I need help with my Futaba Skysport6 radio system. The problem is that when the airplane passes approximately in front of me while flying, it makes one quick but significant "twitch" in the controls. By twitch, I mean that the airplane makes a sudden dip or change in position and then returns to normal control. The twitch seems to occur mostly in the elevator control but may also affect the throttle and the ailerons. The twitch only seems happen when the plane is in one location - right in front of me. The plane is a Hobbico Extra 300 with an OS 61FX engine.
One person at my R/C club thought that the twitch was due to the transmission pattern of the radio antenna and was not too concerned about it. However, another person thought that there was a problem with the radio system and said I should not fly the model until the problem is corrected. The twitch is quite noticeable, even by spectators.
It twitches when the airplane flies through a point directly in line with the end of the transmitter antenna. There is ZERO signal at that point. Always be sure the transmitter antenna is at an angle to the aircraft.
| It twitches when the airplane flies through a point directly in line with | the end of the transmitter antenna. There is ZERO signal at that point.
Incorrect.
The signal is indeed greatly reduced if the antenna is pointed straight at the plane, but it's not ZERO. Exactly how reduced it is I don't know -- 10 dB or so? The signal is bouncing off the ground and any metal objects around you, so the signal will never be ZERO.
| Always be sure the transmitter antenna is at an angle to the aircraft.
For the strongest signal, having the plane at approximately right angles to your antenna would be best, but in practice it really doesn't matter unless the plane is at the limits of your vision, or something is seriously wrong.
| > One person at my R/C club thought that the twitch was due to the | > transmission pattern of the radio antenna and was not too concerned | > about it. However, another person thought that there was a problem | > with the radio system and said I should not fly the model until the | > problem is corrected. The twitch is quite noticeable, even by | > spectators.
If it does it repeatedly, and is enough to make a signifigant change in the plane's trajectory while it's flying reasonably close-in, you need to figure out what it is. If it happens during landing, it could crash your plane.
Does anybody have a transmitter on your channel? (of course, the shifts will have to match too.) Let them try it (a range check may be adequate, but you may want to try a flight test too) with your plane. Try your transmitter on their plane -- see if you can narrow down the source of the problem.
Often it's something to do with the antenna placement in the plane. Or there's two metal objects rubbing against each other, creating noise that way.
It is not likely that it has anything to do with your transmitter. Your transmitter doesn't know where the plane is so it just keeps radiating. The signal off the end of the antenna is strong enough to keep control at normal flying distances.
More likely you have one of these occurring:
The antenna placement in your plane causes a dip in signal strength when the plane is at that particular orientation to you. Try flying flat circles at both ends of the field and see if it still happens. Try moving the antenna to another position in the plane.
There is a source of interference/attenuation at the field. One field I flew at did exactly the same thing over a particular area. Turned out to be a barbed wire fence. Once the fence was removed, the interference went away. Does anyone else on the same channel have the problem?
i had the same thing happen to me years ago - a particular airplane would twitch at a specific place at the field. as my other airplanes didn't do it, there was something in the set-up of the airplane that caused it. i never pursued it, because it was quick burst and wasn't going to crash the airplane. you might try turning slightly as the plane passes in front of you, also be aware of how many and how close other pilots are to you when you are flying, all can cause what you are describing. and for your next radio...pcm.
Better go back to school on how the antenna radiates. If you want to point your antenna directly at your airplane, then so be it. And don't complain about glitches if you do. It's always just a little momentary twitch while the aircraft passes through that point so normally no harm done other than a nervous pilot!
I haven't observed any fliers that stand rigid in one place with the antenna pointing to only one point in the sky. What I have seen is fliers turning and following the plane about the sky. If it was merely the lack of tip radiation from the antenna, you would expect the glitches to be at just about any point in the sky and randomly inserted.
I originally posted this over 24 hrs ago but it has not shown up anywhere. Anyway here it is again.
