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.
Thursday, September 25, 2008
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.
Wednesday, September 24, 2008
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.
Posted by M.E. at 9/24/2008 05:56:00 PM
I've tried a handful of kickstand placements but on this bike they don't balance out right, and it tends to tip over too easily, regardless of stand height. So I figured I'd have to weld up an A-frame kickstand, but then a lucky accident gave me an idea:
I had the handlebars unsecured inside the stem, so they flopped down, and the bike happened ot push on them unevenly from side-to-side, keeping the bike and bars stable just like you see here. I decided for now that I'd just clamp them into this position to help me work on the bike, but that later I would use a quick-release of some kind to hold them in place for steering position:
Yet still let me quickly flip them down to use as a "quickstand" and re-lock them in place. They're much wider than any A-frame I would have used, and thus much more stable; the bike isn't going to fall over even if pushed with a stand like this.
Of course, there are disadvantages: I can't put anything on the bars in a way that will stick out past the surface that will contact the ground, and it's going to wear away at the bars at that spot. I can help both of those problems by adding skid pads of some type and thickness to that spot, though. Another problem is that the steering cables I'd been planning to connect to the bars will now need a way to allow their mounting hardware to rotate freely around the bar but not slide along it. Either that, or add a pivot point bar separate from the handlebars to the stem, and have the cable hardware there.
For welding, I'm sure there are better ways, but since I don't want to build jigs just for a one-off experimental bike, I tend to use a bit of packing tape to hold things in place while I tack weld them, then once I'm sure it's still in the right place, I finish the weld. Takes multiple tries, sometimes, as I still occasionally bump the workpiece with the welding tip before the welds cool or even before I have started the actual tack weld, without realizing it.
Here I've setup and taped a seat support tube to weld in place, with a square to help me line it up at the right height. I used a square only because it will lean up against the bars in the right way to stay in place by itself without securing it while I setup the right angle and height for the tube to be taped to before welding it. The last frame shows the tack weld.
Below is setting up the other side's support tube the same, then taping it.
The most difficult part is getting them mounted symmetrically, without a jig. If you're willing to do it, I'd definitely recommend building a jig instead of this method.
Two pics of the fully-welded-on support tubes.
Of course, I didn't realize that a few days later on I'd make a seat-mounting and angle decision change that would require me to cut these off and reweld them at a much higher angle. :-(
This just shows the piece of downtube I welded to the end of the ex-front-fork to make my rear seat support and cargorack hanger.
The last pic shows the hardware actually mounted in it's final position. I simply took a multi-size punchout discard from some metal box I'd saved years back, and punched out the center of 3 rings, just large enough for the bolt to fit thru that secures the assembly together, and welded the nut for the bolt on what would be the inside of that ring plate. Then welded the plate to the top of the ex-downtube that had been ground to the angle necessary to put the seat-holding ball in the right place.
I left the wheel-axle on the ex-skate-hardware so that I can use that very sturdy axle as a potential mounting/swivel point for my cargo rack later.
Posted by M.E. at 9/24/2008 05:18:00 PM
Friday, September 19, 2008
Over the last few months, I've gotten a number of requests from readers for help motorizing their own bikes, and most seem to want plans and parts lists for whatever scheme they read about here, but there are no plans and no parts lists--it's all done on-the-fly, with whatever I have on hand, whenever possible. Since I doubt most people will happen to have the exact same bike or set of parts available as I did for a particular scheme, I don't think knowing what exact parts or having exact plans of what I did will help them much. If what I show and explain on these pages isn't enough to get the basic idea across enough for someone to build their own out of what they personally have access to, they'll probably not be able to build it from plans and parts lists either--simply because it's highly unlikely they'll be able to find the exact same parts, or that they'll fit on their bike exactly the same way, and if they can make it work anyway with what they *can* find, well, they could have done it without the plans, too. :-)
So this post is a ramble on what is needed to do all this, sort of a more in-one-post gathering of some of the thoughts and choices I've made along the way. By no means is it complete (or it would be almost as long as the rest of the blog, by itself), but it might help those interested in doing this gather their thoughts and figure out what they want to do and can do.
First, you're going to need some kind of battery system, no matter what motorization scheme you choose.
