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Open Source Downhill Project

fluider

Monkey
Jun 25, 2008
440
9
Bratislava, Slovakia
I'd very appriciate a way of mounting the BB-shell the same way as it's on Wilson 2011+ that it can serve as one of the pivots (a hell strong pivot!). And perhaps instead of having many pivot mounting holes in the CORE an eccentric pivot-assembly could be designed whit spline circumference (like ISCG05 adapters on Wilson 2011+) where actual pivot position would be determined by its rotation around the assembly center.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
16,127
1,104
01776
Sandwich as always makes some pretty good points,


I think the ideal setup is to come up with specs and get manufacturers on board to build COARs that will slot in to your design. Start simple, and go from there. A small manufacturer like purgatory or potentially FTW could start building ultra-simplistic, single pivot cores, and allowing other people to follow suit. I'd think that people that can't make frames could potentially make other parts, ie; raceface could make seat masts in machined aluminum, and your average road bike company could make a front end out of steel or aluminum.
 

Pslide

Turbo Monkey
I don't think anyone's going to build anything until there are guaranteed sales. No one's going to build cores unless someone else is building stuff to bolt to it.

I think someone will have to build a full frame/bike using the A,B,C concept, and it will have to be well received by the public before a company is going to invest anything in the idea.

I don't think you're going to be able to sell this idea without proof of concept, which means someone's going to have to do some prototyping first. ($$$)
 

TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
I don't think anyone's going to build anything until there are guaranteed sales. No one's going to build cores unless someone else is building stuff to bolt to it.

I think someone will have to build a full frame/bike using the A,B,C concept, and it will have to be well received by the public before a company is going to invest anything in the idea.

I don't think you're going to be able to sell this idea without proof of concept, which means someone's going to have to do some prototyping first. ($$$)
My initial idea was to have a collective effort to come up with a concept AND put things into action, i.e. not just a design exercise.

The concept would be Open source and the design/build would be "Crowdsourced". This is why we need to get amateur (and even pro) fabricators and machinists on board. Rather than one person doing all the work it would be broken down into bitesized "chunks" and individuals would be responsible for their "chunk".

Anyone wanting to then build a version of the bike would then have free access to the files and would only have to pay machining/fabrication costs.

What's in it for the collaborators?- Nothing, apart from the knowledge and kudos of seing "their" bit on the trails.

EDIT- this is not to dismiss the option of companies/individuals also offering fully designed and built assemblies at a cost.
 
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graham888

Chimp
Aug 12, 2009
11
0
UK
I think it's a really interesting concept and would be keen to help out with the design and any CAD work if I wasn't currently in my final year of mechanical engineering at university. I'm a bit to bogged down with other projects right now unfortunately.
Once I finish uni though I've been planning to design and build a carbon gearbox AM bike. It would be a similar sort of set up to the Lahar/Zerode probably. I will be keeping a close eye on this thread and would consider integrating this concept into my design for sure.
I also have an accurate CCDB model and a couple of frame designs in Solidworks that could possibly prove useful to this design process at some point.
 

LMC

Monkey
Dec 10, 2006
683
0
I have enough 44mm diameter 2mm wall thickness tubing for two front ends as well as threaded BB shells, assorted gussets and cable guides, head tubes and some drawn bar.. ill donate this to the cause if someone can do the actual fabrication.

Also i would be happy to produce CAD files if needed.

If this frame gets built someone should twist Dirtmags arm to do a feature on it, could be helpful when blagging forks, wheels etc ;)
 
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TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
Cheers guys for the encouragement.

I have been playing with dimensions of the core, sorry coar! I have had quite a change of thought regarding point A. If it was placed forward near the headtube, potentially (295,495). The advantages of this is that it creates a sort of pin-jointed larger triangle (structurally superior than the previous ABC concept?)

I will post a drawing of what I mean later.

EDIT- here's the drawing;
ABC frame concept.png

What do people reckon? Is moving point A forward getting away from the initial idea or does it make sense?
 
