:
	Low voltage because of dead batterys is not the problem. Low voltage spikes because of load peaks are the problem. There are load peaks in every plane. Some battery packs and switch harnesses are affected more by them, some less. It all boils down to the internal resistance of the voltage source. This is the determining factor of how much voltage drop one will have with a given load. The thing is: The lower the voltage, the smaller the current. It is Ohm`s law. When the voltage will become low enough, the servos will stall and hardly draw any current any more. This means, even with the worst battery and switch harness, the voltage will never drop below the point where the servos are stalling because the load, that caused the voltage to drop, is not applied any more in this case. In fact, it is a kind of control loop: Load increases-->voltage decreases-->load decreases-->voltage increases. When using a normal battery pack, one will never be likely to experience a voltage drop so severe that ist leads to a permanent servo stalling. But, it might be possible to have voltage drops that go quite deep. In fact, when a servo begins to move, it draws the blocking current for the split second it takes the motor to begin to turn. Once the motor turns, the current is considerably lower. This means, that a pack can be totally appropriate for operating all servos - but the voltage will still drop in this tiny split second where the servo draws the maximum current, as the motor begins to turn. Now, we come to the critical part: How will a reciever react on these voltage drops, which are inevitable concerning the nature of batterys and Ohm`s law? We learned, that the battery voltage can never fall beyond the stalling point of the servo - if this was the case, no servo would move in the first place, and this would be suspicious even to the sub- average modeller. For best safety of the complete RC setup, one would want a reciever that locks out at a voltage so low, that this level is never likely to occur. As the servo stalling level is at about 3.1V, and the voltage cannot be any lower, the best reciever would only lock out when this level was undershot. Futaba Fasst recievers lock out below 2.6V. This way, Ohm`s law works like a safeguard that lowers the load to a value where the voltage will not longer decrease. This happens at a level where the voltage is still above the level where the RX would lock out. Spektrum recievers, however, seem to lock out at 3.5V. This is a voltage leven that one is much more likely to experience in an RC setup, as it lies above the servo stalling voltage. In fact, this level can be reached when having a battery that normally does just fine in powering the servos. I have read about many Spektrum lockouts, where the pilot was able to move the servos in the remaining plane wreck. Low voltage because of a flat battery can thus not have been the cause of the crash. To me, using a reciever, which is safeguarded against lockouts by Ohm`s law, offers the following benefits: - The only concern I must have when choosing batterys, is the capacity. Of course, a low internal resistance is a valuable quality, too. But I will never loose my plane just because my batterys do not hold the voltage too well under load. - Mr. Ohm will protect my plane in the case of one dead cell in a 4-pack. 3 cells will sustain 3.6V normally. Voltage drops will be lower now, but my attention will be caught by slower servo movements, and not by faster plane movement (finally stopped by ground impact). - I will be able to use singe LiPoly or LiIon cells in my planes. When every gramm counts, this is an important feature for DLG pilots. Cheers, Julez PS: FASST reboot time: 0.9s

[Hammbone]

	Quote: Originally Posted by bodywerks
	Jim, have you ever flown with the 2.4 on anything other than a foamie or parkflyer? Have you ever had glitches due to ignition/other radio noise? Have you ever went up to grab your freq pin at a major event, only to find that it is already in use and there are three other people in line for it ahead of you? Have you ever been hit due to someone turning on on your frequency or other channel bleed-over? Have you ever had an engine fire up at full throttle or crashed a plane, only to find that you were on the wrong model in your Tx? If your answer to any of these is yes (save the first question), then I would say that 72mhz is faulted and can be/has been improved upon. I ask if you have ever flown 2.4 on a large plane, because if you have, you should have noticed a difference in feel. The 2.4 link is ULTRA locked in - hard to describe, best to experience... Not that anyone who chooses to stick with what has worked for them is in the wrong, but analog servos had worked well for several years, for example, then digtal coreless servos were unveiled and changed the hobby significantly. Same can be said for nimh's to li-ions, dope & fabric to monokote, Ambroid to super glue, etc. I, for one, am one of those guys that will sell my DA 100 if they ever come out with a 112 that weighs the same but produces more power, even if it is only 100 RPM...there are lots of guys like me, I am sure...

I'm all for IMPROVED technology. I don't see 2.4Ghz as an improvement when I see stories all over the forums of how 2.4Ghz caused planes to crash. I'll answer some of your questions: I've had one glitch in 18 years of flying 72Mhz and that's all it was, a glitch. I did not loose the plane. I've rarely had any problems with sharing a frequency pin, but I don't fly at busy fields. I've never been shot down by someone turning on my frequency. As for 2.4 giving you a locked in feel, tell that to the guys that have lost their planes because of 2.4 rx lock out (up to 10 seconds lock out). You can fly what you want. I'll stick with 72Mhz until 2.4Ghz is actually (if it ever is) an improvement over what I use now.

Jim

[Julez]

Hi!

	Quote:
	I don't see 2.4Ghz as an improvement when I see stories all over the forums of how 2.4Ghz caused planes to crash.

What makes you so sure that the chosen frequency, and not the hardware design of one manufacturer is to blame?

Cheers,

Julez

[Hammbone]

	Quote: Originally Posted by Julez
	Hi! What makes you so sure that the chosen frequency, and not the hardware design of one manufacturer is to blame? Cheers, Julez

I'm not sure. All I know is that I'm hearing of a lot of problems that people are having with 2.4Ghz, and I'm going to stick with 72Mhz because I know it works.
If they get all the bugs worked out of 2.4Ghz stuff in a few years, and if it is an improvement over 72Mhz, then I might give it a try. For now, NO WAY! I like my planes and want to keep them.

