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  1. #1
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    converting folding bikes to SWB folding recumbents?

    I am planning on purchasing a downtube folding bike. I was impressed with the cruzbike conversion that was successfully utilized on a downtube folder. I think that a recumbent conversion kit for upright folders is a great alternative to a recumbent folder, plus you get the advantage of being able to switch back and forth when it is needed. I think the cruzbike conversion kit is a great kit; however, I believe the price is over-inflated. I just do not see how it can possibly be worth $395 dollars for a conversion kit. Heck, that is the price of a completely new bike! Well, I have been thinking that it should be possible to come up with a diy solution that is much less expensive than $395 dollars. Can someone let me know if this sounds like a crazy idea or if it makes sense? It seems to me that all that would be required for a successful conversion would be a bottom bracket boom tube, a way to effectively mount it to the front of a folding bike via a kind of machined aluminum frame clamp, and a way to mount a recumbent seat to the frame as a replacement for the saddle. There was a kit that was created for the brompton a while ago that did just that; although, they used a rubber belt instead of simply using a straight chain drive. A bottom bracket wouldn't even have to be brazed to the boom tube, as there are sliding bottom brackets that can be clamped to a tube that are sold for about $65 online. It kind of reminds me of the setup various homebuilders used to make a custom SWB recumbent using a bmx frame or bmx donor bike. So, does this sound feasible?

  2. #2
    Eschew Obfuscation SesameCrunch's Avatar
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    There are people who sell DIY kits for recumbent conversions. Go over to www.bentridersonline.com and do a search. All the ones I know of are not of the front wheel drive, movable BB variety like the Cruzbike, though. Don't know how important that is to you.

    IMHO, whether one can put together a DIY recumbent conversion is highly dependent on 1) individual skill level, and 2) available time. The kit was $350 when I bought it. It was worth it for the confidence in the end result. Plus, I'm not a machinist, I can just bolt parts on. I'm happy with the end result of my Cruzbike/DT, it rides very solid. My only regret is that I don't ride mine that much anymore. Got too many bikes .
    Last edited by SesameCrunch; 08-29-07 at 12:30 AM.

  3. #3
    Señor Mambo
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    For that type of recumbent kit, there's probably more engineering involved than meets the eye. By the time you're done getting parts and tooling, you'd probably pay close to $400 anyway.

    As far as the Brompton recumbent kit, Ms. Ness wanted $2500 US (including bike) for one.

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    Eschew Obfuscation SesameCrunch's Avatar
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    Quote Originally Posted by spambait11 View Post
    For that type of recumbent kit, there's probably more engineering involved than meets the eye. By the time you're done getting parts and tooling, you'd probably pay close to $400 anyway.
    +1. The FWD and movable BB features add design considerations that are more challenging than just a boom in front and a long chain to the main crank...

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    Well, that is exactly my point. It seems to me that the recumbent conversion kits are WAY overpriced. How is it that they are considerably more than the cost of a completely new bike. It just doesn't make sense. Furthermore, consider that the following individual projects that built SWB recumbents on very tight budgets.

    http://www.wideopenwest.com/~lipetz/...s/bicycles.htm
    http://www.recumbents.com/wisil/junkbike/junkbike.htm
    http://www.recumbents.com/wisil/junk...orrestbike.htm

    I realize that the brompton and the cruzbike conversion kits were quite pricey, but I do not believe that the price is justified.

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    Ok, for some reason most of the text of the last post I made was cut off after I made the comment about the unjustified price. I wanted to clarify my ideas so that I can get some feedback that is accurate to the concepts I have floating around in my head. I agree with SesameCrunch. Going the route of FWD brings up some serious design concerns. In my mind the main concern is long term stress on a part of the bike that was not designed to be the point of power application and transmission. I do not think that the front forks have the engineering margin that make long term fracture and premature failure due to fatigue an insignificant issue. In my mind this is especially true of folding bikes; consequently, I believe the best design for a recumbent conversion kit for a folder would be something more akin to the Ness recumbent conversion kit that was developed for the brompton. I believe that there are a few high quality moderately priced parts that make such a DIY kit feasible at significantly below the $400 price point of a Cruzbike conversion kit.