The cheapest one is SLA, or Sealed Lead Acid. Scooters and computer battery-backups use these types, though the ones from scooters could generally be capable of higher output power for a longer time, often they are identical batteries, at least in the larger battery-backups. It's hard to find good used batteries, though, so you will likely have to buy them new, which can cost upwards of $40-$50 each for 12V/12Ah, which is the smallest size I'd recommend if you want any range, and you'll probably need at least two and probably three of those, to get 24V or 36V, to get the kind of power you need out of your motor (this depends on your motor type/etc). They're heavy, because they're made of lead, and don't hold a lot of power for all that weight, plus a few other disadvantages like slower charge times than other battery types, etc.
There's other kinds like NiMH that are much better in capacity vs weight, but also much more expensive. Li-Ion or Li-Po or Li-Fe-Po (like A123) are better than NiMH, but cost even more, and have a few other drawbacks, such as complexity of chargers and battery pack design, if you intend to roll-your-own instead of buying prebuilt packs with chargers.
Then you'll need some kind of motor, preferably high-torque and low-speed, but you can use a high-speed low-torque motor if you have something to convert the speed into torque. That means gears (like car transmissions use), or sprockets and chains (which bikes use). Little bitty gears or sprockets on the motor, and really big ones on the wheel.
The most effective way to do it that I've found so far for the low weight and lack of complexity is a friction drive with something really small on the motor shaft transferring power directly to the tire's outer surface on the wheel, because the smaller the diameter of the motor end of things vs the greater the diameter of the wheel end of things, in such a situation, the greater the change from speed to torque you get.
It's difficult to get anywhere near as high a ratio as that in *one stage* of reduction with gears or sprockets that are of a size or weight that's practical on a bike. Multiple stages of reduction are possible, but that adds weight and complexity, which means less range and more chance of something breaking that you can't fix on the road.
Best is to get a motor that will already do low speed/high torque, like a treadmill motor or some other kinds of load-bearing motors, some of them industrial. Permanent Magnet DC motors are best, because they use less power than Shunt DC motors (the other option for a reasonably small DC motor). Then there's two kinds of PMDC's, the Brushed and the BrushLess--the latter of which will need a more complex controller, but is more efficient. Some AC motors can be converted to DC, either by wiring them as Shunt motors if they already have a set of coils for the rotor and a separate set for the stator (like most of the hand drills I've taken apart), or replacing the outer diamagnetic ring with permanent magnets, making them PMDC motors (like I did in the Cieling Fan experiment). But easier to just find the kind of motor you want to have and leave it as it is.
Then you need some kind of motor speed control, which is best done with an electronic version, or ESC. The ESC can be built from scratch easily enough (there are basic schematics around the web, though rarely with values matching what you'll need, thus you'd have to adapt them to your purposes), and fairly cheaply if you can find enough old motherboards or computer power supplies that use high-enough voltage MOSFETs on them to parallel enough MOSFETs together to get the current load divided up between them enough to keep from blowing them up. And if you do parallel them, make sure you have a few extra in there, or some sort of current limiter to shut off power if one blows, otherwise the extra power being drawn thru the rest of them after one dies will quite possibly catastrophically destroy the rest of them in less than a second. Probably so fast you won't even know that's what happened--there'll just be no motor power anymore, and maybe some smoke (not always even the smoke). Probably all the parts you need can be found in old circuit boards, if you have enough of them and/or a place to look thru old discarded electronics for them.
It's way easier to just buy an ESC, and the ones from http://4qd.co.uk are a good choice, depending on what you want out of your ESC. Just remember that if you think you're going to run a lot of current, get an ESC that can easily handle *more* than that current at it's running stage, not just at it's *peak* stage, or else you'll eventually burn out the ESC, especially if you put a lot of strain on the motor. Don't forget that you need to choose your battery pack voltage before you choose your ESC, or else you could blow up the ESC by using too high a voltage on it.
It's possible to get by without an ESC, and just use a switch to turn power on or off to the motor, but then you only have two speeds--pedal, and full-motor-assisted. :-) It's kind of hard to control acceleration that way (I've tried it). A slightly better way is if you have battery packs with taps at different voltages, such as 3 12V SLA batteries, you could set up a switch or set of switches to engage just 12V for low speed, 24V for medium speed, and 36V for high speed. Again, not much control, but better than none, though I can say that having tried it this still doesn't provide a really workably safe solution.
After you have these three things, you'll have to actually get them mounted on the bike, and work out all the little things you didn't plan for when considering what you'd need originally. :-) If you do it like I have, with simply whatever is available at the time, it's harder to predict all of what's needed till you're in the middle of it, but it can be more fun this way, if you like the challenge. More frustrating, as well, when you realize that because the bolts you happen to already have are 2mm too short, you can't use them and have to either go buy some that are long enough, or rethink your mounting strategy, or something else entirely. :-( This has happened a few times, with different kinds of parts, including on my current homebrew recumbent that's still in-progress.