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iRider

Turbo Monkey
Apr 5, 2008
1,963
330
I am not an engineer but to me it looks like you try to achieve something similar that motorcycle designers do: use the engine as part of the frame and bolt the other parts to it. I think your plan will work for gearbox bikes where the core can be designed to accommodate all the different styles of gearboxes out there. However I think you would have to make too many compromises to be able to include all the different conventional suspension systems.
Other thing: how massive do the connection points have to be? I can imagine that there is a lot of force on them, especially the ones on the top and downtube.
 

Pslide

Turbo Monkey
Hmmm, deceptively simple drawings hide surprisingly complex engineering problems! :)

You might have to do some simple statics / FE analysis on these different options to see what your forces will be at those points and if additional stays will be required.

Point A nearer the headtube scares me slightly. I think post #50 with a unified core seems like a safer bet, but this is only my gut feel and I have been wrong before.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
16,127
1,104
01776
Or, is this better? More in keeping with the Core theme and more possibilities for shock mounting. But heavier?

View attachment 109582
I like this design. Now you can have ultra-light seatmasts and vary the front section independent of other bits. It's likely to be a bit heavier than a normal tube frame, but I'd imagine it's lighter and more universally compatible than anything else.
 

offtheedge

Monkey
Aug 26, 2005
955
0
LB
Seems as though the "boxed" core is going to really limit shock placement and stroke.

I think you have to have a starting point of travel/stroke/rate to design around. At least that is a Parameter I try to start with, so I don't do a bunch of design work that can't move. I also usually design around a concept that I feel I can actually produce without needeing a 7 axis, live tooling milling center.

Im all for helping with any CAD, solidworks, or modeling/animation work needed.
 
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TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
Other thing: how massive do the connection points have to be? I can imagine that there is a lot of force on them, especially the ones on the top and downtube.
The connection points don't have to be too large- if you think about it DH bikes are already pin-jointed at the shock with just M8 bolts.

Seems as though the "boxed" core is going to really limit shock placement and stroke.
The "boxed" core can be shaped to fit most types of suspension systems- it only has to join the 3 points- it could be C-shaped or U-shaped for example. Remember it is only the "points" that we are discussing.
ABC orange.PNG
ABC sunday.PNG

I'm not an engineer but to me option #49/b (without strut) looks the weakest and #50 the best not only because of stiffness.
Remember that a pin-jointed triangle is a strong structure and #49/b is the nearest to that shape.
 
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marshalolson

Turbo Monkey
May 25, 2006
1,439
73
just an idea for simplisity's sake...

can you make "point c" the main pivot, so the pivot axle connect seat-mast to core, and "point b" the lower shock mount?
 

TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
just an idea for simplisity's sake...

can you make "point c" the main pivot, so the pivot axle connect seat-mast to core, and "point b" the lower shock mount?
BINGO!- that's exactly what I have been thinking!

I would put point point C lower (that's why I said initially to put it about 200mm above the BB) and integrate it with the main pivot and also a idler/jackshaft. This means that all drivetrain options have the same chainline for anti-squat characteristics. see simple pic;
ABC esc.PNG
If the idler/jackshaft sprocket was smaller than the rear hub sprocket you would get a high anti-squat response and still be able to run the chain taut!!! (I have been considering this option for a while- even the first diagram on this thread shows this idea)

If the shock linkage was integrated with a Split-Pivot type chainstay you would alsobe able to fix the brake caliper to EITHER the chainstay or seatstay for different Brake Squat response!

Cool huh!

Also, like my unfinished gearbox bike I would use a 110x20 dual-disc FRONT hub as a rear hub (since the freewheel is in the gearbox). This would allow you to have a spare wheel that could fit either front OR rear!!!



