BBSHD DIY Build Report: Motobecane

Editor note: On our new forum there is an entire section for members to document their BBSHD builds and show what bike they started with what parts they bought and how they assembled them into a working electric bike. Here is a build report taken direct from user “JP LABS” on the electricbike.com forum. Its great build reports such as this that will pave the way to new builders on how to build an awesome bike for not much cash. Come join our forum here.

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.

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

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 PAS mode 1 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. The 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 BBSHD 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.

Here’s how that battery pack fits the frame. Note that this is a 14S/7P pack, so their smallest 20-Ah triangle pack, I believe:

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.
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/…?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:

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:

EDITOR NOTE: Luna Cycles provides spacer kits with every BBSHD Kit now so custom fabrication like this is not needed.

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:
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.

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:
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.

The mighty mini 30T. There is room for a bigger chainwheel to clear the frame, without making the chainline worse. I know there are a couple of 42T chainrings 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

Pretty straight chain line in mid gear.

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Speed Sensor Mounting, pic #1

Speed Sensor Mounting, pic #2

Speed Sensor Mounting pic, #3

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. Spare tube=frame padding! 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:

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
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.

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Parts List:

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/

Here’s my parts list with prices:
Total Spent $3307.