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Wednesday, January 20, 2010

Xtracycle-style Sierra?

I don't know if it's possible to do this with an actual Xtracycle due to it's frame construction, but I am pondering an Xtracycle-like addon (that will do this) to that Schwinn Sierra I fixed up recently, perhaps with a motor assist, perhaps not.

Specifically so that I am not dealing with a longer shiftline and the problems reported with it where shifting can be finicky in one gear or another, I intend to put a regular rear hub with the derailer still on the Schwinn's dropouts, so the original chainline stays as it is, as does the shifter cable. Then there will be a separate sprocket from that hub to the rear wheel, which will be re-laced to a no-dish single-speed wheel to make it stronger for cargo use. (actually I will probably just take a front wheel with a sprocket bolted to it, for simplicity of testing out the idea).

I will probably build the addon frame around an existing rear triangle off of some other bike. I am tempted to use the one off the white Huffy, simply because it is called a "Nevada", which would make this bike a "Sierra-Nevada". ;-)

But that is a silly reason to pick a frame, so I will more likely start with one of the old chromoly tenspeeds I have, whose frames are way too tall for me to use for myself normally. I'd remove the entire rear triangle from the donor frame, but not including it's BB. I would cut down the seatpost from the bottom end, leaving that extra on the BB itself. Then reweld the seatpost and chainstays to a new crosstube from something else. This would all be welded to a subframe that can then bolt to the Schwinn Sierra's rear frame and keep the whole rear end stiff. It would mount in such a way as to leave a clear chain path between the Sierra's rear dropouts and the new rear wheel position, and would be able to slide back and forth for chain tension adjustment and lock in place to hold it once set.

I would like to make some bottom/side rails that let me rest cargo on them (like some Xtracycles do) that are removable, so I do not have to carry them for typical rides, but instead only when I will carry more than normal stuff with me.

Then a top deck to cover the entire space from over the rear wheel to the back of the seat.

I am also considering a more recumbent seat design that would fit down into the gap that could exist between the tire of the new rear triangle and the Sierra's seatpost/seatstays. Then I would move the steering handlebars back to fit in a bushing in the seatpost, and a linkage for remote steering to a stub-bar up in the original stem. This is a very similar arrangement to Justin's (of cross-Canada bike, and inspired by it.

The problem with such a design is that it reduces the cargo I could carry on it, so I would (as Justin did) likely leave the option of pulling off the remote steering and inserting the original seat and post, and riding it just like that. The 'bent seat would stay, as it would make a nice carrier for some cargo. Well, unless the cargo was too large and needed to fit across the full length of the area behind the seatpost.

Just some thoughts for another possible cargo bike, most likely quite short range in nature.


  1. I've been thinking about a combination like this one

    Are you talking about something like that?

  2. A lot like that--that silver part is an Xtracycle addon to what looks to have once been a delta trike.

    The major difference would be that my addon frame would leave the dropouts themselves clear, so i can leave a rear hub and cassette and derailer there to do the shifting on, eliminating the problems with the longer shiftable chainline. Just a straight chain would run to the back.

    On that Xtracycle, it also has the removable bottom frame parts (not shown in the pic) to support cargo or panniers. It doesn't look like it has the rear rack, though, just the tubing frame for it.

    Their store page has a lot of accessories and modular bits to build up different types of back ends for different bikes or purposes. If I had that kind of money, I wouldn't mind buying from them if they made what I have in mind. :)

    There are a whole bunch of variations on the theme.

    For an assist, if I put one on it, I will probably end up creating something along the lines of the StokeMonkey but with one of my wheelchair motors, or perhaps that treadmill motor, all enclosed within the original rear triangle.

  3. What's going one with the latest project? You have been pretty quiet secret this time?


  4. No, just been sick, had some injuries (non bike related), and really really tired. So what little I have worked on has only been posted on Endless Sphere, because I keep forgetting to put it up here until I am too tired to actually do it, and then I forget again.

    I'll be back-posting a bunch of stuff as soon as I have the time, hopefully this week (but I told myself that last week, too).

  5. Hello, I am very interested in electric bike conversions especially battery technology. I built / converted a bike and am using SLA but it is too heavy. Any recommendations on other technologies?

