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Old Jan 01, 2013, 11:59 AM
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Cloudpeak's Avatar
United States, WY, Buffalo
Joined Oct 2012
10 Posts
Question
Converting Spectra push rods-wood to ???

I'm building a Spectra e-glider. My last RC build was a 2 meter glider built 30 years ago and I'm just now (at 65) getting back into the hobby.

The stock Spectra comes with 1/4" square balsa and .070 wire for both ends of both the elevator and rudder push rods, threaded for a clevis at the servo and a "Z" bend at the control horn bend.

I'm going to replace the Speed 600 with an outrunner and use a Lipo battery and plan on mounting the elevator and rudder servos, receiver and battery as far forward as possible but do not have any of those items purchased, yet. I also intend to move the stab & rudder aft approximately 3 inches. As a result, I won't have enough square balsa or wire for the increased length required and think I would like to use a different set up having a clevis at both ends. My control push rods will have to be 28 to 32 inches depending on how everything fits in the fuselage.

I think something like the S503 from: http://www.sullivanproducts.com/GoldnRodMainFrame.htm would work as I can cut it to the lengths required. Comments on this setup or any other ideas would be great.

My understanding is that the sheath should be attached at points inside the fuselage to prevent buckling. The rudder pushrod would have a 9 inch unsupported section from where it exits the top of the fuselage to the attachment to the rudder horn. Should this be anchored in some way?

Thanks, folks.
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Old Jan 01, 2013, 12:23 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,095 Posts
The Golden Rod works OK. Be advised though the Golden Rod tends to expand and contract as the temp changes. This will cause some minor trim changes.

With the Golden Rod you may be able to change the location rudder exit closer to the rudder. I would support the outer sheath every four or five inches for a flex free system. Easy to do while the fuse is open.

Another option is carbon push rods. Central hobbies has a "kit" meant for dual elevator control on pattern planes but would work for elevator and rudder for you. http://www.centralhobbies.com/contro...age/deps1.html There is a instruction page on how to use them also. I would personally lean to the carbon.

Ken
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Old Jan 01, 2013, 12:41 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,411 Posts
Just a thought.

But if replacing the brushed motor with a brushless, the Nimh? with a Lipo, and moving the stab and rudder back 3", isn't that going to give you a problem getting the CG correct without some lead up front ?

Brushless and Lipos are so much lighter than brushed and Nimh.

If you do need to keep the back end as light as possible, consider using pull-pull systems for the elevator and rudder.
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Old Jan 01, 2013, 01:29 PM
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Cloudpeak's Avatar
United States, WY, Buffalo
Joined Oct 2012
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Ken, Thanks for the speedy reply and your control rod suggestion.

The Carbon pushrod you mentioned is a bit more than I'd like to spend (retirement = less hobby spending) but I will give it some thought.

Quote:
Originally Posted by eflightray View Post
Just a thought.

But if replacing the brushed motor with a brushless, the Nimh? with a Lipo, and moving the stab and rudder back 3", isn't that going to give you a problem getting the CG correct without some lead up front ?

Brushless and Lipos are so much lighter than brushed and Nimh.

If you do need to keep the back end as light as possible, consider using pull-pull systems for the elevator and rudder.
eflighttray, You're right. The c.g. will move aft for sure with the moving of the vert. stab and rudder. I hope to offset this by moving the battery and servos forward.

Plans for the Spectra show the ele. and rudder servos below the wing trailing edge and the 7 cell Nicad mass just slightly ahead of the C.G. The plans also show a receiver battery above the nicad and a throttle servo behind the motor, neither of which I will use. I think I should be able to move the Lipo and the elevator and rudder servos way ahead of the c.g. as there appears to be enough room. I'll know more when I obtain all of the components

Bob
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Old Jan 02, 2013, 02:36 AM
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BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,427 Posts
My advice from trying them is to avoid Golden Rods for THIS application like the plague.

My issue with them is that the nylon used for the GR's is heat sensitive. This produces a significant change in the neutral position on a glider/sailplane that is set up with the CG well back and using minimal elevator throw. It also produces a very visible shift in the rudder neutral as you move from warm to cold or the other way around.

I happily still use GR's for casual sport models. But for anything I build for soaring where I'll be tuning the CG back for optimum performance it's all about pushrod stability for me. That means I like to use either the wire ends with spruce in between or to go with a small diameter carbon tube to replace the spruce or balsa. Mostly though I go with the traditional choice of spruce or bass for the major portions of the pushrods. Hey, it works and it's FULLY consistent to the wood of the fuselage for any temperature changes. So no control surface movements that you're not expecting.
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Old Jan 02, 2013, 04:56 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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In case you may want to consider a pull-pull system, you can do them remote from the servo, so the wires and bellcrank can go where convenient.
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Old Jan 02, 2013, 05:03 PM
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Cloudpeak's Avatar
United States, WY, Buffalo
Joined Oct 2012
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eflightray, Interesting bellcrank setup. Thanks for sending the diagram.

