Author Topic: Cheap Electric fatbike  (Read 24964 times)

PonoBill

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Cheap Electric fatbike
« on: January 24, 2016, 06:44:42 PM »
I tagged this onto the downhill video, but shouldn't have. Just being lazy.

Here's my latest project. Built this yesterday. It's a cheap fatbike ($250 from K-Mart) mated to a REALLY good Chinese crank drive electric. These Bafang BBS02 drives are beautifully engineered. This is the new 100mm, version that fits most fatbike bottom brackets. I had to cut 15mm off my braket to fit it, which would be shameful with an expensive fatbike but for $250 it's no biggie. The power electronics are in the drive, so there's just one waterproof harness for the control circuits, one for the battery and one for the speed sensor. Super clean installation and a TON of power. 1200 watts peak, 750 continuous. Highly configurable and very good UART control system (tons of info available on line). Or just stick it together and ride with default settings (like limited to 20MPH). Super powerful, especially with the seven speed gearing on my cheapo. Even has discs. 

The 100 mm versions are hard to come by here, no one wants to ship them to Maui, so I bought 11 of them straight from Bafang and imported them. If someone wants one on the Hawaiian Islands I'll sell it to you at my cost. I don't know exactly what that is, but it's somewhere around $600. I had plans to do something exotic with them, but other priorities arose. If you're on the mainland you can get these pretty easily for about $700, but be sure you're getting the right length for the bottom bracket. Standard is 68mm, but most fatbikes are either 100 or 112.

Got to be the cheapest way possible to build an electric fatbike with a quality drive. I'll never build another hubmotor bike--too clumsy. The K-mart here in Maui has three of the model I used left in stock.









I'm using three 14.8 V 5000ma RC LiPos to power mine. Super cheap way to do a fatbike battery if you already have a 4 channel LiPo charger. I already had four of the batteries for multicopters.  The photo shows 4 but I had to drop to 3--the drive errored out from overvoltage. Nice that it just says "sorry, can't do that" instead of just toasting. I'm eventually building a set of three batteries that will sit in parallel with two sets diode-isolated and one switchable as a spare. With 15 amps at an actual 50V it should give a lot of range. . 750 watt/hours, or about an hour at full power. More like two hours at 20 mph. Kind of bitchy to charge, but a few hundred bucks less than a standard bike battery and much lighter.
Ponohouse is for sale: http://www.ponohouse.com
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Subber

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Re: Cheap Electric fatbike
« Reply #1 on: January 24, 2016, 07:04:31 PM »
Nice!!!

Looking forward to the Ride Report.
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PonoBill

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Re: Cheap Electric fatbike
« Reply #2 on: January 24, 2016, 08:15:49 PM »
Rides great. I can break the rear wheel loose in dirt. Very zippy and super smooth. I don't like how the pedal assist system works. It's backwards. If you pedal lightly it supplies more power, when you pedal hard it backs off. I'm going to disconnect that or change the parameters in the controller. I prefer to throttle the power anyway. I think the automatic stuff is kind of dangerous.

I have the speed cutoff set at 20mph and the bike reaches that really quickly in second gear (with five to go). So I'm going to set that to thirty, though thirty MPH seems like time for a full helmet not just a bike one.

Got to say I LOVE the fat tires. Ways smoother than suspension bikes. Going to be fun on sand. It would be great in snow too.
Ponohouse is for sale: http://www.ponohouse.com
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

covesurfer

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Re: Cheap Electric fatbike
« Reply #3 on: January 24, 2016, 09:23:30 PM »
I gotta come over to Ponohouse and ride that thing. Seriously. I want to try it out.

LB Surper

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Re: Cheap Electric fatbike
« Reply #4 on: January 24, 2016, 09:49:56 PM »
Curious, how are you packing the batteries so they don't get damaged while riding?
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dabigkahuna

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Re: Cheap Electric fatbike
« Reply #5 on: January 25, 2016, 08:37:47 AM »
Nice!  Definitely on my list of fun things to build...

PonoBill

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Re: Cheap Electric fatbike
« Reply #6 on: January 25, 2016, 08:56:18 AM »
Curious, how are you packing the batteries so they don't get damaged while riding?

