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Pull-Pull controls - Bellcrank material question

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Pull-Pull controls - Bellcrank material question

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Old 05-13-2003, 11:31 PM
  #1  
CafeenMan
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Default Pull-Pull controls - Bellcrank material question

I'm using pull-pulls on my latest project for the elevator and rudder. The fuselage is not wide enough to use a servo horn wide enough to create a parallelagram. Therefore I am using an intermediate bellcrank for both controls arranged on a piece of music wire. The elevator cables will turn 90 degrees before exiting the fuselage.

The only thing I have a question about is the bellcrank material. I'm at the point now where I need to install them and don't want to wait for an order through the mail.

I have two choices - aircraft ply or fiberglass pc board. My concern is that the PC board may cut through the cables. I made the bellcranks already and radiused the edges. I'm just not confident in it.

Has anyone ever done this? If so, how did it hold up? Also, suggestions for other materials to make the bellcranks from are welcome.
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Old 05-14-2003, 12:31 AM
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Default Pull-Pull controls - Bellcrank material question

What size plane is it Caffeen?
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Old 05-14-2003, 12:39 AM
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Default Pull-Pull controls - Bellcrank material question

.46 w/600 inches of wing. Did you look at my "How to build a wing" thread? That's the plane.

I'll post a couple pics of what I'm playing around with.
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Old 05-14-2003, 12:47 AM
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Default Pull-Pull controls - Bellcrank material question

Here's what I've got so far. I'm just playing around with this and haven't decided if I'm going ahead with it or not.

The two blocks are identical. They capture the music wire and will bolt to the top and bottom of the former behind the wing. The lower block will be glued in place permanently. The bolts are just to help clamp it while the glue dries and some added security.

The top block will remove so I can pull the assembly if needed. I plan to use 1/16" music wire with Z-bend at each end to hook up the bellcrank to the servo. All that seems to be fine. I'm just concerned about the fiberglass board cutting through the wire.
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Old 05-14-2003, 12:48 AM
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Default Pull-Pull controls - Bellcrank material question

Pic #2
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Old 05-14-2003, 12:52 AM
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Default Pull-Pull controls - Bellcrank material question

I've used AC ply for a bellcrank and have made some servo arms from G10. But I used ball links and rigging couplers to connect my cables to the bell crank, and ball links on the servo arms. I do have some servo arms that I will be using pull-pull cable directly to the servo arm (G10), but I haven't flown it yet.
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Old 05-14-2003, 12:57 AM
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Default Pull-Pull controls - Bellcrank material question

What's G10? My plan was to first attempt to use no connectors at all - just knot the line. I'm using fishing line, but can't remember the name. Power Pro maybe?

If I can't get that to my satisfaction I made some rigging connectors by drilling small holes in the non-threaded portion of a piece of threaded rod. I planned to use clevises outside the plane where they're easy to adjust and use knots on the bellcrank.
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Old 05-14-2003, 01:03 AM
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Default Pull-Pull controls - Bellcrank material question

This was my first attempt at making a coupler for a .15 size model. Hence the mini clevis. The hole was drilled larger than necessary so on subsequent links I used a smaller bit.
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Old 05-14-2003, 01:05 AM
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Default Pull-Pull controls - Bellcrank material question

This is what I will be using if I use them at all. Simple to make. I just used a micro-bit (can't remember the number) in my drill press. Then I chamfered the hole with a countersink.

After that I chucked the couple in one dremel tool and a brass wire brush in another dremel and spun them together to remove burrs around the hole.
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Old 05-14-2003, 01:20 AM
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Default Pull-Pull controls - Bellcrank material question

G10 is basically printed circuit board material, not the brown phenolic stuff..the translucent stuff (I'll bet it is what was in your pics).

And I have made the couplers using 4-40 screws..now I just buy the dang things. Never tried to make 2-56 ones!
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Old 05-14-2003, 01:25 AM
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Default Pull-Pull controls - Bellcrank material question

You are correct. In a former life that was fiberglass pc board. I used some etch to take off the copper.

