I am going to build a Boomerang for my home grass field. The designer tells me that one of my servo leads will be up to 7.5 feet in length. I have never run leads more than half of that (and I have never had any issues). But now I am worried. I was going to get the Electrodynamics Opto Isolator. I am certain it is a fine product, but like most opto isolators available, it allows you to use a small battery for the receiver and a separate big one for the servos. I am currently very happy with the 12 channel MPX receiver that allows me to connect two separate power systems to give me an isolated, redundant power system. To get this same capability with the opto isolator, I would now need four battery pack and an additional isolator circuit. I feel that this is too much complication and added failure modes, I wanna keep it simple. So here’s what I need advice on: is it worth a try to just use the super long leads and expect a reasonable probability of not having RF issues or can I use those little ferrite donuts that you wind the servo leads around. If the ferrite donuts can do the trick, where can I get the appropriate ones? I see that Radio Shack.com has them, but they have many different sizes and many different materials. Which are the best for my application? How should they be installed (I will use heavy gage servo wire, 22 or better)? One at each end or one every foot or what? Is there a better option not yet explored? Thanks in advance guys, and merry Christmas!

Woketman,

I have had much success using 3 conductor 22 ga. shielded wire in lengths up to 78". At the RX end, I twist the shielding and solder it to the negative wire where it goes into the connector. At the servo end, do not solder the shield to anything. I've never experienced any problems and have used this method of making extensions in quite a number of jets. Also, buying the wire in length is much cheaper than buying "brand" extensions. I usually buy 50 ft. at a time.

Merry Christmas from the soon to be snowy white North!

Mike, I too have done this, but am out of the shielded wire, and the stuff that I had was only about 24 gage. Do you know where to get 22 gage, three conductor shielded wire? Thanks.

Anyone know more about the Ferrite cores? I found this place: http://www.universal-radio.com/catalog/misc/amidon.html Can this be an effective solution? If so, what size and what material or AL rating? Thanks.

Hi Mark:

I answered you on the Jet List before I saw your post here. I am building a Boomer and, have used in the past, and will use Andy's Opto-Isolator with his 60 strand/22 gauge wire with his excellent connectors.

I have used and continue to use Andy's in-lead chokes as well, and ferrites. They all work, but the Isolator makes a clean install on the Boomer.

To be absolutely safe, Andy recommends some sort of RF suppression on any lead over 36" long.

Tom

Tom, if I go Andy's route (which I may) I need four batteries to sleep at night: two small redundant packs into the MPX 12 ch RX, and two coupled with a Battery Backer for the servos. I am getting worried about all of the extra gizmos to fail, not to mention the added weight. Can anyone address the ferrite cores? Are they the same as the "chokes in the leads" as you mentioned? Thanks.

Mark,

Congratulations on the Boomerang. Wait till it starts coming together. It's huge!!! I'm finish sanding and sealing the obechi surfaces at the moment, although I still have a bit of work to do on the fuse before I am ready to cover. The Christmas thing has put a dent in my building progress.

I'm going with ferrite rings for my Boomerang. I think they are 15mm from memory.

These are small and light and I'll just wind the servo wire through the donuts before attaching the plugs.

A friend of mine who is an electronics techo suggested getting hold of some ferrite beads. Apparently these are some sort of clam-shell type fitting that simply snaps shut over the wire and will do the job. I had already bought the rings before he suggested it.

Yet another option. From memory, I thought multiplex either makes their own chokes or can sell extension leads that incorprate some kind of choke.

Regards,
Garrett

Here's the photo Mark.....

I still like the isolator. This Boomerang problem is faced every day by the 40% Giant Scalers with their long leads and (10) or more 8411's all going at the same time on large surfaces, and lot's of them swear by it. I have one in a big F-15 that I have. Works flawlessly. You can make up your own leads, or have Andy make any length you want.
Actuall the battery backer is icing on the cake. You can have almost perfect redundacy with two packs and switches thru a Y-connector--I know some guys will claim it can't be done, but Giant Scalers do it all the time. Lots of post on this subject on Giant Scale on RCU and on the Battery and Charger section as well. The backer just balances the current draw-done more evenly between the cells, and protects one pack in case there is a dead-short in the other pack or switch.

Tom

Mark,

Here's a link to what I am going with ->

http://www1.jaycar.com.au/productVie...Max=&SUBCATID=

Garrett

Garrett, where do you place the ferrite cores, at one end of the wire, the other, or both? Thanks.

Mark,

From my understanding, the leads just need to be looped through the rings at some point along the lead. I'll check with a friend and double check, but I believe the location along the leads makes no difference.

Again, I'll have to double check, but I believe that using multiple rings on a lead won't make much more of a difference.

Garrett

Hi Mark and others.

http://www.rpelectronics.com/Default...ies/Cat_66.asp
This is a local Vancouver electronics shop with lots of techie gizmos.

These guys have a decent selection. I dropped by the shop on Saturday hoping to pick some up for my hotspot's elevons+rudders, but I immediately came a cross the various material designations.

