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Shaft Coupler - Good/Bad Idea ?

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Old 04-05-2012, 06:29 AM
  #1
wxman2
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Default Shaft Coupler - Good/Bad Idea ?

I am looking for a wider response pool so I am creating a new thread for this question

For my Scale Wings LA7 I am working on making all the control surfaces have internal linkages (internal controls) and for the elevators I am thinking about using a shaft coupler and control the elevators this way. I would plan to drill the rod shaft side and use a cotter pin to add a bit of extra safety.

The servos I will be using for each elevator are:
Savox SB-2270SG
Torque(@6.0V oz-in): 347.2

Since I haven't done this before, is this a bad idea?



My LA7 Assembly Thread
http://www.rcuniverse.com/forum/m_10...m.htm#10695805


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Old 04-05-2012, 09:23 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

Trying to make it where Idon't have to see these linkages on the bottom of the elevators. Maybe I am just being to picky...

This image is from the CD that came with the ScaleWings LA7.

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Old 04-05-2012, 09:28 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

The problem I see is: Can you fit two servos, side-by-side, in that small area between the elevators?
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Old 04-05-2012, 09:34 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

I would opt for security over scale fidelity! Too much invested time, effort and $$$ not to be able to check linkages with ease and simplicity!

That's just an opinion, which you asked for.

Awesome plane, by the way... I've been watching it come together!

Noah
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Old 04-05-2012, 09:35 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?


Quote:
ORIGINAL: MinnFlyer

The problem I see is: Can you fit two servos, side-by-side, in that small area between the elevators?
Mike,

You are right... Idon't have that much room to work with. The servos are 42.7 mm tall. Moving to plan 2, which Iwill post here shortly.



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Old 04-05-2012, 09:36 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?


Quote:
ORIGINAL: butlern

I would opt for security over scale fidelity! Too much invested time, effort and $$$ not to be able to check linkages with ease and simplicity!

That's just an opinion, which you asked for.

Awesome plane, by the way... I've been watching it come together!

Noah

Thanks Noah...

Posting plan No. 2 here shortly...

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Old 04-05-2012, 09:55 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

The second thought is to run a rod into the fuselage and use an aluminum clamping hub on each side. Mount a carbon fiber arm to each clamping hub and install the servos farther forward in the airframe. Then use the CF push rods that Central Hobbies sales to connect the servos to the clamping arms.

The clamping hubs would allow for some fine tuning aligning the elevators once everything is installed.

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Old 04-05-2012, 10:18 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

Sounds like you're making it too complicated. Why not just use one of [link=http://shop.dubro.com/products/productdetail/Heavy+Duty+E/Z+Adjust+Strip+Aileron+Horn+Set/part_number=558/101.0.1.1.5161.5164.0.0.0?pp=12&]these[/link]?
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Old 04-05-2012, 10:50 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?


Quote:
ORIGINAL: MinnFlyer

Sounds like you're making it too complicated. Why not just use one of [link=http://shop.dubro.com/products/productdetail/Heavy+Duty+E/Z+Adjust+Strip+Aileron+Horn+Set/part_number=558/101.0.1.1.5161.5164.0.0.0?pp=12&]these[/link]?

Not sure this Dubro would hold up on a 29% (110" wing span) plane..., but it is basically what Iam thinking about, just a bit more robust




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Old 04-05-2012, 12:16 PM
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Default RE: Shaft Coupler - Good/Bad Idea ?

If I am following you correctly, it looks like in your first post that you are considering using the RDS system (http://www.irfmachineworks.com/rds/) for your control surfaces. I have not personally used this system before, but there are plenty who have and have threads written on their setup. Of course it would require some work and would not be as simple as the layout in the instructions. From a security and safety standpoint, you couldn't go wrong with the "standard" approach, but as you point out, you loose out on scale fidelity.

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Old 04-05-2012, 12:44 PM
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Default RE: Shaft Coupler - Good/Bad Idea ?

I like it
Hate those ugly unscale rudderhorns [:'(]
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Old 04-05-2012, 12:48 PM
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Default RE: Shaft Coupler - Good/Bad Idea ?


Quote:
ORIGINAL: LarsL

If I am following you correctly, it looks like in your first post that you are considering using the RDS system (http://www.irfmachineworks.com/rds/) for your control surfaces. I have not personally used this system before, but there are plenty who have and have threads written on their setup. Of course it would require some work and would not be as simple as the layout in the instructions. From a security and safety standpoint, you couldn't go wrong with the "standard" approach, but as you point out, you loose out on scale fidelity.

Lars
Yes, my first thought was to do something like the RDS concept. I had enough room in my head for this type of install but the servos are 42.7 mm tall and while there is enough room at the leading edge of the elevator, this concept won't work due to the shape of the elevators.

The "standard" approach is the safe route, but for some reason exposed control arms on a scale plane just bug me.






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Old 04-05-2012, 01:43 PM
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Default RE: Shaft Coupler - Good/Bad Idea ?

It's a question as old as the hobby. Scale looks versus non scale functionality. After having planes crash due to problems associated with trying to look scale and seeing dozens of others bite the dust I opt for functionality over looks every time.
Larry
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Old 04-05-2012, 02:17 PM
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Default RE: Shaft Coupler - Good/Bad Idea ?

