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Discussion in 'Racing' started by wrk2surf, May 4, 2011.
Here is another foto, but with the old cockpit:
nice ride Sven !
That's part of my plan after this race. Make some CF bits. I already did my light bracket in FG. I want to do the towers and RB bracket in CF also.
Just a word of caution there, CF parts look, (and are... ) really really sexy.
Their impact resistance though is not that good (I would say non existence but I am trying to be modest here... )
There is a specific reason that everybody so far goes to either aluminium or special plastics/thermoplastics and not fibers. KTM for example could have made the tower side plates from CF. Straight forward design. They did not. And there is a reason for that.
That part, on the head of the bike supports the whole tower. Damage it and your tower will be hanging like there is no tomorrow. Remember that you support:
And God only knows what else. Even if you do not have all the above, still there are lots of parts that will not be in a good position if this, head part, breaks.
That is why KTM has this massive aluminium part there. Not that it cannot be done any other way. It can. But you need impact resistance due to the nature of the crashes that this part sees.
If I was stuck with CF I would make this part to break first upon impact. Then replace it with a new one (4 bolts) and off I go. It needs some thought but it is a good starting point.
Part looks really nice though
It's a bit of a myth that carbon has no impact resistance, especially when mixed with Kevlar (as I have done here). There have been huge advances in the base material, weave, processes and resins since carbon first came out in the 60's when there were some high profile failures.
KTM don't use carbon on their nav towers but the do on their bash/skid plates which should tell us something.
FYI, I've been running a carbon/kevlar nav tower for about a year now with no issues, this is just mk2.
For the bash plate you are correct.
You save enormous amount of weight from a very heavy part. Then again with a damaged bash plate you can continue to ride without major problems regarding speed and navigation.
KTM is using CF for their bash plate. I agree. It should tell us something, because they are using it for the bash plate. Not for their tower. I have seen KTM's tower and I have designed parts for it. It takes years of perfection to make this KTM design. It is both light weight and the one I got my hands on had survived years of accidents... :huh It's mechanics in my opinion are very, very good. (and I don't work for KTM... in fact I pay them whenever I fix my bike )
Don't get me wrong, I love CF as much as the next guy.
But when it is damaged (the resin I mean) it is almost useless. At the same time, both PE, thermoplastics and Aluminium would survive in better shape. May be bent, but I have seen my fair share of damaged towers making it to the end.PE you can heatreat it, thermoplastics the same, Aluminium a little difficult but doable.
Of course, I have seen Nav plates made of carbon fiber, Touratech used to make an RB holder out of Carbon fiber and took it out of the market, wheels have been made out of this material, canoes ... I even designed a speargun made out of CF... The material has huge benefits. I agree
In any case, If this part fits the 640A then I would like to give it a try
That can be arranged!
I totally understand your point about it braking completely vs plastic or alloy which might just bend etc. the kevlar will help with this, even if the carbon cracks the strands of kevlar will stay intact, the act as a sort of tether between the two cracked pieces. But yes, if it breaks it breaks and there is no bending it back in place.
In reality I'm much more confident in something I make from carbon/kevlar than aluminium but that has more to do with my metal working skills or lack their of...
CF's impact resistance is relative to the laminate design and product shape. Its ability to withstand bending can be misunderstood as impact resistance but when it fails it fails brilliantly.
Integration of Kevlar and in some cases eglass will assist impact resistance through absorbtion of forces but the laminate design again is determined by the product to be manufactured and forces to be withstood.
The photo you posted shows a vac bagged mount. Id be interested to know the thickness of the laminate and its make up - this being based on what loads you believe you will encounter (vibration, static and dynamic loading as well as impact forces at ??? speed)
The use of substantial cast alu mounts in numerous factory bikes indicates there is a lot more going on than simply carrying the tower and instruments. If CF was superior in this function Id bet the parent companies would be using it. Resins are another variable to add to the equation..
Its a weight vs function equation that I couldnt possibly understand or solve which will be made more complicated by the introduction of thermoplastics. (which are perfectly suited to the task and can be mass produced relatively cheaply!)
Like Dimitri and Pete have said, CF is great in some applications, for a high vibration environment, the cracking following a substantial impact and the propagation of them would not be good in a structural part such as this.
While the fabric will retain the strength, the resin will not retain the structure/form, it'll be tethered well, but flap around.
Beautiful part though.
Just more unwanted 2cents.
The layup is 8 layers of carbon twil and one relativly heavy layer of kevlar, epoxy is the matrix.
edit: I'll be testing this one over the next few weeks the might make some improvements, probably going a little thicker in the layup, possibly some uni's.
