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Old Mar 13, 2012, 09:47 PM
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United States, NC, Cary
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Servo question

If this is the wrong group for this thread, I apologize in advance.

How does one reverse a servo? Is there an extension cable that reverses the direction of rotation by changing polarity? Or, are there specific reversed servos?

Let me explain why. I am relatively new to the sport. I bought one of those big Sky Raiders from banana hobby. After a recent crash, I ordered a new main wing. In anticipation of the new wing arriving, I stripped the old wing of its servos and retractable landing gear. Turns out, I stripped the insulation off of the wires of 2 of the servos when I dislodged them from the epoxy, so I threw them away. I ordered a 5-pack of 9g servos from ebay and used all new servos when assembling the new wing. Everything works fine EXCEPT for the flaps. One flap is going the wrong direction. I have oriented the new servos EXACTLY as they original were. I took pictures. So, I can only guess that one of the 2 flap servos rotated in the opposite direction of the other. I haven't changed ANY settings in my DX 8, so it has to be the servo.

If there are servos that are designed to rotate opposite of most, how are they designated? I would like to buy one, but cannot figure out the model designations on most websites.

Please help someone...
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Old Mar 13, 2012, 10:12 PM
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Chesterfield (St.Louis) MO
Joined Jan 2004
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It is not easy to reverse the direction of a servo in the servo itself. Rather, you reverse the direction of the servo by changing a setting in the transmitter. For the DX8, this is found in the servo menu of the transmitter.

There is no standard direction for servo movement. Some manufacturer's servos go clockwise when given a longer pulse and other brands go counter-clockwise. That's why the transmitters have a reversing function for each channel they transmit.

Every once in a while you will find for sale a "reverse direction" servo. But you don't need this since you have a transmitter with reversing capability.
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Old Mar 14, 2012, 03:35 AM
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Letchworth, Great Britain (UK)
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I'm sure you're right in thinking that one of your original servos was a special reverse-rotation one.

Servos can be reversed, but it requires you to swap over two (I think) sets of wires inside the device. With small servos, that requires good eyesight and good soldering skills.

Assuming that both flap servos are Y-leaded into one channel in your receiver, the simpler way is to install a servo reverser like these ones http://www3.towerhobbies.com/cgi-bin...erse&search=Go in one of the leads. Having said that, I'd be concerned then that you might not get the two flaps operating at exactly the same speed due to the effect of the reverser.

Alternatively, use a separate channel (if your receiver has enough) for each flap servo, then mix one channel to mimic the other, and then reverse whichever channel is not working the right way, in your transmitter.
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Old Mar 14, 2012, 03:52 AM
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Las Cruces, New Mexico, United States
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...---or---... flip the flap servo so that the left and right flap servos both point in the same direction, i.e. control horn to the left side of the plane, rather than sitting opposite of each other like the ailerons do. The reversing Y lead is the easiest way to fix your problem (if you have one on hand!)
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Old Mar 14, 2012, 07:16 AM
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abenn has hit the nail on the head. Both servos for the flaps are y-ed together and plugged into aux1 on the receiver.

I tried reversing the servos through the radio as the first respondent suggested. All that accomplished was to switch which flap went up and which went down.

I did try removing the y-cable and plugging one servo into aux1 and the other into aux2. But figuring out how to configure that through the programming of the radio is NOT for the faint of heart. Man is it confusing. I did kind of get it to work. But I could not get the flaps to go down more than an inch and one of them kept buzzing. It did not do that in the original config. I am seriously considering just flipping the servo base 180 degrees in the wing and moving the control horn. But the flaps are not flat. They are triangular in shape. I would need to cut a flat spot to mount the horn as the screws pass all the way through and fasten to a backing plate. My skills with an exacto knife are not that great.

I may see if I can get one of those reverser things.
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Old Mar 14, 2012, 07:48 AM
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Letchworth, Great Britain (UK)
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I'm not familiar with your radio, but sounds like aux1 and aux2 are the simplest answer, if you can get them to work.

Your flap that's plugged into aux1 should move exactly the same as it did when the two servos were Y-leaded into aux1. Is that not the case? Then you program aux2 to move 100% of what aux1 is doing, or more likely -100%. Simply doing that shouldn't lead to any reduction in travel, or buzzing.

You haven't adjusted the servo end points while experimenting, have you? That would cause reduced travel, but buzzing indicates that there's some physical restriction on the servo's movement -- stiff hinges on the flap, or something binding in the servo.
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Old Mar 14, 2012, 08:53 AM
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United Kingdom, England, Norwich
Joined Aug 2008
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Here you go mate try the Hobbyking servo reverser if all else fail and it is a lot cheaper than the TH one is even after the postal service,you could always add more parts in the box if you needed any that is.

I've always used the HK ones with out any trouble,hope you get it sorted soon though no matter what you do or even what servo reverser you use.

http://www.hobbyking.com/hobbyking/s..._Reverser.html
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