Holmes' v3.1 Santa Cruz Bullit

[johnrobholmes]

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

http://endless-sphere.com/forums/viewtopic.php?f=6&t=6494

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.

 

[deecanio]

Hi John,

looking good, i like the bullit frame and thought about trying an orange patriot for the same mounting area, thats dual reducion to what? left side direct drive instead of disk? and are you mounting to the swigarm direct with the bracket? then motor to the bracket?

cheers,

D

 

[johnrobholmes]

Yes, left side drive. Total of three stages of reduction. More than I want, but it is just right for the 3210 6t motor.


I am attaching to the swingarm, and not the frame. Bracket holds to swingarm, and also holds the drive unit. I will take some pics once I get the mount a bit closer.

 

[deecanio]

i see, freewheel at the output shaft? does that mean you'll use bicycle chain and sprockt for the drive?
won't the motor be prone to shock mounted there?

D

 

[johnrobholmes]

Yep, bike chain and a freewheel on the output of the drive unit. The motor will be suspended pretty close to the pivot point actually, so it isn't totally non-suspended weight. The motor won't see any more vibration or shock load as compared to a typical RC drive setup. Maybe a bit less because of the rubber mount and suspension. The only drive shock will be when the motor spools up to meet bike speed or when the wheel hits bumps. There will be no issues regarding chain length and suspension actuation with my mount location.


I may even go hog wild and make a cast silicon bushing around the frame. I have a gallon of silicon mold here, might as well use it.

 

[johnrobholmes]

Got a few more minutes of welding today, between classes. Just another hour or two on the mount and it will be done.

I may put the rear brake on the drive freewheel. That would be pretty trick. The only problem would be boiling off the freewheel grease under heavy use.

 

[Thud]

John,
I am loving the 17 "wheel build. Did you get spokes made to fit? Or did the sizes line up with off the shelf stock. 12 gage or better?(from the photo)Can't wait to see it finished.
T

 

[johnrobholmes]

The first post outlines the parts, about mid post has the wheels. 10ga, 200mm spokes cut at Buchanan.


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

 

[Grinhill]

Nice work john.

Does that last photo mean you have sorted out the clearance issue with the rear disc caliper?

So the disc is offset from its usual position by how much? About an inch?

Do you have an estimate of top speed at this stage? (looks like it will be geared fairly low).

 

[johnrobholmes]

Nice work john.

Does that last photo mean you have sorted out the clearance issue with the rear disc caliper?

So the disc is offset from its usual position by how much? About an inch?

Do you have an estimate of top speed at this stage? (looks like it will be geared fairly low).

rear brakes are not solved yet. I may mount a disc on the freewheel body (E drive freeewheel) and do something funny if I have room. I rarely use the rear, I will just need it for snow riding and adjusting speed/ attitude during cornering anyway.

Disc is offset by just a few MM. enough to bump the frame, but only the thickness of the sprocket adapter.

Top speed I am going for- around 35 to 40mph last I did the math. I have room for a lot more reduction, which is nice for offroad or icey situations. I fully plan to use this bike for riding to class in snowy weather. Big Fenders!!

 

[recumpence]

Looks good so far.

Matt

 

[deecanio]

wow, that wheel looks bomb proof!!!
you shouldn't have too many issues with shortening the crank, i took 40mm or so off a set and had them drilled and tapped 9/16" and they worked fine, it was actually quite nice with a shorter stroke
is it possible to swap the sprocket and the disk and go to a 200mm rotor to solve the caliper clearence issue?
Also what type of hub is that surly?

D

 

[Thud]

I see it now John but really, those wheels are the shiz.

 

[johnrobholmes]

Surly hub, yes.

A larger rotor won't fit, as the bike barely fits 6" rotors. Back in 2002 you couldn't buy anything bigger than 160mm, but of course the next model year allowed for 8" :lol: . I need the sprocket spaced away from the frame as anything larger than 36t would hit the swingarm, and then the chain has to be considered too. Otherwise, a bigger disc would be the perfect solution- maybe on another build. Very minor detail for me really, I have ridden multiple other bikes with no rear brake. The only one I really NEED it on is my trials bike anyway.


Thanks for the comments fellas. I don't have a lot of "work" for the day so I should be able to get a few more hours of work on it.

 

[johnrobholmes]

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. You can notice that my top tube and steering angle is just a bit slacker because of this.



