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Old Jul 26, 2010, 02:40 PM
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Miami, FL
Joined May 2009
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Custom Servo arm for duel Aileron

I had Electrifly Yak 54 and totaled it.

Since then I have built several EPP foamies and am using the same custom servo arm from that yak on them all. (1 servo controlling both ailerons)

Its starting to be a pain in the butt.

Everyone at the hobby store tells me that all you need is a very long servo arm but I have a ton of those that came with my HS55 servos and they do not work. The servo never returns back to center.

Once I put on the custom servo arm the problem is solved.

The servo arm has two long arms then at the end they curve inward. It screws onto your existing servo arm so that it can be used with any servos.

How do you all solve this problem?
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Old Jul 26, 2010, 02:47 PM
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Miami, FL
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Its called an Anti Differential servo arm, here is a photo of it.

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Old Jul 26, 2010, 02:56 PM
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Dayton Intl, Ohio, United States
Joined Jan 2000
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I buy Radical RC's laser cut versions. They have them in two sizes.

Azarr
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Old Jul 26, 2010, 03:22 PM
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I think I am going to take 2 super long duel ended servo arms and cut the ends off of one about .35'' and epoxy that at an angle onto the other servo arm. Hopefully that will hold up.
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Old Jul 26, 2010, 03:53 PM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
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Quote:
Originally Posted by airbagit13 View Post
I think I am going to take 2 super long duel ended servo arms and cut the ends off of one about .35'' and epoxy that at an angle onto the other servo arm. Hopefully that will hold up.
I've done that wrapped with Kevlar thread and CA'd, worked great.

Azarr
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Old Jul 26, 2010, 11:24 PM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
Joined Feb 2010
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I've never had a problem with one servo and its stock arm controlling the two ailerons and getting equal throws.
You just need to take care where you place the horns relative to the aileron hinge.
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Old Jul 27, 2010, 06:06 AM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
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Quote:
Originally Posted by Whiskers View Post
I've never had a problem with one servo and its stock arm controlling the two ailerons and getting equal throws.
You just need to take care where you place the horns relative to the aileron hinge.
How do you determine the placement of the horns? Back in the days of metal torque rods it was easy to bend them off vertical, but still a try and see type of thing. Doing it at the servo just seems easier. The Radical horns and the horns that come with some of the F3P planes come with enough adjustment holes to get the rods at the correct angle.

It would be nice to have an alternative if the arms weren't available.


Azarr
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Old Jul 27, 2010, 09:42 AM
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Kingston, Canada
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I screw a 1/32 ply plate roughly 1/2 in. wide to the existing servo arm and drill holes at the proper distance to get the right angles.

Gord.
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Old Jul 27, 2010, 09:46 AM
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I figured it out, you figure out the angle of the control horns by making a 90 degree angle from the servo arm with the push rod. That is the anti-differential, you are trying to get it as close to 90 degrees as possible.

I love these forums.
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Old Jul 27, 2010, 10:00 AM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
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Quote:
Originally Posted by airbagit13 View Post
I figured it out, you figure out the angle of the control horns by making a 90 degree angle from the servo arm with the push rod. That is the anti-differential, you are trying to get it as close to 90 degrees as possible.

I love these forums.
That's true if you are adjusting at the servo, which is why I asked the question of Whiskers. Adjusting at the surface requires that the horn pivot be either forward or behind the hinge line and I can't understand how you'd compute that distance.

It seems much easier to adjust the differential out at the servo.

Azarr
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Old Jul 27, 2010, 05:09 PM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
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Quote:
Originally Posted by Azarr View Post
That's true if you are adjusting at the servo, which is why I asked the question of Whiskers. Adjusting at the surface requires that the horn pivot be either forward or behind the hinge line and I can't understand how you'd compute that distance.

It seems much easier to adjust the differential out at the servo.

Azarr
It just seems to work that way for me when I eyeball it.
OK, this is with the servo and aileron horn underneath the plane and the push rods angled out.
With a straight arm on the servo you'll get more 'up' than 'down' but if the hole in the horn is in front of the hinge line you get more 'down than 'up' so they cancel out.
Having said that, mostly now I use 2 servos.
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