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Friday, August 29, 2008

Recumbent Thoughts

Today I took a trip to pickup some frames and a bag of assorted parts, basically. Since it was so far away, I'd already planned on stopping at some food place for an hour or two to cool off and stuff after I'd picked them up, but I had no idea my day was going to be quite as bad as it was. :(

The good stuff happened while I was at the food stop halfway thru the trip, for about two hours (only finally feeling cooled off over an hour and a half of being there!), I had my sketchpad out and doodled up thoughts about the new bike I am making.

I have had trouble figuring out a simple way to do the steering, because there is not enough room under my legs for a regular handlebar/etc, without hitting my legs as i steer, no matter how I shape the handlebar around the other things it has to clear. I can't put it *over* my legs kinda like a normal bike because then it would be like what is called an "ape-hanger" which for me is really really uncomfortable after a few minutes, and impossible to use on any normal ride.

So instead I thought that if I put a sprocket for a chain welded to the steering tube just above the actual front fork (but below the place the fork is mounted into), and a short length of chain (just enough to allow full movement range of the front wheel steering by pulling that chain to one side or the other), and regular bike cables (like brakes or shifters use) running from each end of that chain thru guides to a handlebar that just sticks out from under the seat on each side, which pivots under the center of the seat, I can get usable steering without interfering with anything else on the bike. It's more complex than I wanted, because it adds a bunch of parts but it is less complex than linkage bars and stuff. I can adjust it's tension and whatnot just by changing the length of the cables to the chain. I just have to figure out where the best points to mount the cable ends are on the handlebar, to give the easiest steering, and pick the right size sprocket to give the right turning sensitivity so I don't have to move the handlebars 1:1 with the wheel like I would if the handlebars were directly connected to it like on a regular bike, but aren't' so sensitive that I can't easily learn to work it safely. That's some thing I wish I could do on my regular bike, but never figured out a way to do before (I could do it now, that I've figured this out, but it's significantly more complex on the upright bike to do, so I won't).

Another thing I want to do is have the pedals (which stick way out front over the wheel) be adjustable in distance from the seat (since I can't easily make the *seat* adjustable), which means basically using two different sizes of frame tube so that the one holding the pedals is small enough to fit inside the one connected to the bike frame itself, and have some sort of clamp (a seat tube clamp, probably) that holds them at the desired inserted length. That way I don't' have to worry about rewelding the thing over and over to get the length right for my legs, because since I've never done one of these before I have very little idea of how exactly I will be pedalling it, and the amount of extension my legs will find ideal while producing the torque I need to drive the bike.

The problem with this adjustable length is that there will then be potential slack in the chain running from that pedal sprocket (#1) to the mid-front sprocket where the front gearshifting will take place (so that I don't have complex delicate stuff hanging off the front end of the bike where it can easily be damaged by even a minor scrape/bump/etc). The normal front shifter will not do anything about slack n a chain, but the *rear* shifter, in the form of a derailer, *does* do this as part of it's normal functions. Since I wanted to use a freewheel on this mid-front sprocket anyway, to keep the pedals from being moved by the motor if the motor is running faster than they are, that ends up being perfect, because I can use a complete rear derailer and cassette setup off a rear wheel, instead of the typical 3-gear setup usually found on the pedal end of the chain on most bikes. Yeah, the sprockets are significantly smaller on that, which presents an issue with gear ratios probably not being enough, but I may be able to partially solve that with one translation sprocket set at the mid-rear sprocket on the motor shaft, which also needs a freewheel (to keep the pedals from turning the motor shaft if they're running faster than the motor). If I use a larger sprocket for (I think) the chain on the rear wheel end, and a smaller sprocket for the chain on the mid-end, it should compensate for the difference in total number of teeth that using the smaller rearwheel cassette in place of the regular front pedal chainrings (sprockets) creates. I'll have to do some drawings and calculations to see if that really works that way, but my melted brain says it ought to be fine. I should trust it, right? :)

Mounting the rear derailer will require some extra welding to put a tab in the right place to bolt it to, but that isn't' much extra work. Getting the spacing right so that it neither hits the ground (or speed bumps) nor interferes with the front wheel during ride or steering might need more figuring out, since by my estimate there's not a lot of space up there for it, and it'll have to stick out more to the front than downward, unlike a normal rearwheel derailer. I have to make sure there's also room for it to extend during shifting, etc, without hitting anything. More work than either of those will be inventing something out of scrap bike parts that will let me mount the cassette/freewheel there in a usable way, since I won't be able to just use the normal pedal-bearing/bottom-bracket combo as I'd planned, which would have been very easy. Most likely, it will be done simply using the entire hub and axle off of a rear wheel, mounted on just the tabs from a rear triangle frame from a bike, welded in the right place on the underframe. Gotta draw that up more to figure out details.

