120mm BBSHD build: Motobecane Sturgis Bullet & 20 Ah Triangle Pack

[JPLabs]

NOTICE: Photobucket ruined this thread; the images no longer work. I refuse to pay their extortion to restore my hard work. However, I have an archived copy of an early version, with photos, stored at the below link. Feel free to download it and reference it for your own builds.

https://drive.google.com/open?id=0B-...mtzYlBOTmVLZWs


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This is my first build, an e-Fatbike. I installed a BBSHD and 20 AH Panasonic PF Triangle Pack, both from Luna Cycles, onto a Motobecane Sturgis Bullet. I'll try to provide enough details and photos to make the process clear.




Below, note left thumb throttle replaced the front shifter. That is not a sleek looking looking or comfortable throttle lever, but it isn't horrible, either. I'd like to eventually replace it with the old shifter lever:


This is not the first such BBSD/Sturgis build - MountainTime posted a very similar build at Endless Sphere a couple of weeks ago. I owe him thanks for his advice and help with dimensions, such as confirming that a medium frame could fit my triangle pack, and that a 100 mm BBSHD would not quite fit this frame without shimming and an offset left pedal.

This bike is a blast to ride. I put a 30T Mighty Mini sprocket on it from the start. I only have 5 miles on it, at sunset tonight, after finishing up the build. I was in PAS1 most of the time - it is the highest PAS setting I can keep up with, pedaling for real to help. I was not disappointed by how quiet and powerful this drive is, and I'm nowhere maxing it out yet. Tire knobs drown out the drive noise, which itself is very smooth and pleasant sounding. Sweet!

Frame size is 17.5", Medium. I'm 6'1, but I wanted my 5'4" daughter and wife to be able to ride it once in a while. It fits me fine, and they can stand over the frame. Barely. I cut one inch off the seat tube so it can go low enough for them. I set it to the full recommended extension, and it fits me well. Inseam 36".

I chose that model bike in particular because it comes with a ($600+) Bluto fork and has a relatively open frame triangle for battery clearance. It also comes with nice components such as Mulefut tubless-ready clincher wheels and Snowshoe tires.

I chose the 120 mm BBSD kit. I wanted the crank arms centered on the frame. The right side pedal clearance is set by the motor, and nearly all the shimming was on the left side, so a 100 or 110 mm kit would have resulted in the same pedal spacing anyway, if I added a offset LH crank arm to get the pedal spacing symmetrical. You need to cut off about 5mm from the front derailer mount on the frame to center the install (motor just touching rear triangle) and that gave me the best chainline. That 120mm kit fit very nicely, with only shimming, once the frame was slightly modified. More on that, below...

Here's the crank to frame gap I wound up with. I wouldn't mind finding some inwards offset crank arms to reduce that gap, (EDIT: I just realized that's a horrible idea, as crank arms like that would hit my ankles!). It didn't feel bad to pedal.

[JPLabs]

Here's how that battery pack fits the frame. Note that this is a 14S7P pack, so their smallest 20 Ah triangle pack, I believe:




EDIT: Medium Size Sturgis Bullet frame inside measurements are 11" x 18" x 22.5". There is a slight kink in the seat tube, and there are bosses, so usable package space is slightly less.

[EMPowered]

