Author Topic: Carbon Bellcrank (Read 8526 times)

Jeff Traxler · « **on:** March 09, 2016, 07:50:38 AM »

This is the third bellcrank mold I have made and I think it the best so far.After spending a week with Bob Hunt and Bill Werwage last January Billy and I had a nice conversation during the 8hr ride home from Bob's and some of it touched on a carbon fiber bellcrank that is no longer available.I did some thinking and this is what I came up with.It has a .040 center web with 3/16th beads and cable ends/pushrod attachment.The center bearing pad is 1/4" and will accept the needle bearing.!2 gr. undrilled.I am making a mold for a 1/8th bead ect. for 40 sized ships.That should be a couple grams lighter.

Motorman · « **Reply #1 on:** March 09, 2016, 09:21:46 AM »

Nice design, looks retro. Do you use tow, cloth or chop? Can you add some pins to the mold so you don't have to drill the carbon?

MM

Jeff Traxler · « **Reply #2 on:** March 09, 2016, 10:35:04 AM »

There are 4 layers of 3K 6 oz.over the entire area.I stuffed 12K tow down in the beads and filled the pockets with little pieces of 6 oz. and chop.It has the retro look because I wanted curves in the shape.With the beads not being parallel and curved makes for a far stronger structure with no added weight disadvantage.Lightening holes could be added to the web with not much structural degradation.Still a work in progress but I think I'm headed in the right direction.

Steve Helmick · « **Reply #3 on:** March 09, 2016, 06:33:22 PM »

It would be wonderful to mold forks into the ends for the leadouts. Teflon strips that you could pull out might work ok to mold the slots in?

Steve

Jeff Traxler · « **Reply #4 on:** March 10, 2016, 06:55:08 AM »

Hi Steve,I was trying to think of a way to do just that and after reading your post I started looking for a way to make it happen.

:!I have been experimenting with molded CF X bracing on some of the acoustic guitars I build.The center lap joint gave me fits until I put a small piece of balsa where I used cut the lap in.Now it's a piece of cake to fit them.Since I am laying up equally on each half of the mold and the tow will be above/below the center so a balsa disc(3/32-1/8?

) could be placed in the middle and ground away after cure leaving a structurally sound fork.The disc will also cut down on the amount of chop/fill that has to be added to the ends.Since I am kind of new to mold making,no-drill pins will be added(Thanx MM)and Bob Hunt gave me the hint of slipping the center bearing and bushings over the pins and molding them in.I have 100 bearings ordered and as soon as I get them in I will post pics of improved version Carbon Bellcrank II.

Avaiojet · « **Reply #5 on:** March 10, 2016, 07:07:30 PM »

Jeff,

Nice work.

Could you mold CF bellcranks with a rased center in the middle? Then they can be placed together.

Like these two aluminum ones, but CF. Would it be strong enough?

Steve Helmick · « **Reply #6 on:** March 10, 2016, 07:31:31 PM »

Quote from: Avaiojet on March 10, 2016, 07:07:30 PM

Jeff,

Nice work.

Could you mold CF bellcranks with a rased center in the middle? Then they can be placed together.

Like these two aluminum ones, but CF. Would it be strong enough?

That's exactly what the above two posts are about, but made all in one piece. Grape mimes, etc.

Steve

Avaiojet · « **Reply #7 on:** March 10, 2016, 10:09:03 PM »

Quote from: Steve Helmick on March 10, 2016, 07:31:31 PM

That's exactly what the above two posts are about, but made all in one piece. Grape mimes, etc. Steve

I see. What is "Grape mimes?"

Howard Rush · « **Reply #8 on:** March 10, 2016, 11:37:01 PM »

Grape mimes sink a bike.

Tim Wescott · « **Reply #9 on:** March 11, 2016, 10:38:43 AM »

Opinions are split on whether ball bearings will help or not. Searching on "ball bearing bellcrank" may or may not get you some useful info. If you're going to make them for all (which I assume you are, 100 airplanes is a bit excessive for stunt) then you may want to offer journal bearings.

A balsa core ala Brett Buck (meaning, end-grain balsa between the CF sheets) might be pretty cool, and easy enough to make into forks at the ends.