Man, I have just given away all my secret plans for my gearbox bike (now we HAVE to build it:thumb:)
 
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fluider

Monkey
Jun 25, 2008
440
9
Bratislava, Slovakia
Don't consider me as bad message courier but integrating pivot axles with another joints and shafts brings a dictatorship of space restrictions upon you. It's very nice but a lot of thinking and compromising goes into it. And, wanting a gearbox somewhere in there calls for a series of headaches :). There is a hell of things you must consider so I would not go at very details at this stage of concept.

Assembly_1.jpg

Assembly_2.jpg
 
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offtheedge

Monkey
Aug 26, 2005
955
0
LB
Don't consider me as bad message courier but integrating pivot axles with another joints and shafts brings a dictatorship of space restrictions upon you. It's very nice but a lot of thinking and compromising goes into it. And, wanting a gearbox somewhere in there calls for a series of headaches :). There is a hell of things you must consider so I would not go at very details at this stage of concept.

View attachment 109590

View attachment 109591
^^^This.
I'm not trying to piss on anybody's Cheerios but there are a dozen variables that have to be finalized before ever considering a design. Add in a modular approach and you are looking at massive limitations.
MS paint explanations do little to address actual hurdles. IMO, you have to start with some basic geo numbers to eliminate the impossible.
 

TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
Fluider-nice Solidworks- good work!
You are right, integrating fixtures on the same point is tricky, especially with large items such as internal hubs and BBs. However, I think a jackshaft sprocket and swingarm pivot at point C is possible. See attached sketch (ignore the proportions!) to see one way it MAY be possible;
pivot assembly.png



^^^This.
I'm not trying to piss on anybody's Cheerios but there are a dozen variables that have to be finalized before ever considering a design. Add in a modular approach and you are looking at massive limitations.
MS paint explanations do little to address actual hurdles. IMO, you have to start with some basic geo numbers to eliminate the impossible.
Dont worry about pissing on anybody's Cheerios, the whole reason for these posts is to get a wide range of views and experiences.

I do think, however, that we differ in our approaches- due to my training as an architect I always sketch first the main CONCEPT ideas, then work on the nitty gritty of the EXACT points and dimensions. The MS Paint sketches were just that- sketches. Think of the them as "back-of-napkin" doodles that inform the direction not the exact outcome. I was not suggesting by any stretch of the imagination that we design a bike on MS Paint!!!!!

Incidently, I have got CAD drawings (only 2d) of my idea that have been designed to give a very nice leverage ratio, high Anti-Squat Percentages (around 100% at sag falling ever so slightly throughout it's travel) and with a nice low COM.

This discussion is not about my design though, it is a place to throw around ideas at a primitive stage. I only suggested the "Core" design to get the imagination flowing as to how a modular/open concept may work.

Thanks for your previous offer to help with design/CAD, this will immensely help later on.
Keep the comments coming!:)
 

offtheedge

Monkey
Aug 26, 2005
955
0
LB
Fluider-nice Solidworks- good work!
You are right, integrating fixtures on the same point is tricky, especially with large items such as internal hubs and BBs. However, I think a jackshaft sprocket and swingarm pivot at point C is possible. See attached sketch (ignore the proportions!) to see one way it MAY be possible;
View attachment 109594





Dont worry about pissing on anybody's Cheerios, the whole reason for these posts is to get a wide range of views and experiences.

I do think, however, that we differ in our approaches- due to my training as an architect I always sketch first the main CONCEPT ideas, then work on the nitty gritty of the EXACT points and dimensions. The MS Paint sketches were just that- sketches. Think of the them as "back-of-napkin" doodles that inform the direction not the exact outcome. I was not suggesting by any stretch of the imagination that we design a bike on MS Paint!!!!!

Incidently, I have got CAD drawings (only 2d) of my idea that have been designed to give a very nice leverage ratio, high Anti-Squat Percentages (around 100% at sag falling ever so slightly throughout it's travel) and with a nice low COM.

This discussion is not about my design though, it is a place to throw around ideas at a primitive stage. I only suggested the "Core" design to get the imagination flowing as to how a modular/open concept may work.

