Carbon FR gearbox project

bluechair84
bluechair84 Posts: 4,352
edited May 2014 in Your mountain bikes
Okie dokey, I've been thinking of making my own carbon frame, and here's what I've come up with.

3622_10151422189786262_474937537_n.jpg

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

  • turnerjohn
    turnerjohn Posts: 1,069
    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 :-)
  • bluechair84
    bluechair84 Posts: 4,352
    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 crashing :s
  • lawman
    lawman Posts: 6,868
    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?
  • bluechair84
    bluechair84 Posts: 4,352
    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?
  • VWsurfbum
    VWsurfbum Posts: 7,881
    Looks awesome, I keep thinking about doing it, once you've done it and ironed out the issues, i'll follow ;)
    Kazza the Tranny
    Now for sale Fatty
  • bluechair84
    bluechair84 Posts: 4,352
    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.
  • VWsurfbum
    VWsurfbum Posts: 7,881
    I'm thinking a 160mm full suss 29er, the forks are out there now so why not hey ;)
    Kazza the Tranny
    Now for sale Fatty
  • chick0
    chick0 Posts: 338
    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 ?
  • bluechair84
    bluechair84 Posts: 4,352
    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?
    Sort of. I'll be using an oven. The epoxy cures at around 80-140 degrees, so very attainable at home (but not in your own kitchen over obviously :? ).

    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.
  • jairaj
    jairaj Posts: 3,009
    would it help to make the blank frame using a 3D printer?
  • pesky_jones
    pesky_jones Posts: 2,890
    Haha were you were loving the spline command in the first pic?

    Looks good!
  • 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!
  • bluechair84
    bluechair84 Posts: 4,352
    edited May 2013
    jairaj wrote:
    would it help to make the blank frame using a 3D printer?
    Yes, yes it would. I'm going to put together a CAD version which could be sent away to someone. That will be better than me hand carving one like we live in the medievil period... But I don't have any CAD software and not much experience since college, and after a quick look around the net, it looks like AutoCAD will empty our house deposit in one felled swoop. Know of a cheaper alternative anyone? edit - just discovered Blender.org
    Haha were you were loving the spline command in the first pic?

    Looks good!

    Que? and; Thanks :)
    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!!
  • bluechair84
    bluechair84 Posts: 4,352
    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 :D (crudder response already predicted!) Happy days!
  • surely to get a more linear suspension curve with an air shock you'd need a falling rate swing arm?
  • bluechair84
    bluechair84 Posts: 4,352
    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?
  • 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 shock
  • bluechair84
    bluechair84 Posts: 4,352
    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 :-)
  • 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 rate
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    Looks pretty. Doesn't look like a particularly strong shape though. Too many curvy bits where a straight bit would be much stronger.
  • bluechair84
    bluechair84 Posts: 4,352
    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.
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    You have got some nasty stress points in that rear triangle. Before building it find an engineer to run the model through FEA.
  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    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.
  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    In the latter quarter of the suspension movement, the suspension moves less of the shock for travel at the wheel.
    Ah, hang on. That's commonly referred to as falling rate.
  • bluechair84
    bluechair84 Posts: 4,352
    There we go then, two for falling rate. I had a look around but couldn't find a decent clarification on this conundrum.
  • 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 now
  • bluechair84
    bluechair84 Posts: 4,352
    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.
  • paul.skibum
    paul.skibum Posts: 4,068
    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.
  • 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?
  • bluechair84
    bluechair84 Posts: 4,352
    We're buying a house, once we're in I'll have room to get started on this.