    The first piece of the puzzle is having a way to mount the bottom bracket boom to the front of the bike. Here is a collection of pictures of the Brekki conversion kit to provide an idea of what I am talking about.

    http://www.velomobiling.net/modules....9e4f3c2683ca3a
    I believe that it would not be to challenging or expensive to design a simple aluminum block frame clamp to secure the bottom bracket boom. I am sure it would not cost much to get a local machine shop to machine a block of aluminum into the type of frame clamp that would be required to do the job. I believe that the frame clamp would be the most complex part of the project. The bottom bracket boom itself would be a simpler matter. Suitable aluminum tubing for the boom is easy to find. It would not be an expensive purchase. The bottom bracket shell itself would not have to be welded to the boom as a sliding bottom bracket shell can be purchased for a bit more than $60 dollars online. Here is one such example.

    http://www.bikemannetwork.com/biking...CRNKTDM/CR8951

    Obviously the sliding bottom bracket would allow for adjustments to be made so that the rider could fine tune the bikes feel to make for an efficient ride. This basically kills two birds with one stone. Obviously the bottom bracket and crank assembly from the upright folder itself would be used to complete this assembly.

    Longer chains to fit such a configuration are easy to find. Since I propose having a chain run directly from the chain wheel to the back gears one would require a chain management system. The simplest system would seem to be a couple of spans of flexible PVC tubing to route the chain and keep it from making inadvertent contact with the rest of the bike and rider. Other options are the use of roller blade wheels to make custom routing pulleys, or even the use of a few chain tensioners set up to keep the chain in the desired position. Obviously a combination of all of these could be used.

    Another point of price reduction would be finding a quality recumbent seat at a reasonable cost. Most recumbent seats that you find online are anywhere from $150 to $250 dollars. That seems quite steep to me, since that matches the better part of the price of many folding bikes. I did some searching and found a solution. Atom bikes makes an excellent product for a project such as this.

    http://www.geocities.com/atombikes/seat.html

    It wouldn't take much imagination to devise a way to mount the seat in place of the folder's saddle and seat tube. There are many bits of hardware around that would make mounting the recumbent seat easy and affordable. The gentlemen I mentioned previously that experimented with DIY SWB recumbent projects of their own are testament to that fact. The application of the desired seat foam should also not be a major undertaking as it would simply involve a little cutting and glue once the material was acquired.

    Finally one would possibly have to make adjustments to the steering mechanism by either getting a tilting steering tube or bars that make it comfortable with which to reach and steer while in the recumbent position. There are quite a few products out there that would allow you to take care of this issue.

    Designing the system to fold up into a compact shape would be a little more challenging if it were required, but it would by no means be impossible.

    So, what are the thoughts on the feasibility of taking a project such as this to completion while keeping cost substantially below the cost of a new bike?

    Thanks :-)

  7. #7
    Señor Mambo
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    You definitely will have to choose your base bike carefully. Will the head tube be able to handle the stress you're about put on it?

    Your "aluminum block frame clamp" will have to be well thought out and designed. It will have to withstand the stresses of hard pedaling while eliminating the pogo effect. Come up with a good design and you yourself will probably be selling it for $400.

    IMO, you're not thinking correctly about the seat. For recumbents, seat comfort is the entire key, otherwise recumbents have little advantage. It's not just a simple matter of popping a seat down a seat tube: what about back recline? What about adjustable seat base angle? The most comfortable position, to me, is the position of a low rider: laid way back with a high bottom bracket. Does your design take that kind of adjustment into consideration?

    Lastly, what about the weight? The advantage of FWD's is that they're not only efficient, but can save a lot of weight without having to consider extras: for example, no need to design around long chains with tensioners all over the place; much easier to fold or take apart. If you want to see a very slick design that is also beautiful (which most home-builts are not), then you ought to study Bram Smit's work. Poke around his site and also check out his tilting trike. If you have machining help, you're in business.

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    Spambait11, thanks for the feedback. Hey, I looked at Bram Smith's low racer take apart design. Wow, that is certainly sweet; although, if I were to do a low racer design I think I would rather try building one of those 2x4 wooden low racer designs.

    To answer some of the concerns you pointed out.

    As far as the stress on the head tube and the aluminum block frame clamp are concerned I think the design of the clamp would take that into account. I was actually thinking of using a downtube full suspension folder. Those bikes have nice strong rectangular frames that would be ideal for my idea. I was actually thinking that the aluminum mounting bock would clamp to the frame and head tube and extend past it a little. What this means is that the extra stress placed on the bike would be absorbed by the whole frame and not simply the head tube as in the brompton kit design. Frankly, I think that was a weak point in their design. I come from a nuclear engineering background, so I believe in a generous engineering design margin to eliminate stress failures. Head tube stress would not be a problem.

