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servo extensions, ferrite rings & signal amplifier

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Old 11-29-2005, 03:05 PM
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aars
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Default servo extensions, ferrite rings & signal amplifier

Guys I need your advice.
I am building a large plane which includes servos in the wings for flaps and ailerons. As you can imagine the distance from the servo to the Rx is relatively large (say 25"-30").
I have read in some places that if the distance is long, it is better to loop the extension wire around a ferrite ring to avoid interference. The ring should be a few inches away from the Rx.
When is this necessary? Is there a specific extension length from which this ring should be used? Do I need a signal amplifier as well? Is it better to change the wire of the servo for a long one instead of using an extension? or using the regular wire and a long extension is OK?

thanks for the input
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Old 11-29-2005, 03:19 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

ferrite ring can be added later if you are getting interference...
just use a good quality extension and you will be fine...no amplifier needed....

What plane?
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Old 11-30-2005, 06:23 AM
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Default RE: servo extensions, ferrite rings & signal amplifier

I agree with exeter.

I'm going to put some long extension on my stab servos (42"), and people suggested me that no other things are needed, apart good heavy duty extensions (JR is the one suggested). Also if you look back to older posts, you will find one of mine in which I asked the same things...

Good flying!
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Old 11-30-2005, 08:44 AM
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Default RE: servo extensions, ferrite rings & signal amplifier

Thanks guys for the info!!!

I'm building a topflite FW 190. What is your opinion on building your own extensions? when you mention heavy duty extensions, is a 22 gauge OK? or should I go for 20 ga?
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Old 11-30-2005, 09:20 AM
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Default RE: servo extensions, ferrite rings & signal amplifier

You're welcome!

Considering nowadays prices, IMO there is no longer the need to make extensions by myself: I paid some euros to get an extension of 42 inches length.

I don't know how many gauges it contains, they are the JR ones. I don't know if, for that length, there are options within JR products: people told me JR heavy duty, here in Italy I purchased not better specified JR extensions, and in fact they are quite thick.

Some good pilots told me to buy the twisted extensions, which can be a better choice since the magnetic field is reduced this way. But other well known pilots I asked this question told me that they simply used JR HD plain extensions, which is what is purchased!

Good luck with your bird!!!
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Old 11-30-2005, 12:30 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

It is highly doubtful that ferrite beads or twisting will do any good. The twisting won't hurt anything though the ferrite beads might. The two most important things are 1:good gold plated connections and 2: adequate gage wire, at least 22 gage 20 preferable. Minimise any connectors, i.e. don't insert extensions with the added connectors, solder in adequate length wire by breaking in between the present connector and servo and splicing in an extension by soldering in the wires. Hidden connectors have been the cause of many model demise as they corrode and become high impedance connections with time when not repeatedly excercised to keep the corrosion worn off.
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Old 11-30-2005, 12:36 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

I"m moving this to the general radios area. Discussions don't belong in the direct support areas.
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Old 11-30-2005, 02:05 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

Thanks for the input Rodney!!

You mentioned a procedure: "breaking in between the present connector and servo and splicing in an extension by soldering in the wires". Instead of breaking the wire and soldering, would it be better to simply replace the current 3"-4" servo wire for a 30" wire with no connections/soldering in the middle?
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Old 11-30-2005, 03:37 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

I agree, great explaination Rodney!

Could you be more precise about the minimisation of connectors? Are they source of impedence more than the extensions itself?
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Old 11-30-2005, 04:37 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

Stek79, yes, connectors can be a problem. As is always the case, you can buy several grades or quality of connectors. Good ones are gold plated with a well designed contact area. In the typical price wars in the hobby industry, many connectors do not meet these specs. How serious can the problem be, depends on the current being drawn. Most servos are drawing peak currents of 2 amperes or less but when you get into the more powerful servos, this instantanious current can jump up to several amperes. While these peaks only last for milliseconds, the resulting momentary voltage depression can effect the servo response and even cause chatter or jitter. If one of these high impedance connectors happen to be between the battery and the receiver, it can cause the receiver to loose lock and you will think you are getting interferance when really it is just the receiver not getting enough voltage 100% or the time.
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Old 12-01-2005, 09:01 AM
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Default RE: servo extensions, ferrite rings & signal amplifier

Great advice guys, thanks!!!

I think I will replace the regular servo wire for a long wire with no unions/soldering in its way to the Rx, instead of using an extension. For what you say, it seems the best way to avoid unwanted disconnects and unwanted corrosion. I found some places on the internet where they sell the wire and the connectors. These places are: MPI, Servo city, RC Accessory and FMA. Dou you guys have a good experience in any of these places? Is there any supplier where you recommend to purchase these items?

thanks
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Old 12-01-2005, 12:47 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

I tried one of those connectors and crimper kits they sell in the hobby stores. I didn't have much luck with it. I think you have to spend like $250 for a crimper that works good. It would be more economical to have custom extenders made for your application. Let someone else spend the money for a good crimper.
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Old 12-01-2005, 02:34 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

Thank you Rodney for your thorough and very interesting reply!
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Old 12-01-2005, 05:06 PM
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Default RE: servo extensions, ferrite rings & signal amplifier

Ferrite choke cores definitely can help and I have a good deal of experience with them. Usually they are only needed on long elevator and throttle runs (i.e. those parallel to the antenna or pull-pull cables)... ailerons don't need them because typically they are shorter runs and they lie perpendicular to the antenna and cables..

I have dramatically increased my range (both engine off and engine running) using chokes. If the range is excellent (as opposed to good) chances are a small amount of RFI will be rejected. I routinely get 120 feet antenna off on my 10x. That is about right. If I only get 80 feet, its time to choke.

As far as extensions... you don't have to worry about them if they are not there! Most of us solder everywhere we can to eliminate connections. The less connections overall the better. The only connectors on any of my large planes are those at the RX. I buy the 36" flat 20 guage HD extensions from Troy Built models and cut them to size as needed (i.e. cutting off the pin end on the cable and the connector on the servo ) then soldering directly to the servo leads)

BTW - splicing new leads on servos does not void the warranty (unless you mess up the polarity) ..

The leading causes of electrical failure - Batteries, Switches, and Connections
Leading causes of noise (RFI) - switches and connections...

DP
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