Not being an electrical type myself, anyone out there have any info to share? Am I right in assuming we are looking for the type that allows transmission in the 1-50 MHz band, limiting transmission of frequencies above 50Mhz? What materials are commonly available and what RF bands are they typically associated with?

Hopefully this hasn't been addressed in the email lists and I've already missed it...

Thx,
Kelly

PS, I haven't had a chance to look around at prices but if anyone finds anything at RPE, I could pick it up and send it off for you.

Mark,
Call Jetcat, Bob Wilcox has a good selection of ferrite rings that should do the trick. One loop around the ring at the reciever should be all thats needed. Just make sure you are using 22 gauge leads. I have used leads almost as long as you require with one ring on each lead and never had a noise issue.

Regards,
Todd

The Amidon site has information on their materials.
It would seem that material 43 would be good for servo lead suppressors, since it attenuates between 40 MHz and 200 MHz.

The servo control signal need bandwidth only up to a few kHz, so you don't have to worry about attenutation of the wanted signal with any toroid until you have hundreds of turns. We only use one or two turns (passing the wire through is one turn). More turns is not necessarily better since the noise can couple between the wire in the turns, bypassing the toroid.

http://www.amidon-inductive.com/asso...s_ferrites.htm

For other manufacturers of magnetic material, go to their website.

Amidon, Philips, Siemens, and TDK are the big ones I remember from when I had to design this stuff.

Eddie, do yourself a favor and talk to Andy. He has some interesting thoughts on the length that even aug 22 wire can be without chokes..... If your planning on twisting the wire, Ive heard it makes a difference on how its twisted. Ive heard for longer lengths the three wires should be seperated then twisted. My 4 8411's on the elevators of my Fiber Clasics 40% 330 run about 88 to 90 inches and are single twisted. No problems after 11 flights. Come to think about it, Im not running chokes either.... Later.... Ray Blair

Hi Woketman,
If all you want to do is trap RF ferrite rings or beads will do the trick. If you want to keep RF away from your servo amp to prevent TX's in close proximity to "break in", place them close to the servo. If you want to break the groundplane effect of the wiring system, place them close to the RX. Do both if you want, it can do no harm.
However most perceived "RF" problems are because the servo pulse has to travel on the same ground return path (negative lead) than the servo power. This induces noise to the servo amp output.
The ways to get rid of it is:

1> use an opto isolator at the SERVO end driven by SEPERATE signal and ground return wires, twisted if possible. This eliminates all common mode noise as well as power supply noise. NOTE: Some opto sets sold actually use the same ground return again when using opto isolation. Absolutely pointless. The slight slew rate limiting effect of the isolator is then what actually reduces the noise.

2> use an optoisolator with battery next to servo, same effect as above.

3> put a 10 nano ceramic cap accross the signal and ground wire (reduces noise and limits signal slewrate a bit) as well as a high value low esr cap accross positive and neg wire at the servo end (1000 uF or more, reduces current peaks in the long lead) Most simple and harmless solution. Requires good soldering technique for reliability.

This is all pretty straight forward signal transmission line techniques.

Cheers
Andre

You may also have a problem with signal degradation due to the lengths that you are proposing. I use 5 cells, heavy duty extensions and I keep the lenghts as short as possible. The P120 rev4.0 ECU is a HUGE improvement over the old one, hence if you are using that engine with the rev 4.0 ecu you should be ok assuming the installation is clean and sound. I would keep it simple first, range check with engine at diffirent rpms and attitudes and if you have a problem, then go the isolation route. One more idea, You can use a reciever close the the distant servo, and another reciever for the rest.....just thought about this, may be i'll try it in my L39 once I sell most of my jets to get it

Don Edberg (Futaba), suggests using a 47-100pf capacitor between the signal and ground wires as close to the servo as possible for noise supression

WoketWabbit:

Another method that has worked well for me is the use of RG-179 coax. Leave the power and ground wires alone, run the signal only through the '179. As Mike said, in post #2, tie the shield to ground (negative batt lead) only at the rx end.

Advantage is it's lighter than the 3-cond shielded, and you eliminate the possibility of cross talk through the positive lead.

Crosstalk and RFI cause glitches,
. and they're nasty little sons-a-b.........

Bill.

Anyone got a good source for the shielded 3 conductor or the RG-179 cable that is 22 gage or better? Thanks.

Fudd Prey (WoketWabbit):

Just about any wire you want -

http://www.allcompc.com/toc-coax.htm

I said RG-179, but at the frequencies used for servo control you could even go to Radio Shack and get some small audio extensions and cut the ends off. Probably cheaper, work every bit as well.

If you want the three conductor RS may have some heavy enough, but use two conductor with shield. The third inner wire is not needed.

Three wires, two, or one. Doesn't matter, with a twin you've won.

Bill.

PS: Just to clarify, the signal cable does not need to be 22ga - it just about carries NO current - 36ga is heavy enough if it has the mechanical strength you want. wr

I think you have some very real concerns about the reliability issues in regard to going with an isolator, and loosing the redundancy on the power system. I've always had a problem with taking what is commonly the most common items prone to failure, and adding two more of them, each with their own ability to bring the whole system down. You have greatly increased the probability of failure, and significantly reduced the overall reliability of the entire system, and for the most part in an attempt to solve a non-existent problem (load sharing, interference that doesn't already exist, etc).

