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RF Interference

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Old 08-19-2003, 01:06 AM
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Moparmaniac
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Default RF Interference

Hi Guys: I cant seem to get an answer to a perplexing question.Even tried emailing Hitec with no response.So here it is one more time(Please somebody Help)Can you use a noise trap,such as Ace noise trap y harness with digital servos?Is there another product that you guys are using to safe guard against RFI when running long servo leads?Or is twisted wires sufficient?
I am running six 5945 digitals in my GP Pitts. 4 for ailerons,two for elevator.I am going to y the aileron servos channel1&6.the leads are pretty long,also will y the elevator sevos to channel 2 ,they are also fairly long.I just dont want to have a problem with RFI interference,even used Kevlar for tail bracing.Any Help on this question would be greatly appreciated!


Thanks Terry Allen
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Old 08-19-2003, 11:14 AM
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Default RF Interference

Terry,
Noise traps are a problem for Futaba, and I believe they are for Hitec as well (but not certain.)

What many giant scale modelers do is...
1. use heavier gauge wires
2. make your own leads so there are NO connectors in line
3. twist the wires
4. stay FARRRR away from kevlar/carbon fiber with the servo leads and esp the antenna
5. consider using a JR matchbox or Futaba synchronizer for your aileron servos and provide them their own battery power.

some use fiber optic leads, and a variety of other possibilities as well....
you might get more answers to your q if you repost it as "servo leads in giant scale models" or something like that....
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Old 08-19-2003, 03:01 PM
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Originally posted by amcross
Terry,
Noise traps are a problem for Futaba, and I believe they are for Hitec as well (but not certain.)

What many giant scale modelers do is...
1. use heavier gauge wires
2. make your own leads so there are NO connectors in line
3. twist the wires
4. stay FARRRR away from kevlar/carbon fiber with the servo leads and esp the antenna
5. consider using a JR matchbox or Futaba synchronizer for your aileron servos and provide them their own battery power.

some use fiber optic leads, and a variety of other possibilities as well....
you might get more answers to your q if you repost it as "servo leads in giant scale models" or something like that....
Items 1,2,&3 are good advise.

In item 4 there is no restriction for the the use of kevlar. Its non conductive.
Item 5 In my opinion the matchbox or synchronizer are just another box that can cause trouble. The same for fiber optics. Its just an unneeded complication.
As to your question about noise traps. Forget them- you don't need them
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Old 08-20-2003, 01:19 AM
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Default Rf interference

Thanks for the information AnneMarie and Dirty Bird it is GREATLY APPRECIATED

Terry
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Old 08-20-2003, 02:15 AM
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Default RF Interference

I know what you need. JR calls em noise traps to soak up bad RF. Everyone else calls em torad coils. Call an electronic parts shop (radioshack no longer has them) and ask for torad coils (sounds like a dinosaur). Anyway, get the ring type coil and wrap your servo leads aound it 3 times. These things work wonders. JR sells them for $12 for 2, local electronic parts store has them for ~a buck a piece.

Hope this helps,
brian
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Old 08-20-2003, 07:30 AM
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Default RF Interference

Virtually every electrical device I've ever seen uses those things. Every keyboard has one (some at both ends) The wireing harness of a PC case is usually going through one. Ect.. ect.. They're cheap and good at eliminating high frequency noise. Don't work so well with low frequency stuff, otherwise they'd interfer with the signals sent through them.
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Old 08-20-2003, 04:14 PM
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Default noise traps

Originally posted by Lynx
Virtually every electrical device I've ever seen uses those things. Every keyboard has one (some at both ends) The wireing harness of a PC case is usually going through one. Ect.. ect.. They're cheap and good at eliminating high frequency noise. Don't work so well with low frequency stuff, otherwise they'd interfer with the signals sent through them.
And in almost every case they are not needed.
You appear to work in electronic repair. Try clipping them off and you will see that they do nothing.
Having worked in electronic design I know that engineers stick them on because they are cheap and easy to do and might possibly be of help. They rarely help.
In our case, the only thing they would do is help eliminate noise created by arcing at the motor brushes in the servo. If you have this problem, this servo should be replaced. You have a serious problem with it like a broken wire or something.
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Old 08-20-2003, 07:45 PM
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Rodney
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Default RF Interference

Its "toroid" not torad. And, the above comments are correct in that they probably only help your mental attitude, not the interferance. The same goes for twisting the leads, only helps in some rare and unusual cases. Most of your problems will be solved by going to large gauge wire and very good (or no) connectors. The impedance on the positive and negative wires must be kept very low.
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Old 08-21-2003, 01:14 AM
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Default RF Interference

Well, the information about the toroid coil was given to me by an electronics engineer who just so happens to work at a manufacturing plant, where you would see many parts to boeing 777's are made, not to mention the space shuttle parts.

