Search all of my sites with Google

Thursday, September 25, 2008

Planning Ahead Sometimes Isn't Enough

Sometimes a concept fails to include a detail or two, which is why prototypes are made, to find the flaws before production. This won't be a production bike, but the principle still applies.

I somehow managed to fail to consider a number of things in my design for the scrap-recycled-recumbent bike I'm building, many of which I figured out in the last few days, as noted in the previous post, but one major flaw I only discovered today, as I was about to fit some of the drivetrain components on: I did not leave enough clearance for the rear chain to move side to side as it is shifted between the three front chainrings, so that only in the middle one does it not rub on anything. The small chainring causes it to rub on the tire, and the large one on the frame itself. Both are very bad.

Only practical fix for it is to change the frame so it uses the original rear triangle's bottom bracket (where the pedals go normally) as the actual front chainring spot, where it normally would be, and add a new BB up above it for mounting the swivel point for my rear shock (instead of using the original BB for that as planned).

Changes a number of things about the bike, from it's length (a couple inches longer), it's height (up to a couple inches taller, depending on where the BB goes), and the shape of the frame itself, all of which changes the tilt of the seat, unless I redo the mounting points for THAT, too, which I probably will, as the seat is the most important thing about this bike--if it's not comfy, there's no point in building it.

I might end up just starting over with different parts, since so much has to be changed, and chalk this one up to stupidity.

No comments:

Post a Comment

Alternate suggestions or improvements to anything that's been posted is very welcome, and extreme detail is preferred to brevity.

Keep in mind that unless you leave an email address in your comment, I haven't any way to reply to you except to reply to your comment here. That means if you want a reply, you'll have to come back to *this* blog entry and it's comments to see my reply to you, unless you leave some method of contact within your comment.