Have never had problems with more scalelike and hidden rudderlinkages
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Old 04-06-2012, 07:12 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

How about an elevator joiner with a control horn in the middle, hidden inside the fuselage?
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Old 04-06-2012, 07:47 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

I would be the full scale has a single torque tube that connects the two elevator halves together. Then it either has a pull-pull cable setup with an arm on top and bottom of the tube, or a rigid push-pull setup that has a single arm.
If you want the safety of two servos, I would go with two torque tubes with permantly attached arms instead of the clamp deal. The less bolts the better in my book. Either bend 3/16" music wire, or use some aluminum rod drilled and tapped for a bolt/arm that your clevis would hook to. If you have access to a Tig machine you could weld an arm to the end to hook the clevis to. I would also include a hole in the elevator end so you could insert some sort of rod that would glue into a block inside the elevator to prevent roation of the entire tube.
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Old 04-07-2012, 03:41 PM
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Default RE: Shaft Coupler - Good/Bad Idea ?

JeffH and DaddySam have the right idea...solid rod or welded horns...double the servos if need be...the elevator is the easiest control horn to hide. As long as you have clearance for the horn to move inside the fuse. Don't worry about adjustment...set the horn 90 degrees to the L bend in the rod and make your adjustments at the servo end using threaded couplings if you must...you'll be more likely to be looking inside the fuse there for inspection and service of other things. I think everyone is saying the same thing though... stay away from a friction fit clamp especially in an area that may be hard to inspect...if those bolts loosen from vibration or the clamp spins from too much torque or because the material under the clamp compresses, you will have zero elevator control...and while any control surface failure can put you into the ground...the elevator would put you there the fastest IMHO.

Rick
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Old 04-08-2012, 03:14 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?


Quote:
ORIGINAL: larry@coyotenet

It's a question as old as the hobby. Scale looks versus non scale functionality. After having planes crash due to problems associated with trying to look scale and seeing dozens of others bite the dust I opt for functionality over looks every time.
Larry
How many reports of the RDS system failing are there? I've never used them, but I have read quite a few threads were guys sware by them. Even the DS'ing glider guys who are flying at 200mph + and at heaps of G's have used them??

I guess i'm asking it there is any actual data or just some age old, "it's new, so it can't be trusted?"

Thanks

dave
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Old 04-08-2012, 06:17 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

One last comment on "adjustability" of control surfaces: You see lots of people here (myself included) who get anal about precision - slop in linkages, angle of deflection of the control surfaces, washout in the wings, etc. etc. Since you have a split elevator I am speculating that your concern for adjustability relates to being able to independently adjust each half to perfection via independent servo trim. I used to think that way myself...til I started flying real planes (including a recent opportunity to pilot a fullscale P51C- it was awesome). What I realized was that the wind and airflow is such a larger and more dynamically variable force in the equation (even at full scale) that it is ridiculous to worry too much about a degree or two of differential between elevator halfs, control surfaces, etc....the surface itself will distort to a greater degree in flight in completely unpredictable ways and the airframe probably has some twist and distortion. Even if you built your airframe with laser precision...it is a dynamically adjustable entity in the airstream. That's why there IS trim. And that's why ARF's from China fly just fine...haha.

I don't think the issue here is so much scale look over reliable functionality...at 29% both should be possible using fullscale like hardware. But concerning the use of clamping shaft couplers I'd rather join the elevator halves and weld a steel bellcrank to a piece of steel rod and eliminate the possibility of a failure. Even standard servo horns and the servo pinion have teeth to prevent spinning...the smooth inside surface of that clamp and the fact that you'd probably be clamping it on some solid (or worse tubular) aluminum rod scares me. If you ran with independent servos for each elevator half and one servo stripped or the setup stretched...you would be all fouled up and from the ground won't know what really happened. The failure would induce roll, and instinctively you would think you had an aileron failure and yet pitch control would be introducing more roll...you might be hard pressed to correct with aileron, and simultaneouly retrim the elevators, if it even occurs to you in time...If I was your scale pilot figure I'd be hoping you packed me a parachute...and installed a sliding canopy.

Rick
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Old 04-08-2012, 09:38 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

I appreciate all the input and will take this information into account as I design the internal controls for the elevators.
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Old 04-08-2012, 02:30 PM
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Default RE: Shaft Coupler - Good/Bad Idea ?

TA152's system is the one I use, with 1/8 music wire torque rods.

I try to keep them as short as possible to minimise any twisting.

I thread the music wire (heat & quench it to take the temper out
of the end I'm going to thread) & use the screw on connectors.
They can be moved up or down the thread one thread at a time
to match the travel on each side. - John.
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Old 04-09-2012, 03:15 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

I like to hide all linkages also. I subscribe to Transatlanticflight's thoughts about this. I would first consider a single U connecting the two halves with a pull pull if possible, then a single pushrod, then two servos if I had to seperate the the halves. I also do not like putting servos in the rear if there is any possibility of it impacting the CG. I have been able to hide controls in a twin rudder HE-162 with some work. I always check flight control surfaces before each flight. Make it simple make it light.
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Old 04-09-2012, 09:34 AM
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Default RE: Shaft Coupler - Good/Bad Idea ?

I would want two servos in the event one quit. I have seen planes come back with one elevator servo burnt up, unplugged, horn fell off etc etc. If it had been just one servo, you ARE going to crash with no hope of saving the plane. With a Moki radial up front, I would want some margin of safety. Even if a servo locked hard over, you still have one to at least try to get the plane to hit flat instead of straight in.
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