Thanks for your previous offer to help with design/CAD, this will immensely help later on.
Keep the comments coming!:)
Right on! Thanks for not taking offense, non was intended.

If you have cad drawings and a baseline then let the brainstorming commence.
My engineering and manufacturing background have me always working from function to design, so I tend to get hung up on what works and then try to make it look good.

I think a U or C shape is a good start. Something that could be cast or milled out of some billet would be a clean way to maximize the strength of A, B and C.

Let me know some of your geo/spec ideas and I'll start laying out some mock ups in my spare time.
 

Pslide

Turbo Monkey
This thread has been simmering in the back of mind. I think what bothers me is that the idea itself is only as good as the end result. That is, the end result has to be more desirable than what is currently available out there, which is pretty darn desirable. So I've been trying to think of an end result that would make me leave my current bike. This is the best I could come up with...

- Core containing 6 speed derailler in a box, using Shimano Di2
- Enclosed belt drive to rear hub
- Single pivot swingarm, conventional mid-high pivot
- Linkage driven shock with linear rising rate curve
- Carbon monocoque front section and integrated saddle (seat tower and headtube would not be separate pieces, but one large piece bolted to the core)
- Integrated saddle would be fixed height (to my preference), cafe racer styled

Yep, that would about do it. Cost would be ridiculous though.
 

TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
- Core containing 6 speed derailler in a box, using Shimano Di2
This could be cool- I will have a play about to see if my dimensions would fit a D.I.A.B. One big issue I see is the need for a sliding primary drive gear to allow for chainline problems. Not to say it can't be done! Check out the old Petespeed boxes.
- Enclosed belt drive to rear hub
If it was enclosed would you need a belt drive? This could be a problem as Gates only make CarbonDrive belts in specific sizes.
- Single pivot swingarm, conventional mid-high pivot
Yup, possible.
- Linkage driven shock with linear rising rate curve
Again, possible. what is your ideal ratios?
- Carbon monocoque front section and integrated saddle (seat tower and headtube would not be separate pieces, but one large piece bolted to the core)
Cool as! Still possible with the ABC concept.
- Integrated saddle would be fixed height (to my preference), cafe racer styled
Sweet! Although this would have to be custom designed and built- but still an option.

Yep, that would about do it. Cost would be ridiculous though.
Cost may not be that ridiculous if it was designed in the main part by the "crowd". Remember the concept, for the non-custom stuff, is a free design that you would only have to pay for the manufacture by the most competitive means.
The beauty of such an open system is that you only need enough people to share your view and design something collaboratively within the framework that it could happen!

(Man, I need to get a life- it's after 2.30am here and I can't sleep for thinking about cool bike concepts! )

EDIT-Inspired by Pslide's post, here are my top desires;

1. Pinion DH or similar 6 speed gearbox at BB.
2. Mid to high idler with concentric main pivot.
3. Split-Pivot activated rocker link- decreasing brake squat response throughout travel.
4. Slightly progressive shock curve.
5. Taut chains/belts throughout travel- no need for extra tensioners.
6. Integrated carbon seat tower and saddle would be fixed height (to my preference).
 
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Pslide

Turbo Monkey
- Core containing 6 speed derailler in a box, using Shimano Di2
This could be cool- I will have a play about to see if my dimensions would fit a D.I.A.B. One big issue I see is the need for a sliding primary drive gear to allow for chainline problems. Not to say it can't be done! Check out the old Petespeed boxes.

Yeah, that's how I've figured it in the past. Chainring would be mounted centrally between the BB bearings and slide. Not sure if it would work if it was free floating, or if it would have to be indexed with the rear der. Regardless, it would need to be protected from hits.

- Enclosed belt drive to rear hub
If it was enclosed would you need a belt drive? This could be a problem as Gates only make CarbonDrive belts in specific sizes.