Jeff Traxler · « **Reply #10 on:** March 11, 2016, 02:00:53 PM »

I have made a couple CF bellcranks in another mold I made and used the roller bearings in them.Couldn't feel a difference but I have a few left and they will go in my personal cranks.I have some plain bearings that will be molded in future models.I think my sacrificial balsa disks are going to work to make the forks on the end.It layed up without to much extra headache.I have one in the mold right now.I'll set it free after supper.

Jeff Traxler · « **Reply #11 on:** March 11, 2016, 06:40:43 PM »

After modifying the mold just a bit I layed up this one.The center bearing was slipped over the pin and molded right into the bellcrank.The balsa discs in the forks ground away without much trouble.The remaining fork is very strong and will work out nicely.I am pleased with the outcome so far!

Steve Helmick · « **Reply #12 on:** March 11, 2016, 07:07:04 PM »

The ends may seem strong enough, but they sure look thin to me! I'd be modifying the mold to put more beef at the ends. But Mike says I worry too much. This is not a good place to have a failure. Could you post a picture of your mold halves and describe how you made them? Silicon rubber mold? Looks like a lot of FUN!

Steve

Motorman · « **Reply #13 on:** March 11, 2016, 10:25:07 PM »

I think his molds are made from Dupont Corian and CNC machined. I want to know what resin and what mold release.

Jeff Traxler · « **Reply #14 on:** March 11, 2016, 11:11:42 PM »

   The mold is displayed in the top of the thread and is made from Corian.I stacked 2 pieces of Corian with a 1/2" piece of ply in the middle and drilled a hole in 2 corners on the drill press.I put pins in the corners to keep them aligned and marked one face of the stack for reference before I took them apart.I used the ply in the middle to make a template for my router to follow.I used a colllar and a flat bottom bit to rout(remove) .020 over the entire bellcrank pattern to provide relief in the mold for the web.I then switched to a round bottom bit and different collar using the same pattern to make the beads.Then I attached the template to the other mold half by simply flipping it over and making sure the pins and reference marks were in the correct places.Rout as before and you have 2 mirror halves.After the routing on both halves is finished I install permanent pins in place of the temporary alignment ones.I clean up any chatter with some 220 and then bring the mold to a dull sheen with OOOO steel wool.Pretty much ready for wax then.

   I plan on making a new modified mold to allow for a bit more CF in the fork area.The 3/16 beads are a bit of overkill so I may go down to 1/8 to save a gram or two.The center bearing area may loose a little weight as well.I will take pics as I go thru the mold making process and post them.Got busy on the first mold and just forgot to take some.

Jeff Traxler · « **Reply #15 on:** March 11, 2016, 11:29:51 PM »

Quote from: Motorman on March 11, 2016, 10:25:07 PM

I think his molds are made from Dupont Corian and CNC machined. I want to know what resin and what mold release.

Don't know what the brand of the resin is.I get it in bulk from my friend Kevin Matney,Matney's Models.He makes composite R/C pylon racers,sailplanes.4 to 1 mix,4 hr. cure.The mold release is Partall #2 paste wax.No CNC here.......I've been making jigs to do complex tasks with a router since the early 80's,well before CNC was a twinkle in the computers eye.Thanx for the complement tho!!

Steve Helmick · « **Reply #16 on:** March 11, 2016, 11:59:25 PM »

Regarding bearings, I'd plead the case for a sleeve bearing...a long one, maybe 1" long. Probably oilite bronze would be my choice, but not without some consultations. And I'm really not a fan of oilite bronze. I just can't think of anything better, being a machinist and not an engine-ear. OIL with some synthetic oil on installation, and provide for adding more if possible for PM. I'd consider a tube axle, maybe it could be case-hardened or chromed or something like that. I did machine up some bushings once, that were something like Delrin, but impregnated with graphite. Might have started with a "V"

I may have one around someplace. Neat stuff. Made hundreds of them on a Hardinge "Chucker".

I would be afraid of ball or needle bearings getting a "hitch" in their giddyup and ruining the smooth controls. But one of the better stunters of my teen years used a Perfect "ball bearing" bellcrank, and it was excellent for what it was. Not that it had to take a lot of tension from the mighty steel finned Fox .15.

