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Surly Instigator: Steel frame HT + Bafang BBS02 Mid-drive

COAR

100 W
Joined
Feb 11, 2021
Messages
171
Location
Colorado
Recently finished (or mostly finished at least) my e-bike build, so I figured I'd make a quick thread. The bike is a 17" Surly Instigator 2.0 with 26" x 3" tires. Component spec is decent - Fox fork up front, Shimano SLX hydraulic brakes, and a 11-42 10 spd cassette with a Saint derailleur and shifter.

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I went with the 500c display (primarily due to the compactness and all-in-one unit) and the left thumb throttle. When ordering I forgot about my dropper post control on the left side so the result is a bit crowded. Neither the dropper control or throttle are in a a great position but I can’t make one better without making the other worse.

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The install was fairly straightforward. The only modification I had to make to the frame was cutting off one of the ISCG chain guide tabs. I never used a chain guide anyway so this is no real loss. The steel on the bike is not hardened so a hack saw and file made quick work of it. Added a dab of touch up paint to prevent any rust.

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Based on my reading, I chose to clean out the factory grease and pack it with Lucas Red n Tacky. Much easier to do this with the motor out before mounting the chainring and crank.

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I'm using a 30T chainring on the BBS02. This keeps the gearing the same as it was before the conversion and my top speed is still around ~27mph. I never even mounted the 44T that was included. I think a 32-34T would be ideal but a ~10% gearing change is not a huge difference. The offset of the BBS02 means there’s a very angled chainline If I try to grab the lowest 2-3 gears. Those aren’t really needed with the motor though.

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The battery I'm using is a 52v 8ah pack of Samsung 40T cells I picked up from an eBay seller. It fits nicely into a cheap ($9) frame pack from Amazon.

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I may have been better off just going with a shark pack, but I had made a cardboard mockup of the dimensions of a ~14ah pack and really did not like the form factor. I also find the frame pack a bit more discreet (need to hide the wiring better), in the event you find yourself on a trail where e-bikes are not expressly permitted.

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I tried the standard speed sensor setup with the spoke magnet and included mount but couldn't find enough clearance on my chainstay. Fortunately I saw Karl G's blog post on the speed sensor and the magnet-on-wheel seemed a much cleaner way to attach it. So I cut off the old mount, molded JB Weld SteelStick halfway around the chainstay, attached the speed sensor with 5min epoxy, then secured everything down with zip ties. A neodymium magnet was attached to the rim with JB Kwik Weld.

Previously I had just Gorilla-taped and zip tied the speed sensor to the bottom of the chainstay and added ~1/2" of magnets to get it to register. However after seeing the speedo reading had a pretty slow response time, I decided to move the sensor inward with the above process.

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Edit 3/6. The speed sensor didn't work in the vertical position so this was my solution:

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I ordered the optional gear sensor and the kit included 2 brake sensor cutouts. So far I've just installed a cutoff for the rear brake. I'm primarily using PAS and on [relatively short] test rides so far, I don't really feel the need for any of the cutout sensors, but I installed one just to be safe. The SLX levers don't leave much room to attach a magnet, so I epoxied one to a thin strip of metal and attached it the lever with some 3M tape. I positioned it as far as possible from the Hall sensor so it trips almost as soon as the lever is pulled.

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Finally I configured the controller before even riding the bike. My intent is to primarily use PAS so I wanted finer control over the lower PAS levels. I wanted feel similar to a torque sensing bike. From reading reviews I was worried this wasn’t easily attainable, but my programming seems to work well and I’m satisfied with it. I also reduced the factory Luna 25W programming down to 18W for an additional safety margin.

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So it turns out the speed sensor does not work in a vertical orientation. Just removed the epoxy with a heat gun and will be redoing to get the sensor horizontal.
 
After a few decent rides, this battery pack seems to have a range of 30+ miles.

Ride 1 was ~16 mi paved with some moderate hills and a 10-15 mph headwind at times, avg assist level was probably 5-6. Battery went from ~52v to start and finished ~42V, and I ended up pedaling a basically dead 45lb bike about a mile home.

Ride 2 was 20 mi paved, very flat and no wind. Avg assist level was 3-4. Started at 54v and finished at 52v.

I verified the voltage with a multimeter and the 500C display is pretty accurate, though reading will bounce up and down slightly while riding.

Also based on the 40T spec sheets (which specify a 2.5v LVC per cell), I'd say I can safely lower the battery protection to 38V.
 
Very nice build :thumb:
I'm in the finishing stage of my BBS02b build. And the programming you did is something I need to look into. Especially the 100% speed limit in every assist level while increasing the current limit gradually seems a good idea!
 
SlowCo said:
Very nice build :thumb:
I'm in the finishing stage of my BBS02b build. And the programming you did is something I need to look into. Especially the 100% speed limit in every assist level while increasing the current limit gradually seems a good idea!