Belts are lighter, cleaner, lower maintenance. And no snapped chains. Would need to see if any of Gates stock sizes would work. Imagine you could just size your pulleys to get to fit a Gates belt size, then use a chain tug type design at the dropouts or eccentric in the front to tension.

- Linkage driven shock with linear rising rate curve
Again, possible. what is your ideal ratios?

3.1:1 rising to 2.5:1, linear

Cost may not be that ridiculous if it was designed in the main part by the "crowd".

Pretty sure it would be. Don't think the "crowd" is gonna end up saving you any money...
Man I'm a geek. :rolleyes:
 

TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
Man I'm a geek. :rolleyes:
Don't worry- you're amongst friends!

Let me know some of your geo/spec ideas and I'll start laying out some mock ups in my spare time.
Here are the geo/specs i have been thinking for my own design- this is not to say that it will work with any other designs (e.g. point C maybe too low,etc) but it might give a starting point. It would be good if other people also input the data into Cad/Linkage- see what you think;

reference point (0,0) is the BB centre.
"jackshaft" type chain guide (with 16t chainrings)
Point A- (140,389)
Point B- (158,123)-this is also Shock Eye 1
Point C- (-58,174)- this is also the Main Pivot and chain guide roller centre.
Swingarm Link Pivot/Rear Axle- (-442,-12)
Rear Bar/Rocker Pivot- (-77,-53)
Rocker Fix Pivot- (-38,53)
Shock Eye 2- (-82,109)

Overview of design.
Esc mach2 2012.jpg
The rocker pivot is just outside the Pinion mounting dimensions- I will have to check this further to make 100% sure it doesn't conflict.

Pslide- you must have read my mind- check out the leverage ratios!
Esc mach1 2010_LevRatio.jpg

Anti-Squat- It is possible to get the AS levels up to at least 100% by increasing both the Pinion and rear hub sprockets to around a 30t (whilst maintaining a 1:1 ratio) but at the disadvantage of higher pedal feedback (according to the Linkage program- I think they may be wrong as the "chain pull" is still geared up and down by identical ratios, but maybe my brain isn't working!). Therefore I have settled for a lower AS percentage.
Esc mach1 2010_Anti-squat.jpg
Also notice the squat under braking (a2)- high to start with, but decreasing throughout it's travel, reminiscent of a Devinci Wilson (2011 type).

Feedback welcomed- remember these points may not be suitable for a "general" core.
 

Owennn

Monkey
Mar 10, 2009
128
1
2. Mid to high idler with concentric main pivot.
5. Taut chains/belts throughout travel- no need for extra tensioners.
6. Integrated carbon seat tower and saddle would be fixed height (to my preference).
Picked out some of your points here:
Point 2 and 5 are linked, but I don't think they are necessary. The problem you will have with no tensioner is that chain length AND both cog sizes are fixed, you need to keep the same number of total teeth when changing ratios (EG 32 front, 16 rear = 48 teeth, so the only other acceptable ratios would be 26 front, 22 rear, etc) otherwise the chain needs to be changed out if you want a different ratio for a weekend. Not ideal.

With a half inch chain you need 25.4mm of adjustibility (since you need to take out 2 links at a time) which may be difficult to achieve. For example having a rear axle that is able to move that far increases the swingarm weight (since both dropouts need a lot of extra material), probably more than a tensioner + mount would add.

My Zerode suffers from this. It has just under 25.4mm of vertical adjustibility on the Alfine, so I'm stuck running either 32 front, 16 Alfine (which is the standard) or 26,22 if I feel like doing some XC on it (which is what it has at the moment). The steel Alfine mounts could be modified or replaced with versions capable of more adjustibility, just haven't bothered yet.