Bruce, The simpler system with spruce sticks and .070" wire appeals to me as that's what I used 30 years ago on my first and only glider (which I had over a hundred flights on before giving it away due having to work longer hours in my business). All I have to do is come up with some more threaded wire and some spruce sticks. (Nearest source for balsa/spruce is 37 miles away and I'll need another piece of .070 threaded rod.)

I think I should use threaded wire on both ends of the rudder and elevator. I'm not a fan of "Z" bends and like the idea of screwing off a clevis and sliding the assembly out as opposed to removing a control horn to "undo" the Z bend connection.

I appreciate all that have helped me with this. I know it's old hat for most of you but for a beginner, there's a lot of stuff to learn, especially for an old guy.

BTW, I finally figured out how to post an avatar. It's a picture of my "last build", a 150 hp RV6. It took me 5 1/2 years and I flew it for 475 trouble free hours. I started out building models when I was 9-10, built some "U" control, some hand launched gliders and a couple of rubber band planes using tissue and dope. I got my pilot's license in 1975 and started restoring certified airplanes and building experimental's in the mid 80's to mid 90's. I built one of the first Glasiar's, a RV6 and most of a Glastar and also helped 10-12 RV builders. Now, I'm back to the little guys as I can't get a medical and flying got too expensive.

Thanks, Bob
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Old Jan 02, 2013, 10:01 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,095 Posts
Bob, go to your local home improvement store and look in the selection of dowels.. I'll bet you can find something there that might work for you.

Ken
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Old Jan 02, 2013, 10:28 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,427 Posts
Bob, that rod you have is almost certainly 2-56 threaded rod. There's really only two standards for RC model fittings for kits and home built stuff and that is 2-56 for the small to medium size fittings and 4-40 for the big quarter scale stuff.

The good news is that rods with 2-56 thread on them are only as far away as your local bicycle store. Or if you score an old dumpster bike you'll have rods apleanty merely or the time needed to strip the wheels.

The hardwood dowels is a good option as well. But DO check to ensure that the grain is nice and straight. I see LOTS of hardwood dowel that snaps and splits with rediculous ease due to a nasty short angle grain runout at points in the dowel. Note that I'm not talking about the dowel being curved. That can be steamed out if it's got good grain. I'm talking about the grain not running along the length of the dowel. Those ones are VERY weak.

If you have or know someone with a table saw it's not a big deal to rip some lumberyard clear stock into 1/4 sq to make your own pushrod stock. You won't find aircraft grade Sitka spruce but almost any wood you can find which is clear of knots and grain irregularities and that has around 12 or more growth rings per inch would be great for pushrod stock.

So even if you're not making the pilgrimage to the hobby shop for a while there's local options.
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Old Jan 03, 2013, 02:29 AM
Art Schmitz
United States, TN, Crossville
Joined Jan 2012
392 Posts
FWIW: RC pioneer Harold De Bolt came up with a system that I have used since the 60's.
It uses 1/16" music wire fairleaded every 6 to 7 inches with the exit counting as a fairlead.
I use the yellow inside GR tubing in 1" lengths as fairleads.
On the horn ends I silver solder a 2/56 thread fitting.
The servo ends use EZ connectors with slight flat spots on the 1/16 M.W. for positive screw engagement.
This gives a zero slop installation that works up to 1/4 scale.
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Old Jan 03, 2013, 07:29 PM
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Cloudpeak's Avatar
United States, WY, Buffalo
Joined Oct 2012
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Great ideas, folks. I appreciate the help.

Bruce, I have a buddy who owns 5 bicycles. I figured for sure he'd have some old spokes. He didn't. He's never replaced a spoke! I guess with 5 bikes he never wears anything out.

There's a bike shop 37 miles north in Sheridan so I'll stop by next time I get there and check out dowels, as well.

Thanks, Bob
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Old Jan 03, 2013, 09:07 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,427 Posts
Check your local second hand stores or local version of Craigslist. If you can't score a $20 dollar bike from one of these sources then something is seriously a'kilter... Or even check out the local dump or scrap dealer. Old bikes are tossed out constantly. Meanwhile spokes bought new from a shop run about $1.50 a pop.
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