Carbon actually has better resistance to crack propagation than aluminium, each strand acts as a barrier to the crack.
Yes, I agree that was my point, if it does fail the kevlar keeps the pieces together. Not the best option but it does keep everything together.
Like I said before I've been running a cf tower for more than a year now and have had some quite big crashes, the tower held up very well.
I'll post some photo's of the rest of the setup later this afternoon. I'm using aluminium for the sideplates, they can bend and absorb the impact/energy, the idea of the CF base is to have it as stiff and strong as possible.
Here you go;
Hi Paul !
It is nice to have a discussion about new materials as a lot of people will benefit from that at the end of the day and it is always nice to add to the knowledge pool so don't feel that we regards composites as a no no
I think we are confusing here the impact resistance with penetration resistance.
Penetration resistance is excellent. If you are using Aramid , the more the better. Aramid is used for the bulletproof vests without any resin for example. Indeed its penetration resistance is something out of this world (if used properly).
Think of the F1 cars when crashing around. You can put a grown up man's weight on the front wing but the slightest hit makes it go sky high . The direction of the thing plays also a very important role, as the wing mentioned above is designed to create downforce, not sustain impacts... :huh But it gets complicated when you add factors such as impact to weight ratio.
Impact resistance on the other hand is not as good in composites. Why? Mainly because of the resins. The resin will crack if you hit it with a hammer. Why? Because it is not flexible enough. Polycarbonate for example, has excellent impact resistance, it is used in bulletproof glasses and it is flexible enough to distribute the hit in a larger volume of material if you like. That is what I mean by penetration resistance. Polyethylene the same. It can be bend back to shape.
I made a shell when was gathering data for our roadbook. You could stand on it, no problem. Two men standing on it. Still no problem. Hit it with a hammer and ... boys, we are going in :huh It was a vac part. It is this impact strength that I a worried about. And then again, Polycarbonate, Polyethylene, Aluminium can be simulated relatively easy in a computer to give you a quick idea of what will happen. With composites, it can be done, but it is relatively difficult at the moment. I guess it depends on what you need. By the time I could not penetrate the Aramid with the hammer, the shell was thicker as heavy aluminium :huh
The info that you give on the strands is correct. This for example would be of great benefit in a bash plate. The resin gives up and the sheet stays there until the end of the stage. You do not need rigidity there at all.
My latest r&d is hybrid assemblies. For example you could use thin thermoplastics to gain weight and reinforce them with aluminium plates wherever is needed to achieve rigidity. One could use thin composites and reinforce them with metal plates or use special resins or even use thermoplastic plates to shield them against penetration. Better make something as flexible as you can and keep it as rigid as it needs to be to perform its task. AntiPaul's Polyethylene tower is inspirational in my opinion . The design allows to be rigid in the axis that it needs rigidity and allows to be flexible in the side direction.
Always happy when discussions like these arise here, this is how people move forward
It looks beautiful on the bike
Yes, that's what's great about this place, plenty of nutters willing to give things a try!
Thanks, yes I think it looks great, I'll be testing over the weekend to see how it holds up.
Let us know how you go on your project.
What "project" would that be D? One I may know something about? Photo's in my thread later tonight hopefully.
The type of fasteners used will also plays a big part with composites ,
You will want maximin clamping with out over stressing so big washers to get a large clamp area ,
For starters you have one of the project Nav Towers
I am trying to make a hybrid Back plate for the 450 RFR (polycarbonate or PE with aluminium). The flexibility of PC and PE is very very helpful in this area of the bike and you can increase its rigidity by bracing it with aluminium.
Then you have the ''Lego'' switch which you have seen in CAD and we have already started hammering down Mk I to see how it performs during side impacts. The good thing is that even after a 200 kg impact the internals were still able to get to the end of the day. The other huge benefit is that you only need to change a couple of parts from the cartridge to get the unit back into shape. Will post destructive videos later in the week. We will get to the bottom of this
''Never Give Up ! ''
Hi D. Good to see there is more going on in this thread, was kinda stalled for a while, maybe with the Dakar coming up......
I found a site that had the details on making one way clutches with lego parts. That was the one thing that had stopped me from trying to make a lego fully functioning road book. Now I don't plan to make this a retail part or anything, actually &^$%s and giggles really. I reckon its possible so maybe for laughs sometime there will be a build sheet for that!!!!!
That is quite simple...
Actually I was thinking something along these lines for the transmission