I have a 'plane that used to do that. I had a length of twisted wire connected to the plug for a remote igniter. The wire had one (yes, just one) broken wire in it right at the plug that was making intermitent contact. When the 'plane was passing overhead, directly in front, it would twitch noticably. What I think is that as long as the signal was strong the occasional contact at the broken point did not matter, but when the signal was weak it allowed the interference. You may have something similar in some metal to metal, or a frayed wire somewhere, or even in the routing of the antenna. The best way to find something like this, is to 1st check for all these sorts of things then start swapping out with a buddy if he has a radio on the same freq. Swap the rx, then the pack, then the switch etc. BTW, have you checked the antenna on the tx to make sure that it has not unscrewed from the base. I have on Futaba tx that comes unscrewed very easily. Every time I pick it up now I give the antenna a little twist to ensure that it is tight. Gord Schindler MAAC6694
----- Original Message ----- From: "Rich B" Newsgroups: rec.models.rc.air Sent: Sunday, September 26, 2004 9:46 PM Subject: Need Help with Control Twitch
Another poster said the signal strength was down about 10 dBs off the end of the antenna. That's a LOT of loss for only 500 mW.
The moral: Never point your antenna directly at the model, and fix any SMALL problem before it becomes a BIG problem. Frankly, if this was my plane, I'd be going through it with a fine-tooth comb to fix that twitch. Dr.1 Driver "There's a Hun in the sun!"
| Better go back to school on how the antenna radiates. If you want to point | your antenna directly at your airplane, then so be it. And don't complain | about glitches if you do.
If you're going to correct me, at least be correct. I do have an idea of how an antenna radiates, but this is the real world. We're not talking about an antenna and airplane in outer space here -- the Earth plays a large part in how the waves propagate.
Since you don't seem to have understood, I'll state it again :
Pointing your antenna directly at your plane does not drop the signal received to ZERO (you capitialized the word, so I will too.) It greatly reduces the signal, yes, and may cause a glitch if the signal is low enough, but the signal does not drop to ZERO.
| It's always just a little momentary twitch while the aircraft passes | through that point so normally no harm done other than a nervous | pilot!
If you were to *keep* the antenna pointed right at the plane, as long as the plane were fairly close in (less than 1/10th of a mile?) and everything was set up properly, you'd probably not notice any glitching at all.
| > In article , jeboba | wrote: | >
| > | It twitches when the airplane flies through a point directly in | > | line with the end of the transmitter antenna. There is ZERO | > | signal at that point. | >
| > Incorrect. | >
| > The signal is indeed greatly reduced if the antenna is pointed | > straight at the plane, but it's not ZERO. Exactly how reduced it is I | > don't know -- 10 dB or so? The signal is bouncing off the ground and | > any metal objects around you, so the signal will never be ZERO.
And as somebody else mentioned, yes, 10 dB is a lot (though it's just a guess on my part.) A 10 dB reduction in signal would reduce range by 67% or so in theory. But since the normal range is usually more than 1.5 miles if everything works properly, dropping that to 0.5 miles for a second here and a second there is usually ok. (Unless you're trying to accurately land your plane one mile away, I guess.)
Let me state it another way: Your plane should *never* glitch if your antenna is fully extended and the plane is within 500 feet (about
1/10th of a mile), no matter what orientation the two antennas are in
-- even if you point your transmitter antenna right at the plane, and the plane antenna is pointed right at the transmitter. If you do find your plane glitching anyways, then something is wrong and probably should be tracked down and corrected.
Even still, that drop is in a VERY small pattern and if that was the problem, it would show up EVERY time the antenna was pointed at the plane, not just when it flew by the center. Also, I think that if you get that much signal loss that close to the transmitter you must have some other larger problem to deal with.
I agree with you Doug. At our club we have one spot on the field that give a split second glitch. It effects my elevator on another pilot radio it's the throttle. We're all on different channels, the only thing common is it only effects PPM receivers not PCM.
We have the same problem where I fly and it's caused by reflections off a row of large iron hangars.