If you're not just using whatever you already have on hand, and are going to go out and buy whatever you need for it, you'll either want to keep costs really low by planning every single thing out first and making sure you find the three most expensive things recycled somehow, or else just go and get one of those cheap conversion kits, probably a few hundred dollars at most, and save yourself the trouble and money of figuring all this out after having spend more than a kit cost on the parts you need. (If I'd gone out and bought new all the parts used in the last scheme I've used so far, I'd've spent enough to buy one of the low-end kits that might do the same job or better--but I've spent virtually nothing on it so far).
If you're wanting to build one of the same ones I've built, reply to this post with which one, and I'll make a new post with all the details of what I used to make that, and as much of how I did it as I can explain. There is an Instructable in the works for the last friction drive one (that I'm still using), but I don't know how long that will take to finish (weeks, probably, since I'm occupied with the recumbent as well, and it's associated Instructable).
If you're just wanting to build one generally like what I've built, well, it depends on what resources, tools, and skills you have available as to which version you'd be best off with. Also, you'd be pretty much on your own as to how to adapt it to your bike, since your parts would be different from mine. Replies to this post with questions will still be answered, but it's going to take a lot of back-and-forth to figure out exactly what's needed, most likely.
If you are very mechanically handy, and have lots of good tools around (including welders, lathes, drill presses, and other machine-shop tools), with easy access to whatever parts you might need, it's pretty easy to make a number of different kinds of motors work, such as the two different kinds of radiator fan motors I have shown on this blog.
If you're very mechanically handy but don't have much in the way of tools, say just hand tools, then there are a lot of things you won't be able to try. At least, not without a lot of patience, and/or alternate ways of doing some of the work, potentially building some tools to do the work first, before you can build the actual devices. That's pretty much where I started with this, but now with only a few power tools, like an angle-grinder and a welder, I have a lot more options than I did before. With the lathe from a previous post now nearly usable (made a belt for it), I have even more things I can do, especially since there are ways to use it as a drill press.
If you are also electronics-saavy, you can probably build your own ESC from scratch, which will save you money but might not be as good as the ones already out there (and I'll tell you from experience that having your ESC smoke out on you when you're 3 miles from home with a heavy load you had expected the motor to help you pull is no fun at all. :-(
Access to parts can mean anything from having a bunch of stuff already stashed away in your storage areas or garage or whatever, to lots of yard sales or thrift stores nearby, or even just being on the Freecycle.org mailing lists for your area to be able to pickup (over time) whatever you might need for free (which I do reasonably often). Almost everything ends up on Freecycle eventually, if the groups you are near are large enough. There's also Craigslist, and if desperate, Ebay. :-) I prefer to use Freecycle and yard sales because that way I'm recycling things that probably would have been thrown away and wasted otherwise. Also because Freecycle is free, as are all items posted on it, and often yard sales are cheap or free for some things, especially if they see my bike and I talk about what I'm doing with it, and how I'd be using the things I want that they have.
So, questions and comments are welcome as always, though I don't get too many. :-)
Sunday, September 7, 2008
First up is the stowable and extensible pedal tube, also removable with a quick release as an anti-theft device. If you don't have any pedals, you can't ride away with it (and it's a little heavy to carry very far).
Originally, I was just going to try calculating out the right length and angle needed for the pedal tube to put the pedals where I would be better off with them at, and weld the tube to the front headstock at whatever that came out to be, and fix it if I had to later. Then I decided it would not only be better to be able to adjust both length and angle (especially since this is my first recumbent), but that I could also set it up to be removable to make one more anti-theft device.
I decided that using the bottom bracket and the seat tube still welded to it, along with the seatpost clamp, would be the easiest way of doing it. I also left a little bit of the bottom rear tubes with the kickstand plate on the bottom bracket, so I could use it later as a mounting point for things way out front, like lights or more likely a fairing. This way I could just use a seatpost bolted or welded to a bracket of some kind on the front headstock to secure it to the bike.
I had been planning to just weld a couple of flat tabs to the front headstock above the wheel fork, so that the tube could be bolted to those. However, in staring at an old seat while cutting some other parts, I had an idea.
I could use the heavy pre-shaped rod from the bottom of one of my zillions (not really) of old seats, weld that rod to the headstock instead, and use the actual seat-mounting hardware (bolt and clamps) to secure the seatpost to the headstock.
