Carbon FR gearbox project
bluechair84
Posts: 4,352
Okie dokey, I've been thinking of making my own carbon frame, and here's what I've come up with.
Frame spec is along the lines of:
Travel: 175mm
Wheelbase:1140mm
effective top tube: 645mm
effective seatube angle 68
headangle 67
rear centre: 429mm
Fork length: 170mm
Suspension arc is has a slight rising rate which should counteract some of the air shock's progressive nature, to make it feel a little more linear overall. Transmission is based around an Alfine 11 gearbox. The rear sus pivots at the Alfine so there is no chain stretch. As there is no rear mech, it uses horizontal dropouts which are designed to be fairly long so the chainstay length could be adjusted with a few extra links in the chain.
Frame spec is along the lines of:
Travel: 175mm
Wheelbase:1140mm
effective top tube: 645mm
effective seatube angle 68
headangle 67
rear centre: 429mm
Fork length: 170mm
Suspension arc is has a slight rising rate which should counteract some of the air shock's progressive nature, to make it feel a little more linear overall. Transmission is based around an Alfine 11 gearbox. The rear sus pivots at the Alfine so there is no chain stretch. As there is no rear mech, it uses horizontal dropouts which are designed to be fairly long so the chainstay length could be adjusted with a few extra links in the chain.
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Comments
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composites engineer or just have a few hundred thousand for R&R ?!
making your own frame out of steel would be hard enough ....CF is a whole different ball game !
Like the idea tho :-)0 -
No no no... none of the above. But, this sort of thing should be easy to model in carbon fibre (well, actually the first mold will be in fibre glass). I've been doing my homework and I should be able to make one. I'll find out about frame strength through real world crashing0
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There was an article in dirt about a chap who made his own carbon frame around a 3d printing machine. Split the frame into parts an made them, bonded together and wrapped in carbon. His latest version took him just two weeks to make. Personally if go for something abit slacker with that much travel, circa 65/66 but it doesn't look half bad!! Why go gearbox out of interest?0
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I want a suspension system that is really plush, and it seems to me that the chain and the way it creates anti/squat will spoil the feel. The flip side will be that there will be no chain tension to resist pedalling induced bob.It's going to be interesting to see how it rides.
I do however have a question for the forum: I'm going to make a fibreglass 'female' mold which I plan on filling with expanding foam to make a blank frame - this approach will make the whole thing easily repeatable as I experiment with CF layups. The blank will be wrapped in CF like Adrian Smith (from the Dirt article) and the blank burnt out. Now, I planned on using polystyrene and acetone to remove it. But I don't think I'm going to be able to expand polystyrene in the female mold - more a problem of getting hold of the EPS in the first place. Anyone got any other bright ideas on what I can 'blow' into the mold, wrap, then dissolve out again?0 -
Looks awesome, I keep thinking about doing it, once you've done it and ironed out the issues, i'll follow0
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Cheers I think... What ya thinking of doing?
This is now updated to 150-175 adjustable. I'm redesigning the rear triangle too. This week I'm ordering materials to have a first mould ready in a few months.0 -
I'm thinking a 160mm full suss 29er, the forks are out there now so why not hey0
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Will be following this project closely, so keep the posts coming
I have not read the Dirt article, but will you be using a Autoclave to harden the Carbon ?0 -
chick0 wrote:Will be following this project closely, so keep the posts coming
I have not read the Dirt article, but will you be using a Autoclave to harden the epoxy?
As an update, I have bought materials to start making the first 'blank' frame but need to make same specific tools for the job. I also found an answer to my earlier question - I can get hold of a two part polyurethene mix that expands when combined which I will use instead of the polystyrene.
I'm also going to putt together a complete CAD version of the frame which I don't really have at the moment; I've only done a basic CAD production for the suspension design.0 -
would it help to make the blank frame using a 3D printer?0
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Haha were you were loving the spline command in the first pic?
Looks good!0 -
Will be interested to know how you make the jig for this... its the one thing I've now idea how I'd make it lol!0
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jairaj wrote:would it help to make the blank frame using a 3D printer?Pesky Jones wrote:Haha were you were loving the spline command in the first pic?
Looks good!
Que? and; ThanksThe Northern Monkey wrote:Will be interested to know how you make the jig for this... its the one thing I've now idea how I'd make it lol!