Thanks!

If you want to contribute pedaling effort (especially at lower speeds), programming in smaller steps for the first few levels is definitely the way to go. The stock Luna programming started at 10% in level 1 and I believe the standard Bafang programming starts at 30%. Both of those are way too high IMO. For sub-10 mph speeds that would require little to no effort from the user.
 
Hopefully it's fairly subtle since e-bikes are not technically allowed on dirt trails in my county.


I've since cut an opening in the frame bag to hide the wires. The charger has its own side now. A bonus of the frame bag is it can store my oversized smartphone that I hate carrying in my pants pocket while riding (and we'll be out of jacket season before long). I also need to figure out water storage before this summer. Options are basically top tube, down tube or backpack (which I like to avoid on shorter rides).

I added some basic drop protection to the battery, just hot glued on some double walled polypropylene sheet. Ugly, but it's much better than nothing and not visible in the frame bag.

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I was hoping to adjust the cassette gearing (remove a couple middle gears, move the lowest gear inwards), as I can't really grab the lowest 2 gears without a really crooked chainline, but these spider-group sprockets put a stop to that.

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You should be able to move the thumb throttle to the right side, above the bar. That's what I did with mine, and after a short acclimation period it works great that way. Every once in a while I have to think about whether I'm shifting or applying throttle, but no mishaps after 2+ years.
 
Luna has a frame bag that has openings for the wires and is large enough that I was able to protect the battery from hitting the frame tubes on bumpy trails. Also SK (German company) has several systems that allow you to attach a water bottle cage to the seatpost (I've been using one successfully for six years) or frame tubes.
 
Not a bad idea on the water bottle seat post mount. I didn't see an SK specifically but Amazon sells a bunch of mounts like these <$10. A vertical bottle might interfere with the dropper post but a lot of these mounts let you rotate them. https://www.amazon.com/Topeak-66008...ndlebar/Seatpost+Mount&qid=1615086089&sr=8-1


I've gotten used to the throttle on the left so even though the positioning could be improved, it's not terrible.
 
Well it didn't take long to break something. Not surprised the bag tore out given the $10 price point but I figured it'd last longer than it did.

Now I'm on the hunt for something heavier duty. The Luna bag mentioned earlier might be strong enough but it's an eyesore IMO.

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Just a thought, if you decide on a triangle bag, it looks like you could route those cable zipped to the downtube, through the bag instead, and the cables on your seat tube too.
 
That's an interesting idea. It would help clean the wiring up a little bit. Speaking of wiring, I think I'll reroute the controller cable along the top tube to better hide it.

I thought about drilling a couple holes in the frame for internal routing but decided I'd rather not compromise the frame strength (even though I suspect the previous owner drilled the seat tube for the dropper post).

I'm considering fabricating a battery box out of Al or ABS sheet. This is about as big as it'd need to be so that leaves plenty of space for a water bottle.

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You have enough triangle space for battery placement of course. But I had to find a different place on my build and used a triangle shaped battery pack (52V, 21Ah) placed in front of the downtube just above the BBS02b. The front wheel just clears it on full compression. It has the added benefit of a low center of gravity for me as a slow rider keeping the bike feel light in maneuvering. Just a thought for anyone finding this thread with not enough room in the triangle for battery pack placement:



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SlowCo said:
You have enough triangle space for battery placement of course. But I had to find a different place on my build and used a triangle shaped battery pack (52V, 21Ah) placed in front of the downtube just above the BBS02b. The front wheel just clears it on full compression. It has the added benefit of a low center of gravity for me as a slow rider keeping the bike feel light in maneuvering. Just a thought for anyone finding this thread with not enough room in the triangle for battery pack placement:

Most of the OEM e-bikes I've seen go with a downtube-mounted battery. They might have other design considerations besides packaging but I would bet that's the primary factor. In my case, since I'm riding on rougher trails, I don't want the battery to act as a bashguard (especially given the limited protection it will have). And this is just speculation, but I feel with the battery farther back it will make pulling up the front wheel over obstacles slightly less difficult (albeit at the expense of a slightly higher CoG).

Was your battery box a DIY build? If that's the case, what material did you make it from?
 
I made the battery box out of hardboard and welded a frame out of 6mm wire rod to pull it against the down tube. The box is about 10mm wider inside then the battery pack and centered with glued in drinking straws. With small holes in the top and bottom it will hopefully allow the warmth of the battery pack to be vented out. As I'm a slow forest trail rider I will not be pulling the front up to go over anything larger then a twig :wink:

As for the chainline problem I left out the two smallest sprockets and made a spacer that I placed behind the largest sprocket. And I'm using the original offset Bafang 44T front chainwheel. So I made a 7 speed with 9 speed spacing. I've not been able to actually ride it off road yet. Hopefully next week.
 