It turned out not to be quite as easy as I'd thought, because the shaped rod is very hard to bend (so much so that it broke before bending when I tried it in a vise), so a bit of creative thought was needed. It would not sit properly against the side or front of the headstock/downtube if I used it the same way it was used in the seat itself. However, if I used the left side rod on the right side, and the right side on the left side, cutting off the entire U-piece that goes to the front narrow part of the seat, I could then easily weld at two points as shown in the pics above, and still have the jutting ends of the rods properly align and mate with the seat-mounting hardware.
Positioning it all to get it welded was a bit of a chore, but worked out ok simply using the actual seat-mounting hardware to hold the two rod pieces in the positions they needed to be in against the metal, tackwelding and then fully welding those two places per rod as shown. For good measure I also tackwelded the rods to the hardware's D-clamps (to prevent slippage), and the hardware's inner clamp for the tube itself is tackwelded to the tube, to prevent rotation of that tube during use/etc.
Now the entire pedal assembly can be stowed for easier transport inside another vehicle if necessary, or for easier parking inside a building (like inside my front room when I'm home and not out riding it), with fewer sticky-outy bits to get hurt on. :)
Here you can see it in it's extended "ride" and it's stowed positions. It can be clamped with the seat bolt to any angle in between, too, though I imagine I will probably only use it in the farthest-down position. I might alter it a bit to allow it to angle even closer to flat parallel to the ground, rather than sticking up so far, depending on how well it rides this way. The tube is shown extended about halfway down the seatpost, and could go from the six inches or so out it is now to another 3 or 4 inches out, or all the way back up against the seat mounting hardware, for either different riders or just different experimental positions.
It would probably require a shorter front chain when in the extreme close position vs the extreme extended position, since the front derailer will not take up that much slack. :) That can be made easy to change, if I'm careful about how the derailer mounts up and what order the chains go on in, to make the front chain the outer one. However, it is likely that I will have the front chain the inner one for freewheeling reasons. Not entirely sure yet, as I'm still working that out for simplest possible setup with the parts I actually have on hand.
A couple of photo updates to the previous post:
The underseat steering headstock, where the handlebars will mount and pivot from, is now welded in place. The pink fork that forms the center of the bike frame still has it's steering tube that would go inside the headstock in place, and that is positioned inside the downtube in such a way that downward pressure on the bike presses it agaist the downtube, hopefully helping to spread the stress load thru the frame forward to the front wheel better than if it was simply the edge-welds to the downtube holding it in place. I'm pretty sure the factory welds that hold the fork and steering tube together are better than my beginner's welds holding the disparate frame bits together. :-) The image is about parallel to the ground, so the angles you see should be the ride angles, more or less, plus or minus whatever changes occur with rider weight on the shocks springs.
These are a couple of closer better shots of the 24" to 20" fork modification.
The flash makes the grinding marks really stand out--they're not anywhere near as deeply grooved as they look. :-) I do need to go back over the welds again, though, because I don't think I did a good enough job there. Don't want to find that out while on the road. :-(
Since I don't have a rear shock designed and built yet (just a few good ideas and a lot of crazy ones), I just took a rusty old spring from a junk box I found in an alley and tackwelded it in place.
This will hold the frame positions about like they will be when I have an actual shock in place, so I can manipulate and guesstimate better. It doesn't actually do much springing, as it's very compressible at the angles I have everything at, though I cannot squish it by hand even a millimeter, so it's not much use beyond that.
Now, the second part: Seat Vibration Absorbers. I don't really think the shocks are going to do much about the road vibration, since they sure don't on my existing bike, and the ones on this one won't be much different in design or execution. So something to dampen the vibration to the seat is necessary. I'd like to do the same thing to the handlebars, but haven't figured out a good way to do it that won't also either make the steering potentially sloppy, or add too much complexity to the mounting point for the headstock (or force a change to some completely different steering method).
So, Roller Skate parts to the rescue. See, this is why I don't throw out the rest of something after I use what I acquired it for. :-) The wheels were very useful, even instrumental, in making the current motor drive scheme work as well as it does. But there are a lot of other nice parts on these skates, which have a rudimentary shock absorber built into the wheel mount design, with independent front and rear axle suspensions using a plastic/rubber grommet stack, thru an aluminum wheel mount/axle, bolted into the aluminum shoe plate itself. The shoes are size 7, too small by far for me, and thus donated to someone else I know that does wear that size. The lacings I kept, as they may be useful for things like lacing the seat back to the frame. The rubber stops/brakes I might use for something but I'm not sure yet what.