    As far as the seat is concerned, I think you misunderstood what I was trying to say. I was also not clear enough in my description. Here is a picture of a guy that created his own cruzbike like recumbent without resorting to actually paying $400 for the cruzbike kit. I believe that his idea of mounting the recumbent seat could easily be adapted to the downtube frame. Notice how simple and straight forward it is.

    http://recumbent-canada.blogspot.com/

    If you read through his building log you will find an interesting point he makes about his project. That point is that recumbents do not have to be expensive. I would guess that his entire bike cost less than a cruzbike conversion kit while performing as well if not better than a bike modified with such a kit. That kind of observation from a home builder gives me a bit of confirmation that the concept I have for converting a folder should not be outlandishly expensive; otherwise, I would not think it worth the time of my thought. If one was a little worried about proceeding without a set of actual recumbent seat mounting plans, then Atom bikes offers a set of recumbent seat and mounting hardware plans for only five bucks.

    http://www.geocities.com/atombikes/plans_index.html

    Another seat mounting design to consider is the one that was used on the brompton conversion kit. Here is a set of detailed pictures of the seat and mounting hardware.

    http://www.velomobiling.net/modules....9e4f3c2683ca3a
    You will notice that they basically mounted an adjustable mounting rail to the bike using the seat post and a simple frame clamp. That design is also a possibility; although, if I used something like that I would rather it have a bit more flexibility as far as the tilt angle of the seat is concerned. Such additional flexibility would be simple to add to the design.

    I agree that the seat and boom angle of a low racer are ideal for power application. It should not be a challenge to design the boom angle and seat angle of such a conversion project to give the rider something close to that body position; although, I believe that many people would rather choose a slightly more upright seating posture. Frankly I would rather go with the more reclined posture for better power application.

    As far as any weight penalty goes, well I think you are overstating the difference in the weight of a cruzbike like conversion as opposed to my idea. Most of the components are included in both kits. The only real weight difference will be from the weight of a longer chain and any chain management hardware. I believe these hits are minimal as you can choose chain management hardware that is very light. Heck, if you use flexible pvc tubing you will hardly notice the chain management hardware weight at all.

    You are correct in stating that the FWD designs are slightly more efficient in their power application; however, there are some serious drawbacks to the cruzbike like conversion designs. These drawbacks are the additional stress placed on your front fork and head tube. Keep in mind that the front forks of a bike were not designed to be the bearers of the continual flexing and stress of pedaling. Also, FWD kits that attach to the steering mechanisms of a bike introduce the phenomena of pedal-steer. That is the tendency of the bike to oscillate its steering direction due to the changes in the force of pedaling. I believe that it is better to eliminate those compromises by utilizing the rear fork for power application, since it was designed for it, and isolating the pedaling mechanism from the steering components.

    Do my explanations help a bit more? Thanks, I appreciate any feedback.

  9. #9
    Senior Member defjack's Avatar
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    folding recumbents

    The nice thing about the Cruzbike kit is it can be used on more than one bike. I have had mine on a Downtube and a mt.bike for the 2nd time.I have over 1200 miles on these bikes with a Cruzbike kit with no structure problems.Pedal steer is a non issue after a few hundred miles. Jack

  10. #10
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    Quote Originally Posted by danielmramos View Post
    Do my explanations help a bit more? Thanks, I appreciate any feedback.
    Yeah, I hear you.

    In terms of chain management, I was thinking that extending the chain to the rear triangle would make the bike hard to fold. Even the Brompton recumbent has to have the belt removed in order to fold the bike. Your point about stress bearing on the front forks is intriguing. I'll have to ponder that more. I've also heard that chain tubes (PVC, etc.) can cause a lot of friction when pedaling. If you're going to use roller guides (a la RANS), then it will be an extra step to figure out how and where to mount those rollers. Not impossible, but just another bit to think about.

    I'm glad you clarified your ideas about the seat. At first, it sounded as if all you cared about was seat mounting hardware and budget. I know the HP Velotechnik's Grasshopper uses a seat that is strong enough to be mounted without braces, so there are ways of doing it. Also, I didn't notice it at first, but in the pic you posted, it seems Ness used a front fork as a seat brace. Ingenious!

    I'm also curious how your boom will be attached; that seems to be the most challenging part of your project, esp. if it's going to attach to the frame and head tube. Can't wait to see it.

    Oh - and here's more inspiration for you.
    Last edited by spambait11; 08-30-07 at 09:59 AM.

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    Spambait11, that is a great observation about the brompton kit. I hadn't noticed that myself. You know I have seen and read about the monty home built recumbent folder. That guy sure did put some good work into that bike. I think that the steering mode he used is not for the inexperienced. Although, it is certainly a commendable project.

    I understand your reservation about the utilization of tubes for chain management; however, it is most likely the simplest design, and it is certainly the least likely to fail. If one was to choose to use the home made roller blade wheel or chain tensioner method I believe the simplest mounting method would be a few clamps that provided mounting points for such hardware.

