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Building Tips and technical articles. => Building techniques => Topic started by: Jim Mynes on November 14, 2016, 01:05:33 PM
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I started with two Fox bellcranks. Drilled the centers out to 5/32", as it was sloppy on 1/8" wire. Then I cut a brass tube bushing to make it work with 1/8" wire.
Three more pieces of 5/32" brass tubing, as close to .095 as I could get them, and 4-40 hardware to fasten at the leadout and ball link connection points.
The leadout wire goes through 1/16" brass tubing that had previously been heated with a torch to facilitate bending. With two inches of wire sticking out of the end of the one inch tubing, I bent the tubing around a piece of 1/8" music wire until it had a lightbulb shape, spread it a little so it fit around the 5/32" brass tubing, wrapped with copper wire, and applied heat shrink. Bolted it all together with nylock nuts.
The 1/8" music wire post is supported top and bottom by 1/8" ply. Duracollars hold the post in position inside the two ply plates, and one more collar holds the bellcrank in place. The music wire extends through both ply plates and stops just shy of the center sheeting.
The only problem area I can see is the brass tubing on the leadouts rubbing on the brass tubing sandwiched between the bellcranks. Because the screws are tight, the sandwiched tubing is held fast and can't turn like a bearing. But I think that arrangement is better than the leadouts rubbing on the screw threads.
Other than that, I think it's bulletproof.
I know, a 4" Bellcrank would be preferable, but I have several of the Fox bellcranks on hand, so I thought I'd try to engineer me something.
It's going in a Banshee.
Thoughts? Comments? Recommendations?
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I like the spacer under the ball link, you make that?
MM
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I like the spacer under the ball link, you make that?
MM
No, those little cones are included with the Dubro ball links. They even give you 4-40 screws and locknuts.
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Wow!
What an idea. Who would have ever thought about putting two bell cranks together.
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Now Avaiojet, aren't you the one that showed us that trick. I did it with 2 Perfect bell cranks as that is what I had and didn't like the idea of a single Perfect bell crank the plane it went in. I thought I had a picture of my set up on here but can't find it. H^^
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Jim, looks nice and strong. What are the advantages over using a 3" Nylon Bellcrank (with post) by Brodak?
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The advantage is it's more work and cost 4 times as much plus it'll stand a 500 Lb pull test.
MM
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The advantage is it's more work and cost 4 times as much plus it'll stand a 500 Lb pull test.
The advantage is that the bellcrank end of the leadouts can be much more reliable, and it's lighter than most of the alternatives.
Brett
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... and I believe Jim said he had those bellcranks on hand, so material cost = (not much more than) $0
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Jim, looks nice and strong. What are the advantages over using a 3" Nylon Bellcrank (with post) by Brodak?
I've not used one of those Brodak bellcrank, but I had a 3" nylon Sig bellcrank in the works, and it didn't spin freely on it's bushing. Seemed like something was out of round. I'd had this idea floating around, so I started cutting and drilling.
Seems it's been done before, but it's a first for me.
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The advantage is it's more work and cost 4 times as much plus it'll stand a 500 Lb pull test.
MM
The plywood will fail long before we get to 500 lbs.
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Try This:
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Try This:
I like it! Bicycle chain quick release links?
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Try This:
I don't think I like having two pivot points. It would probably work fine, but if the chain link gets on the other side of the bellcrank there will be chaos.
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I prefer metal-plastic pairs, everywhere if possible. Never metal-metal, thinking on the wearing without lubrication and the vibrations. Mostly at invisible parts, like the bellcrank.
In the ancient times we used 8 mm ( 1/3" ) textile-bakelite (Novotex, Textolite etc.) Now I prefer ZX-100.
Looks primitive, but I have some, older than 20 years and 2000+ flights, without any wearing. See:
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089448145107762?pid=5715089448145107762&oid=117790355930193335731
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089525767871586?pid=5715089525767871586&oid=117790355930193335731
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089533111614258?pid=5715089533111614258&oid=117790355930193335731
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089616610138770?pid=5715089616610138770&oid=117790355930193335731
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The two bell crank method does seem like a lot of work, but I am sure it will work well. However, since I am pretty lazy, I just order complete custom made, fully adjustable ball link control systems from Tom Morris at a price that I think is very reasonable.
They can be ordered from this site too!
Don
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... and I believe Jim said he had those bellcranks on hand, so material cost = (not much more than) $0
How did he get them on hand without buying them?
2 Fox = $16
2 Perfect = $5.64
1 Brodak = $4.99
MM
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Istvan,
Wow! Man I love your work.! H^^
I would really like to try construction like yours one day.
It's really a different mindset.
Outstanding.
Charles
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How did he get them on hand without buying them?
2 Fox = $16
2 Perfect = $5.64
1 Brodak = $4.99
MM
I did in fact buy them. About 30 years ago I bought a bunch of them. I was all into speed limit combat then, and building foamies in bulk. I don't remember what they cost back then, but at this point it doesn't matter.
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Dear Charles,
Thanks for nice words, but nothing is special in that system. I wanted a correct "(cylindrical, metal) pin in the (cylindrical, plastic) bushing" -junction. Instead of usual "some wire loop in some diabolo-shaped hole". As you observed, the metal parts do not move on each other, this is the reason of that "?" -formed handle of the pin. Furthermore, this is fastened forever in a brass tube (formerly a piece of some R/C antenna :):) )
I never solder, or glue in such a place, I am supersticious...
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I prefer metal-plastic pairs, everywhere if possible. Never metal-metal, thinking on the wearing without lubrication and the vibrations. Mostly at invisible parts, like the bellcrank.
In the ancient times we used 8 mm ( 1/3" ) textile-bakelite (Novotex, Textolite etc.) Now I prefer ZX-100.
Looks primitive, but I have some, older than 20 years and 2000+ flights, without any wearing. See:
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089448145107762?pid=5715089448145107762&oid=117790355930193335731
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089525767871586?pid=5715089525767871586&oid=117790355930193335731
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089533111614258?pid=5715089533111614258&oid=117790355930193335731
https://plus.google.com/photos/117790355930193335731/albums/5715088163776972593/5715089616610138770?pid=5715089616610138770&oid=117790355930193335731
Nice work!
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Tom Morris at Stunthanger Hobby has this style in stock now. It's listed as "new bell crank". It doesn't say if it comes with the lead outs attached like his other cranks but i bet it does! EVERYTHING i've ever bought from Tom has been absolutely top notch stuff. I called him once to ask a question...he talked to me like he had known me for years...like i was a contender for the Nats, an absolute gentleman and professional vendor.