As anyone familiar with basic wave physics will know, when you have two sets of waves interacting (such as a transmitter and the reflection of that transmitter signal from a large reflective surface such as a metal hangar) you get interference patterns that create areas of very high amplitude (where the waves reinforce each other) and areas of very low amplitude (where the waves cancel each other out).
When I fly a PPM receiver through this dead-spot (caused by the reflected signal virtually cancelling out the direct signal from the transmitter), I get a momentary glitch. This occurs at exactly the same place every time -- unless you stand in a different place with the transmitter -- then the dead-spot moves a few yards.
This dead spot turned out to be a real pain because it was right on the approach path for landing and would affect my models when they were about 10-15 feet above the ground, causing the throttle to blip open momentarily and the elevator to twitch down -- exciting stuff!
This happened when using "dumb" PPM receivers -- I had a Hitec 555 and a Hitec Supreme -- they both responded identically.
After I switched to using FMA M5 and Berg DSP receivers the effects of the problem disappeared.
Yes, the signal was still lost momentarily as the plane passed through the dead-spot but, even though they are PPM receivers, both the Berg and the M5 have computer-based decoders that respond to bursts of interference or loss of signal by ignoring the spurious signals and simply maintaining the servos at their last valid position.
This experience really sold me on the Berg and FMA M5 receivers -- they're absolutely amazing. What's more, they're cheaper than the Hitec units and the Berg even does automatic shift detect and locks itself onto the signature of your transmitter with its TSR system.
In theory, this means that once it's recognized *your* transmitter (brand/model), the Berg won't respond to any other transmitter (of a different brand/model) that might appear on your frequency.
No, this doesn't mean that two people can fly Berg receivers on the same frequency at the same time, but it *does* provide another very useful level of insurance against getting shot down by some idiot who turns his transmitter on in the pits while you're flying on the same frquency.
I checked this out the other day with the following results:
I turned on my Hitec Eclipse 7 transmitter then turned on the Berg 5 DSP II receiver. Everything functioned as you'd expect -- no problems.
I then turned off the Eclipse 7 and a friend turned on his Airtronics transmitter on the same channel. The Berg refused to respond at all to his transmitter.
Then, while his transmitter was still on, I turned the Eclipse back on and (despite the fact there were now *two* transmitters operating on the same frequency and both were equidistant from the receiver), the Eclipse once again had full control without any twitching or glitching of the control surfaces.
Just try that little exercise with your old-fashioned "dumb" PPM receiver!
I don't know why people still spend good money on old-fashioned "dumb" PPM receivers like the Hitecs and others when, for *less* money, they can get a state-of-the-art unit like the Berg or M5 that is smaller, lighter and vastly more resistant to interference and being shot down by an idiot without the right transmittter flag.
Okay, Hitec's support is a strong selling point for their gear -- but if you ever call on Berg's support you'll *really* discover what "best in the business" means. When I had questions about the Bergs, I got emailed answers from the designer within a matter of minutes -- on a Sunday! Even Hitec aren't that good!
-- Yes it's true, I really am crazy! Look what I'm doing now
The Berg 5 DSP II is $51.95 from Aircraft-World.com, $49.99 from RC-Direct.com, and $49.94 from allerc.com Note, these prices
*include* crystal.
The FMA M5 is $55 from RadicalRC.com *including* crystal.
By comparison, the Hitec 555 is $52.99 and the Supreme is $45.99 from ServoCity but you have to add another $7.95 to those prices because a crystal is not included.
If you need more than 5-channels then the Berg and FMA offerings are a little more pricey than Hitec's "dumb" receivers -- but the 6-channel Berg ($79.99 @ RC-Direct) offers PCM-type programmable failsafe and very high levels of interference rejection so it would be more realistic to compare it to the Hitec PCM receiver which Servo City sells for $94.99 + $7.95 for the crystal.
-- Yes it's true, I really am crazy! Look what I'm doing now
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