    On the note of examples for inspiration, I found this thread that contains some good pictures of what appears to be a folding recumbent bike based on a brompton. It is not an add on kit as the Ness kit is; rather, it is a custom built dedicated recumbent folder that utilizes a brompton like frame. The reason I am referenceing it here is that it contains most of the basic design elements I have discussed in this thread. There are a couple of substantial differences that I want to point out. The Pocket SWB recumbent folder does not have an adjustable seat or a sliding bottom bracket boom mechanism. What this means is that their design would be very frustrating for many people. It does contain the basic shape and idea of what I am proposing. It certainly makes a great visual aid. Also, notice that unlike the Ness kit, the Pocket SWB does not have to have the chain removed in order to fold the bike. I think that is certainly an accomplishment as it makes for quick folding and unfolding. In my opinion any kind of drive train disassembly would remove too much of a convenience factor to keep anybody wanting to use the bike. I mean, who wants to be removing and replaceing a greasy chain or belt when you are trying to fold up your bike to take it up to your office cube on the 3rd floor of your building?

    Packable recumbent - HP Grasshopper?
    http://transportcycling.com/_wsn/page3.html

    About the attachment of the boom. I agree that it will be the most challengeing part fo the project. The boom will actually attach to the frame clamp. The clamp is what will come in contact with the frame and the head tube. If anything fails due to stress failure it will most likely be the frame clamp, so it will have to be a good design. Keep in mind though that it is better to have the frame clamp fail if anything fails at all. The frame clamp will be replaceable, while your bikes frame is not. Another thing I was considering is a thin rubber sheet which would be inserted between the frame and the frame clamp prior to tightening. It would act as a type of gasket. That would keep the frame clamp from scratching the paint of the bikes frame. After all if you ever needed to remove the recumbent conversion kit and go back to an upright configuration you don't want to have a scratched bike.

    What do you think of the pictures of the Pocket SWB folding bike's configuration?

  12. #12
    Señor Mambo
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    Quote Originally Posted by danielmramos View Post
    What do you think of the pictures of the Pocket SWB folding bike's configuration?
    Ha ha! I know that guy. He has a partner who does all the welding while he does the designing. I don't think he's making 'bents anymore (he's actually a pedicab maker) as he has a new job designing wheelchairs, last I heard.

    The model you pointed out is based on the Breezer i3. I never got to see this one in person, but it looks heavy and unwieldy to carry. Still, the functionality is there. I do not know where he got the hinges for the boom or seat post, but I can say that he attaches much of the intricate parts by welding/brazing.

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    Ok, my next job with this project is to do some CAD work and some pencil and paper work and get all these parts down on paper/computer. It seems to me that nobody that has read this thread has flat out said that it will not work or that it is not worth the effort; consequently, I think it merits further thought and design refinement. The more I think about this project the more I realize that with the correct design such a project could be applied to almost any folding bike. There would only have to be very minor changes from bike to bike to get this to work on anybody’s folder. The first challenge that I will put my mind to will be refining the design for the forward frame clamp that will secure the bottom bracket boom to the frame. What I would like to do would be to put in enough thought and design refinement into this project to be able to buy a folder and have it up and riding as a recumbent within a couple of weeks of purchase. I am fortunate in that I have a friend that is a professional bike smith. If I run into any serious trouble I am sure he can help me think my way out of it. If anybody has any other ideas or thoughts that they would like to add please feel free to let the ink sparks fly and the ink flow. More thoughts and ideas are always better.

    Thanks

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    I thought I would post this link to the Dutch KS2 recumbent kit bike. It is not a folder; however, it does have a clamp on bottom bracket and RWD design that I think is worth looking at.

    http://www.dutchbikes.nl/pagina/frame_r_kits.html

  15. #15
    Eschew Obfuscation SesameCrunch's Avatar
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    Have you posted on the Framebuilder forum in BikeForums? They might have more feedback for you on this DIY project. You might find more experience with frame building there...

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    I've been giving some thought to this also, and while I have no experience in design and fabrication, these are some of my ideas.

    Goals
    My longterm goal specifically is to have a bike that isn't simply a folding/recumbent conversion, but something which can easily switch back and forth between the two with minimum tools/fuss.

    -Switch back and forth between upright and recumbent.
    -Easily and quickly (no tools) adjust bike for different size riders, in either configuration.
    -SUPER redundant. As many parts that can be used in either setup.... obviously there'll be leftover parts when you switch from one setup to the other, but aim to keep this to a minimum.

    Preferences/Prejudices
    Not required, but I give preference towards:
    -ERTO 406 (20") wheels, for both rear and front. ERTO 349 (16") as a secondary contender.
    -FWD, because it requires less fuss in terms of chainruns, tensioners, grease on legs/clothing, and because it (possibly) allows for easier quick-resizing the bike to different riders.
    -Underseat steering. Can USS be combined with FWD? I know that FWD recumbents will have a certain amount of legsteer. I know also that it'd probably be easier to go with a hinged stem, but I just like the look/comfort of USS recumbents.

