is this Frame buildable?

[lotec]

Well as a lot of you will know ive been playing around trying to design a bike that in my eyes is "perfect" and have it built by someone who knows what the hell they are doing, I would be scared to ride something i welded myself. ;)

I've downloaded linkage v2 and a few CAD programs went to design something and had no idea where to start, I was thinking base it off an m3 and tweak it a lot, still awaiting pics of an m3 side on the driveside with no chainring on. :)

Anyway, long story cut short Inoticed theres a lot of saved bikes in linkage v2 including "dh prototype" "what the hell is this" i say to myself an open it, well in my eyes its pretty well perfect, (pics below) theres a few things that would of course need to be taken into consideration building it, e.g the traingle shaped linkage obviously passes through the BB which couldnt be possible but if you were to cut it down to an L shape it would need to be massivly thick to have the required strength and stiffness but i think its entirely doable.

Anyone fron an engineering point of view, would this work? i dont wanna go and spend hours designing it in CAD to find out when its built it wont work :) also, grip, i know you dont normally do this sort of thing but would you be willing to build an entire frame from tubes or would you be able to recommend someone who could?

Anyone thats built frames before, tubing selection help would be great too, which companys make square tubing etc what should i go for, wall thickness and diamatre etc, also for the swingarm its going to need a lot of guesseting etc to keep it at all stiff, can you buy tubing thats reinforced like honeycomb on the inside?

im not gonna completly rip this frame off btw but if i go ahead it will be similar, but with 222 style ssliding rails for adjustable geo and what not also would like to have adjustable travel from 8-9.5" :)

Thanks for reading such along post to anyone that bothered, as you can see I put in a very "un-lotec" like ammount of effort :D pics are below

Also another thing, it has a fair bit of chain growth, not an abnormal ammount or anything, but where would I go about placing a balfa style pulley to eliminate or reduce this? I enclosed a pic of where I think it would go best but maybe you guys have some better ideas, and S. if your thinking of saying anything smartarse, dont bother. You have me on MSN ;)

[S.]

90mm of chaingrowth is "not abnormal"? Have fun pedalling that on anything the slightest bit rough. And it'll pedal like crap unless you have an idler anyway.

[lotec]

thought i saw a few other bikes that were close to that... on a second look i added another 0 in my head, definatly needs a pulley but PDC racing seem to have done ok with something very similar as you said...
edit: looked again and a bb7 without the pulley has 86 mm of chain growth, and with it they have next to none or none at all (dont remember) so that problems easily fixed

[brisneyland]

an idler pulley won't reduce chaingrowth

[lotec]

an idler pulley won't reduce chaingrowth
yes it will i edited my above post, bb7s have 86mm of chaingrowth without the pulley and with it they have next to or completly none

[S.]

an idler pulley won't reduce chaingrowth

It will for the part of the chain that's under load, which is the important bit with regards to performance. Won't stop the derailleur having to take up chain extension in the unloaded section.

[brisneyland]

ahhh... I just realised. I'm a bit slow.

The chain length on the tight(upper) side won't change, and thus no 'chain growth'

But the chain length on the lower side will lengthen, but it doen't matter anyway.

You are correct.

As for location, it really should be exactly on the pivot axis. But near enough is prolly good enough.

[S.]

As for location, it really should be exactly on the pivot axis. But near enough is prolly good enough.

Yeah a concentric pivot is the way to go if you want zero chain extension (actually, very slightly negative chain extension but so insignificant that I may as well have not typed this sentence). However you can use a non-concentric pivot to alter the pedaling characteristics by allowing slight amounts of chain extension and changing the chain tension lines etc etc. You'd wanna know what you were doing before you went nuts playing round with that stuff though, best just to keep it simple otherwise.

[lotec]

thanks guys, sounds like the pully goes as close to the pivot as pisslbe, maybe even on it... :)

[hardtail free rider]

[img=http://img23.imagevenue.com/loc292/th_902_cool_frame_design.jpg] (http://img23.imagevenue.com/img.php?loc=loc292&image=902_cool_frame_design.jpg)

looks similar to this ey?

[S.]

[img=http://img23.imagevenue.com/loc292/th_902_cool_frame_design.jpg] (http://img23.imagevenue.com/img.php?loc=loc292&image=902_cool_frame_design.jpg)

looks similar to this ey?

Yeah, that's the PDC (that pic is the original prototype) which he already mentioned.

[lotec]

as seen here http://www.pdcracing.com/products-dhone.html damn thats a good price, im surprised there arnt a lot more of them around...