Nice job on your customization for motor fitment! Well done. I just wanted to comment for others considering the same build to get the 100mm BBSHD kit with an offset left crank arm. It will fit perfectly and have centered pedals when complete. Installation will be much easier and require no custom machining of spacers. I install these regularly and know how hard it can be to tell which size motor to got with. Its would be awesome if we could dry fit first before ordering, but that's not feasible for an online order. A simple measurement to make that reveals if the BBSHD motors will fit without BB spacers is to measure flush against your shell face on the drive side back toward the frame chain stay. You need about 2 3/4 inches for the motor to clear without hitting up against the frame chain stay. The Bottom bracket on this particular bike is 100mm. The motor does not seat all the way against shell, it does the frame chain stay and needs a few mm of spacer to fit flush against the shell facing, and clear the motor from touching the chain stay. I know of one person who actually bent the motor casing and dented the frame while tightening the M33 nuts, unaware of this important issue. Any way, if the gap was very large like 10mm, you should use the 120mm size BBSHD motor, in this case the 100mm motor would fit better and be much easier for the next builder without the customization skills and tools of these installers (fine job guys!). Bafang makes two crank arms, an offset AC-08 and a standard AC08-2. For this 120mm build I would recommend the standard crank (to compensate back for the extra spacers). For a 100mm motor the offset crank will get pedal spacing centered and avoid the left pedal from hitting the non drive side chain stay. Here is a pic showing a simple measurement you can do to help you determine if the motor will hit requiring spacers and potentially a longer spindle drive unit. If you have 2 3/4 inch clearance with this simple measurement, get the motor that matches your shell width. To determine how much spacing you will need to fill, simply move out your ruler and measure how far out the ruler moved away from the shell face to get 2 3/4 clearance, 1mm, 2.5mm etc...
Hope this helps!
Matt

https://drive.google.com/open?id=0BwlG_xMyE4xFYjJ3LUNOaGZtTHc

[JPLabs]

OK, on to the actual build.

First of all, removing the stock crank arms was not easy! I bought a puller tool that would thread into the arm, but the crank is hollow, so there was nothing to push on with the puller's center bolt. I wound up heating the right crank arm to maybe 200F, and then pounding on a steel rod inserted through the crank from the left, hitting the puller tool hard enough to drive the right arm off. LBS said it should be 'self extracting, no tool required. Well, I don't agree. My stock bearings would probably click if I tried to use them again. Not recommended, but I didn't want to wait a day for the shop to do it.

This tool fits the outer nuts on the stock crankset, but only after cutting off the 'rear cassette removal' half of the tool. With that 2nd tool still attached, it didn't fit over the splines on the crank. Not hard to cut with a bandsaw, but I'd advise buying the same socket style WITHOUT the bonus tool on the back of it:

https://smile.amazon.com/gp/product/B005X76YZK/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

For the inner nut, I used a Fox spring perch wrench from a snowmobile/dirtbike sized shock. I needed a 12" total length handle to get that one off. Not bad.

Here's what the stock bottom bracket looks like with the RH crank removed:


And, the bottom bracket, empty:

[JPLabs]

OK, on to fitting the drive unit.

Here's how it lined up before trimming the front derailer mounting bosses. As mentioned above, with this frame, you need to trim the bosses. I cut the long boss off flush with the short one, and then chamfered the short one, in order to get the required clearance so I could set the gap between the motor and frame to 'just touching':


Once the frame was trimmed, I needed a small (0.1") spacer on the RH (drive) side, so that the motor wouldn't be side loaded into the frame. I found a piece of aluminum scrap the right size. If you need to come up with your own, take the Bafang crank nut with you as a gauge. You don't need 'exactly' the right size:

[JPLabs]

On to the Left side...a longer spacer is needed here. 0.8". Same diameter as RH side.





Here's the shape of the bottom bracket and frame interface, from below, for reference:

[JPLabs]

The downtube on the Sturgis is flattened on the bottom, and the back of the bolt boss on the BBSHD hits the downtube, leading to a rather low mounting position, with the BBSHD rotated further down than I liked. So I ground away some of that boss to gain more ground clearance. I did not hit threads or motor interior - this was extra metal, not apparently needed. I went very slowly, in case I broke through, knowing a dab of metal epoxy could repair a small hole well enough, but not a big one:



The square space you see below is not a through hole, just an exterior feature:




I put a piece of innertube between this boss and the frame, then allowed the whole motor to rotate while I tightened the bottom bracket nuts. So, it is pretty tightly held to the frame. I used adhesive to attach the rubber pad to the motor, so that if the motor ever comes loose, it won't damage the frame when it swings back up under torque.