If he thinks they work, then surely they work.
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Old 08-21-2003, 03:18 PM
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Default toroid

Originally posted by smartman300
Well, the information about the toroid coil was given to me by an electronics engineer who just so happens to work at a manufacturing plant, where you would see many parts to boeing 777's are made, not to mention the space shuttle parts.

If he thinks they work, then surely they work.
Sure they work. They work great where they are needed.
Its just that they will not do anything in our case. I am sure that your engineer will agree if he would look carefully at our system.
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Old 08-21-2003, 11:21 PM
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Default RF Interference

Then what could you use to absorb the bad RF you're getting from servos and their leads? JR recmmends those Totoid coils for just that purpose. They carry them on their website.

What other solutions other than this are there?
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Old 08-22-2003, 12:14 AM
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Default RF Interference

I'm going to have to give my vote towards toroids, at least when they are used in R/C applications that benefit from them. They can help some situations that involve common mode EMI/RFI noise.

I have personally used them to tame conducted RFI from a JR gyro, as well as other R/C related noise issues. I usually use Type 43 ferrite toriods for common-mode cures.

The big issue is that there are several different causes and cures for the glitch issues that R/C'ers run into. There isn't a single cure for them all. The secrete is knowing how to troubleshoot and determine the fix.

Sometimes it is as simple as bigger wires. Other times it requires EMI/RFI solutions that are not as obvious -- like toroids.
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Old 08-22-2003, 02:32 AM
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Very small value ceramic capacitors will kill RF as well. You just have to test it out throughly, because this smooths the usual square wave the servo is used to getting somewhat.
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Old 08-22-2003, 03:29 PM
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Originally posted by Lynx
Very small value ceramic capacitors will kill RF as well. You just have to test it out throughly, because this smooths the usual square wave the servo is used to getting somewhat.
I agree. The servo has these installed internally. They also have the case of the motor grounded which forms a shield around the motor brushes. This is one of the reasons why I say the toroids are not necessary.

Digital servos create much more problems than our older servos because their pulsing is asynchronous to our systems. I made some carefull checks when I first started to use them and found no extra RF noise created even with the extra pulsing. They can ,however, cause large current surges on the power lines to the servo. This can cause cross coupling to the pulse lead. But this coupled pulse must be great enough to pulse the servo- at least .5 volts. In this case the toroid would be of no help at all. The only help would be larger wire and bigger batteries.

I am sure JR and others will be happy to sell you toroids if you think you need them.

To RC-CAM -I have not used gyros, perhaps toroids are useful there if they have no internal RF protection
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Old 08-23-2003, 05:36 AM
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A large capacitor would get rid of some of those problems with digitals if you connected it between VCC and ground. Don't know if that's really practical though.
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Old 08-23-2003, 02:25 PM
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The large capacitors would only help if they were mounted right next to each servo; a single one near the receiver would do some but very little good as you would still get the voltage drop due to the servo wire impedance.
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Old 08-23-2003, 03:39 PM
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Default RF Interference

Originally posted by Rodney
The large capacitors would only help if they were mounted right next to each servo; a single one near the receiver would do some but very little good as you would still get the voltage drop due to the servo wire impedance.
It would have to be a very large capacitor to prevent much of any voltage drop. You would be better off using a battery- or increasing the size of the battery we already have and increasing the wire size
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Old 08-23-2003, 06:19 PM
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Default RF Interference

It's not to stop voltage drop though it's to stop the micro fluctuations that are caused by the increased update rate of the digitals power pulses.
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Old 08-23-2003, 11:14 PM
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Originally posted by Lynx
It's not to stop voltage drop though it's to stop the micro fluctuations that are caused by the increased update rate of the digitals power pulses.
Just what will these micro fluctuations bother? Any rf will be bypassed out by the caps in the servo. You may see something on a 'scope but its not big enough or high enough in frequency to do anything.
Line loss due to high current surges is the problem. See my previous post for the cure
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Old 08-24-2003, 12:13 AM
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or increasing the size of the battery we already have and increasing the wire size
...are you talking about the servo wire??
22AWG will go 4.4amps before showing any significant losses.
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Old 08-24-2003, 06:13 AM
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Define significant Blkbird. That's true Dirty, after re-reading everything I see what they're talking about. I hope that over the next year, or two at most, super capacitors will get to the point where they can be used in servo applications to fix just that kind of problem. As it is they would work, and then some. But they increase size and add a little bit of wasted electricity to the system. Even the highest of the high end super caps have relatively high leakage rates. But they're also still expensive because of the way the materials that make them are made. It's really scarey though, you can actually do spot DC arc welding off a 9 volt battery with those things =O
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Old 08-24-2003, 06:18 AM
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I call approx. 0.1V drop @ 3amps insignificant on a 36" extension...but you have to replace the "stock" connectors to achieve that...

...and the 4.4 amp level I referred to earlier is the point were losses passed 0.5V drop. after that point losses increased rapidly.
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