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james folkes
03-22-2010, 08:11 PM
before he's finished one, he's already started the next...

why 2.0? i want lower cranks, slightly more upright seat, easier cockpit access, better steering ergonomics, more stable handling and most importantly, a softer ride.

how? largely by converting to 20" front wheel, dropping the main boom, adding long travel front and rear suspension, upgrading the seat and adopting either linkage operated or direct under seat steering.

progress so far? i have secured an early pair of 98 model rock shox sid forks in need of a little tlc, they aren't exactly what i'm after but it will do for now. i have identified my intended damper and airspring assemblies for the rear, high bidder on the former and following up some promising leads on the latter. i have an aluminium rear triangle from a single pivot suspension frame, mechs, shifters, head and steerer tubes, stems, steel for frame, bars and seat, fabric for seat and a bottom bracket shell.

today at work i made a life-size 2d cut-out of myself from scrap hardboard, jointed in all the key places. it will be instrumental in helping design the new frame by laying all the bits out on the floor and being able to see myself in relation to them.

there will be pictures...

james.

likebikes
03-23-2010, 01:20 PM
Looking forward to this! I'm a fan of suspension, weight is a factor that makes it difficult so I'm encouraged to hear that you have obtained an aluminum rear section.

james folkes
03-26-2010, 11:16 PM
weight, the killer weakness in all my best laid plans...

so then, from a weight perspective this might not seem like such a good idea, but...

consider using a single ring chainset on the narrowest bottom bracket you can find, with minimal offset cranks, giving you a super efficient, kind to the knees, streamlined pedalling profile. when i had a mismatched bottom bracket and crankset on version 1.0 (1.1 by that point actually) i really felt the extra inch or so my feet ended up apart. my knees definitely protested, so i would like to really hone this minimal pedal separation thing.

from here you drive a stirmey archer three speed hub gear, nestling in some dropouts in the frame. attached to the wheel hub section is another ring driving an (eg) eight speed nexus hub gear, which in turn has another ring which drives the rear wheel. there are some points to note about this arrangement, both in terms of the logic behind it and the mechanical implications.

the supposed benefits are based on chainline, gear range, mechanical reliability of the gear assemblies, the aforementioned crank offset and the reduction of the sprung to unsprung mass ratio of the rear wheel assembly.

the rear wheel can now be a fixed hub, ditching the weight of the freewheel and reducing the spoke dishing required, making for a stronger build. reducing that mass will make for quicker reacting suspension, and the combination of a cassette, freewheel and rear mech must all add up.

the supposed advantages of hub gear mechanisms include minimal adjustment and maintenance, on the whole impeccable reliability, a more efficient chainline as it can be totally linear and run at optimal tension, plus the ability to select gears from stationary without pedalling. probably some more too, but anyway, i was thinking that you could use the stirmey to give you basically a little bit of overdrive on the nexus for touring on the flat or occasional speed antics, but mainly an extra set of low gears beneficial for a high cadence riding style and climbing the offensively steep hills that litter my local habitat. presumably, this can be achieved by careful selection of the sprockets used at all points in the system, although i clearly haven't put any effort into working that out yet.

the first real hurdle is the fact that every hub gear and sprocket combination you go through will displace the chain to the left. the obvious solution seems to be to let it do exactly that. the stirmey archer (order of mechanisms can be substituted, naturally) puts the chainline down the middle of the frame, the nexus then displaces it to the left again, just the right amount to line it up with the single sprocket on a flipped wheel, which as it is running a fixed hub, doesn't care which way round it goes.

an adjustable or sprung chain tensioner would allow for a travelling bottom bracket assembly, but an adjustable seat my prove better. the thinking is that there is already going to be some flexibility in the seat mounts, so just extending that range to cover different rider sizes saves all the weight of the boom overhang, clamp, bolts and the tensioning device, plus brings the chainline force axis closer to that of the boom, hopefully reducing chassis flex.

the middle of this bike, under my seat, is starting to look a little bit busy, containing a fairly substantial air spring, separate damper, under seat steering pivot mechanism and clearance for the arc of swing of stem and bars, and now a pair of hub gears too. some of these things are bound to want to occupy the same space, this is sure to be interesting.

perhaps i should fire up sketchup, that said i love my 2d cardboard cut-outs!

james.

Odd Man Out
03-27-2010, 12:14 AM
James
With all that hardware you might want to incorporate an electric drive
or
go the route I am going with my Warrior builds; Rohloff and Schlumpf speed drive -- no chain lateral travel whatsoever -- very elegant.