[Hex515]

I maybe having a bad day, but won't the seat scrap on the rear wheel when at 230mm rear travel?

And what colour/decals are you looking at putting on it? Whats the rear swing arm going to look like?

[lotec]

yea the wheel will scrape the wheel if it low enough but name a long travel bike that doesnt :) i havnt thought far enough ahead to colours and stickers yet, the swingarm is going to look pretty rmx ish atm just wokring on drawing it in cad... im still working on the dropouts :(

[Rory]

Try to find standards for stuff. Sram have a fair bit of info and technical drawings on standards they use. This one is for their 12 mm maxle rear axle frame mounts.

http://www.sram.com/_media/pdf/rockshox/manufacturers/RearMaxleFrame_ES4-310498-000_B.pdf

Also for the swingarm due to the locations of the pivots something similar to the pdc (like the attached picture) would be better than a rocky mountain rmx.

[lotec]

yea i was thinking itd be a better idea to go for something like that, for starters it would be a hell of a lot lighter

[spinner]

Rory's on the money with the brace on the swingarm. You could make the lower linkages L shaped to get around the BB.(see pic)EDIT: cant upload pic sorry

Anything is buildable for a price. As far as I can see , the idler pulley mounting/pivot would be the tricky part. Definately do able though.

If you did go ahead with this , get 2 or 3 of everything made. The cost of the extra material will be bugger all compared to the setup times to machine/fabricate the parts for the frame and you'll have a spare frame or one to sell at the end to recoup some of the cost.

[bradh]

can someone please explain to me why it's such a special design? isn't it just a high single pivot with an overly complex linkage to actuate the shock?


p.s. that pdc's an uuuugly thing.

[lotec]

axle path, nice and progressive rate with a decent cuve i.e no sudden jumps harder or softer then ramps up a lot near the end of its travel and yea, the pdc is UGLY, ive decided to build a ht first though, just to get a bit of experience then work up to this

[Anthonaut]

I admire you for giving frame design a go and actually having what you designed made. Best of luck to ya, and make sure you keep us updated on the progress!

[Red Rocket]

can someone please explain to me why it's such a special design? isn't it just a high single pivot with an overly complex linkage to actuate the shock?


p.s. that pdc's an uuuugly thing.

ROFL so true. I would imagine wheel path etc are much the same as a balfa or the like. You should change the design Lotec to make it a vpp. Then an advantageous situation would arise from getting one built.

[emp]

90mm chain growth is huge, my bike has 5mm over 220mm which is much better i feel

[S.]

ROFL so true. I would imagine wheel path etc are much the same as a balfa or the like. You should change the design Lotec to make it a vpp. Then an advantageous situation would arise from getting one built.

Yeah the axle path is pretty similar to a Balfa, so are the pedalling characteristics. Having a rearwards axle path makes a very noticeable difference over a low-pivot bike in terms of bump sensitivity, particularly as the hits get bigger. The tradeoff though is that the wheelbase changes more under compression, and this can mean that you have a greater front weight bias when you're cornering (whether that's good or bad is subjective), if you don't take into account the geometry under sag/compression. Balfas have reasonably short stays at topout (I think it's 16.9" or something?), and the new PDCs are apparently going to be cranked down to 16.5" or something static; both of these should prove to be pretty good (well I already know the Balfas are, haven't ridden a PDC yet).

Why would it be advantageous to make it VPP?

[S.]

can someone please explain to me why it's such a special design? isn't it just a high single pivot with an overly complex linkage to actuate the shock?


p.s. that pdc's an uuuugly thing.

It's not an "overly complex" linkage, it's exactly the same in terms of complexity as any other linkage-driven singlepivot except rearranged. High single pivot + chain pulley gives you two main advantages over other conventional setups: superb bump absorption (due to the axle path), and firm pedalling without signficant chain extension.

[Kyle@PDC]

If you also look in the 'open files' section of that program, right after mongoose NX 8, there is 'PCD DH Prototype' bit of a typo but you can see what they were going for.

Open that, then open the 'DH prototype' - they're unmistakenly similar.
I suppose it would be flattery in its finest form, but they're X,Y Co-ordinates arn't as close as they could be.

As far as Ugly - sure, but the old DH-ones kicked ass. We have a new DH bike being released at interbike that I think you will find more appealing both functionally and cosmetically.

Funny though, I donwloaded the program a while back and didn't notice, when I opened it last week I thought I had saved that file there myself!


Cheers all - and thanks for the kind works on the FR bike in the other thread.

-Kyle

[lotec]

^ Kyle, you need to sort out an australian distributor :)