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Recumbent What IS that thing?! Recumbents may be odd looking, but they have many advantages over a "wedgie" bicycle. Discuss the in's and out's recumbent lifestyle in the recumbent forum.

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Old 08-04-09, 04:39 PM   #1
fitek
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DIY Recumbent Fit Jig

I've always managed to come out a few inches off when building my ghetto recumbent frames. I usually don't copy existing designs, just sort of slapping things together, so there are a lot of guesses made. I was thinking I should try building a jig to hold a seat, handlebars, and a set of cranks so I can do a better job of fitting myself and trying out different layouts and I'm soliciting your folks input to see if you have any clever ideas on how to construct such a device.

I have a long (7 foot?) piece of rectangular tubing with "legs" at the ends. This lays flat on the ground. I was going to cut 3 pieces of flat plate and weld seat tubes to them. These plates/seat tubes can be clamped to the 7 foot rectangular tube. I can then attach the handle bars, seat, and cranks to seat posts and insert into the seat tubes. The height of each component can be adjusted then by just using the seat post clamps. Backward/forwards can be adjusted by just moving the clamped flat plate forward and backward. I already wrote out a ruler on the side of the rectangular tube using a sharpie to measure along the axis of the rectangular tube.

I can imagine that the handlebar part might be kind of tricky if it interferes with the seat, and being able to change the angle of the steering tube might be handy too.

This is not as fancy as something like the Fit Kit, but should be way easier to build, and hopefully take a lot of the guess work out of measurement.

The measurements can be transferred to the next project, some sort of frame jig...
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Old 08-04-09, 10:22 PM   #2
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Quote:
Originally Posted by fitek View Post
I was thinking I should try building a jig to hold a seat, handlebars, and a set of cranks so I can do a better job of fitting myself and trying out different layouts and I'm soliciting your folks input to see if you have any clever ideas on how to construct such a device.
An intelligent build always starts with rider dimensions. Have someone take a side view picture of the seated rider holding a ruler or yard stick, then scale it in CAD and digitally build around him/her. Moving the seat, idlers or repositioning the cranks, etc, ect, is done in seconds with the click of a mouse. Here's a excellent read: http://www.jetrike.com/ergonomics.html - and yet another excellent read: http://bikesmithdesign.com/Design/12Steps.html

One of the easiest 2d CAD prgs I'm aware of - 45 days free use, works on older machines, imports jpg's and prints pleasingly smooth and legible hard copies: http://www.deltacad.com/demo.html
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Old 08-05-09, 05:40 AM   #3
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Most recumbent sizing starts with your X-Seam. Here is how to measure it. I'm sure that depending on your design you would probably want a few more measurements, but none of them should require anything as elaborate as what you're considering.
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