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Servo reversing on Futaba S3151 digitals

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Old 04-02-2004, 11:03 PM
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Pook
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Default Servo reversing on Futaba S3151 digitals

Ive got a plane that uses two elev servo's I need to wire them together but reverse one.

I know (or think) the white is the feedback lead and red is +, black is -, When I try to reverse one of the servos both stop working? Im just changing the +and- leads, is this wrong? or is it due to the fact they are digital?

Ive read bad stories about y-harnesses and reversers causing unequal travel.
Any help would be great!!!
Thanks,
Danny
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Old 04-03-2004, 04:33 PM
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Default RE: Servo reversing on Futaba S3151 digitals

"Im just changing the +and- leads, is this wrong?"

Yes, that is wrong! The red servo lead is the +4.8 V (or 6 V) to the battery and the black lead is the negative -4.8 V to the battery. By reversing these 2 leads on 1 servo, you may have damaged that servo and possibly damaged the receiver also, not to mention shorting out your battery. I would suggest putting these leads back to where they were and if you're lucky the servo and receiver will still work. Many modern radios have multi-channel mixing and servo reversing functions in the transmitter. Try mixing 2 separate channels and reversing 1 servo. If your radio can't do this, you'll need a servo reverser.

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Old 04-04-2004, 08:00 PM
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Default RE: Servo reversing on Futaba S3151 digitals

Then how does a servo reversing lead work? [&o]
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Old 04-05-2004, 09:06 AM
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Bill S
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Default RE: Servo reversing on Futaba S3151 digitals

"Then how does a servo reversing lead work?"

Servos work by comparing the width of a pulse from the receiver on the signal lead, to a reference pulse generated inside the servo, usually 1.5 milliseconds (ms) at neutral. Moving a transmitter stick in one direction increases or decreases the signal pulse width causing the servo motor to move the output arm and also moving a variable resistor or potentiometer in the servo in the direction necessary to equalize the internally generated pulse width to the incoming transmitted pulse width. When the incoming transmitted pulse width and the servo's internally generated pulse width are equal, the servo motor stops.

A servo reverser works by using an electronic circuit chip to reverse the direction of the transmitted pulse width. That is, it will decrease the width of an increasing pulse width signal from the transmitter and increase the width of a decreasing pulse width signal.

That said, it is possible in some servos to internally rewire them to reverse their direction. As explained in other threads here, you can open the servo and reverse the moter leads and also the two outer leads of the servo potentiometer (pot). This is not recommended unless you are highly adept at precision soldering of micro electronic parts. Also, this may not be possible on some servos that have their motors and/or pots mounted directly on circuit boards.

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Old 04-05-2004, 05:05 PM
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Default RE: Servo reversing on Futaba S3151 digitals

Thanks much Bill! I think I will just order the Futaba Reverser then!
I have a plane that uses two elev servos and nothing Ive tried gives equal travel rates, I can get eqaul rate and different end points or vise versa, also cant get trim to work on different channels at the same time, only channel two!
Thanks again for the info.
Danny
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Old 08-04-2005, 03:16 AM
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Default RE: Servo reversing on Futaba S3151 digitals

Althought this is kinda old, anyone that might read this, here are some other options:
First, make sure your linkages and geometry match side for side, that is where the most error comes from. To reverse and fine tune your split elevators, if you can't do it on the radio, then something like a MSA-10, Matchbox, Smartfly Equalizer, you can reverse the servo direction, and adjust the center and endpoints very easy.
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