Below are some pics of the suspension units, of which I have four. This one doesn't show the top metal cap on the grommet stack or the nut that holds that on and compresses the stack, because I have it off to weld the nut to for an idea I need to test.
If I weld the nut to the grommet cup, I can then weld the cup to the inside end of a top tube frame piece (it happens to be a hair smaller than the inside diameter of the top tube on that red frame).
Then I can easily bolt the whole thing to that tube in such a way that I can use the ball-pivot you see there to secure the seat to, using part of the shoe brackets that contain the pivot-recess (which is filled with the same plastic as the grommets are made of, giving me a double set of vibration absorbing layers). Depending on how I do this, I might then be able to just use old innertube bands to lash the seat itself down to the suspension's axles, making it secure from coming loose with no direct metal-to-metal connections to the bike.
This is one possible way it might mount, though the ball joint actually needs to point the other way so the seat is resting on it. I'd only be cutting the ball joint section out of the shoeplate to bolt onto the side of the seatframe, to minimize the hardware sticking out.
This is another possible method that wouldn't stick out as far to the sides, but doesn't give me that second balljoint-layer of vibration resistance.
In this, I'd weld two of the wheel bearings to the seatframe, as far apart as they'd go with the nuts fully threaded on, so it wouldn't have any movement along that axle's length. The only reason for using the bearings is that I already have them, and they came off those axles and thus I know they'd fit perfectly. :-) Well, they also would provide a pivot so I could not have to worry about getting the weld angle of the axle just right.
In both of these variations, a short (6" to 8") length of that red tube would be welded at an upright and outward angle to the pink fork, just about even with the USS headstock. Exact angle is not known yet, as I have to do some measuring first to see what fits me best, and gives enough clearance for the suspended seat's laced-on bottom to clear everything below it (especially that headstock!) when I'm actually in the seat. :-)
Back to the experimenting!
Saturday, September 6, 2008
I'm still working out a few things, but today's post includes pics of progress on the recumbent-from-scrap bike, as well as pics of donor frames/etc similar to what I used to build it (since I did actually forget to take pics of them before cutting up).
First up is a side view and front/rear views of the parts so far completed:
It's propped up on bricks at the shock-hinge point, with just a rusty old spring in the approximate spot where the actual shock will go. The seat frame is only set on top of it, as there are as yet no mounts for it. Those still have to be designed and made, since I'm trying to come up with a decent vibration-absorbing mount (the shock probably won't take up enough of the vibration for my liking--the one on my Columbia's seatpost sure doesn't).
It's kind of long, but not as long as I had been afraid it would end up, partly because I am going to mount the rear shock alongside the frame, rather than between the former seatpost and back of the seat. That gives me back 8 inches of clearance, as now I only need to allow for frame movment space rather than that *plus* the actual shock hardware and mounting points.
This is a pic of it laying on it's side, in better light.
These are the wheels off the red 20" frame in a later pic. They're both aluminum rims, which will help with weight. The rear wheel in this (on the left) has two things I really want to use: a tubeless foamcore tire (no worries about front flats, thus no need to carry that second spare tube I'd otherwise have to have), and a single-gear reversible freewheel, which I need for the motor's freewheel. I just have to get both of them off the existing wheel, which is proving quite difficult, as I don't want to damage any of the three things. :-(
These are some possible cranks and chainrings I could use for the pedals up front:
I will most likely opt for the longest cranks (one of the middle two) and the smallest of the single chainrings (on the upper left), as that gives me the best initial torque on my drivetrain, which I'll need for hill climbing, as there's no standing-on-the-pedals to get that with a recumbent, or at least not with this design.
There won't be but one chainring on the pedals, since I don't want to put the derailers/shifters up there for a few reasons. First, it precludes my anti-theft idea of quick-removable cranks. Second, it adds complexity in an area up front that would be "first contact" in the event of a front-impact, causing less likelihood of riding away from a minor crash (something I expect during self-training on this bike, in non-trafficked areas and paths). Third, it's uglier with more stuff up there--I'd like a cleaner look wherever possible. :-)
So the other chainrings might be used, but they'll be down underneath (where yeah, there's less ground clearance for them, but more place for me to put stuff out of my way), at the first or more likely second power-transfer point. Probably the one just in front of the rear wheels, just under the shock-pivot. I'll probably use the common three-ring design, as most of my shifters for the handlebars were made for that number.
