hi guys, i'm looking for some input on a piece i'm looking to make for my bike.

i wanna replace the steel subframe with a carbon fiber piece to reduce weight, and yet be safe enough so i don't nut myself on a 180mm mc wheel going 120 mph.

so far i've got 2 design options:

1) a truss member design using CF for tension members and aluminum (or CF) for compression members. I would fabricate cylindrical members and use either bolts or some sort of bond to fasten the members. i could paint it red and pretend i have a ducati jk.

2) a one piece CF design that's roughly shaped like a C-beam.

i'm looking at using a polyurethane or silicon mold rubber to make the pieces. vacuum is an option, but i won't bust my bank to get it. i'm also thinking about using foamcore or Al honeycomb in the design for added strength.

what would be easier? stronger? any input on creating high-strength pieces in multiple axes? since hanging off the bike puts lateral pressure on the subframe (as well as dropping the bike) it'd be nice to have a durable piece.

thanks!

 

I couldn't resist posting. One thing that really got my attention was the following comment " vacuum is an option, but i won't bust my bank to get it." You can't seriously be thinking this "could" be a wet layup non vacuum project right? There is no way you are going to buiild this without pressure of some kind. I would suggest you get someone to model your design first so you have some idea of the loads involved and you can build in a factor of safety into the design without making the part too heavy. Just that part alone is going to be difficult and costly unless you have connections. It's pretty easy to factor in the direction of load but how much load is another story. You need to have somesort of ballpark on theload transmited when you hit a bump at 60-mph or whatever speed you will see a bump. On a race only bike it would be easier to design in some respects but a street bike sees all sorts of conditions. I've got quite a bit of composites experience but this job scares my because a life is in the balance if you screw it up.

Once you have a design you have to figure out how to build to that design and live up to the numbers you feed into the computer. The tooling on this is going to be complex and expensive even if you do it yourself. You would have to design mounting points into the molds for brackets, engine mounts or any spot where a metal component will be bonded etc. I guess I'm just saying be prepared for something like this to break the bank if you want it to be safe and lightweight. Maybe a monocoque (stressed skin) design would be better. Google confederate motorcycles and look at some of their frames. They are doing some interesting things with carbon and aluminum that might give you some ideas. Don't mean to be a downer but I do want to help you see what you are in for if you start this project.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by crx12 &raquo;</TD></TR><TR><TD CLASS="quote">I couldn't resist posting. One thing that really got my attention was the following comment " vacuum is an option, but i won't bust my bank to get it." You can't seriously be thinking this "could" be a wet layup non vacuum project right? There is no way you are going to buiild this without pressure of some kind. I would suggest you get someone to model your design first so you have some idea of the loads involved and you can build in a factor of safety into the design without making the part too heavy. Just that part alone is going to be difficult and costly unless you have connections. It's pretty easy to factor in the direction of load but how much load is another story. You need to have somesort of ballpark on theload transmited when you hit a bump at 60-mph or whatever speed you will see a bump. On a race only bike it would be easier to design in some respects but a street bike sees all sorts of conditions. I've got quite a bit of composites experience but this job scares my because a life is in the balance if you screw it up.

Once you have a design you have to figure out how to build to that design and live up to the numbers you feed into the computer. The tooling on this is going to be complex and expensive even if you do it yourself. You would have to design mounting points into the molds for brackets, engine mounts or any spot where a metal component will be bonded etc. I guess I'm just saying be prepared for something like this to break the bank if you want it to be safe and lightweight. Maybe a monocoque (stressed skin) design would be better. Google confederate motorcycles and look at some of their frames. They are doing some interesting things with carbon and aluminum that might give you some ideas. Don't mean to be a downer but I do want to help you see what you are in for if you start this project.

</TD></TR></TABLE>

no this is great feedback. as of right now i've got 2-d drawings and a vague idea of what i want to do. you ask good question/bring up good points.

since this will be a unstreetable track bike, and also because i'm not trying to build the absolute lightest piece in the world, where every gram counts, i think there's some room for me to overbuild/use methods that may seem clumsy and overdone.

the big question for me was mounting, as the steel subframe mounts to the frame in 4 points. i suppose my options are to mold sleeves into the piece or come up with an alternative.

also, regarding pressure. since my first post i've found some basic vacuum bagging kits that i can afford. so it looks like bagging is back in play.

 

sounds like ur on the right track and its a perfect peice for u to do this to so good luck and post pics, lol..

 

Here's a link to build a vac pump with an old fridge compressor. Plenty of people have used these with great results:

http://www.berkut13.com/sucker.htm

Just goes to show that part can be had cheap. As far as mounting stuff to the sub frame you can co-mold metal inserts that can be tapped or used as through holes. Those inserts can also be very tough resin or solid carbon laminate. This is a common method used in composite race car chassis.

 

you have no idea what you are getting into

I would highly recommend against this. Steel is almost impossible to beat when it comes to things like this. You will need to do some detailed analysis to make this work.

Carbon also doesn't fail like metals do. it is linear elastic until failure. meaning you have no idea when it's going to fail. also it fatigues is a different way.

if you really want help with this you can PM I do design with structural composites.

 

You'd probably be better off building a part out of titanium rather than designing a part in carbon fiber.