Steve

Avaiojet · « **Reply #17 on:** March 12, 2016, 05:29:18 AM »

Jeff,

Your CF mix, would that be of the same mix or similar used for R/C engine mounts?

Charles

Jeff Traxler · « **Reply #18 on:** March 12, 2016, 08:22:26 AM »

Hi Charles,I use a combination of CF cloth,tow(CF yarn) and small leftovers I cut into small pieces(chop) to help act as a binder for the epoxy.I would imagine the motor mounts would have all chop as longer fibers would probably cause problems in the injecting process.Trax

Tim Wescott · « **Reply #19 on:** March 12, 2016, 01:35:34 PM »

Quote from: Steve Helmick on March 11, 2016, 11:59:25 PM

Regarding bearings, I'd plead the case for a sleeve bearing...a long one, maybe 1" long. <snip>

Brett Buck has written on this, and I've read what he's said and quietly agreed.

Yes, a long bearing is probably good, because the various pivots on a bellcrank are not all on one plane*. This means that when you exert force on the thing with the lines, and the elevator & flaps exert force via the pushrod, that the thing will tend to rock**. Having a long bearing on the bellcrank will keep it lined up with the pivot rod.

If I were going to make a bellcrank with ball bearings I would either use a pair of them on a carrier that spaces them out by at least an inch to control rocking, or I'd use a large-diameter (relatively) thin-section bearing, for the same reason. Here's a link to a thin-section bearing: http://www.vxb.com/MR6702-Radial-Bore-Dia-15mm-OD-21mm-Width-4mm-p/mr6702.htm. Note that a pair of "normal" bearings makes a lot more sense to me than a thin-section bearing, but if you're determined, they're out there.

If you wanted to make a journal bearing with oilite or other bushings, you could make a long housing and only put bushings on the ends -- when rocking forces are present this is probably the only place that the bearings will really make contact anyway. That's getting too fancy for me -- I just use an aluminum journal riding on a drill rod or even a nice smooth piece of music wire, and I think it works just fine. Steve's idea of oiling the thing is probably a good one, and I may see if I can work that into my current project.

* Geometric plane. They're all on the same stunt plane.

** "Rock" as in "undesirable motion", not as in "man the way that works is really awesome, duuuuude".

Tim Wescott · « **Reply #20 on:** March 12, 2016, 01:38:49 PM »

If you're going to mess with ball bearings, pay attention to the fit rating of the bearing -- they can come all the way from stiff to dreadfully loose, and if you hang out with aerospace or other high-end motion-control people, you'll find that you can even custom-order pairs of them that are ground to specific preloads.

You want a bearing that turns freely but doesn't have a lot of slop -- and you have a tradeoff between the amount of slop and the distance between a pair of bearings to get the same amount of resistance to bellcrank rocking*.

* Just raising a bellcrank on a steady diet of classical music does not help. Sooner or later they hear Led Zepplin or Rush, and then they just start rocking away.

Jeff Traxler · « **Reply #21 on:** March 12, 2016, 07:21:23 PM »

The bearing I am going to use is a bronze oilite 1/4 O.D.x1/8 I.D.x 1/4 H. A bargain at $0.35! Slip it over the center locating pin during the lay-up and mold it in.A ball bearing was never in the equation,needle bearings are what have used in the past.They had a 283 lb. working load,overkill on a high order but were silky smooth.Unfortunately my hinge jobs and linkage wreck a very smooth bellcrank in short order

Steve Helmick · « **Reply #22 on:** March 12, 2016, 09:08:48 PM »

I'd bet that a bushing only 1/4" long is going to wear fast, due to that rock'n roll. A 1" long bushing would suit me better, but flex in the pivot shaft could become a problem. I'd really consider a 1/4" OD steel tube for the shaft. Have not looked in McMaster-Carr for a likely product, however.

Steve

Jeff Traxler · « **Reply #23 on:** March 24, 2016, 07:07:42 AM »

I took a little time and made an improved version of the mold to allow for larger,thicker fork ends and a thinner center web.4 layers of 6 oz. cloth in the web was WAY overkill and now I can get away with 2 and still can't flex it.Popped the first one out of the mold before work this morning.I'll clean off the flash and post pics when I get home later.One thing is for sure,Bellcrank structural failure will NEVER occur even under the most extreme flight loads with these beauties.If you can hang from them(And you can!!!)probably good to go.

