Holmes' v3.1 Santa Cruz Bullit- Missouri Moped

Discussion in 'Electric Bicycles' started by johnrobholmes, Nov 2, 2009.

  1. johnrobholmes

    johnrobholmes Member

    Time to start a new project for this bike. Here is the old version using a bafang hub motor and RC motor drivers



    Now I am taking it into a different direction to really make it a Missouri Moped. The dropouts really don't lend to large hubmotors, so I will be doing a divorced driveline.

    Current Parts list:
    Fully built Santa Cruz Bullit
    Recumbence two stage RC drive
    Recumbence disc hub to chainring adapter
    HV 110 ESC
    Magura throttle
    Castle BEC pro
    MPI servo tester

    17x2.5" Shinko dual sport tires (244 "golden boy" I think)
    17x2.5" 32 hole Pro-Wheel rims
    200mm 10ga spokes from Buchanan spoke
    Front qr20 marzocchi hub
    Rear 135mm Surly single speed (thread on freewheel style)

    To do:
    Finish welding up the drive mount
    drill out rear hub for large spokes
    lace up rear wheel
    figure out rear brakes- frame only allows 6" rotor and so far I can't get the caliper to clear sprocket without disc hitting frame or chain hitting tire.
    Get pedals working around drive unit (least important to me on this bike)

    A new rear sprocket adapter may be needed. I have a few ideas that could be done to get it all copacetic.

    Here is the drive mount. It simply bolts onto the swingarm. 1/8" rubber is used between frame and mount for cushion and void filling, as the tubes are not exactly round.


    As you can see here, the smaller motorcycle wheel allows the drive unit to tuck under the swingarm nicely. The ride will be lowered about three inches, so I may use shorter cranks. I plan to have about 15mph pedal power, just fast enough to get me home in emergency but not too hard to pedal with the stupidly meaty tires.


  2. bluegoatwoods

    bluegoatwoods Well-Known Member

    Looks like you've got an interesting plan in the works. Can't help respecting folks who do their own engineering.

    Hope it works out for you.
  3. johnrobholmes

    johnrobholmes Member

    Thanks! The only part that will present an issue is the rear brakes. I can get everything else wrapped up in about 10 more hours of labor I think.

    Mounting batteries will be another issue. I already have the design, just need to finalize the attachment points.
  4. johnrobholmes

    johnrobholmes Member

    Drilled the hub with a #27 or 28 wire size bit for the spokes and laced up the wheel today. I didn't interlace the spokes like a typical bike wheel, so the inbound and outbound spokes don't all touch. It really made it easy, and it is so overbuilt that I don't think it will affect the stiffness much. Spokes ended up poking 1.5mm past the nipple, not bad for an off the cuff guess on what I needed for the hub/rim combo. Pop on the tire and I will have a roller!! After that is mocking up the gearbox and getting a template for the final part of the mount.

    I can't wait to see how the stance is next to a normal 26" mtb build. I have two of this model of bike at my house right now.


    I think the hub looks like a medieval weapon with the motor drive cog and disc on there

  5. johnrobholmes

    johnrobholmes Member

    Got the rear tire popped on, it didn't take as long as the last time since I was smart enough to just stand on it and use my feet for much of the grunt work. Two long spring-steel tire levers that I made did the final bead set.

    The rear canti studs will have to be ground away for some clearance, as the tire is wedged into them. The front canti studs can't be ground much, but luckily I picked up a 2003 Super T Pro and it doesn't have studs on it. The 2003 fork is all black, so it will match nicely too.

    You can see how my bike compares to a Bullit set up "normally". My buddies bike is the same year, with exception that his fork is not the "pro" model and it has 6 inches of travel instead of 7 like my fork.

    I think it looks HOSS like this. I am sure it will handle mint. From 2002 to 2004 I put about 20 hours per week on this bike jumping around and being a younger, less injury prone version of myself. It will be nice to get back on it and beat it up.




    I have a few sets of Profile bmx cranks, so I may use them on this bike. I am thinking about doing a crank lock on it too. I have decided to just keep this bike single speed. I can't lie, I won't pedal a **** bit unless I am starting from a dead stop- much like a normal moped.

    1. Finish the gearbox mount
    2. Think about a rear brake (no action implied)
    3. Cranks that clear the gearbox
    4. Battery subframe
    5. Clearance frame for tire, swap out front fork
    6. Something I am probably forgetting that is very important
  6. safe

    safe Active Member

    You know this setup would work great for the Halbach disc motor idea.

    Where did you get this?

    This is a Recumpence "special" right?

    How do you prevent the freewheel from "unscrewing" itself since these drives / brakes work in opposition to each other?

    The hubs left drive side must use left handed threads.... (if it's favoring the drive) or it uses right handed threads... (if it's favoring the brakes)

    Or is this a case of "tighten it up really hard and pray"?
    Last edited: Nov 4, 2009
  7. johnrobholmes

    johnrobholmes Member

    Recumpence did provide the chainring adapter. It sits on the ISO disc side (bolted into the hub shell), and the driven (pedal) freewheel is on the normal rhs. The driving freewheel is flipped on the left, so it still tightens.

    I have a few chainring adapters that I have designed, but this one will do the trick for now.
  8. safe

    safe Active Member

    Oh I get it... the drive side is threaded and the brake side is bolted.

    So in effect it's just an aluminum spacer that brings the drive sprocket closer to the spokes. (so the adaptor actually sinks the drive sprocket inwards of the level of the brake disc)

    That's actually a good idea... for the Halbach too... will think about it some more... :thinking:
    Last edited: Nov 4, 2009
  9. AussieJester

    AussieJester Member

    Just dawned upon me John, your in same state as your pal Safe !!(condolences BTW) :p When your bikes finished whack some motorcycle slicks on it SuperMotard stylin' (fastest way around a go kart track on a motorcycle FYI Safe.).....and hook up for a lap of his "race track" and show him how its done mate hehe

  10. johnrobholmes

    johnrobholmes Member

    Yep, I haven't ventured over to see him yet. Every time I go around KC it is to visit one of my manufacturers.

    I hit a little snag in the build. With the tire I want to use, there is not quite enough wiggle room to mount the folded drive behind the BB. One rock would be havok in the system. With the drive unfolded it is much too low, so that isn't a good option.

    I have a few options.

    1. Lace up a 16" or 15" motorcycle rim for the rear to give a bit of breathing room
    2. Fab up a new rear triangle and mount the Recumpence drive inside
    3. Get a 3120 6t astro so I can use a single stage drive instead of two.
    4. Think hard about more options

    1 would be fastest and cheapest but I really don't want to change up tire sizes and mess with the geometry.

    Two would take the most time and planning, but really be the best solution in the long term. Time is not on my side right now. Additionally I would need to make a jig.

    Three is the easiest and most expensive (of course).

    I need help on number four.

    So I am stuck here. I need to get past this block to continue, and I would really like to start riding this bike soon so I can chop up my current DD.