    Parts with potential
    I found that the Swift is perhaps ideally suited to this conversion, and not just because it uses mostly standard components.

    -There's already a seat in production (price I think = ~$150) which can be ordered a la carte. HPM's Phaser folding recumbent is a close cousin of the Swift, and uses the same seatpost diameter for its seat. Addtionally, it's folding mechanism uses the same (I think "trusfold") mechanism, where the seatpost itself is the lockpin which holds the frame in place.... pull it out and the rear triangle folds under and up. More than that, the seat folds. It's already built for a folding recumbent, and the seat can get tiny too. Even better, I believe the seat can be gotten with a forward-back adjustable rail. Adaptations needed: connection points would have to be installed onto the rear triangle to support the back of the seat. Some sort of clampdown/tiedown method to secure the seatrail to the frame. The seatpost would be one anchor point. I'm thinking that if USS is used, a custom clamp might be possible.... clamped near the front of the seatrail, the underside of the clamp could possibly serve as the pivot point for an USS linkage.

    -Quick detach cables. These would be enormously useful for changing the bike from upright to recumbent, and for breaking it down/packing. Adaptations needed: braze-on cable stays.

    -Quick release/quick detach front fork with....wait for it.... the same OLD as the rear triangle (132.5mm), and same axle width dropouts (10mm as opposed to 9mm). Basically, the bike would always use rear wheels, regardless of whether they're being attached in the front or back. Ideally, I'd want a flipflop hub for the front wheel at most times (when upright). When changing the bike from upright to recumbent, the rear wheel would come up front, front wheel go to the back. This would also allow for the upright version of the bike to be switched back and forth easily between geared, SS and fixed gear. Adaptations needed: This would probably have to be a one-off, maybe custom fabricated. If planning on using a derailleur system (I wouldn't), a hangar would also have to be fitted onto it.

    -Internal hub. The drivetrain would be easier to manage, and the Swift's folding mechanism keeps the bottom bracket at the same distance to the rear axle, so chain tensioner would be potentially unnecessary. Adaptations needed: Hub gears will usually have less gear range than a derailleur system, or else be very, very expensive. Gearing would have to be compromised somewhere, probably cutting out some of the very low gears for uphills. Or, you could take out a second mortgage on your house and spring for a Rohloff.

    My brain's exhausted from pulling all that out and putting it (somewhat) in order. I'll look over it later and add to it, if I forgot anything.
    Last edited by bookishboy; 08-31-07 at 01:17 PM.

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    jur
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    For hub gearing you could combine a Nexus 8sp hub with a Schlumpf Speed crankset. Biggest gear range in cycling history. Much much cheaper than a Rohloff.

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    Quote Originally Posted by bookishboy View Post
    I've been giving some thought to this also, and while I have no experience in design and fabrication, these are some of my ideas.

    Goals
    My longterm goal specifically is to have a bike that isn't simply a folding/recumbent conversion, but something which can easily switch back and forth between the two with minimum tools/fuss.

    -Switch back and forth between upright and recumbent.
    -Easily and quickly (no tools) adjust bike for different size riders, in either configuration.
    -SUPER redundant. As many parts that can be used in either setup.... obviously there'll be leftover parts when you switch from one setup to the other, but aim to keep this to a minimum.

    Preferences/Prejudices
    Not required, but I give preference towards:
    -ERTO 406 (20") wheels, for both rear and front. ERTO 349 (16") as a secondary contender.
    -FWD, because it requires less fuss in terms of chainruns, tensioners, grease on legs/clothing, and because it (possibly) allows for easier quick-resizing the bike to different riders.
    -Underseat steering. Can USS be combined with FWD? I know that FWD recumbents will have a certain amount of legsteer. I know also that it'd probably be easier to go with a hinged stem, but I just like the look/comfort of USS recumbents.

    Parts with potential
    I found that the Swift is perhaps ideally suited to this conversion, and not just because it uses mostly standard components.

    -There's already a seat in production (price I think = ~$150) which can be ordered a la carte. HPM's Phaser folding recumbent is a close cousin of the Swift, and uses the same seatpost diameter for its seat. Addtionally, it's folding mechanism uses the same (I think "trusfold") mechanism, where the seatpost itself is the lockpin which holds the frame in place.... pull it out and the rear triangle folds under and up. More than that, the seat folds. It's already built for a folding recumbent, and the seat can get tiny too. Even better, I believe the seat can be gotten with a forward-back adjustable rail. Adaptations needed: connection points would have to be installed onto the rear triangle to support the back of the seat. Some sort of clampdown/tiedown method to secure the seatrail to the frame. The seatpost would be one anchor point. I'm thinking that if USS is used, a custom clamp might be possible.... clamped near the front of the seatrail, the underside of the clamp could possibly serve as the pivot point for an USS linkage.