Point 6 I like very much. Fixed seat tower like HaveFaiths' machine (http://gallery.me.com/colin.godby/100113/IMG_6572/web.jpg?ver=12548024900001) but removable like VProcess' steel version (http://autobus.cyclingnews.com/tech/2002/features/probikes/?id=NV02) and the Hondas' carbon (http://www.trialscentral.com/forums/uploads/post-114-1148848852.jpg)

Ooh you could also do a seat like the old Scott Octanes' (http://www.dh-rangers.com/we_our_bikes/pictures/parts_scott_octane_tom.jpg). Replace the TT with a moto style lounge.

Or not, but its possible.
 
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TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
Sorry Owennn, I meant no need for any sprung tensioners. I realise the need for an inch of adjustability- I would probably do it with movable rollers rather than adjustable dropouts, etc.

P.S.- have you tried a chain 1/2 link? It would open up a load of gearing options.
 
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LMC

Monkey
Dec 10, 2006
683
0
Wow. It's like stereolithography, but with real, actual metal. Laser fused titanium. Flippin heck, what will the Germans think of next. I need one of these in my garage, now.
Yeah, they are a good job, the part strength is likened to a cast part. The only thing is the machine costs about half a mil.
 

TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
ttp://vimeo.com/34293503


Just to throw this into the mix...
Unbelievable!- How long before you purchase frame plans and "print" them out at home/local workshop?

This is kinda where I was getting at with this thread, I just didn't know this tech existed yet.
 

TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
Right, to get this back on track.

I have been thinking more about the "core" and the different drivetrain options it would need to encompass. So I plotted out all the fixing points for different drivetrains- G-boxx2/v-boxx (slightly redundant, but hey, i've got one!), Pinion gearbox, standard drivetrain and high mounted Alfine/Speedhub (ala Lahar and Zerode). I then orientated a 9.5" shock both horizontally and vertically and came up with this;
mach1.2.png

As you can see point C is higher (250mm above BB) than before to allow more options.
One potential issue is that point B may need further forward to allow more shock positioning options. I will play about a bit more and see what I reckon.

This would be the shape of the Core with a G-boxx/V-boxx;
core g-boxx.png

This would be the shape of the core with a pinion and idler (see my previous design) ;
core- pinion.png

And this would be the shape of the core with a high mounted Alfine/Speedhub;
core- alfine.png

Of course you could also have a non-gearbox option with conventional drivetrain and pivot location.

What do you reckon?
 

graham888

Chimp
Aug 12, 2009
11
0
UK
It looks like its coming along nicely. It's good to see the idea set out properly to scale. I would agree that point B should probably be raised slightly though, possibly a tad further forward as well to increase compatibility with designs that use a downtube mounted shock. I think C is in a good place and that A can only really be finalised once B is, though at the moment its position seems good.

Once these points are set do you think we should work on how the front end and seat tower will join to the 'COAR'? Getting the fixings right will be crucial to ensure a good stiff frame, especially at A and B.

EDIT: I've checked those points out with all the frame designs I have done and they are all compatible, which is good. I will have a bit more free time next month as well to put together some 3D cad work for this, I'm keen to get some 'COAR's etc. modelled.
 
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TrueScotsman

Monkey
Mar 20, 2002
270
2
Scotland
This is the beauty of this system- as long as points A,B and C are spaced carefully anyone can build a Core/Coar to suit their wishes.

I personally would only design one Core at the moment (to suit my G-boxx2 and get my current build finished!) and then in the future I/we/anyone could design one for a different design or gearbox. The good thing is that we only have to build a new core and suspension for it, the head assembly and seat assembly can be retro-fitted. It gives a great degree of flexibility for prototyping and small-scale building.

This is why I am only worrying about defining point A, B and C at the moment.

graham888- yes, once the points are fixed in space we can get on to design the real life fixings.
 

fluider

Monkey
Jun 25, 2008
440
9
Bratislava, Slovakia
I see the point C as crucial. The Core must be wide enough in that area to be able to contain 135mm wide Speedhub/Alfine. Other gearboxes are much narrower (83mm max?) which makes me think that Core side faces should be 3d in all three versions of Core. Such a structure is advantegeous, however it's more expensive to manufacture.