The 20" wheel vs 24" shock fork dilemma produced the following solution:
The left pic shows the light blue 20" fork I wanted to use, but which is A) broken inside where I can't get in to fix it right now, and B) at least a whole pound heavier than the 24" fork that works fine (and has more shock travel to boot), in about the position it would be if it were there instead of the 24" one, which is the darker blue one.
The middle pic is a closer shot of just the 24" fork and wheel, with my modification. I cut the rear wheel mounting tabs off of what was left of the light blue donor frame (the one that provided the curved down tube plus headstock), which were similarly made as the ones in the pic on the right of another small 20" frame.
Then I put both tabs in my vise (which happens to have the threading bolt between grip halves that exactly match the axle groove in the tabs) and clamped them together such that the axle grooves were perfectly aligned. I ground the outside edges of the tabs down to be perfectly parallel wherever they weren't yet (symmetrically manufactured these were not!), both for looks and for ease of parallel mounting on the 24" fork.
I scraped and sanded the paint off the front edge of the 24" fork to provide a clean surface to weld the tabs to.
I put the 20" wheel in the tabs and hand-tightened the nuts to clamp the tabs as parallel as I could to each other, then held the wheel into the 24" fork so that the wheel's rim lined up with the brake pads on that fork, temporarily super-gluing the tabs to that spot at each end of the tab--the glue will hold it just long enough to tack weld it.
Once tack welded, I made *sure* that the wheel was as perfectly parallel as possible to the forks, so the brake pads would line up and whatnot, and it would steer straight (there is some adjustment play in either one without a great deal of trouble, so it did not have to be absolutely perfect), then took the wheel itself off, and fully welded the tabs to the fork.
Now I have a way to use a 20" wheel on my 24" fork without having to modify the shock portion of the fork, and the shocks still work like they did before. The center of thrust and the trail of the fork/wheel combo is of course different, but it still operates more than well enough for what I wanted. I still wish I could mount it more straight-up-and-down, but there are a number of reasons I can't, with the parts I have available, with the design goals I have in mind. I could do *some* cutting-and-rewelding such as on the headstock to change it's angle, but I don't want to do that unless it's absolutely necessary, as I'm sure my welds are not as good as the originals, even on the cheap junky frame I'm using as a donor in this case. There's not really anything I can do on the shock fork itself to make it shorter than it already is, to allow a steeper angle, without way more work than I think I can safely do to it (which is part of the reason i wished I could use the 20" shock fork to start with).
Now for some pics of donor bikes similar to what I've used:
The lefthand pic is of 3 20" bikes that have most features in common with each other and certain parts I used already or will use later. The red bike will donate it's seat tube and bottom bracket as the front pedal-mount tube and bracket for my removable/adjustable pedals. One of the long seat tubes and some other seat-mounting pivot hardware, along with a quick-release seattube bolt will mount it all to the headstock up front. It will also donate it's headstock to the actual steering handlebar mount for under the seat. That headstock will be mounted as vertically as possible in the "U" formed at the front of the pink ex-front-fork that's under the seat of the recumbent. It's likely that some of the thin rear triangle tubing from it will become parts of the seat mounts.
The middle pic shows a silver and purple 24" very similar to the brown metallic one I used for the rear-triangle of my recumbent. This silver/purple one also donated it's front shock fork. The one on the brown bike was bent up and all but destroyed on the righthand side, though the left side is possible usable separately (and may become part of the rear shock system).
The righthand pic shows a Huffy 24" almost exactly like the ones that provided the pink and the purple U-shaped forks forming the middle of my recumbent. The two donor bikes also gave their rear triangles to make the sides of that cargo trailer in earlier blog posts, and I've used most of their other parts here and there along the way, too. Their down tubes are almost all that's left, and those will likely become parts of the seat mounting system on this recumbent, and possible parts of the rear shock.
Pics of other assorted parts:
The left pic is a bunch of handlebars, some forks, a rearview mirror that was in a bag of stuff I got last week, etc. Parts of a couple of those handlebars will be put together (probably have to cut and weld) to make my under seat steering bars and grips.
The fork on the left side of the righhand pic is the upper remains of the wrecked brown bike mentioned above. There is only one spring, as the other was damaged along with the outer casing. The fenders and chainguard might end up on this bike; I am pretty sure I'll need them. THey came off a pretty old Huffy Sportsman frame that looked unsafe to actually restore to use.
So there's this week's eye-candy, with enough verbiage to spoil it for you. :-)