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Discussion Starter #42
I guess my next task is to figure out the pull out force for M8 aluminum threads. It's not a simple task though. It may be better to just use steel instead.
 

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Static loading is one thing, shock loading quite another. What's the worst case condition you'd use to figure out the highest shock loading? I'm guessing you can't answer either of those questions (I can't either, I'm just saying)

So here's a different idea. Don't worry about what loading it will see. Ducati should have already done this and designed a part that would work. What you need to do is to build a part at least as strong as the stock part, right? I'm not sure the best way to do that, but I am sure it's easier than trying to figure out what sort of loads the rod might see.

FWIW - I think the choice of figuring max required load from the torque of the engine is so arbitrary it's not worth figuring out. That compares to stabbing the rear brake during a panic stop from 140mph how?

And while theoretical strengths are a decent place to start, are you certain you're using the material in a way that it's going to provide maximum strength? What sort of safety factor are you going to use?

I'm not trying to discourage you, just asking the same questions I'd ask myself if I was doing this.
 

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Discussion Starter #44
Static loading is one thing, shock loading quite another. What's the worst case condition you'd use to figure out the highest shock loading? I'm guessing you can't answer either of those questions (I can't either, I'm just saying)

So here's a different idea. Don't worry about what loading it will see. Ducati should have already done this and designed a part that would work. What you need to do is to build a part at least as strong as the stock part, right? I'm not sure the best way to do that, but I am sure it's easier than trying to figure out what sort of loads the rod might see.

FWIW - I think the choice of figuring max required load from the torque of the engine is so arbitrary it's not worth figuring out. That compares to stabbing the rear brake during a panic stop from 140mph how?

And while theoretical strengths are a decent place to start, are you certain you're using the material in a way that it's going to provide maximum strength? What sort of safety factor are you going to use?

I'm not trying to discourage you, just asking the same questions I'd ask myself if I was doing this.
Oh sure, I agree. I could find a stock one, and load it up until it breaks and use that as a reference.

I'm just getting started on the math though. I should calculate the moment of inertia of an oem rear wheel @ 140 mph and see what kind of forces would be applied to the rear brake rod if the brake were fully applied.

I haven't decided on a safety factor yet. So far, it appears to have adequate strength, but I have not calculated the pull out strength of M8 aluminum threads. I can find the equations, they are just complex.

Then, after building one, I get to hang some heavy stuff from it and watch it break! :eek:
 

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I guess my next task is to figure out the pull out force for M8 aluminum threads. It's not a simple task though. It may be better to just use steel instead.
I converted a original pre 92 reactionrod into carbon.
Both of the balljoints are connected to the aluminium middlesection by m8 threads which fit in the middlesection for about 7mm deep.
If you make the threads of your inserts let's say twice as long you 're on the save side.
A bigger problem is the connection between the crp hose and the inserts.

If you don't want any worries find a pre 92 reactionrod, srew one balljoint of, slide a carbontube over it and put it together again.

You can find tube's here:http://shop.r-g.de/en/Semi-finished-products/Carbon-tubes/
 

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Discussion Starter #46
I converted a original pre 92 reactionrod into carbon.
Both of the balljoints are connected to the aluminium middlesection by m8 threads which fit in the middlesection for about 7mm deep.
If you make the threads of your inserts let's say twice as long you 're on the save side.
A bigger problem is the connection between the crp hose and the inserts.

If you don't want any worries find a pre 92 reactionrod, srew one balljoint of, slide a carbontube over it and put it together again.

You can find tube's here:http://shop.r-g.de/en/Semi-finished-products/Carbon-tubes/
Thank you very much for that information!

I have 20 mm available of thread for these rod ends, so I guess that's plenty.

I'm well aware of some of the issues of bonding aluminum to carbon fiber composite. I intend to get West Systems Aluminum Etch kit, which is intended to prepare the surface of aluminum for bonding with epoxy. I have read that roughing the aluminum with 80 grit sand paper first is important as well. I've read the instructions on preparing the carbon fiber tubing.
Here's one place we can get C/F tubing in America:
http://www.carbonfibertubeshop.com/
Another place is Dragon Plate:
http://www.dragonplate.com/
Both sites have information on working with their products.

Another somewhat critical thing I have to deal with is getting the sizes correct. Epoxy develops maximum shear strength with a bond thickness of I think it was 0.003" to 0.007", so the difference in diameter between the insert and the tube has to be twice that, or 0.006" to 0.014". That's going to take some careful measuring and possibly require some machining.
 

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Dirk,
I see big danger here.
Carbon fiber is really strong, but in compression. Not in extension. The brake rod will be seeing extension forces, and big ones as you already calculated.
Metal is really good in extension. Composites are not. Failure is imminent, and most likely catastrophic. It will not live a long and happy life, and neither might you. This is not a good application for Italian Chrome.

The other factor is fractures and damage to the carbon fiber matrix. Bruised or dinged carbon fiber soon fails after being flexed. Your brake rod is in a location it will easily see rocks and dings from road debris. Small impacts will degrade is capabilities very quickly, as many mountain bikers with broken frames have found out.