Get two sheets of hardwood or metal, lay one on top of the other, mark out all your main hardware locations micrometer perfect on the top one; axles, BB, pivot locations; drill through both sections, stand the two sheets parallel with plenty of room for a bike to be built between them and brace so both are vertical, then pass a threaded rod though your hardware point holes. You can then use nuts and washers to locate the 'z' dimension of each part; dropouts, BB, pivots... So long as your threaded rods pass through the centre of each of your hardware points, you can build the bike around them. For the BB, I'd get a cylinder the same dimension as the shell and pass the rod through that so the bottom section is held correctly. One other thing you can do is to drill slots instead of holes, so if you wanted to change the head angle, you could slide the rod along a little bit to a little mark notating each angle of difference (it's all the trig I know).
Hope that creates a nice visual image!!0 -
I don't know why I didn't think of this... I'm sure Freud would say it's an Oedipus complex... My Dad made a career out of AutoCAD! A quick chat on the phone has revealed he B.S.ed his way through most of his career though so is of no use whatsoever... but his old employees would be happy to help me drum up a render as back in those days, I was a sweet innocent kid loved by them all (crudder response already predicted!) Happy days!0
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surely to get a more linear suspension curve with an air shock you'd need a falling rate swing arm?0
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In the latter quarter of the suspension movement, the suspension moves less of the shock for travel at the wheel. It thus provides a greater leverage against the shock; less force is required if the shock itself was linear. For the same amount of effort at the end of the travel, a greater amount of work can be done against the spring. That's the way it's designed, which i believe is a rising rate, unless i have my terminology wrong? Anyone care to confirm?0
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well we're talking about the same thing!
to me, if you had a linear spring you'd use a rising rate ratio linkage, it gets harder towards the end of the travel.
air shocks are naturally a rising rate or progressive curve
so if you want a linear curve using a standard type air shock you'd need a falling rate linkage to counter the rising rate of the shock0 -
The way it looks on the graphs is that the swingarm can push force more per mm of shock as it progresses (the line between movement/force goes up). An air spring would look the same an a graph, an increasing amount of effort per mm, so they both go by the same name. As the spring requires more force, and the suspension presses more force, they cancel each other out. Both are rising rate. We need a third person to adjudicate this :-)0
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i've changed my mind, we're not talking about the same thing!!
if you plot the spring rate curve on a graph, then plot your ideal linear line, then the linkage rate would have to mirror the spring rate curve on the opposite side of the linear line to get one to cancel out the other and achieve the linear line rate.
if both are rising rate then then you'd get a higher rising rate0 -
Looks pretty. Doesn't look like a particularly strong shape though. Too many curvy bits where a straight bit would be much stronger.Transition Patrol - viewtopic.php?f=10017&t=130702350
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Yeah, I originally designed a straight downtube, but played with a design where the shock pierces with DT instead of having strutts to mount the eyelets on. It's a bit complicated for a prototype so I think I'll go with straight tubes first of all. And like you say, straight tubes will be more functional. I also need to redesign the rear triangle. I don't like it.0
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You have got some nasty stress points in that rear triangle. Before building it find an engineer to run the model through FEA.Transition Patrol - viewtopic.php?f=10017&t=130702350
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Stevieboy's right, a rising rate suspension design with a rising rate shock will result in a VERY rising rate.
Move the frame-mounting point of the air shock to give a slight falling rate, and you'll get more neutral.
I also reckon, at a glance, that it's going to squat under pedalling, causing some mad bobbing, but being a high(ish) pivot, means it will be very active over the bumps.0 -
bluechair84 wrote:In the latter quarter of the suspension movement, the suspension moves less of the shock for travel at the wheel.0
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There we go then, two for falling rate. I had a look around but couldn't find a decent clarification on this conundrum.0
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thats a big project your taking on there
a suggestion build it from tubes test the concept first, forget all the 3d printed voodoo for now0 -
Yup. I'm gonna build the jig then chop down some old skip bikes to see if the concept works. I know a couple of guys who might weld it up once it's on the jig. Solicitors are still working on the contracts and it won't start until we're into the new place and I have enough room for this.0
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Learn to weld it yourself - its a long term project may as well fill some of the gaps in progress with learning new skills!
I love riding bikes this would be a little beyond my interest but I have no engineering background or knowledge - good luck!Closet jockey wheel pimp whore.0 -
bluechair84 wrote:Yup. I'm gonna build the jig then chop down some old skip bikes to see if the concept works. I know a couple of guys who might weld it up once it's on the jig. Solicitors are still working on the contracts and it won't start until we're into the new place and I have enough room for this.
solicitors?0 -
We're buying a house, once we're in I'll have room to get started on this.0