    Here is my electric bike project:

    Some other bamboo frame bike ideas that would be neat if electric:


    Otto Belden

  6. Depending on a number of factors, there are several possible battery chemistries you could use.

    --What kind of range and speed are you after?
    --How much current does your motor require at absolute maximum, and how much to keep you cruising at your typical riding speed?
    --What kind of budget do you have?
    --Are you willing to buy or build a new charger?
    --Do you mind having to use a BMS module of some type to at least keep track of lowest voltage on the battery pack while in use, and highest voltage when charging, with a safety cutoff to prevent cell damage?
    --What size and/or weight and/or shape limitations do you have for the pack?
    --Are you willing to build a battery pack from individual cells, or do you want to just buy one pre-packaged that you can mount on the bike and just go?

    I'll give you some recommendations, but I'll have to take a look at your project first, which won't happen until at least tommorrow night given other things I need to do before then.

    In the meantime, you might want to look over at where I have been hanging out lately (part of why I have not added to the blog since this post; I got busy and also am a bit lazy/procrastinative, and kept meaning to duplicate my posts between there and here but have not gotten to doing that. Now there are a lot of them and it is something of a chore to do. I will still do it eventually, though.

    Anyway, go over to ES as linked above, and take a look while I read up on your project to be able to give suggestions.

    Alternately, you could post your project as a new thread over there on ES, and you'll probably get quite a few people helping you with info (some of whom know a lot more than me).

    I recommend making a list of answers to those questions I posed above, as you will need that info to decide on a replacement pack.

    I've used both PbA (lead-acid) and NiMH successfully so far; the PbA has far higher instantaneous current-delivery capacity, and is more tolerant of abuse in charge or discharge than NiMH, but is significantly heavier, and has a much worse Peukert effect.

    NiMH is lighter than PbA, and will with care last longer (more cycles). More expensive, requires a NiMH-specific charger, etc. Nice an energy-dense compared to lead.

    LiCo (one of the more flammable LiPo chemistries out there, in it's older incarnations at least), is probably the highest energy density of all chemistries I know of. I've got a bunch fo loose cells I'm working on building a set of packs with, very slowly.

    LiFePO4 is the "safest" of the lithium chemistries, and I will have some of those to use by next month at the latest.

    LiPo, like RC hobby airplane, helicopter, boat, and cars use, is these days very safe, very cheap (for lithium), very light, and very energy dense. I don't have any of these yet.

  7. Do you know of a motor that will produce only 1hp at 12 volts? I want to use 12volts DC to slow down the RPMs enough to need only a sigle stage reduction.

  8. That's gonna be a big motor, to have 1HP at low RPM. Even though you're not talking about a hubmotor, the nearest size comparison is pretty much like the 9C hubmotors, perhaps down to the 400-series Crystalytes.

    I don't know any specific motors really, I just use what I run across and figure out what it is capable of, and build my drivetrain stuff around that. :-)

    To get 1HP (750W) at only 12V, it will take 62.5A, which is going to require a very hefty battery pack to be able to supply that kind of current without killing the battery, and rather thick wires and hefty connectors and switches.

    I'd strongly recommend going to *at least* 24V, which will cut the current requirement in half, but 48V would quarter it, making it reasonable even for lead-acid to get a decent range with 17-20Ah SLA, for instance. Using NiCD, NiMH or Lithium of some flavor would be even better and lighter.

    I note on your linked blog post that you say "48 volt motors are not more efficient than than using lower voltage, except in the thickness of the wire from the battery, because the higher voltage draws less current.", which in it's strictest sense is true, but given the reality of batteries is actually not quite true: If you draw high currents from batteries at a lower voltage to get the same watts out of the batteries, they will last less time than if you draw low currents at higher voltage, for the same watts out of the same kind of batteries. It is especially noticeable with lead-acid, but even with other chemistries it makes a difference of varying degrees.

    All that said, if you really want to use 12V to run the motor, you will probably want to find one meant for 12V or less operation, which is not all that easy, for powerful motors. Most 1HP and up motors are wound to run at 24V or higher. Some of the 12V motors out of cars and trucks I have seen and used could take shortterm bursts of 1Hp, but if you tried to run them at that constantly they'd meltdown.

    The very best of all that I ever found in automotive stuff was a pair of 12V radiator fan motors, axial-flux brushed 4-pole pancake style. Even so, in order to drive a bike (via my Friction Drive 2.0.2), I had to go to 36V to get any real power out of them.

    Of the 24V motors, powerchair motors with built-in gearboxes work pretty well. My CrazyBike2 ran on one until I got tired of it's power (at 36V) destroying chains and sprockets when the chain derailed.

    Lee Bell (one of the commenters above) has also used them, at his Packrat Workshop.


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