Note LH spacer is painted black now. Also, the M6 spacers that go between the motor mount plate and the motor needed to be shortened, and I required shorter M6 bolts to match. I used stainless bolts, the longest size that would thread in fully, for maximum strength. Thread engagement is same as stock, not compromised. I think this is important, it's worth selecting the right length fasteners, when putting high loads into thin cast aluminum!

The outer bottom bracket nut is not installed in the below picture, so you see exposed threads. These are not visible with that nut installed.

Finally, notice the little dents around the crank hole on that motor bracket? On the other side are bumps which help keep the bracket from rotating. Make sure you put the bumps towards the bike frame when you put the bracket on:


Final motor position. It looks so tiny on this big bike:

[JPLabs]

Update: I'm building a second, nearly identical bike now for my wife. The newer BBS-HD from Luna, delivered a week ago, is redesigned slightly in this area. It is the Shift Sensor version.

The above modification was NOT necessary to achieve optimal ground clearance. The threaded bosses which retain the mounting bracket screws have been shortened by design, and the material which I removed is not present on the newer unit.

This was a pleasant surprise! Great little example of continuous improvement.

[JPLabs]

So, how's the chainline? Not bad! Centered, at least. But there is a fairly big zigzag at the extremes. Tire clearance is real good to the chain. I have not had any trouble with shifting, after re-adjusting the shifter cable length. I have not applied full power in top gear at high speed yet, though, either. I have floored it in low gear, no issue.

There is room for a bigger chainwheel to clear the frame, without making the chainline worse. I know there are a couple of 42T out there, like the Luna Eclipse. But they move the chain inboard. Perhaps too much, as this lines up pretty well in #5&6 gears (10 speeds). I think I'd like to try to put a 36T on there for slightly higher gearing. But I can't find an adapter to fit the BBSHD for standard chainrings:



First gear:




6th gear. 6th is a little better than 5th. Pretty straight:

[Christian Livingstone]

Gee, that chainline looks good.

And does the chain completely clear the Bafang housing without any chaffing as the chain is shifted to the lower/taller sprockets on the rear cassette? I mean, a little initial chaffing would probably resolve itself if it was too serious.

It looks like it probably does, as the chain height must rise a bit along that housing point.

So, I guess I'm noticing that that "Mini" front sprocket from Luna is pretty strategic in its number of teeth.

Or, was that spacer/shim that you added at the bottom bracket important in this area?

I mean, the Cyclone mid-drive I'm doing doesn't have these issues, as the chain will be fixed inline to a IGH. But the crank arms that come with the Cyclone kit are offset, which is helpful for the motor side, even though I may have to scooch the motor mount up a bit where the offset in the crank arm becomes more pronounced.

I'm rambling a bit, or maybe using your thread as a sounding board for my own mid-drive issue.

Anyway, nice finished product!

[JPLabs]

Speed Sensor Mounting:

[Samwize]

Hi. I can't seem to find anything about what distance the sensor should be set at on a 26 inch fat bike wheel ? Does it matter ? Thanks for your help.

[JPLabs]

Radial distance (how far out from axle) does not matter, nor wheel size, for mounting. Only sensor-to-magnet distance matters. Make that 1/8-1/4" or so.

[JPLabs]

Bag and battery packaging, and wiring. This Luna Cycles triangle bag is a little big for the frame, but squashed to fit nicely. I was going to add foam around the perimeter, but realized I wanted to carry a spare tube, too. Tube=frame padding!:cool: Once I get a rear rack and bag, I'll put the pump there, and add some foam between the pack and the inner tube, as well.

This is a well made bag. Tough, good shape, straight seams, and a water seal on the zipper.

Be sure to remove the bolts from the water bottle bosses on the seat tube and down tube, or they will create concentrated impact points against the inner tube and pack. Or use thicker, firm padding. I would NOT recommend just using the battery bag without extra padding, while also leaving the bolts in the frame. I think the pack could be damaged. The bag does have some padding, but why make it's job harder than you need to?


