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Old 05-11-17, 11:31 AM   #26
unterhausen
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if by "underseat pivot" you mean the suspension pivot, that's going to be something you need to have fabricated. Maybe go with a more mountain bike-like design.
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Old 05-11-17, 12:05 PM   #27
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if by "underseat pivot" you mean the suspension pivot, that's going to be something you need to have fabricated. Maybe go with a more mountain bike-like design.
The steering "underseat pivot" is somewhat comparable to head tube and headset on a conventional upright bike. The bearings inside the tube allow the whole front end to rotate on the rear seat portion of frame. I'm leaning toward adapting a mountain bike headset for strength. The rider's weight is concentrated right over this pivot point. In the drawing below, the pivot is below the "i" in flevo bike.
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File Type: jpg flevobike seat pivot.jpg (77.5 KB, 31 views)
File Type: jpg Flevobike drawing.jpg (10.3 KB, 31 views)
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Old 05-11-17, 02:57 PM   #28
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ok, that's not the configuration shown in the article you linked, as far as I can tell. Those bikes both had DF-style forks in a traditional steerer tube. I believe you will have to have that fabricated, although you could use a 44mm head tube and a fabricated "steerer." The tapered steerer that Pargon makes would be something to look at, they do have drawings. You would want a more symmetric design. 44mm forks have more of a cantilevered load than mid-bike steering does.
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Old 05-11-17, 03:06 PM   #29
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I'm interested in seeing what you come up with.
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Old 05-11-17, 03:48 PM   #30
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ok, that's not the configuration shown in the article you linked, as far as I can tell. Those bikes both had DF-style forks in a traditional steerer tube. I believe you will have to have that fabricated, although you could use a 44mm head tube and a fabricated "steerer." The tapered steerer that Paragon makes would be something to look at, they do have drawings. You would want a more symmetric design. 44mm forks have more of a cantilevered load than mid-bike steering does.
My design is like none of these photos. These contain various elements that I've drawn upon. I want to use existing components if possible. What are DF-style forks? Will look at Paragon steerer. Yes, a symmetric design would work well. Will need fixed fork in the front with a pivot at rear end of the adjustable boom tube. The crankshell will be attached to the front end.


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Old 05-12-17, 11:01 AM   #31
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Paragon steerer tubes: LINK
Head tubes LINK
A fork, as used on most two wheel 'bents and diamond frames (DF) takes a lot of load along its length, i.e. axial. If you are using it for a mid-bike steering setup, then the load will be mostly radial. So you'll have to do some engineering work to check the design to see if it is going to work. I think the head tubes will be ok, but the steerer probably will not meet your needs and will require some redesign.
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Old 05-12-17, 12:21 PM   #32
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Thanks Unterhausen, very helpful. I ordered threaded 44X90mm steel head tube and 1.5 ODX68.5mm BB shell from Paragon. Have decided to braze weld joints with a torch and 1/16" silicon bronze rod so I can adjust things if need be. TIG is too permanent for prototype testing.
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