Eventually I'm going to enclose most if not all of the triangle in the center with a carbon box the width of one battery, which is about the width of the downtube. I'll fill the lower section with batteries. What kind is a bit of an open question. If I find I use this thing often then I'll do a big A123 array with a BMS (Battery management system) to handle charging. If it's just casual, occasional use I'll use LiPos and manually charge them. I can do four at a time in about half an hour with my current charger. Doing 12 (15 Amps if I put three series sets of three in [parallel) is no big deal if I'm just playing around.

Currently I built a little tray out of sheet metal that attaches to the bottle mount and holds my three batteries.
Ponohouse is for sale: http://www.ponohouse.com
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

TEX_SUP

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Re: Cheap Electric fatbike
« Reply #7 on: January 25, 2016, 05:44:43 PM »

Got to say I LOVE the fat tires. Ways smoother than suspension bikes. Going to be fun on sand. It would be great in snow too.

I run mine at 4 psi in the soft stuff, works great!

I ditched the stock tires and went with Vee Rubber Missions 26x4". Almost a pound less rotating mass each tire.

starman

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Re: Cheap Electric fatbike
« Reply #8 on: January 25, 2016, 06:04:32 PM »
Looks good. I am wondering just how long the Kmart spec drive train lasts with all that torque. May want to include an iPhone charge port so as not to get stranded.

Although I half expected to see your name associated with a project like this;

http://www.npr.org/sections/thetwo-way/2016/01/25/464322851/dont-blink-robot-solves-rubiks-cube-in-just-over-1-second



Ichabod Spoonbill

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Re: Cheap Electric fatbike
« Reply #9 on: January 25, 2016, 06:39:10 PM »
Seriously impressive. When the zombies come, I hope I have a PonoBill nearby!
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PonoBill

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Re: Cheap Electric fatbike
« Reply #10 on: January 25, 2016, 07:16:52 PM »
Looks good. I am wondering just how long the Kmart spec drive train lasts with all that torque. May want to include an iPhone charge port so as not to get stranded.

Although I half expected to see your name associated with a project like this;

http://www.npr.org/sections/thetwo-way/2016/01/25/464322851/dont-blink-robot-solves-rubiks-cube-in-just-over-1-second

Not much left of the drivetrain, just the freewheel in the back, and it's primitive sounding (clicks loudly) which is probably good. But if it dies I have a nuvinci hub sitting in the shop, tanned, rested and ready.
Ponohouse is for sale: http://www.ponohouse.com
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

stoneaxe

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Re: Cheap Electric fatbike
« Reply #11 on: January 26, 2016, 10:39:12 AM »
Looks like fun bro.
Bob

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yugi

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Re: Cheap Electric fatbike
« Reply #12 on: January 26, 2016, 10:55:55 AM »
...
Not much left of the drivetrain, just the freewheel in the back, and it's primitive sounding (clicks loudly) which is probably good.
...

Oddly, the really high end freewheels are very loud clicking.

I'd have thought pedal assist was more power the more you pedal. Is it easy to bypass that with a throttle?

PonoBill

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Re: Cheap Electric fatbike
« Reply #13 on: January 26, 2016, 01:03:38 PM »
This pedal assist is backwards to others I've used. Usually its as you describe Yugi, for some reason they designed this backwards, and I can easily see myself backing off for a turn and having pedal assist shove me into a tree. the only way to cut it off without modifying the system is to touch a brake lever, which is fine, but I don't nee4d counter-intuitive help. pedal assist can be disconnected by clipping one wire inside the power control system, which is what I'll do. well documented on the web.
Ponohouse is for sale: http://www.ponohouse.com
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

GOTWAVZ

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Re: Cheap Electric fatbike
« Reply #14 on: January 28, 2016, 02:14:52 PM »
Looks like the battery element is still a little vague. They appear to have $400-$1,000 options out there.

For the home made solution they have Chinese 5000 ma Lipo batteries online for $60 each. How do you wire them together? Series? Do you cut the wires and put three together for 44Volts to a 50 Volt motor?

These guys have a "bottle" shaped option that looks clean.

http://lunacycle.com/motors/mid-drive-kits/bafang-mid-drive-and-parts/bafang-bbshd-1000w-mid-drive-kit-in-stock/

My fear is that I take It to the beach and it gets stolen, im thinking of trying to make it look UGLY so no one wants it.  Even if you lock it up the battery is a costly and easily stolen component.

I still cant get over how cheap that Kmart bike is. $260??
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