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 damn bit unless I am starting from a dead stop- much like a normal moped.

Todo
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

 

[johnrobholmes]

Just realized that my buddies bike has a flat front tire and is sitting off the rug. Disregard the comments about head tube angles and such, although my bike does handle a bit slacker than his.

 

[johnrobholmes]

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.

 

[mud2005]

3. Get a 3120 6t astro so I can use a single stage drive instead of two.

did you mean a 3220 6t or did I miss something?

 

[johnrobholmes]

yeah, typo.

 

[johnrobholmes]

I did some lengthy talks with a local machine shop. I think he convinced me to remake the rear out of chromoly. Found some semi-local heat treaters too, so If I want to work in aluminum I can do.


But with a new rear end I can use that fatty 3.0 tire and a huge disc brake.....



Off to take measurements for the jig. Bearing pockets are going to be my only real concern. The rest is relatively easy.

 

[johnrobholmes]

Jig measurements are done. Now I need to figure out exactly what I will tweak for the build. Since the drive will fit between a wider swingarm I will build the interior width at 135mm- the spacing of the rear dropouts. This will necessitate a wide spindle on the crank arms most likely, unless I do some creative bending and welding.


I could lengthen the rear a bit if I wished.
I can integrate the gearbox jackshafts into the swingarm, or just fully enclose Matt's drive unit. I would like a removable drive unit for servicing.
I can add a ton of mount points for who knows what.

Any good extra ideas for what to integrate here?

 

[liveforphysics]

I did some lengthy talks with a local machine shop. I think he convinced me to remake the rear out of chromoly. Found some semi-local heat treaters too, so If I want to work in aluminum I can do.


But with a new rear end I can use that fatty 3.0 tire and a huge disc brake.....



Off to take measurements for the jig. Bearing pockets are going to be my only real concern. The rest is relatively easy.

Chromoly is a fantastic material. You might be a pound heavier, but you will have something you can trust, and easily adapt by welding whenever and wherever needed.

 

[AussieJester]

+1 for chromoly over ali..also if you have the chance i would definitely consider adding a lil extra length, seeing your making a jig if you have the $$$ possibly knock up two rear ends, one stock length one lil extra length, 12 inches or so shouldn't look silly and might give you some extra stability ...would be worth moving the seating position back also, bent seat post would do the trick... best of luck anywayz once you have a jig knocked up its plane sailing IMO ...

KiM

 

[Timma2500]

Great build, I too am a fan of the S.C. Bullits. Now i know you said you wanted to run single speed but I wonder if a mtb cassette could be beneficial in your application...

Take an 11t- 34t or the new Shimano 12t - 36t mtb cassettes, use the motor chain on the 34t or 36t gear with a 16t Eno fw on Matt's drive output giving you 2.125:1 or with the 36t - 2.25:1 final stage motor reduction.

Retain your derailleur and pedal using 3rd (if clearance permits from motor chain to derailleur) or from 4th to 9th gear with your normal chain, with a 24t or 26t granny gear on your cranks. This would make pedaling easier with your chunky motorcycle tyres when/if needed.

Dunno if the motor chain would clear your tyre in 1st gear though, even using 2nd gear (30t) would still give 1.875:1 reduction with a 16t Eno fw. Just thinking outside the square

Chromoly is a very nice material and would be easy for yourself to weld mounts and brackets to. Although don't forget modern enduro, high powered roadbikes and racebikes use aluminium for their swingarms with geat results :wink: or then again I could just be biased lol...

If using the bike properly offroad, i myself wouldn't play with the wheelbase too much so as not to upset the known good handling. Ya could extend the swingarm by an inch or so to give extra reduction unit clearance.


Paul

 

[johnrobholmes]

I have petered out on this for a few days. School is just kicking my ass, multiple papers and presentations in every class, every week, until the semester is over. I really want to get this guy going so I can start hacking up my 4 stroke bike.

No new progress on the jig building. Still haven't decided on what size of materials I will build from. Probably just large box steel or something. Getting it all square will be my challenge.


I'm just being real when I set it up for single speed. I won't be pedaling this guy except at super low speeds around stop signs and traffic lights. Probably use the pedals for track stands more than anything else.



I am thinking that too long on the WB will be bad. The pivot point is in front of the BB, so if I added a foot the swingarm would be a full 2/3 of the WB length :lol: That may be a bit funny handling.