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Retract servo

Old 01-06-2017, 10:51 PM
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kcc
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Default Retract servo

Hi guys,

I'm building a couple of classic pattern planes at the same time, and have a question on retract servos. I have two Futaba S136G retract servos, but would like to have a spare. I can't find an interchangeable replacement out there. I'm sure the new S3170 is a good servo, but it isn't low profile..... There are a couple of low profile servos out there, but I'd like to find one where the output arm is compatible with Futaba. No one at Tower seems to know if the Tower TS 63 output arm is compatible with Futaba--it seems likely, but I'm not convinced enough to buy one or two.

I'm using MK mechanical retracts (tri-gear). Does anyone have experience that might help me?

Thanks for your help,

Kevin
Old 01-13-2017, 10:29 PM
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doxilia
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Kevin,

I'm afraid I can't help with your question but why is it that important that the servo be compatible with Futaba splines? Can't you simply use the servos arm and adjust for the needed throw with the arm holes?

Also note that modern retract servos such as Spektrums are proportional as opposed to 180 degree. They allows you to more easily attach the pushrods at the ends of the arm and "dial down" the servo until appropriate throw is achieved. Also, if you plan to use two servos in a trike setup, the NG doesn't require a 180 degree retract servo - a mini will do the trick.

David
Old 01-14-2017, 05:47 AM
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Hitec makes programmable servos but I have no idea if that would help here.
Old 01-14-2017, 05:48 AM
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I suppose Ebay is another idea.
Old 01-15-2017, 04:16 PM
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kcc
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David/doxilia,
Thanks for your reply. I think part of it is force of habit, as I used the Futaba 136 in several planes. I have one or two of them, and want to make the equipment/setup identical in both planes. You're correct in that if the servos are physically close to the same size, I can just swap them out, including the arm. I'm probably over-thinking the issue.....
I'm not familiar with a programmable (for end points) retract servo. If the servo can be adjusted/programmed for the end point, does it draw current at each end? I've always set retracts up using one servo and it's worked.

David/dhal22,
I've had a nasty experience with Hitec and would prefer use another option if possible, but I appreciate your suggestion. I'll keep an eye on eBay, 'cause you never know what'll show up!

Thanks again for the input.

Kevin

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Old 01-15-2017, 08:11 PM
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The Spektrum A7040 retract servo is proportional so you can adjust the end points, making mechanical retract set up easy as pie. I have been using one in my EU-1A, and 50 flights later, I am still satisfied.

Edit: The A7040 is a high voltage capable servo. No regulation required. Beware that a lot of retract servos are limited to 4.8V.

Robert

Last edited by KLXMASTER14; 01-18-2017 at 04:07 PM.
Old 01-18-2017, 01:39 PM
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J Lachowski
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JR 791


http://www.jramericas.com/45182/JRPS791/?pcat=296
Old 01-18-2017, 03:37 PM
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Originally Posted by kcc View Post
....I'm not familiar with a programmable (for end points) retract servo. If the servo can be adjusted/programmed for the end point, does it draw current at each end? I've always set retracts up using one servo and it's worked.
Just like any other servo, it will draw current if it is loaded. If the end of travel, the servo is not loaded, it will draw the minimum current the servo is rated for. If it is loaded..........

Now, since you seem to be a little old school (take it as a good thing, LOL) you are most likely going to set up the retracts where the servo is not loaded when retracted (arms 180 degrees apart, links pulling against each other) and lightly loaded when extended, using the gear design to take the load. Then almost any servo with "extended" end points should work. I have used the end point programming on my radio to arrive at the same configuration using a normal servo in the retract job.

Rafael
Old 01-18-2017, 11:34 PM
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kcc
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Thanks for the replies. I appreciate the input. One of my flying buddies gave me the answer to my output splines question. The Tower TS-63 is a private label Hitec, so the arms it uses are Hitec-compatible.
Rafael, Yes, in some ways I would qualify as "old school"--especially because I'm building a design from (gulp) 42 years ago....and I take that as intended--with a wink and a smile!

Kevin

Last edited by kcc; 01-18-2017 at 11:37 PM.
Old 01-19-2017, 04:25 PM
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woodie
 
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kcc

Check your PMs here on RCU

Woodie
Old 01-19-2017, 05:57 PM
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Well, gawsh durn, Kevin. I've got a couple of 136Gs.

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