For this part, I would stay with metal.
You scared me today, and I haven't even seen you ride yet.

Cheers,
 

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Dirk,You will have no problems with properly cut threads in a good grade of aluminum.And in tension the 8mm rod end won't pull apart.The carbon fiber tube will probably handle the load in compression too,tension is another matter.You should contact the manufacturer and get their take on it.The problems will be with bonding the ends to the tubing.My admittedly limited knowledge of bonding carbon and glues in general make me very cautious when dealing with potentially deadly failures.The idea of a .003" layer of glue holding a potential couple of tons of shock loaded brake rod together would make me very nervous.Bicycles may use glued pieces but their speeds are lower and their tires don't generate the grip that a motorcycle tire can.What broke your old brake rod? The picture isn't very clear but it looks like it suffered from a non linear input. That is something else you might want to factor into your calculations as carbon fiber is damaged pretty easily and the dings weaken it.You never know what will pop up in front of you while riding and somethings you just can't miss.
 

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Discussion Starter #49
Carbon fiber is really strong, but in compression. Not in extension. The brake rod will be seeing extension forces, and big ones as you already calculated.
Metal is really good in extension. Composites are not.
Cheers,
Huh? Carbon fiber composite has extremely high tensile strength. The exact strength depends on the weave and the ratio of epoxy to fiber, in addition to the obvious size considerations. I would be more concerned about compressive forces with carbon fiber composite tube. I've ordered some woven fabric type of tubing from here:
http://www.rockwestcomposites.com/index.php?p_resource=home
They are very inexpensive. They also sell the unidirectional tubing too, but it was much thinner.
 

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I'm just getting started on the math though. I should calculate the moment of inertia of an oem rear wheel @ 140 mph and see what kind of forces would be applied to the rear brake rod if the brake were fully applied.
Great, you'll figure out the forces to stop the wheel. Assuming you've already lofted the rear tire off the road with the front brake your calculations will be useful. Assuming the rear wheel is still in contact with the road, you've neglected to include the inertia from the other 600lbs attached to the wheel that also needs to slow down. Might I note that maybe 200 of that 600lbs is made up of the rider, aka you.

Again, you don't have the information you need to figure this out. Stop trying to fool yourself that you can. Build one that's stronger than the stock one.

Carbon fiber is really strong, but in compression. Not in extension.

...
Metal is really good in extension. Composites are not.

...

The other factor is fractures and damage to the carbon fiber matrix. Bruised or dinged carbon fiber soon fails after being flexed. Your brake rod is in a location it will easily see rocks and dings from road debris. Small impacts will degrade is capabilities very quickly, as many mountain bikers with broken frames have found out.
Huh? Carbon fiber composite has extremely high tensile strength. The exact strength depends on the weave and the ratio of epoxy to fiber, in addition to the obvious size considerations. I would be more concerned about compressive forces with carbon fiber composite tube.
Gotta agree with Dirk on this one. Carbon fibers by themselves have about zero strength in compression. It's all about the material holding them together when you talk about compressive strength. Well, ok, fine, that's grossly oversimplified but still. Bare carbon fiber strands will bend under their own weight. Good luck trying to break them by hand in tension. I'm wondering if maybe you're not thinking of something else??? Perhaps the material they make carbon brake rotors out of perhaps?.

I DO wholeheartedly agree with the point about nicking it though. Any nick will create a stress riser in the material. No argument there. Stress risers are bad.

All in all, if I had to have a carbon fiber brake rod, I'd do it the same way the original one was done. Cosmetic cover over the structural metal. Call it a nick guard if it has to have a use. But I think carbon fiber is probably the most overused/misused material out there right now in the sportbike world so the chances of me using it are about nil.

P.S. It possibly may require machining to reach the tolerances specified? You're talking about thousandths of an inch. Plan on it! I'm kinda wondering what the tolerance on your parts will be and how that will figure in too...
 

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Huh? Carbon fiber composite has extremely high tensile strength. The exact strength depends on the weave and the ratio of epoxy to fiber, in addition to the obvious size considerations. /QUOTE]

Yes , you 're right about that!
I used the unidirectional tube (because it had the rigth innersize) and reinforced it with a braided carbon hose and epoxy resin. Also used a special epoxy resin to glue the tube.
 

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Discussion Starter #52
Huh? Carbon fiber composite has extremely high tensile strength. The exact strength depends on the weave and the ratio of epoxy to fiber, in addition to the obvious size considerations. /QUOTE]

Yes , you 're right about that!
I used the unidirectional tube (because it had the rigth innersize) and reinforced it with a braided carbon hose and epoxy resin. Also used a special epoxy resin to glue the tube.
Thanks, in hindsight I probably should use the unidirectional product, but I looked closely at the woven carbon fiber and half the fibers are axial and half are circumferential. Maybe the circumferential ones would help it from rupturing in compression? I don't know. Thanks for sharing your experience.
 