My feeling is to always keep electronics simple. The most reliable designs are usually simple ones. A piece of wire is always more reliable than a piece of wire with a circuit soldered in the middle of it, or even just a connector. Adding more electronics can have negative effects overall. So, I tend to try to exhaust the simple solutions prior to adding gadgets (even though I am a gadget freak by nature )

If you only have one long lead (or maybe two), why compromise the entire system in an effort to solve the issue of a single long lead. I would leave the dual battery and switch setup as is, not use an isolator, and try using higher gauge and/or shielded wire for the long leads, and twist them to further reduce the effects of any RFI. Then, range check it, and see where you are at.

I routinely use .22ga wire (non-shielded, no chokes), and run lengths to around 50" or so in my 40% planes. I've never had any issues with interference so far. The majority of pilots flying the big 40% Aerobatic planes are not using isolators, but instead using just a single or dual receiver, and dual battery packs with two switches. Some are using amplified extensions, shielded wire, or chokes, but most of the ones I know personally are just twisting the wires, using a heavier gauge wire, and avoiding the use of Y connectors at the end of long runs.

I would think any issues with regard to the extra 20-30 inches could be resolved with some combination of chokes, twisted and shielded wire, and/or an amplifier. Any of these in my opinion are far more reliable than any of the isolators on the market. And you won't compromise the integrity of the whole system.

Its worth doing some bench tests, and then trying it in the plane, before going with a more complex setup.

Steve:

I agree with you in principle. Keep it simple. One of our club members has been flying 35-40% planes with DA-150 and 3W-120's for the last 5 years. As far as I know, he has never had a radio issue or failure.

Just like you mentioned, he uses dual receivers, dual battery packs and switches, keep the rx's away from the ignition pack, twists his wires, and that's about it. The wire runs on his 40% Carden 540 are not quite as long as the Boomerang, but close.

Unfortunately, I am not an electrical engineer. I have been using toroids and ferrite beads for years with my ham radio stuff, and they work wonders for getting rid of RFI from computer monitors, and stray RFI generated by all the peripheral equiptment in my station. That's basically why I have used some of them in my R/C installations, but really have never had a significant RFI problem that I am aware of in my jets or giant scale, just using clean wiring techniques. I have used Andy Low's opto-isolator, but after reading Andre's post, I have a few questions for Andy about his unit.

I agree with you that every additional item is another failure point. I lost my Bandit 2 weeks ago when an old voltage regulator burned up while I was on final. No more of those for me. I took them out of my other planes and noticed no difference in range check---using 10x with 5 cell Rx packs.

Tom

You might be interested to know that my Fiber Optic servo extensions can go up to 100 feets, not that you will need it but its nice to know.

The power wires are via 22 gauge high flex wires.

Have current issues with short range checks on 27% Extra. I tried five new RX (different brands) and three major TX all with similar results. Long metal push rod in tube to throttle replaced with nylon tube in tube increased range check by a couple of feet.
Now trying different forms of chokes etc.
Information found =
RF Noise in Audio, Video & R/C Systems - chokes.
http://www.vantec.com/noisein.htm
RF Noise - Solving the Servo Jitters
http://www.charlesriverrc.org/articl...rvojitters.htm
Jamara Snap Shut Ferrite Choke RF choke. For stopping interference along long servo lead runs. 3 sizes available hole diameter 3.6mm, 5mm, or 7.5mm
http://www.sussex-model-centre.co.uk...Choke-1989.htm
Multiplex : http://www.multiplex-rc.de/ - click the English flag, then on search panel, go to products and then to MISCELLANEOUS and scroll down list to =
Ferrite ring for separation filter 5pcs. #85131
Separation filter lead (UNI) #85035 (choke already fitted)
MPX instructions for Ferrite Choke for long servo leads =
ID 8.7mm OD 14.3mm Wall thickness 3mm Number of turns 11. Fit a 100 ohm 1/8 watt resistor (black/brown/red/gold) between signal lead and pin on plug to rx and a n33 capacitor between negative (earth) lead and signal lead at the plug. jpeg copy of instruction drawings and of instalation in my large 3 & 4m gliders available in need.
regards
Alan T.
Alan's Hobby, Model & RC Web Links
http://homepages.ihug.co.nz/~atong/
.................................................. ...............

I only used a Skymaster Whip antenna on the nose of my big boomerang.
I never ran RF filters & Never had any radio problems in 2 years of flying.
1 year with a RAM1000 & this year a P120.

JR 8411's on all surfaces with each servo running 22ga lead direct to JR 950 rx in the nose
elev 89", rudd 82", ail 65", flap 48"

Only 1 2700 NiMH rx pack on a regulator & 3300 NiMH ECU pack

Never any radio problems & I fly out far and hammer that jet thru aerobatics.

I'll be trying RF filters on my Kingcat just because BVM says to use them - but I'm using JR's ring style instead of the clamp style.