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Servo Reversing

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Old 09-27-2007, 07:40 AM
  #1
alexflyguy
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Default Servo Reversing

I know there are lots of ways to accomplish reversing a servo than what i'm thinking of doing but i want to have extra wire installed to add potential complications during flight. My issue is that the flaps for the left and right side of the wing are controlled by their own servo but only have one channel in the reciever. So instead of having both control horns on the same side i've heard that a servo reversing Y harness is the answer. Rather than do this i want to reverse the pos. and neg. that attach to the motor inside the servo so it will spin the opposite as the other flap servo. I was just curious to know if there was anyone who's attempted this or if anyone knows forsure if that will do what i need by switching the leads inside the servo that connect to the elec. motor?

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Old 09-27-2007, 07:49 AM
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Default RE: Servo Reversing

Good question- I need to do this on my new plane for the elevator...interested in what everyone has to say on this. Is there any actual drawback on using a servo reversing wire? Is it safer to just buy a reversed servo?
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Old 09-27-2007, 07:54 AM
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Default RE: Servo Reversing

You would be better off using a reversing Y-harness. The internals of servos have gotten very small in the last few years making working on the circuit boards very difficult to do. It's not impossible to do, just difficult to do it correctly. IMHO it's more trouble than it's worth to do it.

Ken
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Old 09-27-2007, 07:55 AM
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Default RE: Servo Reversing

Does any company make servo's that are reversed specifically manufactured for these types of applications? The only product solution i've come across are the "Y" harness w/servo reversing module built-in.
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Old 09-27-2007, 08:02 AM
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Default RE: Servo Reversing

Yes. Go to Horizon's website and choose a servo you like.

Then type an "R" at the end of the URL and a reversed version of that servo will appear (Providing they MAKE a reversed version of that particular servo)

Example:

http://www.horizonhobby.com/Products...rodId=JSP20050

http://www.horizonhobby.com/Products...odId=JSP20050R
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Old 09-27-2007, 08:02 AM
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Default RE: Servo Reversing

I believe you need to switch the polarity of the motor leads AND the potentiometer inside (it's a variable resistor that senses the output shaft/arm position). As RCKen said, the electronics inside are pretty small, and you'd have to have some decent soldering skills. I'd just put the control horns on the same side.
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Old 09-27-2007, 08:02 AM
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Default RE: Servo Reversing

Would i need to change anything on the circuit board inside? I thought it would be along the same lines as the elec. motors for on-road and off-road cars/trucks. If you just switch the polarity going to the motor it will go the opposite way with no tiny circuit boards involved in that instance.
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Old 09-27-2007, 08:03 AM
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Default RE: Servo Reversing

Not that I know of. Which plane is this on? Is it not possible to position the pushrods on the same side of each servo??

Ken
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Old 09-27-2007, 08:05 AM
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Default RE: Servo Reversing


Quote:
ORIGINAL: alexflyguy
If you just switch the polarity going to the motor it will go the opposite way with no tiny circuit boards involved in that instance.
To save room inside of the servo casing most all servos will have the motor soldered directly to the circuit board of the servo.

Ken
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Old 09-27-2007, 08:08 AM
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Default RE: Servo Reversing

Just a thought - correct me if im wrong..i know nothing about electronics....couldnt you just swictch the wires on the Male servo connector that plugs into the receiver? Isnt that reversing polarity?
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Old 09-27-2007, 08:08 AM
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Default RE: Servo Reversing

Quote:
ORIGINAL: alexflyguy

Would i need to change anything on the circuit board inside? I thought it would be along the same lines as the elec. motors for on-road and off-road cars/trucks. If you just switch the polarity going to the motor it will go the opposite way with no tiny circuit boards involved in that instance.
You are correct, by switching the polarity of the motor, it will spin the opposite way - BUT - As pkh said, you need to switch the polarity of the potentiometer too, Other wise, the servo will go looking to the left for a position that's on the right - which will result in it spinning too far and breaking the gears.
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Old 09-27-2007, 08:11 AM
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Default RE: Servo Reversing

Im just making thing more complicated by trying to make them more simple in the long run. Its for an RV-4 kit from Great Planes. Its very easy for me to have the flaps with the control horns on both sides but i want to find a different solution mainly because i didnt think of this before hand and i dont want to have to change it.
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Old 09-27-2007, 08:22 AM
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Default RE: Servo Reversing

And honestly, it is so simple and easy to place the servo arms on the servos to the same side.

Don't have to buy a special Y harness. Don't need a special "R" servo that might be a pain to use later. No rewiring a servo that probably can't be anyway. No TX mixing. No nothing.