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hmmm interesting thread there dirk :)

wil be interested to see if it works.....

how often do you use the rear brake?? even under hard riding conditions i hardly ever touch the rear brake, maybe to balance myself during a corner, even with a full hard stop at high speed the rear brake isnt doing alot as the weight of the bike is probably atleas 85% on the front brakes. loading up the rear brake as it will most likely have the rear wheel off the ground should have the rear wheel locked pretty quickly and with minimum brake pressure, correct?? i tend to use my fronts and gears to slow hard and fast with rear brake if i start to shit myself haha.

thats my riding style anyway, everyone is different i guess :)

plus more moving patrs = more to go wrong!! lol

i find the non floating caliper works great even under hard conditions :)
i did ride my brothers SP for half a year and to be honest i rode that as hard as i do mine and felt next to no difference under hard conditions.

just my 2c worth :)

hope it all goes well for you, and why not be different!!! thats what customizing is all about ;)
 

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Discussion Starter #55 (Edited)
hmmm interesting thread there dirk :)

wil be interested to see if it works.....

how often do you use the rear brake?? even under hard riding conditions i hardly ever touch the rear brake, maybe to balance myself during a corner, even with a full hard stop at high speed the rear brake isnt doing alot as the weight of the bike is probably atleas 85% on the front brakes. loading up the rear brake as it will most likely have the rear wheel off the ground should have the rear wheel locked pretty quickly and with minimum brake pressure, correct?? i tend to use my fronts and gears to slow hard and fast with rear brake if i start to shit myself haha.

thats my riding style anyway, everyone is different i guess :)

plus more moving patrs = more to go wrong!! lol

i find the non floating caliper works great even under hard conditions :)
i did ride my brothers SP for half a year and to be honest i rode that as hard as i do mine and felt next to no difference under hard conditions.

just my 2c worth :)

hope it all goes well for you, and why not be different!!! thats what customizing is all about ;)
Hey thanks. I don't use it much either. I use it mostly at slow speed, emergency stops, and waiting at stop lights. I'm not skilled enough to use it at high speeds. I don't think there's much stress on it either.

The whole reason I went to the floating rear brake was because the people who made my aftermarket swingarm made a mistake. They provided a pin for the oem non-floating caliper, but it was too short. I suppose now I could have just had my machinist friend make a longer pin to engage the non-floating bracket since the pin is removable, but I got the idea to make a floating rear brake. I didn't have a machinist back when I started this project. In theory it's supposed to be better but like you said it's probably not significant.

I dunno, now you've got me rethinking this thing. The oem bracket might have a better place to mount the hall effect speed sensor I need for my electronic speedometer than the floating one. I just wonder why Ducati used the floating caliper in the first place if they never used it on a Superbike.

OK, I did some looking at it appears that the 851 sometimes used them. The images I've found show some with and some without the floating rear brake. Some are above and some below the axle as well.
 

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Whilst a floating rear brake is technically the best solution, the fact that Ducati themselves played around with pretty well all the options on otherwise identical machines would indicate that in practice there's no great advantage of one over any other. Personally, despite trying everything I know of, to no effect, i'd just be happy for a back brake that does something, other than act as a parking brake at traffic lights.
 

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Discussion Starter #57
Whilst a floating rear brake is technically the best solution, the fact that Ducati themselves played around with pretty well all the options on otherwise identical machines would indicate that in practice there's no great advantage of one over any other. Personally, despite trying everything I know of, to no effect, i'd just be happy for a back brake that does something, other than act as a parking brake at traffic lights.
Thanks. That's pretty much what I think too. I still have not decided on how to attach the rod to the engine. On the later bikes, the master cylinder is at the same location that the bracket for the rod was located on the older bikes. Maybe I just drill a hole in the case and thread in an M8 bolt there.
 

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Thanks. That's pretty much what I think too. I still have not decided on how to attach the rod to the engine. On the later bikes, the master cylinder is at the same location that the bracket for the rod was located on the older bikes. Maybe I just drill a hole in the case and thread in an M8 bolt there.
Dirk,
Had the same issue on my SL, when I fitted a 900ie/916 m/cylinder. Made a small triangular bracket (in Ti of course!), with the three corners picking up (a) the rear mounting bolt of the m/cylinder bracket, (b) the redundant bottom/rear drilling thru the crankcases, ((a) and (b) thus locating the plate) and (c) the front rose joint for the torque arm. Puts the pickup point for the torque arm in nearly the same place as standard. Can post some pics after the weekend if you like
 

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don't drill a hole in your engine case Dirk, there is some oil inside there.

:) ;)

use the standard L-shaped rod-mounting bracket instead, that should
fit beneath the rear brake master assembly with no issues.

:)
 

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Discussion Starter #60
Dirk,
Had the same issue on my SL, when I fitted a 900ie/916 m/cylinder. Made a small triangular bracket (in Ti of course!), with the three corners picking up (a) the rear mounting bolt of the m/cylinder bracket, (b) the redundant bottom/rear drilling thru the crankcases, ((a) and (b) thus locating the plate) and (c) the front rose joint for the torque arm. Puts the pickup point for the torque arm in nearly the same place as standard. Can post some pics after the weekend if you like
That's a good idea. I'd like to see pictures when you have them. How did you use the through hole? A very simple way would be to just get some rod with an M8 thread on the end and fix it in the hole, but would add the weight of all that rod length. I have some carbon fiber plate I could use...
 
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