Thanks to snow and mud I've had limited riding time on dirt trails with the e-bike so far, but it's an absolute blast on flat smooth singletrack. You can hit downhill speeds with no hills. However I suspect it may not be as great on technical terrain due to the extra weight. Since the e-bike is out of commission due to the battery carrier, I took my other [non-motorized] MTB for a ride yesterday. I expected it to feel extremely slow and hard to pedal but that wasn't the case. Granted it's newer and tighter (and also a 29er), so it's not apples to apples. Taking 30% off the bike's weight makes a big difference. Once I can ride both back to back on the same trail I'll have to write up a comparison.


I ordered this Moostreks bag for a battery holder. It's 4x the price of the last one, but it should be much better constructed. I also ordered a sheet of 1/16" ABS so I have the option to fabricate a box should the bag not work out.
 
Sorry, I left out an "S"; actually the seatpost clamp is by SKS which has several products that I've used for mounting other items like controllers.
 
The frame bag arrived the other day, as well as the ABS sheet. The Moosetreks is excellent quality and it easily swallows the battery. It doesn't fit the frame perfectly as the seat tube brace interferes with the top rear strap. I also need to make some type of internal support as the bottom corners of the battery seem to put a fair amount of stress of the bag - I feel this will tear out eventually with rough riding. And will need to burn/cut a cable hole in this nice bag :(

As for the ABS sheet 1/16" is way too thin to be structural. Should've gone with the 1/8". I'm still considering fabricating a battery box but will either need to double the 1/16" up and/or use a bunch of internal braces.

I'm starting to wish I got a shark pack initially and just dealt with the clunky form factor and heavier battery than I need.

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COAR said:
The frame bag arrived the other day, as well as the ABS sheet. The Moosetreks is excellent quality and it easily swallows the battery. It doesn't fit the frame perfectly as the seat tube brace interferes with the top rear strap. I also need to make some type of internal support as the bottom corners of the battery seem to put a fair amount of stress of the bag - I feel this will tear out eventually with rough riding. And will need to burn/cut a cable hole in this nice bag :(

i'm not sure how much you want to invest in a solution, but if the bag is well built already, you could take it so a clothing/shoe/luggage repair place that has the right equipment to alter the bag to a custom fit, and add grommets for the cables to pass through. i think if the bag is custom fitted, it will stay in place better and more easy to secure.
 
COAR said:
As for the ABS sheet 1/16" is way too thin to be structural. Should've gone with the 1/8". I'm still considering fabricating a battery box but will either need to double the 1/16" up and/or use a bunch of internal braces.

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Idea for the rearmost toptube strap: You may be able to cut a "Y" in the strap (both sides) so half goes behind the seatube brace piece and half goes in front.
 
COAR said:
I'm starting to wish I got a shark pack initially and just dealt with the clunky form factor and heavier battery than I need.

If you do go another direction, the EM3EV hard case triangle may look less clunky. I don't know what the dimensions of your triangle are, but the angles of the triangle aren't too far off from the angles of their hard pack, but without knowing the dimensions, can't tell if it would fit or not:
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E-HP said:
i'm not sure how much you want to invest in a solution, but if the bag is well built already, you could take it so a clothing/shoe/luggage repair place that has the right equipment to alter the bag to a custom fit, and add grommets for the cables to pass through. i think if the bag is custom fitted, it will stay in place better and more easy to secure.

I went the somewhat ghetto route of just heating up a nail and using that to cut a hole the width of the battery connector. The bag is double layered so that had the benefit of melting the layers on the edge of the hole. I think I'll try to find a grommet large enough (~1" ID) to fit the XT90 to clean the look up and prevent any tearout.

A custom bag would definitely fit better but this is sufficient. I do wish it had nylon webbing and buckles instead of the velcro though.

SlowCo said:
Foam stress relief.jpg

I actually did that with several layers of an old foam camping pad hotglued together. It's much more stable than before and it's now kept vertical so there's a bunch of spare room in the bag.

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99t4 said:
Idea for the rearmost toptube strap: You may be able to cut a "Y" in the strap (both sides) so half goes behind the seatube brace piece and half goes in front.

I thought about that, I figured I'll do that if it's slips off the way I attached it.

E-HP said:
If you do go another direction, the EM3EV hard case triangle may look less clunky. I don't know what the dimensions of your triangle are, but the angles of the triangle aren't too far off from the angles of their hard pack, but without knowing the dimensions, can't tell if it would fit or not:
surly em3ev.jpg

I have the medium frame...https://surlybikes.com/bikes/legacy/instigator_2

From the em3ev dimensions I believe that triangle battery would fit. The downside is they weigh nearly double what my battery does. That may be a good option if need more capacity down the line.
 
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