Most airplanes that are setup for two flap servos already have the servos and the flap horn locations positioned for both arms pointing the same side of the servos.
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Old 09-27-2007, 08:22 AM
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Default RE: Servo Reversing

RCKen you are to wise and sensible for which I appreciate very much!!!! I'm sure many others are thankful too! I am just going reverse one of the control horns to make it work instead of messing with the servo electronics. Thanks for all the helpful suggestions from everyone, you guys just saved me a servo!
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Old 09-27-2007, 08:23 AM
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Default RE: Servo Reversing


Quote:
ORIGINAL: ro347

Just a thought - correct me if im wrong..i know nothing about electronics....couldnt you just swictch the wires on the Male servo connector that plugs into the receiver? Isnt that reversing polarity?
If you reverse the power leads on the servo connector, you will fry the servo electronics. There's an op-amp and other circuitry inside that sense the shaft/arm position and provides power to the motor (like an ESC does). If you connect reverse polarity to to the power supply of these circuits, you will fry them.
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Old 09-27-2007, 08:26 AM
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Default RE: Servo Reversing

One other solution, different brands of servos turn in opposite directions with the same command input; i.e. Hitec and Futaba will turn in opposite directions. Now, the hard part, getting two different brands of servos that match in speed, travel distance and power. Another solution, if your transmitter supports mixing, it may be possible to put the two servos on different channels of the receiver and use a mix to operate them.
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Old 09-27-2007, 08:30 AM
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Default RE: Servo Reversing

I've got a DX7 transmitter, is it possible to have the flaps installed into different channels on the reciever and have them mix?
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Old 09-27-2007, 09:01 AM
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Default RE: Servo Reversing

Quote:
ORIGINAL: alexflyguy

I've got a DX7 transmitter, is it possible to have the flaps installed into different channels on the reciever and have them mix?
Yes
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Old 09-27-2007, 09:09 AM
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Default RE: Servo Reversing

I have got my ailerons on separate channels right now which leaves me with only the "gear" channel open. Should i change the ailerons to work off only a single channel instead of mixing them which would free up my "aux2" channel? This would end up giving me the ability to have "aux1" and "aux2" free. So can i plug each flap servo into the "aux1/2" and mix them?
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Old 09-27-2007, 09:48 AM
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Default RE: Servo Reversing


Quote:
ORIGINAL: -pkh-


Quote:
ORIGINAL: ro347

Just a thought - correct me if im wrong..i know nothing about electronics....couldnt you just swictch the wires on the Male servo connector that plugs into the receiver? Isnt that reversing polarity?
If you reverse the power leads on the servo connector, you will fry the servo electronics. There's an op-amp and other circuitry inside that sense the shaft/arm position and provides power to the motor (like an ESC does). If you connect reverse polarity to to the power supply of these circuits, you will fry them.
There is a power wire, a ground wire and a signal wire into the servo. The signal wire carries a pulse from the RX that varies in width depending on "where" the RX wants the servo to be. Switching power and ground will do nothing but fry electronics as -pkh- said.
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Old 12-27-2007, 10:21 AM
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Default RE: Servo Reversing

Just FYI, I had the same problem with my flap servos and did try changing the connections inside the servo.
As already stated here, the motor is direct conneted to the circuit board and makes the job very complicated.
I was able to work that out and also reversed the pot wires (red/green) and it worked fine.
Now, I'm wondering how reliable to vibration those new connections are, specially the new wires that had to be added for the motor.
I may endup choosing the y-cable or a reversed servo solution, just to avoid any bad surprises during flight.
Anywhere I can get these reversing y-cables online? Couldn't find on TowerHobbies.

Thanks,

Nilo
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Old 12-27-2007, 02:45 PM
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Default RE: Servo Reversing

For flaps there is a simple mechanical solution.
Connect the pushrods to the servo arms that are parallel with the fuse, with both flaps at zero.
Then no matter which way they rotate the flaps will both be pulled down.
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Old 12-27-2007, 05:00 PM
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Default RE: Servo Reversing

This used to be on the Hitec website.
If you do not know how to solder I would not recommend that you do this, but if you are proficient at soldering it is not hard to do.
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Old 12-28-2007, 08:33 PM
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Default RE: Servo Reversing

I always believed in the kiss Principle. If possible use slaved channels. second use servo reversing wire. third connect to horns on same side. last due soldering. opening up the servos is never a very good idea and soldering them unless you have very good skills is not smart because vibrations just love to break down weak or dirty solder joint
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Old 12-28-2007, 10:02 PM
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Default RE: Servo Reversing

Good thing I know how to solder. I reverse servos as a matter of course at least with Hitec HS-425BB. Just follow the diagram Chasint provided and reverse the wires to the motor and the outside wires to the pot. Use small diameter shrink tubing to provide vibration protection. That and don't over solder getting the solder up underneath the wire covering creates a joint that's prone to failure. A good joint should be bright and shiny.

If you don't know how to solder I would not recommend you do this.
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