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Radio/Control issues with servo extensions.

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Radio/Control issues with servo extensions.

Old 07-05-2016, 07:43 PM
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Default Radio/Control issues with servo extensions.

I've been having a crazy issue lately and wonder if anyone else has experienced it. The problem I'm having deals with servo extensions. I've recently had two 12in extensions turn up bad.
I'm using a Futaba 8UAP (older 72 Mhz) radio that has a Frysky RF module to convert to 2.4 Ghz with Hitec programmable HS-5625MG Digital Super Torque servos. Two servos are master slaved to for the elevator. When moving the elevator controls slowly there isn't a problem but any quick movements and one half of the elevator just goes nuts. Will either be delayed drastically or just quit working all together until stick movement slows down. I've also had an aileron servo in a 26% Fokker DR1 act up on me. It just goes wobbly, it will deflect either up or down with control input but when the stick is returned to center the aileron will just flap up and down a few times before it stops at center. It has a 12in extension in the wing and another 6in extension in the fuselage.

Before it is asked, I changed the 8UAP back to original 72Mhz and it does the same thing. I haven't torn into the DR1 to find out which extension is causing the problem. 2nd time for this Bird.

Any suggestions or input is appreciated.

Keith
Old 07-05-2016, 07:53 PM
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It is called hysteresis. It is cause by high resistance at the plug in connector in the extension. What is happening is the pulse that tells the servo what position to go to is actually seeing an additional reflected pulse from the high resistance at the connector and getting confused. Get some tv tuner cleaner, spray the connector and plug it in and out several times. It will go away. Long term having extensions buried in the plane will cause this problem as the connections we use are self cleaning when plugged in and unplugged. Leaving them plugged in long term is a problem as you have found out.
Old 07-05-2016, 08:28 PM
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So basically it's just dirty connectors. You would think that them being buried in the wing would keep them clean. I'm an electronics person (retired avionics tech, USAF) and just didn't think of that. I've never had issues with extensions, now after 10 yrs in the hobby boom, several at once. Thank You for the info.
Old 07-06-2016, 05:23 AM
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Consider cutting the plugs off inside of the wing and just soldering them together. Eliminates connection points and the issue inside where you can't easily access all of the time. I do this for all of my planes. Especially if you are an ex-avionics guy, soldering shouldn't be an issue for you. Or, buy longer wires and cut them at the servo and make your own extensions.
Old 07-06-2016, 05:49 AM
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As an aside, 72 mhz radios with slow processors exhibit lag between elevator halves. 2.4 radios send out position data to dual elevator or dual aileron servos at the same time, with PPM there's a lag between when the first elevator position is sent and the 2nd one when channel 6 comes around.

That said,Tail Dragger RC has heavy duty extensions with gold plated connectors, if its an extension problem these will solve it
Old 07-06-2016, 06:38 AM
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RCFlyerDan, thanks I don't know why I didn't think of splicing the extension to the servo in the first place, Duh! Great tip, thanks.
Old 07-06-2016, 06:58 AM
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Originally Posted by BarracudaHockey
As an aside, 72 mhz radios with slow processors exhibit lag between elevator halves. 2.4 radios send out position data to dual elevator or dual aileron servos at the same time, with PPM there's a lag between when the first elevator position is sent and the 2nd one when channel 6 comes around.

That said,Tail Dragger RC has heavy duty extensions with gold plated connectors, if its an extension problem these will solve it
Barracuda, the problem existed with both radio systems, thanks for the tip about "Tail Dragger RC".
Old 07-06-2016, 07:49 AM
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You said "both radio systems" but your OP indicates one, a Futaba 72mhz rig.
Old 07-06-2016, 09:27 AM
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Originally Posted by BarracudaHockey
You said "both radio systems" but your OP indicates one, a Futaba 72mhz rig.
The Futaba using the 72 Mhz and the Futaba using a FrySky 2.4 Ghz module.
Not two different radios, but the same radio using the older 72 Mhz and the newer 4.2 Ghz.
Old 07-06-2016, 10:36 AM
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Yes exactly. The lag is internal and due to the way the channels are generated and sent in sequence to the RF deck, switching the modulation or frequency doesn't change that.

There's a huge difference in processing time in an 72mhz/ 2.4 module radio than a native 2.4 system. Its especially apparent in situations like this or CCPM helicopters

That being said, what you're seeing is more severe than the normal lag
Old 07-07-2016, 05:44 AM
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Originally Posted by BarracudaHockey
Yes exactly. The lag is internal and due to the way the channels are generated and sent in sequence to the RF deck, switching the modulation or frequency doesn't change that.

There's a huge difference in processing time in an 72mhz/ 2.4 module radio than a native 2.4 system. Its especially apparent in situations like this or CCPM helicopters


That being said, what you're seeing is more severe than the normal lag
The lag between the two servos is less than 8 milliseconds worst case, you won't be able to visually detect it unless you have super man eyesight.
Old 07-07-2016, 06:49 AM
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Depending on the setup you can easily see it, I could see it on my Funtana on the ground though it didn't do anything silly in flight because I wasn't yanking the elevator up and down.

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