The part that is causing me a bit of trouble is that I need to feed the drive from one chain to the next via the various sprocket transfer points (2 transfer points, mid front and mid rear, from the pedals in the very front to the rear wheel at the very back). I *think* that I will need to run the pedal-to-mid-front chain on the right side, then the mid-front-to-mid-rear on the left side, then the mid-rear-to-rearwheel on the right side again. That's mostly because the only derailers I have (or have ever seen in person) are for the righthand side, and will not work on the left side on the rear wheel, which forces my hand on the other two chains for their order. The motor I need to use is a treadmill motor, which thankfully has a shaft extending out on both ends, which helps tremendously in that I can use that shaft to transfer from one side to the other...except that if I do that, I will *always* be turning the motor when pedalling, which makes me pedal harder when no power is applied--something I need seriously to avoid.

So I have to come up with a way to probably just run all the chains on the same side and mount the single sprocket that I need to not be on the mid-front freewheel in front to the hub directly just behind the freewheel, and something similar on the motor (mid-rear) freewheel. It's the most straightforward approach mechanically, as the other approach I can think of (at least, that's possible for me to build) is to put the motor only *indirectly* into the chain path, by having it's freewheel engage the chain on one side, and not be an end-part of the actual chain loop--instead having the chain loop end at another pedal-bearing bottom bracket with a pair of sprockets (possibly of different sizes for compensation of the previously noted problem of the front chainring). That adds more weight (not a lot, but still), and more complexity, in that the motor needs to then have some sort of way to adjust it's tension against the chain (well, I might have to do that anyway).

There is one more problem...the freewheels are designed to turn in a way that prevents something in back rotating from transferring that rotation to the chain attached to that freewheel. That idea works *perfectly* for the rearwheel and mid-front freewheels, as I only want to transfer power from front to back, never the reverse. But for the motor, I have (I think--I'm having trouble wrapping my brain around it just now) a problem, because if it is rotating forward, it will not engage the chain at all, because the freewheel will do the same thing it would if a rear wheel was turning it--it will just spin and keep the chain from moving. If it were mounted backwards, it *will* work the way I want it to, but I don't have a normal freewheel that can be mounted backwards. I *do* have a couple of those single-gear freewheels with a sprocket that's actually cast into the metal of it, but cannot get them off the hubs they're attached to (I'm not strong enough to turn them in the correct direction with any tools or setups I've been able to make, and do not have the *real* tool to do it right--I don't want to have to buy the tool just to do this one thing, especially as I do not know if all this stuff will even work well enough to use as a bike when I'm done (I have to build and ride it to find that out). But those single-sprocket freewheels are actually threaded evenly all the way thru from front to back, and thus should be able to be mounted backwards on the hub. Then I can just take a hub-section and bolt it to the motor shaft (which I'd already figured out how to do for a previous idea on how to use the treadmill motor for my regular bike, mostly based on Eric Peltzer's belt-drive--but for that idea, the motor would have been already backwards-facing, on the left side, and thus the *normal* freewheel would be backwards and rotate the way I need it to.

I may be overthinking stuff again, especially as much as my head hurts right now. :( Hopefully that's all it is, and it's really not as ahrd as it seems to ensure chains only go the way they need to to get energy only from front to back, never the other way around, and never into the motor, only out of it. I don't intend to use regen to brake or to charge batteries, so freewheeling is exactly what I want.

Another thought I had was about the shock/suspension I need between the top of the rear triangle and the back of the seatframe, to give me rear suspension. I've got springs and stuff like that, but they don't work that well for what I want to do without a lot of added weight for long or large diameter springs, along with the tubing to keep them from warping like an inchworm under compression. :) Now, you may have seen "gauss guns" that use a magnet facing one way to repel another magnet facing the other way to repel yet another magnet, etc., all in a straight line. What would happen if you put all those magnets in a tube with a limited physical space between all the magnets, and the tube were compressible (like a shock absorber or collapsible-ring cup, in segments that enclose each other)? As you compress it more, the magnets continue to repel each other, but don't have anywhere to go, being kept in line by the tube, and pushed toward each other by the magnetic fields of the other magnets next to them. As you get them closer it gets harder and harder to push them together, rather like the way a spring compresses.

Now, I thought I had just had my lucky Eureka moment of a lifetime, and invented something to change the world...but no, it's already been done (there is even an entry right now in one of NASA's contests, according to a Google search on the subject of Magnetic Shock Absorber or Magnetic Suspension--even Wikipedia mentions the idea in the Shock Absorbers article. There's even research going on to use the action to generate electricity!). :(

But still, it's obviously a workable idea, and shouldn't be that hard to build, if I can find the right magnets for it. Oddly enough, cylindrical ones seem to be cheaper than rectangular and other shapes, possibly because there isn't as much demand for them? That means I might be able to buy enough to build a workable one on this bike. An adjustable airshock would be the best option, but I don't have that kind of money for just one of them right now. (actually, I don't have *any* money to spend right now, which is a part why this bike is being built of scrap--the other reasons are just to see if I can do it, and also on the principle of recycling this entire bike project is being done by).

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