Howard Rush · « **Reply #24 on:** March 24, 2016, 03:15:13 PM »

I'd just print one.

Mark Knoepfle · « **Reply #25 on:** March 24, 2016, 06:31:41 PM »

Share the .stl for the win! Uhm. That doesn't look like a bellcrank for CL though...

Jeff Traxler · « **Reply #26 on:** March 25, 2016, 08:45:05 AM »

Quote from: Howard Rush on March 24, 2016, 03:15:13 PM

I'd just print one.

That's cute Howard........Do they come in black? When they start printing the "Dreamliner" instead of making it from CF maybe.Or perhaps a printed Porsche??

LL~All kidding aside I still prefer items proudly made by human hands in the U.S. of A. planet Earth.

Here are a couple showing the larger fork ends.I made the forks to accept a a sleeve with a bolt thru it so the leadout won't wear on the threads.Very similar to full size aircraft cable attachment on many tube and rag ships.

Paul Walker · « **Reply #27 on:** March 25, 2016, 09:58:00 AM »

Very nice Jeff. How much does it weigh?

Jeff Traxler · « **Reply #28 on:** March 25, 2016, 10:24:36 AM »

Thanx Paul,This weighs in at 11.3 gr. I used 30 pieces of 12K tow in the beads and in between the 2 layers of 3K,6 oz. cloth in the web.The 12K and web go past the ends of the forks and several extra patches of cloth are added to the ends for extra lateral strength.I'm going to load up a sling with 200 lbs. of play sand and see if I can break it.With the curved beads and center web it sure is a strong little bugger.I want to load it across the flat to test the side loads as well.They don't want to flex at all by hand so some weight is in order.

john ohnimus · « **Reply #29 on:** March 25, 2016, 11:03:46 AM »

Once again, these look very nice Jeff!!! I hope that you will be able to offer these up in their final form. I too have thought about using my router for making molds for landing gear, etc. It looks doable for sure. Thanks for the inspiration!!

Tony O.

Howard Rush · « **Reply #30 on:** March 25, 2016, 12:28:08 PM »

You can attach one leadout to a nail and pull on the other. Then you only need half as much sand for a given pull.

Phil Krankowski · « **Reply #31 on:** March 26, 2016, 05:34:04 AM »

Quote from: Howard Rush on March 25, 2016, 12:28:08 PM

You can attach one leadout to a nail and pull on the other. Then you only need half as much sand for a given pull.

Its been so long since I took statics I almost got contrary on this statement. Yes, the pulley problem: if the load is connected to both lines then the axle sees 1x and the lines see .5x while if the load is connected to one line and the other line is anchored then the axle sees 2x and the lines see 1x.

Phil

Storm2313 · « **Reply #32 on:** March 26, 2016, 08:15:44 AM »

Incorrect forum post sorry.

Dennis Adamisin · « **Reply #33 on:** March 27, 2016, 07:52:27 AM »

Hey Trax

The best "forked" bellcrank yet. I think you better think about how you are going to mass produce these things for 400-500 of your closest friends..!

Jeff Traxler · « **Reply #34 on:** March 27, 2016, 11:40:20 AM »

Quote from: Dennis Adamisin on March 27, 2016, 07:52:27 AM

Hey Trax

The best "forked" bellcrank yet. I think you better think about how you are going to mass produce these things for 400-500 of your closest friends..!

Dennis,I am set up to make 6 per day right now until I make more molds.Since I have the jigs more won't be a problem.I am also making a new set of templates for the reverse style bellcrank mold similar to the SIG 4" except a little curvier and forked ends.I'll bring some to the show next week.Several have Dennis written on them already..........

Ward Van Duzer · « **Reply #35 on:** March 27, 2016, 12:25:54 PM »

Would you consider a web between the push rod bead and the BC's pivot point? Yes, it would add a little weight but not everyone likes the same push throw!

W.

Jeff Traxler · « **Reply #36 on:** March 27, 2016, 07:00:15 PM »

Hi Ward,Sure.I thought about that myself.......after the fact....as usual.I'll just have them available with or without for the weight minded.