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Old May 10, 2014, 11:58 AM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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My latest hairbrained scheme

First off, this doesn't really accomplish much, if anything in the way of performance. This is just something different and fun with a few small bonuses and a few perils that will need experimentation to eliminate.

A picture is worth 1000 words so here you go. Not to scale or final.





this is a VERY tiny winch attachment for a very small servo... It is to be run with a pull/spring setup.

The line would come from the tail surfaces through a guide tube then to the drum with 1 wrap and then through a hole in the upper drum lip and then to the servo screw for securing and easy adjustment.

What does this accomplish?

Its cool!
very clean looking installation
the moving parts do not displace additional space when they move
the amount of line pull is completely linear
can increase throw on servo to get higher resolution on the flying surfaces
more torque ( which means less current draw in all conditions)
probably lighter than a traditional horn

Things to worry about:

Line coming off of drum with a slacked line....

I am going to experiment with this. I am hoping that with a proper guide tube setup this will not be an issue. The guide tube could be cut with a 45 degree angle and positioned VERY close to the inner part of the drum.
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Old May 10, 2014, 12:03 PM
Aeromodeller by heart!
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Herning, Denmark
Joined Dec 2002
634 Posts
Cool idea!

Maybe the drum needs to be a Little bigger to get enough deflection.
In a pull/spring setup, just wrap the pull-line two times around the drum. Itīll take care of any slack. (The line would be under tension at all times.

Ruben
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Old May 10, 2014, 12:05 PM
AustinTatious
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Hurst, Texas, United States
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Quote:
Originally Posted by RubSon View Post
Cool idea!

Maybe the drum needs to be a Little bigger to get enough deflection.
In a pull/spring setup, just wrap the pull-line two times around the drum. Itīll take care of any slack. (The line would be under tension at all times.

Ruben
the idea is to go to roughly 150% on the throws (120 degrees of travel) and then size the elevator horn accordingly if needed.
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Old May 10, 2014, 01:14 PM
Aeromodeller by heart!
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Herning, Denmark
Joined Dec 2002
634 Posts
Makes sense.

In my case, I can only go 110% on the throws, but sizeing the horn is allways an option.
Are you planning on printing or milling the pieces?

Ruben
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Old May 10, 2014, 01:21 PM
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Canada, BC
Joined Jan 2010
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Very good. I like it.
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Old May 10, 2014, 02:11 PM
Looptastic!
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Enschede, Netherlands
Joined Nov 2009
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What benefit will linear servo travel offer when the receiving end is still not linear?
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Old May 10, 2014, 02:18 PM
Detroitus
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Joined Jan 2007
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Quote:
Originally Posted by sp00fman View Post
What benefit will linear servo travel offer when the receiving end is still not linear?
Maybe a matching +/- 30 or 45 degree pulley style horn with a string attachment for pull/spring at the surface end? Linear at both ends then. A lot of full-size aircraft control systems work like that, before hydraulics and such.

Kevin
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Old May 10, 2014, 02:50 PM
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Cerritos, CA
Joined Nov 2004
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Quote:
Originally Posted by sp00fman View Post
What benefit will linear servo travel offer when the receiving end is still not linear?
Think of it as a little built in exponential. Unless the control system has massive deflection it won't be all that much.

A typical setup with large angular servo throw (short servo arm) and smaller angular surface throw (longer control surface arm) results in some negative exponential that probably could use some positive transmitter exponential to even out.
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Old May 10, 2014, 05:43 PM
Launch high. Fly low.
United States, CA, Lake Elsinore
Joined Aug 2003
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Quote:
Originally Posted by AustinTatious View Post
First off, this doesn't really accomplish much, if anything in the way of performance. This is just something different and fun with a few small bonuses and a few perils that will need experimentation to eliminate.

A picture is worth 1000 words so here you go. Not to scale or final.





this is a VERY tiny winch attachment for a very small servo... It is to be run with a pull/spring setup.

The line would come from the tail surfaces through a guide tube then to the drum with 1 wrap and then through a hole in the upper drum lip and then to the servo screw for securing and easy adjustment.

What does this accomplish?

Its cool!
very clean looking installation
the moving parts do not displace additional space when they move
the amount of line pull is completely linear
can increase throw on servo to get higher resolution on the flying surfaces
more torque ( which means less current draw in all conditions)
probably lighter than a traditional horn

Things to worry about:

Line coming off of drum with a slacked line....

I am going to experiment with this. I am hoping that with a proper guide tube setup this will not be an issue. The guide tube could be cut with a 45 degree angle and positioned VERY close to the inner part of the drum.
I like.
Please keep us updated.

Jun
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Old May 10, 2014, 05:53 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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Quote:
Originally Posted by sp00fman View Post
What benefit will linear servo travel offer when the receiving end is still not linear?
Very good point. as stated this is mostly for cool factor.

However, by making a longer control horn you minimize that factor.... You would also minimize it on the servo end with a long arm, but the cost you pay are very apparent in that setup.
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Old May 10, 2014, 06:36 PM
G_T
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Joined Apr 2009
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About 30 years ago I did something similar, using pull-pull. I did it for rudder on an attempt at an F3B plane. I used center hinge, and a drum buried in the hingeline. That let me get all the control connections internal for minimum drag. It worked pretty well actually, but the hingepoint had to be solid near the drum to take the forces involved. Stab was full flying, and wing surfaces were sealed with no external linkups. It was pretty clean.

Gerald
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Old May 10, 2014, 06:40 PM
Plastic Buddha
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Joined Oct 2005
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That is a very cool idea bro!
Worth it just for the compactness factor if you ask me.

If you could guarantee 1/4 gram weight savings, guys will wet their pants!
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Old May 18, 2014, 07:51 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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Ok, well.... I have been trying to get this part made with no luck from the guy I was trying to work with. (I'll keep quiet on who, cant really blame him!)

However, I think I have found a very easy way to accomplish this, perhaps not as pretty but just as effective and best yet, it wont cost you but a few pennies if you want to do it.... It is also the lightest possible way to accomplish this setup....

Ill be putting mine together like this very soon and will report on how well it works.

Setup: A hole is drilled through the servo output spline towards the bottom near the top of the servo. Heat shrink tubing is put around the spline and shrunken, then trimmed flush with the top of the spline and the parts of the HST covering the drilled holes is removed.

A washer with a diameter = or < the width of the servo and with a hold large enough only for the shaft of the servo arm screw is drilled with a small hole near where the servo spline ends.

The pull spring line is run 1-2 wraps around the shrink wrapped spline, through both holes in the splin, up through the hole in the washer and then wrapped around the screw. The screw is tightened to secure the line. This can serve as an adjustment point.

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Old May 18, 2014, 10:12 PM
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United States, AZ, Arizona City
Joined Sep 2001
5,084 Posts
I'd put a washer on the bottom also, just to make it harder to jam the thread.
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Old May 18, 2014, 10:58 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
1,954 Posts
Quote:
Originally Posted by GaryO View Post
I'd put a washer on the bottom also, just to make it harder to jam the thread.
there will still be a guide tube on the line glued to the flat spot of the servo. there wont be any way for it to get caught in there.
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