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Servo Extensions limit

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Old 09-29-2003, 09:13 AM
  #1  
santiagotor
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Default Servo Extensions limit

I am building a glider with alerons. I will be making my own servo extension.
What's the maximum length before it starts acting as an antena? How can I overcome this? The aprox length i will be using is 1.50 Mts
What should I be aware off?


THanks
Santiago Tores
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Old 09-29-2003, 11:16 AM
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MHawker
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Default RE: Servo Extensions limit

I don't know what length an extension would act as an antenna, but I would think any wire of any length "could" act as an antenna.

I've heard of extensions as long as 48" with no problems. The only precaution I know of is to twist the wires.

As a side note, I just ran into a problem with my Hitec 5625 digital servos and extensions. They have worked fine for 6 months or so using 24" extensions, and now will not work with any extension. It seems to be a voltage issue, but I have gone through various things and it always comes back to the servos.

Just food for thought in case you have Hitec's.
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Old 09-29-2003, 03:22 PM
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JohnW
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Default RE: Servo Extensions limit

Any lenght can act as an antenna. Sections that electrically appear in 1/4 wave increments have a better chance, but I don't think this is your primary concern. I'd be more concerned with voltage loss, both bus voltage and signal voltage. I'd start by using unbuffered unamplified heavy guage wires. Range check well, check for output torque as best you can. If you encounter a problem, then look for a different solution such as chokes/filters, shielded wires, etc.
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Old 09-30-2003, 04:54 PM
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Default RE: Servo Extensions limit

If you use a booster and RF choke's there is no limit.
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Old 10-01-2003, 02:44 PM
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Default RE: Servo Extensions limit

Your main limitation is the positive and negative leads, use as large a gauge as possible, at least 20 gauge for long runs, larger if possible. Very little current is needed on the signal bus so it can remain a smaller gauge. The negative line is the most critical as any voltage drop on it subtracts from the signal voltage on the signal wire.
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Old 10-01-2003, 08:16 PM
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Default RE: Servo Extensions limit

If you use a booster and RF choke's there is no limit.
Not true, you will get limited very soon. The only practically unlimited lenght that I know of is with the Fiber Optic servo extensions.

Tested to 200' long that is from one wing tip to the other of a full size 747.
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Old 10-01-2003, 10:00 PM
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Kevin Greene
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Default RE: Servo Extensions limit

Anything over 36 inches should be amplified---Period. Voltage loss can get critical over 36 inches, especially when digital servos and a 4.8 volt pack are installed. One thing you can do is to run amplified ONE PIECE extensions and a six volt nicad pack regulated to 5.1 to 5.4 volts. The best thing you can do is to run a Lithium Ion 7.2 volt pack regulated to 5.1 or 5.4 volts. This will not allow any voltage drop. Andy Lowe at Electro Dynamics can make extensions for you any length you want----Within obvious reason. If you want the absolute best system---Go with the fiber optics offered by Roger. No loss, no interference issues!!! Just my .02...

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Old 10-05-2003, 07:55 PM
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Default RE: Servo Extensions limit

Kevin,

I need some help understanding the voltage loss you are referring to. About 3 days ago while installing the electrics in a 40% I was worried about this. So I put several extensions together for a total length of 120". I only had a voltage loss of 0.02 volts from the Rx bus to the end of this run.

Can you explain this statement more clearly please, "Voltage loss can get critical over 36 inches, especially when digital servos and a 4.8 volt pack are installed"

My test was done using a 4.8 volt pack. Thanks
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Old 10-06-2003, 07:45 AM
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Default RE: Servo Extensions limit

wrap the extensions in tin foil! this will stop them being used as an antenna.
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Old 10-06-2003, 07:49 AM
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Forgues Research
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Default RE: Servo Extensions limit

wrap the extensions in tin foil! this will stop them being used as an antenna.
This is like shielded wires and will actually do the opposite.. Be carefull
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