The couplers are 2-56. I can make about 15-20 of them in an hour. The hardest part is getting the drill started. It wants to slip off to one side or the other of the rod. Once it gets started it cuts right through. These are tiny wire bits. It amazed me how easily they cut through that material.

So my question remains though. Do you think the PC board will cut through the pull cables?
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Old 05-14-2003, 01:34 AM
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Default Pull-Pull controls - Bellcrank material question

I don't think it would cut through the plastic coated steel leaders, I use Spider Wire which is an aramid fiber and it will fray pretty easily. On the plane I'm hooking the wire directly to the G10 horn I'm using the coated steel cable. It probably wont live long enough to eat through.
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Old 05-14-2003, 01:37 AM
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Default Pull-Pull controls - Bellcrank material question

This is G10...
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Old 05-14-2003, 01:41 AM
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Default Pull-Pull controls - Bellcrank material question

Originally posted by WreckRman2
This is G10...
Yep
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Old 05-14-2003, 01:51 AM
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Default Pull-Pull controls - Bellcrank material question

All I want to know is if anyone knows if there will be a problem putting the wire directly through the holes drilled in the G10. I don't plan to use steel cable. The stuff I'm planning on using is the same as Spider Wire.
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Old 05-14-2003, 02:13 AM
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Default Pull-Pull controls - Bellcrank material question

CafeenMan, it's hard to say... you might be better off to drill the holes just large enough to use a plastic clevis and a rig just like you have in post #8.
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Old 05-14-2003, 02:15 AM
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Default Pull-Pull controls - Bellcrank material question

I think you're right. I really didn't want to use a clevis at both ends, but it looks like I better just to be safe. Why do you suggest plastic instead of metal?

By the way, the exterior of this model will be completely sheeted and naturally finished. Therefore I'm making the control horns out of plywood.

At the bottom of this page you can see the wing in it's current state. I also built up the stabilizer and will build up the fin and rudder as well.

http://www.airfieldmodels.com/wing_construction_08.htm
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Old 05-14-2003, 02:21 AM
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Default Pull-Pull controls - Bellcrank material question

Because of it's small size... you could use a metal clevis also.
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Old 05-14-2003, 02:52 AM
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Default Pull-Pull controls - Bellcrank material question

For a .40 size plane...

Hell yes that'll work.

I though you were maybe talking about something much bigger.
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Old 05-14-2003, 01:13 PM
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Default Pull-Pull controls - Bellcrank material question

Well, I'm still not convinced. If the pc board can cut through the cable then it can probably cut through a plastic clevis. Fiberglass is very abrasive. I'm thinking either go with plywood or use metal clevises and watch them for wear. What I'd really like to do is hook up directly to the servo horn, but there just isn't room to use a large enough horn.
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Old 05-14-2003, 01:16 PM
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Default Pull-Pull controls - Bellcrank material question

Yes but the clevis is already round therefor leaving a lesser chance for it to cut through it. With just a cable it will be sliding back and forth in the hole...
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Old 05-14-2003, 01:21 PM
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Default Pull-Pull controls - Bellcrank material question

I agree that a clevis is the way to go if using the fiberglass. I was just saying that I would trust a metal clevis more. I check stuff like that often enough that if I noticed wear on the metal clevis I could replace it before catastrophe strikes. If I had some nylon material I would make the bellcranks from it and not worry about any of this stuff.

*note to self - order nylon*
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Old 05-14-2003, 01:53 PM
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Default Pull-Pull controls - Bellcrank material question

Without a doubt if you feel better using a metal clevis then use one...
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Old 05-14-2003, 02:34 PM
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Default Pull-Pull controls - Bellcrank material question

If you are using fishing line, why not use fishing tackle? Like swivel links at the bellcranks.
Just my $.02 worth.
Tom
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Old 05-14-2003, 02:40 PM
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Default Pull-Pull controls - Bellcrank material question

Tom - Good idea. I'm not a fisherman so I have no idea what all's available, but looks like they have a lot of useable stuff and if anyone knows how to hook up a cable, it's got to be those guys. Thanks. :thumbup:
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