Jim

[toprudder]

	Quote: Originally Posted by Julez
	What makes you so sure that the chosen frequency, and not the hardware design of one manufacturer is to blame?

I have to agree with you, I think it is more an issue of implementation than the 2.4ghz frequency.

[DR10044]

I have been flying the Futaba FASST 6 channel since late spring, 100+ flights, no problems. When I power up the receiver, by turning on the switch, it takes a second or less to activate and neutralize the servers. My question is, is this the boot time for the receiver? Logically it would seem so. When you turn on a Spectrum receiver, how long does it take to neutralize the servos? Also, does it take longer to reboot a receiver after an inflight voltage drop vs a switch shutoff after a flight?

[dubd]

Jim, just to be clear, the reports of 2.4Ghz crashes are for the most part, with Spektrum hardware. Granted, Spektrum sells more hardware than Xtreme-Link and Futaba's 6 channel radio is too basic programming-wise for most giant scale planes.

[bodywerks]

I wasn't trying to argue with you, Jim. My feeling is that the only reason you "hear" about more 2.4 problems is because 2.4 is the talk of the town. People crash their plane on 2.4 and automatically assume that 2.4 is to blame - kinda like the Salem Witch trials, lol! I bet that for every one plane that has crashed with 2.4 installed - and then posted on the forums as a 2.4 problem (whether it was or not), there are at least 5 planes that crashed on 72mhz due to a lockout, glitch, whatever, that was not posted on the forums.
I would rather go with what I have actually seen or experienced than what I heard...

[Julez]

I also had a crash while using a transmitter I customized with a FASST module.
Because I know that 2.4GHz is more reliable than xxMHz, and FASST RXes do not tend to reboot during flight in contrast to Spektrum counterparts, I ruled out a glitch and searched elsewhere. What I found was a loose connection on the plug of my pulsewidth adaptor.
Other people in my situation would have possibly blamed 2.4 and ranted in forums because this is easier.
And thats how rumors start nowadays.

Cheers,

Julez

[Hammbone]

What about the fact that 2.4Ghz can't see through carbon fiber, metal, fuel tanks, people, trees, etc.? How is this an improvement?

Jim

[bodywerks]

I think that is a misleading statement. 72Mhz has a hard time getting a signal through carbon fiber, too. Glider guys with 100% CF airframes have to run their antennas outside the fuse to get sufficient performance.
I saw the Xlink operate with the receiver covered by a cast iron sink, so I would say that "can't pass through metal" might not be entirely true.
2.4 passes through fuel tanks just dandy, even full of fuel. Now, if you fill it with water, that's a different story - but why would you do that?
I have deliberately put a person in between myself and my plane to test that theory and maintained full control. Others have done the same with the same results.
I never tried trees, but why would I need to? Besides, all my planes are made of wood (just like trees) and the 2.4 receiver is inside it and has been working fine.

The only honest fault I have seen, and experienced, is the looooooong reboot time in the event of a receiver power drop/loss (Spektrum's deal). I have learned not to trust an ESC's BEC to four high-powered micro servos on a 3 pound plane - simple as that.

[Hammbone]

A misleading statement? This comes from the manufacturers themselves.

I think you are correct in saying that 72Mhz can't see through carbon fiber either, but 72Mhz has the ability to go around the carbon fiber as long as the rx isn't completely surrounded by the carbon fiber. 2.4Ghz is line of sight and cannot go around something.
At least that's my understanding.

I just don't see this as an improvement.

Jim

[toprudder]

	Quote: Originally Posted by Hammbone
	2.4Ghz is line of sight and cannot go around something. At least that's my understanding.

Not entirely true.

I have done shielding performance tests of large chambers (faraday cages) at 1ghz and 10ghz. It amazes me how you can aim a transmitting horn antenna at the outside of the chamber and if there is a tiny hole somewhere, the signal will leak in even if the hole is on the other side of the chamber. Granted, it may be highly attenuated (depends on the size of the hole) but it still leaks in. In fact, a 1 or 10 ghz signal will leak in where a 100 mhz signal may not. The shorter wavelengths can squeeze through a smaller hole.

Now, if you want to talk "light", that is another story.

Bob R.

[Hammbone]

Look guys, I don't want to argue with you about this stuff, but the info I am talking about comes straight from the manufacturers of 2.4Ghz systems. They are the ones that say 2.4Ghz is "line of sight", they are the ones that say it has problems going through solid objects.

I don't understand why any of you would risk your planes with 2.4Ghz when this is what the manufacturers are telling you.

It seems like you are just ignoring this info, or thinking it is O.K. because now you don't have to worry about frequencies.

I'll take frequencies over that any day!

EDIT: Then you have the problem of 2.4Ghz rx's locking out if the voltage goes below a certain level................ I've never heard of 72Mhz rx's doing that.

You are free to fly what you want though, as am I.

Take care, Jim

[JEFFRO503]

well..i can't put in my 2 cents on this because i don't own and 2.4 stuff yet.........but i wanted to visit this thread and see if there was any updated info towards the release of the Moduels and so forth. I have a 9Z which is eagerly waiting the release of the fasst moduel.......any news at all? I'm about to just go buy a spektrum moduel i think.