Perminant and most reliable solution-

HARDWIRING A servo FOR REVERSE MOVEMENT

This is a hard wired way to make sure the second "reversed" servo moves in unison with the first servo. I realized i posted dos and donts first but this is the truly solid way to reverse the servo in unison. The reason why is both servos would receive the same signal from the same connection.

This is a modification you should only do once you have a bit of practice using a soldering iron. 4 wires will need to be desoldered and resoldered back inplace.

The first two wires to swap are the potentiometer wires on the driver board. There are three lined up usually all in the same color wire. Of these three you will swap the outside two and leave the center wire alone.

The second two wires we will swap are the leads to the motor itself. These also may be the same color. Carefully desolder and resolder them in reverse orientation.

standard rc servos are all this wiring format , i just used a tower 9g servo for the example. So this will resolve your reversing needs

I guess i should repost this in tutorials section

From the server mentioned above: power hd 1500mg $20 240 oz in @ 6v

$12.50 at this place:
http://www.valuehobby.com/power-hd-1501mg.html

Nice find sir! And looks like they carry replacement parts parts for repair of the 1501mg too.

So for those who had questions about how to reverse a servo for unison rotation , did i answer all your questions?

Yes @Jason, this was exactly what I needed to know and what I was looking for. I thought I remembered someone mentioning this process on this forum a few months ago. Thanks for taking the time to guide me on this.

I'll be ordering another servo to match the one I've already got and wire the servo pots as you show. I may have more questions so I hope you don't leave town again.

I do have one other question. I also remember you commenting on the "whine" the digital servos make when holding load or trying to keep position. Have you found a way to quiet them?

I'll also post my progress with pics. Robot arms always seem to spark a lot of interest.

Thanks again! Dave

@Jason, I've been looking for the tandem servo controller from futuba you mentioned. Do you have a link?

Also, I was looking at the servo I'm using and it's a Digital "programmable" servo. One of the programmable features is reversing the direction from the stock setting. Wouldn't this do the same thing as your rewiring mod? Here's the link to the servo again:

HS-7950TH Servo

Thanks. Dave

By the way its Josh , to answer the first question you have a few options on sound.

That is a awesome servo by the way but that little dude is loud.

First option - you could use a analog servo instead

Why? Digital servos pulse at 300 times per second. This is so they physically move to the designated position quicker. This is important in flying models , like helicopters. Acrobatic models must respond to inputs quickly! Or die a fiery death. 300 pulses per second makes audible noise and gets louder with loud. A analog pulses 50 hertz which is audible but much lower frequency....and less annoying.

Second , in either case digital or analog you can apply dynamat sound suppression material which absorbs high frequency sounds and emits a lower frequency.

Third , you can cut out the servos original driver and implant a mosphet driver running a much higher frequency 20,000 hertz or more. This is wheelchair companies solution to quiet motor controller.

Lastly - you can relieve strain on the servo with a servo city gearbox and also increase your torque which may be needed for a large arm. I have two for shoulders myself. They have gear ratios from 3 to 5 .

http://www.futaba-rc.com/accessories/futm4150.html

This is the part you were looking for. This electronically does servo signal reversing and has a trim pot to adjust the second servo if you mix servo models and need a tiny bit of center adjustment. Realistically if you use the same servos for your dual servo setup then you wont need this box. The only advantage is center position adjustment.

These usually sell for $40 online

Woops, Josh. Sorry, I knew that. blush

Thanks for the quick reply Josh.

I'll keep looking for a servo that will fit into the Gearbox I want to use. Maybe the ones you and Justin point to will work.

Not sure I understand your third option or how to do it.