Looking forward to your completed intricate design.

james folkes
03-27-2010, 08:39 AM
electric drive? pah! i must simply "man up" and eat more pies...

seriously though, that isn't such a bad idea, although as the machine is destined to be doing some long distance romps it does seem a little less tempting as one will be carting around a chunky motor and dead batteries most of the time, plus you've got to find somewhere to charge them at least daily, a potential problem when touring. i will dabble with the elastic-trickery at some point, but not yet i think.

so, hub drive and crankset drive, that's a pretty slick solution odd man, very slick in fact. schlumpf and rohloff gearing systems are the kind of equipment fitted to flagship bents from the likes of hase and hp velotechnik, proper nice kit, but just a teensy bit out of my price range, those two together would be two months wages for me if bought new!

my interest in the other brands stems from having access to a stirmey archer hub and having seen a nexus hub in a pal's garage, possibly looking for a home; the driving force behind component choice being somewhat financial. i shall search out your warrior builds and see how it's supposed to be done though.

james.

Odd Man Out
03-27-2010, 04:43 PM
. i shall search out your warrior builds and see how it's supposed to be done though.

james.

Or better yet how things are NOT to be done...

james folkes
03-27-2010, 05:55 PM
ooh... finite elemnt anaysis frame stress modelling, i might well have to talk to you about that at some time. seriously good work, bummer about your local machine shop place!

ok, ok, ok... how about...

developing this idea of extending the gear range but making a few trade-offs in favour of garage hacking friendliness. i think all of the ideas expressed could end up being wholly, partially or not employed at all, it's all just idea playground land at the moment. this new train of thought was inspired by the freewheel article in the latest zombie newsletter, the system works!

given that stirmey archer gears are ubiquitous and easily available, they still form a key part in my plan. their steel outer casing allows the welding of a flange for the drive sprocket, although i'm sure you'd need to take it to bits first.

keep this narrow profile crank idea going up front, but go back to adjustability by way of a telescopic housing on the boom, chain pick-up can be simply handled by a derailleur cage, utilising the spring mechanism as the designer intended. the stirmey is mounted a short distance behind the head tube and has a flange with a sprocket, taking the drive down to the next gearing axle. this is running roughly down the centreline of the bike and terminates in a standard freewheel cassette with indexed derailleur. the axle can be bar or even tube of the right diameter and wall thickness, riding in pillow block bearings like those employed in many az trike designs. a flange on this caries an additional sprocket which drives the rear wheel with another standard derailleur set, the location of the flange aligning the drive chain to the centre of the rear cassette.

lots of gears. lots and lots of gears...

it's a somewhat cheaper and simpler approach, although the suspension and structural advantages of a single speed rear wheel are lost, likewise the totally linear drive chain. all chain tensioning is taken care of though, be it on suspension or fixed frames, and because both cassettes will be driven from the middle there will be no gears that cannot be used. by shifting progressively either side of central on the derailleur sets, the chain can avoid running at diagonal sweeps as much as possible.

regarding the frame that houses it all, i was thinking about how i've ended up doing my rear triangle and rack on my original high roller, and am now trying looking at the chassis as essentially two pannier racks, rear and lowrider. all the drivetrain, suspension and seat bits being mounted between or off these two sets of rails, birdcage chassis style. the hope would be that by employing tube of the right wall thickness in the right places, the weight could rival that of a comparable boom chassis wearing full touring hardware. it could also be particularly resilient to twisting and flexing forces if designed correctly.

whatever route i choose, i am going to try and make the gearing on 2.0 something a little bit special, most probably by use of a hub gear of some description.

james.

likebikes
03-27-2010, 06:38 PM
Your ideas about the Sturmey Archer gears are really interesting.
I have been entertaining thoughts about a 9 speed for a little friend that wants to try a recumbent. Not wanting to invest too much as she could ride it for 10 minutes and not like it, 4 months designing and building, too bad! So my thought was to build her a 20 inch model for her lovely but short stems to reach the ground. I would re-lace one of my three speed hubs into a 20 inch rim and hang a derailer to act as a chain tensioner only, and equip the bottom bracket with a three ring crank and give her 9 speeds. I could pull that build off cheaply and almost completely from my scrap pile and not throw away several months of evenings if she doesn't like recumbents.

james folkes
03-28-2010, 06:40 AM
aha! check this (http://www.powerandleisure.co.uk/acatalog/Adult_tricycle.html) out.

interestingly, they appear to have used an alloy bodied gear housing and bolted the drive sprocket to the outside of the spoke flange. this gives much less of a chain offset than i had anticipated, but it's still in the wrong direction. i think further speculation would be more enlightened if i first paid a visit to my guru's parts bin, where i am convinced there is a stirmey archer, put possibly also a nexus 8 speed.

your short frame 9 speed hybrid sounds like a really good idea likebikes, i've never seen hub and dreailleur gears mixed but i can't see what's wrong with so doing, it was certainly the idea behind the mid-axle cassette and mech idea i spoke of above. even if she doesn't like it, as well discussed, the exercise will set you up nicely for future experiments.

james.