Bike pump will fit above, snugging everything up nicely. Firm fit, not crushing. Luna Wattmeter fits alongside with no problem:


This is an XT60 splitter I made for connecting the Luna 15W headlight and taillight to the charge port of the pack. I added a 1A fuse, in case of wire damage. I used a 1 1/4" (30mm) ACG fuse and holder. These are only rated for 32V, but I test blew one and it popped nicely, with no arcing. So I think that will work fine.




Rear wiring entrance. The power leads from the motor reached the wire port ok. It would be nice to have a wire entry at the bottom of the pack for the controller harness. It was not long enough to go through the upper wire port while also leaving enough slack to not be damaged if the handlebars got reversed, so I ran it into the zipper gap.

I will probably add a wire entry port at the very bottom of the pack to allow hiding the motor wiring entirely inside the bag, but I'm not sure how to do that without compromising the strength of the bag:

EDIT: Bottom-entry wire port has been added, shown later in thread.



Front wiring entry to pack works well with the provided wire port. There is even a spare frame boss for a zip tie in exactly the right place:


Front view of wiring:


Controls:


Taillight

[JPLabs]

OK, that's about it. Quite a marathon post. I'd be happy to answer any questions. I converted these wheels & tires to tubeless. I can show that process if anybody is interested. I used the Mulfut tape intended for these wheels, and Stan's sealant. It's pretty easy to do, and not hard to find the info elsewhere.

Only one thing surprised me about the BBSHD design. When pedaling with the motor off, the pedals seem to spin the gears inside the drive unit, which adds a noticeable amount of drag. It does not spin the motor, just the gears. I expected the pedals to be able to turn without spinning any of the internal drive parts, more like a regular bottom bracket. I'm not certain it is supposed to work that way, but I suspect it is by design. I haven't seen anybody else mention it, though. I didn't disassemble the motor to confirm this 100%, but I can feel the drag, and it feels like gears meshing, that kind of vibration. If it's not the gears, then the clutch is rather draggy. It's not enough to be a problem when pedaling only, probably not noticeable; I just found it interesting.

Turning the rear wheel backwards DOES spin the motor, with significantly more drag, but I don't plan on riding backwards very much, so no big deal there. But it let me confirm I wasn't feeling motor drag with the pedals.

[JPLabs]

I really love this combination of bike, drive, battery, triangle bag, and lights. Here are links to the actual components and sources I used, except for the XC60 connectors for which I provided a better option in the link:

Donor Bike: http://www.bikesdirect.com/products/...et-mulefut.htm

Motor Kit: http://lunacycle.com/motors/mid-driv...-kit-in-stock/

Mighty Mini 30T chainring: http://lunacycle.com/inventory-contr...n-ring-silver/

Battery: http://lunacycle.com/batteries/packs...650-21ah-pack/

Charger: http://lunacycle.com/batteries/charg...ebike-charger/

Headlight: http://lunacycle.com/black-friday/lu...t-extra-power/

Tail light: http://lunacycle.com/black-friday/rear-light/

Watt Meter: http://lunacycle.com/batteries/guage...le-watt-meter/

Brake Sensor for hydraulic lever: http://www.empoweredcycles.com/colle...r-brake-switch

XT90-S connectors for BBSD Power Leads: http://lunacycle.com/batteries/conne...connector-set/

XT60 connectors for lights - these are better than what I bought and used but I hadn't seen them at the time: http://lunacycle.com/batteries/conne...nector-5-sets/

[JPLabs]

Here's my parts list with prices:

[spinningmagnets]

Awesome post! Thanks for documenting all the details.

[JPLabs]

Sure, happy to. I got a ton of info here, glad to give some back.

[Ravi Kempaiah]

Sure, happy to. I got a ton of info here, glad to give some back.

Really cool build! and excellent documentation.
Front light wiring is easy without soldering anything?

[Louis]

My very best advice for any builder. Learn to solder. Get some practice materials, stream some video instructions. Don't be hobbled by the lack of a technique you will ultimately need. I just gifted a $15 kit on Amazon. More than adequate. Never skip a mod or project again. Needs solder..no big deal. You can too!