Just another awesome commuter e-bike: rear hub BPM, LiPo

headwind

10 W
Joined
Mar 27, 2013
Messages
76
Location
Australia
It's alive!!

Firstly, many thanks to Kabbage, Kepler, Ben Moore, Dogman, Adrian_sm, Spinningmagnets, Andyshirley and others for all invaluable advice I've received. Here is the finished product:

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So the intention was to build a reliable commuter which would pass for a normal pushbike at first glance. The main bits are:
- 2012 Giant Cypress DX hybrid bike (front suspension removed)
- Schwable Marathon Plus 35mm puncture proof (fingers crossed!) rear tyre
- Kool Stop brake pads
- BPM 36V500W rear hub motor
- Ben Moore "little monster" controller, limited to 30A
- Zippy LiPo 44v 4Ah (times 2 packs, the other goes in my backpack for the ride home)
- iCharger 106B (with paraboard to charge all 4 batteries at once)

Thanks to the incredible explosive power of LiPo, unassisted it rides quite similar to pre-conversion. But then twisting the throttle gives it a very nice boost indeed! Personally, I think the conversion is quite discreet, in fact a few friends had no idea until I admitted its "little secret"!

Total cost for the conversion was AU$1200, and it's been worth every cent. E-bikes are an absolute game-changer for urban transportation, and I'm totally stoked with how mine has turned out! :D :D
 
8) Very clean.

Did you managed to cram your batteries into that little saddle bag?
 
What...no cup holder? (and he calls himself a serious commuter...). And I don't see ANY duct tape :)throws hands up and scowls:)...these new kids...I...I just don't know what to think anymore.
 
adrian_sm said:
8) Very clean.

Did you managed to cram your batteries into that little saddle bag?
Yep, there's 2 Zippy batteries snugly sitting in there without any room to bash around, it worked out really well. The other 2 batteries go in my backpack to swap over for the ride home.

spinningmagnets said:
What...no cup holder? (and he calls himself a serious commuter...). And I don't see ANY duct tape :)throws hands up and scowls:)...these new kids...I...I just don't know what to think anymore.
:lol:
 
Kepler said:
Nice job Headwind. Very stealth install. Just make sure you pay good attention to waterproofing the controller the best you can with it in that position. :)
Thanks mate. You inspired me to put some LiPos under my bum, and I haven't looked back :)

Ben sealed up the controller nicely, I'll keep an eye on it though.
 
Speaking of waterproofing, I've just switched from the makeshift "old inner tube held in place with cables ties" sheath for the wiring connectors to some proper waterproof heatshrink. The inner tube never leaked, but I thought I'd give this a try, and it does look a bit neater.
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This heatshrink has glue inside, to create a seal at each end which keeps the water out. Hopefully this glue won't leave a mess if I even need to remove it to access the connectors. Fingers crossed!
 
majornelson said:
Nice! How is the controller holding up?
Yeah, it's been fine. Hasn't copped a hit yet (even though it's close to the road you'd have to be very unlucky for something to collide with it) and seems to keep the water out fine.
 
Xanda2260 said:
This is awesome! Exactly what I want to build. May I ask where I can get one of these motors?
Thanks!

I got the Bafang from a local guy. Sorry, I don't know any UK suppliers, but they're a big brand so it shouldn't be too hard.
 
headwind said:
Xanda2260 said:
This is awesome! Exactly what I want to build. May I ask where I can get one of these motors?
Thanks!

I got the Bafang from a local guy. Sorry, I don't know any UK suppliers, but they're a bit brand so it shouldn't be too hard.

Thanks anyway, I'll have to hunt around.
Fabulous work.
One more question, is that heatshrunk section near your derailleur your controller? It's tiny!
 
Xanda2260 said:
One more question, is that heatshrunk section near your derailleur your controller? It's tiny!
Nope, the controller is under the bottom bracket (see the last pic in the first post).
 
Update on the waterproof heatshrink:
headwind said:
This heatshrink has glue inside, to create a seal at each end which keeps the water out. Hopefully this glue won't leave a mess if I even need to remove it to access the connectors. Fingers crossed!
All good. Yay! I've pulled it apart (so the wheel can be rebuilt with stronger spokes) and it came off fine without leaving any mess.

Here's a link, in case anyone is interested: http://www.jaycar.com.au/productView.asp?ID=WH5643
 
Thanks for the tip.

I'll be using the spokes that the local bike shop recommended, the only thing I know about them is that they're single butted.
 
A little food for thought;
For the last year I did much what you are doing. I ran 12S\5Ah and when I hit the LVC(or I knew they were low), I would swap-out the two spent bricks for a fresh pair I carried elsewhere.
But recently, I added two more to the system for 12S\10Ah and it is all-around better. Aside from not having to fiddle with batteries and connectors, the motor runs smoother and there is less sag(admitedly, not much sag with Lipo).
Also, the cells hold their balance better, probably due to not discharging as low. For the last 10 cycles, I haven't had to balance at all.
I understand this complicates the stealth a bit, but I doubt anyone would notice another small bag.
You could wire up 12S\10Ah temp as a test and see if you notice a big difference like I did to see if it would be worth it.
 
Thanks for the tip. Yeah, running 10Ah would be a more efficient use of batteries, but there are a couple of practical reasons favouring swapping the packs over. One day I might try strapping extra packs to the bike.

Recently BenMoore showed me a build with the 18650 cells. Wow, they're getting compact and lightweight. Perhaps one day I'll switch over to that. Exciting times!
 
The axle in the Bafang motor has snapped :cry:

It lasted 18 months @ approx 70km per week. I can post some photos if anyone is interested, but it's a bit hard to work out what's going on without wiggling it around. Anyway, hopefully it doesn't take long to get the spare motor up and running.

Some general observations after using the bike for 18 months:
- I've been through a few LiPo packs, mainly thanks to occasional brain farts from me. But when a friend recently thought he'd killed his $500+ pack of 18650 cells, I was thankful that my packs are only about $50 each to replace
- Unfortunately the controller I bought off a local guy doesn't have any LVC settings which are useful for LiPo. A higher LVC would have probably saved a couple of my packs.
- Keeping the rear wheel in true is a challenge. The bike shop says it's a good rim and the spokes are strong, so they don't think there's anything else that can be done
- It's still a brilliant form of transport. I can't wait until it's repaired and I'm back in the seat.
 
My BPM2 came with thick 3mm spokes in a 26" rim. I've never managed to keep that wheel straight for more than 50km and had to rebuild the wheel with new spokes and new rim. That new wheel lasted 4,000km without problems till I totalled the rim on a hidden curb under snow.

Since then I've build a dozen wheels and learned a thing or two:
-use 2mm spokes! I use Sapim Leader spokes even with 3kW direct drive hub motor and never had a broken spoke in any my wheels yet (>26,000km).
-deburr the spoke nipple holes of your rim.
 
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