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Wednesday, September 24, 2008

Revisions of revisions

Note: the previous post somehow didn't get posted a few days ago, just saved as a draft, so there's been more time than it seems between these two).

Not everything works out as expected, in any design. This one is no exception.

The seat-mount vibration absorbers are turning out to not be such a great idea after all, and I think I'll probably skip them on this design, until i can come up with a better way to do them. It's just too difficult to find a way to mount them that doesn't either interfere with something else, or will stay in place without moving around as weight shifts on the seat.

The chain/cable steering is a little harder than I thought it would be to implement, as all the ways I've tried to use to fix the cable to the ends of the chain were not sturdy enough for the purpose. Brazing or soldering it is the last option I have, and will have to try that before skipping the idea and going either full-chain or the old tie-rod method many other bikes use for this (which would require me building some ball-joints for the rod, as I have none at the moment).

The drivetrain, however, has given me the most trouble figuring out. Especially on how to integrate the motor into it such that the motor will drive the wheel, but not drive the pedals, and the pedals will drive the wheel, but not the motor. Freewheels are the best answer to this, but it has taken me about 3 weeks to come up with a practical way to set them up that also lets the motor be before *both* shiftable chainring sets, so that I can use all the gearings available on both motor and pedals.

The catch to doing this is that I need a much longer axle for the "front" chainring set to go all the way thru the bottom bracket of it, and allow for both the pedal-chain freewheel and the motor-chain freewheel. That will probably require welding an ex-axle bolt or similar to the cut-off end of the pedal crankshaft used on this BB. I'm not convinced I can do that perfectly enough to keep wobble out of the resulting longer shaft--any wobble in it could cause the chain on the farthest end (the motor chain) to come loose and either simply wear out faster and be noisier, or actually come off the chainrings.

I may be able to use the lathe to help me do this, by clamping the shafts in it and working their positions until they don't have any wobble relative to each other, then welding them while in place there. Never done this before, so it'll be a "learning experience". :-)

Another issue that's come up is that the seat-mount wire bracket I made to hold the pedal post on up front simply has too much give as pressure is put on the pedals, causing the whole post to shift side-to-side, which will loosen and tighten the chain in cycles as I pedal. That could also cause excessive wear and noise, or the chain to come off. I'm going to have to go ahead and make plate-brackets instead, if I want to be able to remove or adjust the pedal post, otherwise I'll have to just determine the best angle and length for it, and weld the post directly to the front of the bike. That's not a preferred option, as I am pretty sure I'll have to adjust this repeatedly during the first few days or weeks as I get used to the whole recumbent-riding thing.

The idea of having the underseat steering handlebars flip down as a stand is looking more like an option now, after having some thoughts about the way the cables would mount to the bars for the steering, and would definitely be doable if I were to use the tie-rod version (as that would mount on a tab on the steering post and not to the bars directly). It won't really save much weight to not have a separate kickstand, but it would certainly be safer to use as the bars are on *both* sides and can be pushed down far enough to keep the bike from rocking at all, a little like having outriggers on it while parked. :-)

Another idea popped up regarding cargo carriers: Attaching one end of the carrier rack to the vertical rear seatpost, with the other suspended on ex-front-shock pieces mounted vertically from the rear axle dropout accessory points. Then if I have loads in the cargo baskets or pods or on the rack, they'll not get quite as bad a jouncing as they would with no anti-shock protection. Disadvantage is it's pretty heavy to do that--another 8-10 pounds, at least. I'd rather use airshocks but don't have those in my junk bins. :-)

The rack itself would have attachment points for either a set of 4 or 6 kitty litter pails converted
to cargo pods, with a locking bar across the top and a padlock, or a pair of long open-topped baskets, depending on what I might be going to carry on a particular trip.

After election day, I can gather up old coroplast signs and make a fairing for the back and sides of the cargo pods (since they're the least aerodynamic option for cargo I've used, and would greatly benefit from a fairing), as well as for the front of the bike. I doubt I will make a full-bike fairing anytime soon, but even just front and rear ought to help significantly, as well as making me more visible, and giving me more surface to put lights on in traditional ways.

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