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Thursday, January 22, 2009

No-Weld Semi-Recumbent Idea, or CrazyBike V1.0

Since I'm looking for the right scrap items to build the several subsystems (especially steering) I need to make my first recumbent bike idea actually rideable, I thought of another way to make a semi-recumbent without even welding anything. I'm still working on the concept to see if it can be done with only existing bike parts, without modifying any of them beyond what commonly available tools would do, just to see if I can actually do it.

So far, the most daunting part is the seat mount, and trying to decide if I want to make a hardtail or use a shock-absorbing rear wheel holder of some type. Hardtail is much simpler, but nowhere near as comfy to ride on our potholed streets. :) At the moment, I have a base idea for each type.

This is one idea for the shock-absorbing version, temporarily bolted and friction-fit together, to see what it looks like:

The idea is that the orange frame is hinged to the gray one at the bottom where they meet, and the seatpost you see at an angle from the front of the orange frame to the middle of the gray one is a shock-absorbing seatpost, spring-loaded inside, which would help absorb small bumps the rear wheel hits on the ride.

The hinging is done via the first method I'd used on the original recumbent idea (in this case bolting the crankshaft to the gray frame's rear dropouts), before I came up with the U-bracket mount. I'm not using the U-bracket idea simply because I wouldn't be putting the big motor and drivetrain on this version, just pedal power and cargo pods. The U-bracket also requires a hard plate to bolt the U-bolts onto, that rests against the bottom bracket shell of the orange rear triangle, and I would have to fabricate something (probably requiring welding) to bolt onto the gray frame without welding to it. Perhaps later I would install a version of the fan-motor friction-drive I had on the Columbia in the summer/fall.

Unfortunately that particular spring is not resistive enough, and fully compresses when I just lean on the bike, so I'll have to find a much harder spring-loaded tube. I've got to look up the shock loading for the old '85 Ford LTD in my driveway, and see if one of those is too hard for this use (probably is). If so, I'll have to keep looking. Perhaps a series of seat-bottom springs inside a metal tube, compressed by a smaller-diameter tube? Dunno, it's going to take some experimenting, which is the fun part. :)

The pedals will still go in the usual place in the middle of the gray frame, they're just removed in the pic because I have the bearings and axle for them soaking in oil to remove any rust, since the bike had been tossed out by someone because it is an old 1970s Schwinn bike, but it was one of the pretty good ones, with a very light brazed-together frame and all aluminum Suntour accessories, etc. Almost all I'm using from it is the frame itself, and the front derailer, and the pedal-axle/bearings.

A possible option is to use a bottom bracket plus a bit of seatpost and rear triangle, just enough to clamp securely to the top tube of the gray frame about halfway between seattube and headstock tube, and put the pedals up there, to get an even more reclined position. That increases the chainline length even more, and to ensure no chain-jumping might be better to run a chain on the left to the bottom bracket of the gray frame, thru it to the right side, then back to the rear wheel. That would also allow me to keep the shifting equipment in it's usual place, and have only a single small-diameter chainring on the actual cranks, with the shiftable pair or trio of chainrings on the main bottom bracket as usual, just with no cranks on them. This is much more engineering work to do, though, so wouldn't be done unless necessary.

The seat is going to make it a very different bike from what you're used to seeing, though--the seat will be a narrow but normal chair-type seat, leaned back a bit (at least 30°) down in between the two frames, in that "V". Just high enough and far enough back that at full extension my legs just reach the far end of the pedal stroke--this will make my riding position more aerodynamic than the upright position, but not be quite as laid back as a full recumbent, and not as low to the ground, either. The seat would be mounted to the gray frame, so it gets the benefits of whatever shock absorption system I can come up with.

The chain has to be about twice as long, and so with the shock absorbing movable rear frame also needs a tensioner on top as well as the normal bottom one, but it's still a shorter chain by far than my other recumbent would have been.

Steering for the simple version is just long-stemmed handlebars that go quite far back from the normal front steering stem, but that's not all that desirable, because it means my arms have to move in a much larger arc (farther sideways) than with normal handlebars right over the stem.

So I have an idea that puts a non-load-bearing steering stem down the seattube of the gray frame, right in front of where the seat will be, and so much more like the usual bike steering in feel. That stem goes down to just above where the front derailer clamps on, then a slit is cut in the side of the gray frame for a bolt to go into a pre-tapped hole in the end of the stem inside the tube, and that bolt also goes thru a rod outside the frame to a connecting swivel point on the front fork, above the wheel but below the frame, so that turning this new set of more-rearward-handlebars steers the front wheel. It's enough more complicated that I'm not doing it unless the other way is really uncomfortable or unworkable for some reason, but I expect it to turn out that way, so I'm preparing the idea just in case. :)

Since I am having trouble finding a spring that will have enough resistance to do shock absorption but not be *too* stiff, I thought of one more way to do it--hang the rear triangle upside down, so the swivel point is on top, and the spring is *stretched* from the bottom rather than compressed at the top, but this adds a number of complications and may be heavier. I do however already have a handful of springs that could work for this kind of thing, including some old hood springs. It's not likely I'll build it, but it is a possible alternative to think about.

Another possible method involves a pulley and cable from the top of a washing machine's tub (the part that keeps it in balance as it spins) and a spring (stretched again, rather than compressed) suspended from a piece of front frame sticking out behind the top of the rear frame. This one I really am not sure about, but it popped into my head while riding (as did most of the other variations), and I managed to remember it long enough to write it down.

All of these versions, due to their extra rear length, have more space for cargo pod up in front of the rear axle, which means I have to worry less about overhanging the axle point and tipping the bike backwards with heavier loads while going uphill or on certain kinds of turn. Also, if using the shock-absorbing rear wheel systems, if the cargo pods are all mounted on the main frame, any cargo in them won't get rattled around as much as it does now on my hardtail Columbia.

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