    -Quick detach cables. These would be enormously useful for changing the bike from upright to recumbent, and for breaking it down/packing. Adaptations needed: braze-on cable stays.

    -Quick release/quick detach front fork with....wait for it.... the same OLD as the rear triangle (132.5mm), and same axle width dropouts (10mm as opposed to 9mm). Basically, the bike would always use rear wheels, regardless of whether they're being attached in the front or back. Ideally, I'd want a flipflop hub for the front wheel at most times (when upright). When changing the bike from upright to recumbent, the rear wheel would come up front, front wheel go to the back. This would also allow for the upright version of the bike to be switched back and forth easily between geared, SS and fixed gear. Adaptations needed: This would probably have to be a one-off, maybe custom fabricated. If planning on using a derailleur system (I wouldn't), a hangar would also have to be fitted onto it.

    -Internal hub. The drivetrain would be easier to manage, and the Swift's folding mechanism keeps the bottom bracket at the same distance to the rear axle, so chain tensioner would be potentially unnecessary. Adaptations needed: Hub gears will usually have less gear range than a derailleur system, or else be very, very expensive. Gearing would have to be compromised somewhere, probably cutting out some of the very low gears for uphills. Or, you could take out a second mortgage on your house and spring for a Rohloff.

    My brain's exhausted from pulling all that out and putting it (somewhat) in order. I'll look over it later and add to it, if I forgot anything.
    Bookishboy, I congratulate you for finally codifying your ideas. I understand the kind of mental task it is to finally take a bunch of little bits and pieces you have been thinking about and consolidate them into the beginnings of one design document. There are a few areas where your approach and my vision depart.

    Firstly you suggest that the swift would make a better chassis for a upright folder to recumbent conversion; however, there are some areas where I think the swift is deficient when it comes to being an enjoyable recumbent. The swift is not a suspension bike; consequently, it would make for a very harsh recumbent ride. As you will read on many recumbent homebuilder websites, suspension is much preferred. On an upright when you come to a bump in the road you utilize you see the road imperfection, anticipate it, and utilize your legs to absorb much of the shock and resulting impact. On a recumbent there is no possibility of doing that. You are completely reliant on your bike design to absorb the impact for you; furthermore, any unabsorbed impact is not dampened by your legs, so it is felt directly by your back and whole body.

    Secondly, you suggest that the Swift uses standard parts. I agree with you on this point. It is a requirement in my book that the bike use standard parts; however, the Swift is not alone in this regard. The Downtube folders also use standard parts, so there are more choices than the Swift when it comes to this point of consideration. The Swift is not unique.

    Another matter entirely separate from the bike design is the price point. A primary concern of mine was being able to do all of this for substantially less than the cost of a cuzbike recumbent kit. I believe your approach will vastly exceed this central tenant in my project criteria. The Swift itself is priced at ~$700. If you add in the cost of the seat your are proposing to use you are automatically at $850 without doing any mounting. Add to that the cost of the FWD bottom bracket shell mounting kit and all of the extra special components you are proposing to use and you are way beyond the range of it being monetarily worthwhile in my book. I mean, at what point do you throw in the towel and simply go with a commercially produced recumbent folder and the separate purchase of a folding upright? There are some rather excellent folding recumbents that would probably fall into that range. The ones that come to mind are Aiolos Speedlight SL, Belize Bike Cool Rider, HPM Phaser, M5 Ligfietsen CMPCT, HPVelotechnik Grasshopper folder, and finally a used Bike SatRday.

    I almost forgot. I expressed another couple of concerns with the FWD type of conversion kit. The first was pedal steer. You do not seem to be too concerned about that; although, it is something I would rather avoid if I were going to put my brain to the matter. The second was the increased stress on the front fork due to it being forced to take on the stress of pedaling and power transmission when it was never designed to do that. There is a reason a rear fork is more substantial than a front fork. It is designed to withstand the rigors of power transmission. Heck, the rear fork is stronger only for the the reason of power transmission; however, the FWD designs require the front fork to not only deal with the stress of the power transmission but also the flexing stress of pedaling. The stress due to pedaling is usually taken by the bottom bracket shell that transfers it to the frame. The FWD recumbent kit designs require the front fork to do all of that work. It just seems to me that the FWD kits ask too much from the bikes and set them up for premature failure. Those are factors I would rather do without.

    If I am not mistaken the seat you are proposing to use has no angle of recline adjustment. I think that is an important consideration when you are dealing with a home built project. Also, isn't that seat a mesh back type of design? I would rather go with the European style hard back conformal seat. All of the latest two wheel recumbents are going with the hard back seat type.

