[python] Some random four-bar-linkage-Python stuff

Hello All,

Here goes a lot of little bits of information / ideas...

First, for those (like me) who don't have an engineering background, I found a decent introduction to the different types of bearings at:

http://science.howstuffworks.com/bearing1.htm

Obviously the bearings used for the four bar linkage need to be pretty top notch -- I'm guessing tapered roller bearings would be a good fit, since they seem like they would be ideal at dealing with the torque caused by the rider's weight around the axis parallel to the wheel axis (not sure if there is a technical term for this when discussing bearings, since the 'how stuff works' article only discusses radial and thrust/axial loads).

One possible advantage (or it could be a disadvantage) of the four bar linkage is that it might act like variable-ratio steering in an automobile, i.e. sportier in the middle range and more stable in the extremes.

Oh, and to summarize what Tom Traylor says about his experience with FWD moving BB ('my' term, he calls them 'pivoting BB' or 'swivel nose FWD') recumbents on his website:

-- tight turns are not a problem, you don't even notice that the front wheel is turning except when making the tightest low speed turns (Tom says he's been riding this style of bike on the road in traffic for 20+ years)

-- can be ridden hands off with practice (and with the proper geometry, you don't have to constantly fight your feet with your hands like some FWD moving BB recumbents)

-- good front wheel traction, even uphill (although personally I am concerned about riding uphill with heavily loaded panniers {they can't be mounted under the seat if it's nice and low} and hauling a heavy trailer)

-- you can use your arms and back like on an upright bike, making it a great hill climber and sprinter

-- stability of a LWB with the wheelbase of a SWB

-- relatively easy to divide for transportation or storage.

-------------------------------(end of summary of Tom Traylor's experience)

For a prototype, you could just use 4 headsets, or 4 BBs or 4 hubs (from old junk bikes).

I was thinking 4 pedals might be good (for a prototype), since it seems like they would be designed to take a torque load, but since their axis doesn't extend out the other end, they would be hard to use.

Otherwise it's just like a python frame, which I don't need to elaborate on! Of course, it would be cool to try to make a mono-stay/mono-'fork' version (front end like the AirLite GT1 with canti-drive, rear end like the Windcheetah trike [ http://www.windcheetah.co.uk/ ] except without the rear cassette since it won't be rear-wheel-drive).

One cool thing about the 'mono' version is that you could buy high-quality carbon fiber tubes and join them with carbon fiber, like Calfee Design here in Santa Cruz does. Here's a quote from the technical white paper available on their website ( http://calfeedesign.com ):

"Another method is the use of a high-pressure lamination process. Here, a lug-less frame is created where the structural members forming the frame are carbon fiber tubes that are melded together with an epoxy-impregnated carbon fiber fabric. Gussets are integrally and simultaneously formed with the joining of the tubes. Along with increased design freedom, eliminating the dependency on lugs also eliminates the inherent weakness found in the tube and lug joints of many other designs. In turn, fine tuning of the frame's ride characteristics is possible since the same material is used in the tubes as in the tube transition areas. The fiber flow between the tubes is continuous which allows for an even distribution of stress flow throughout frame, virtually eliminating fatigue problems."

This is a much simpler process (I think) for the homebuilder than trying to make a plug or a mold for a monocoque carbon fiber frame. It would also be cool to use carbon fiber tubes or aluminum tubes glued to aluminum lugs like Windcheetah, although you would probably need several custom lugs which would probably be really expensive.

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The virtual pivot point moves in a circular arc left and back towards the seat when turning left, which might make it slightly unstable, but this can be countered several ways... But I'm out of time, I have to go to work again! More to come! For now, see some silly name ideas below! :)

Michael

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Name Ideas:

Just call it a Python since that's basically what it is, just with a modified pivot.

Twin-Linkage Python = Twython (silly tongue-twister!)

Quad-Pivot Python = Qython

Etc... Fython (four-bar or floating-pivot) Dython (dual-linkage) Vython (virtual-pivot) you get the idea...

Refraction (stem of a flower in a vase looks 'broken' because of refraction of light across boundry), 'broken arrow', but this doesn't really make sense anymore, in my old design the four bar linkage was closer to the front wheel axis, so it was as if the frame was 'broken' at that point, plus broken arrow and refraction are both bad names.

Virtual-something-or-other (confusing because of mountain bike rear suspension which a lot of people know is virtual-pivot-point, and the name Virtual Rush is taken by a camera streamliner recumbent)

Floating-something-or-other

Another snake name

BuddhaBike (no reason except it could have the same zen-like quality as riding the Python, and it's very simple in some way yet you can't actually pinpoint the pivot point, and it's hard to explain, so it's ineffible like many Buddhist concepts!)

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