    Well, I hope my thoughts help you in your design process; although, I am sure your approach would certainly be successful. There are just those few factors that you have to allow as acceptable risks. I think your budget is obviously bigger than mine.

  19. #19
    Senior Member Leigh_caines's Avatar
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    My aim was somewhat different .
    To make a folder that could be ridden in both the recumbent [down] and DF [up]
    So that when touring and hitting steep stuff I could go into the up position
    It needed to fold for Air trips
    I took a Dahon {steel] [cheapest one I could find] and went to work.
    After not getting it right a few times I now have it.
    Made the seat and used old bits of rubbish bikes.
    So with a quick flick of the seat forward and putting the seatpost up it changes from up to down and back
    Worked so well I then put a Sram 3 hub with 8 and 2 out the front for 48 gears all up
    Gear inches from 15 to 100
    8000ks on it so far [Just back from a trip around Northern Ireland]
    It is a bit heavy at 20ks
    And would be nice to make one starting with something lighter
    But I love my “Updown” bike
    I haven't worked out how to put an Image on hear when I do I'll post a pic

  20. #20
    Eschew Obfuscation SesameCrunch's Avatar
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    Leigh:

    I'm most eager to see pictures! If you want to email me the pictures, I'll post them up for you. Send me a private message.

    Thanks,

    Alan

  21. #21
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    Homebuilt Cruzbike for under $300 w/seat & minimal hacking.

    Thanks for the props on pocket SWB folding recumbent. I built that prototype to see if it could be done, and it was done. I was hoping to inspire Dahon to make something like this bike for the masses. For the record, it did have an adjustable boom to fit riders 4' 5"~5' 10", just the seat was stationary.

    Also, Jerry Hsu, I have moved onto wheelchairs, fwd handcycles, disability adaptive tricycles, and now E-bikes and Scooters design and sales. I still wish I could do pedicabs but they don't pay the bills and keep the wife happy. For that matter nor do folding recumbents.

    OK so onto the cruzbike. My business partner has been sourcing bike production in Taiwan for nearly 2 decades. I showed him the Cruzbike kit and after laughing and picking himself up off the floor, he was like that thing is FOB $50 from Taiwan and less than $75 landed US.

    The reason you are paying $400 is because of design patents, tooling costs, economies of scale, insurance, marketing, and of course the "I want one of those factors" are strong with this design. I know it sucks, the Xtracycle is even worse with the "landed cost vs. end user cost."

    In any event, I have come up with a hack that can get you a semi polished cruzbike w/ seat for under $300 retail. If you are Craigslist and or Ebay savvy you can get the price possibly close to $100.

    1) You need a donor bike and a hack and whack bike with a hinged BB. I have narrowed the hacking bike down to one that is mass market and I think will fit perfect with minimal machining. All you need is a hacksaw, a grinder, and a drill.

    http://www.walmart.com/catalog/produ...uct_id=3610588
    (This bike retails for $200 but I have seen it on Craigslist and or Ebay for as low as $50 used.)

    Strip the bike. Remove the rear suspension triangle linkages, and discard two of the top suspension tubes that bolt onto the rear shock and rear drop-outs. You will only need the lower rear chainstay for the rear end.

    2) Take the front triangle of the frame (the polished alloy part) and carefully hacksaw (bandsaw preferred) the downtube away from the bottom bracket. Not to close to the bottom bracket as you need the BB more than the downtube.

    3) Now cut the seat post tube just below the bike's top tube. You should be left with half of a seat tube, connected to a bottom bracket with an attached swivel bracket for the rear swing arm. Carefully, clean up the excess metal left from the downtube from the bottom bracket and smooth it out. Then grind a 1" slit down one side, in the top of the seat post tube. It helps to drill a 5/16" hole first, 1" down the tube as a guide before grinding. Ad a seat post clamp on top of the seat tube where you just grinded the 1" long slit.

    4) Take the rear chainstay and drill out the tops of the rear drop-outs to about 3/8". Bolt back onto the bottom bracket/ seat post tube. You have just now created an adjustable angle sliding bottom bracket like the cruzbike.

    By now you are asking yourself “That’s great but how do I attach this to the bike?” OK. You will need a recumbent swivel block for a flip it style extended stem.

    http://us.st12.yimg.com/us.st.yimg.c...ent_2000_13885

    From Actionbent this is only $29/ each. Personally, I would get 2 of them for a so I could achieve an adjustable front BB, and a flip it style steering boom for a really deluxe ride. But really one is only needed.

    5) I would mount one adjustable stem block on top of the other facing opposite directions. One for the FWD attachment would have the swivel face the front of the bike. Then the one on top to use for the steering tube would have the adjustable part face the rear of the bike. It would be best to use a donor bike with a 1-1/8” headset/ fork tube. Mount your thread-less headset on the donor bike you will use, and get an 1-1/8” fork that has a longer than needed steer tube to accommodate a thread-less headset, and 2 steering blocks stacked. Cut the fork to size and bang in the star nut for the thread-less headset cap.

    6) Using 1” and 1-1/8” tubing or misc. seat posts and a couple of seat post clamps, telescope outwards away from the adjustable stem block (lower one) now mounted to the donor bike. The recipient part should be the seat post tube from the Mongoose.

    7) Now bolt the tops of the FWD bottom brackets dropouts to the axle receiver of the donor bike’s front forks. This is where in step 4 we drilled out the 3/8” holes. Use small carriage bolts if possible and keep the inside of the fork as flat as possible.

    8) Add in the front wheel and drive train. Adjust the angle to the desired length/ height. Build out from various 1” & 1-1/8” tubing’s and seat post clamps a steering tube in which to attach a stem and handle bars.

    9) You will notice the dropouts are facing the wrong way. This is dangerous. I would buy a set of BMX flat chain tensioners and attach then to the backside of the rear drop out to hold back the wheel from slipping out the wrong way.

    You will also have to either have brake tab bosses welded on or use a drop out disc brake adapter to mount disc brakes to the front with out welding. Or just use rear brakes only.

    10) The seat, ah, yes the backbone core of the recumbent. Sun bicycles makes a seat back for their Tug-a-bug trailer. It is very similar to the Bike-E mid seat back and attaches to a 1” seat post and standard wedgie seat. The width is certainly wide enough for an adult and I used to use these on my adaptive tricycles. The angle is quite upright but if you put it into a vice you can bend it to a more desirable seat back angle. At $35 retail how can you go wrong?

    http://74.8.32.132/nondealer/product.phtml?p=10961

    Or just use one of these seats;

    http://www.geocities.com/atombikes/seat.html

    All in all, if you can get the mongoose hack and whack bike for $50 used the whole project will cost about $100~$150. Depending on how fancy you want to go. At full retail, the price is not that far off from a real Cruzbike, and you might as well save yourself the headache.

    Just my 2 cents…




    Quote Originally Posted by danielmramos View Post
    Spambait11, that is a great observation about the brompton kit. I hadn't noticed that myself. You know I have seen and read about the monty home built recumbent folder. That guy sure did put some good work into that bike. I think that the steering mode he used is not for the inexperienced. Although, it is certainly a commendable project.

    I understand your reservation about the utilization of tubes for chain management; however, it is most likely the simplest design, and it is certainly the least likely to fail. If one was to choose to use the home made roller blade wheel or chain tensioner method I believe the simplest mounting method would be a few clamps that provided mounting points for such hardware.

    On the note of examples for inspiration, I found this thread that contains some good pictures of what appears to be a folding recumbent bike based on a brompton. It is not an add on kit as the Ness kit is; rather, it is a custom built dedicated recumbent folder that utilizes a brompton like frame. The reason I am referenceing it here is that it contains most of the basic design elements I have discussed in this thread. There are a couple of substantial differences that I want to point out. The Pocket SWB recumbent folder does not have an adjustable seat or a sliding bottom bracket boom mechanism. What this means is that their design would be very frustrating for many people. It does contain the basic shape and idea of what I am proposing. It certainly makes a great visual aid. Also, notice that unlike the Ness kit, the Pocket SWB does not have to have the chain removed in order to fold the bike. I think that is certainly an accomplishment as it makes for quick folding and unfolding. In my opinion any kind of drive train disassembly would remove too much of a convenience factor to keep anybody wanting to use the bike. I mean, who wants to be removing and replaceing a greasy chain or belt when you are trying to fold up your bike to take it up to your office cube on the 3rd floor of your building?

    Packable recumbent - HP Grasshopper?
    http://transportcycling.com/_wsn/page3.html

    About the attachment of the boom. I agree that it will be the most challengeing part fo the project. The boom will actually attach to the frame clamp. The clamp is what will come in contact with the frame and the head tube. If anything fails due to stress failure it will most likely be the frame clamp, so it will have to be a good design. Keep in mind though that it is better to have the frame clamp fail if anything fails at all. The frame clamp will be replaceable, while your bikes frame is not. Another thing I was considering is a thin rubber sheet which would be inserted between the frame and the frame clamp prior to tightening. It would act as a type of gasket. That would keep the frame clamp from scratching the paint of the bikes frame. After all if you ever needed to remove the recumbent conversion kit and go back to an upright configuration you don't want to have a scratched bike.

    What do you think of the pictures of the Pocket SWB folding bike's configuration?

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