# My Mid Drive 750 Watt Bicycle



## etischer (Jun 16, 2008)

My build page is here with more info, I'll post a quick summary below
http://etischer.com/ebike/

On flat ground, at full throttle this bike will run 31.8 MPH without pedaling.










This is the bike I converted. I bought it on Craigslist because it had an 8 speed internal hub which allows you to shift while stopped, and also shift while you pedal. It also has a very clean look, no front or rear derailleurs, and no tensioner. The motor is barely visible behind the crank and main gear.










The motor is a Bafang BBS02 750 Watt, it's a Permanent magnet DC brushless motor, the controller is built into the motor housing, and the gear box uses helical gears so it is almost completely silent. The motor is rated 20 amps at 48 voltes peak. 









I'm using 3 RC car batteries (4S Lipo) wired in series to get 44VDC, 5Ah. This gives me about 15 minutes of full current, at full throttle (typically just a few seconds of full throttle gets you up to 25mph, then the bike uses less current). Real world experience, I get about 15 miles using the highest pedal assist mode which gives me a cruising speed of 20 mph. Battery cost was $25/each









Batteries hooked up in parallel for charging, I can hook up to 6 in parallel and charge at once. The charger I'm using keeps track of how much energy (mAh) has been put into the battery, so I get a feel for how much capacity I have used up. 









Pedal Assist Mode (PAS) (+) and (-) buttons on the left allow the motor to amplify how hard you pedal. The thumb throttle on the right will let you run the motor at full power without pedaling. The display is back lit at night which is nice. The brake levers that come with the Bafang kit include a brake switch that instantly shuts off the motor.

Again, full review is here http://etischer.com/ebike/


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## samwichse (Jan 28, 2012)

Nice mid-drive motor. Where did you buy, if you don't mind me asking.


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## etischer (Jun 16, 2008)

samwichse said:


> Nice mid-drive motor. Where did you buy, if you don't mind me asking.


Seller name was BTN (Let's back to nature) on Aliexpress. You pay an escrow account, then the seller gets paid from that account after you confirm you're happy with the package. There is some buyer protection, but still seems a bit risky. The speedometer didn't work on my unit, as a result the LCD would flash an error, the seller sent me a new sensor and that fixed the issue. I paid $20 for 2 day shipping. I left good feedback for the seller, he responded to emails within hours and his english was good. 

If you have a warranty issue after the seller has paid, I'm guessing you'll be SOL, in which case you can pay $200 more for a USA seller. My order was $489 shipped, plus I paid an extra $20 for shipping the replacement sensor. 

http://www.aliexpress.com/store/705369


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## DanGT86 (Jan 1, 2011)

Very clean looking with the geared hub. Nicely done. Do you have any cell level monitoring or low voltage alarms on the pack while you are riding?


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## etischer (Jun 16, 2008)

DanGT86 said:


> Very clean looking with the geared hub. Nicely done. Do you have any cell level monitoring or low voltage alarms on the pack while you are riding?


Thanks!

These are what I have on order, it's taking forever to ship though. It's just a buzzer that plugs into the balance port on each pack. It buzzes if the voltage dips below 3.3V. 

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18987


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## DanGT86 (Jan 1, 2011)

Cool. I have heard they are really loud so that will probably be good. I guess they make them loud enough to hear from the ground if they are on an RC plane.


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## 25784 (Mar 22, 2012)

Thats a clean build. Has the internal rear hub held up OK to the torque of the BBS02 so far? That would be my only concern butI imagine it would go a long time with normal usage. Nice!


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## etischer (Jun 16, 2008)

The hub has been holding up great. It's received the harshest of abuse from numerous test rides with avid cyclists cranking on it with the motor at WOT. The record so far is 37mph on flat ground. When I ride, I typically have our kid in tow with our trailer bike. If you try to shift under load, it will just hang in the current gear until the load is lifted. My other bike with a derailleur setup shifts instantly under load (but doesn't shift when stopped). The motor is way over kill for the bike, the first 2 gears will just do wheelies, even with our kid in her bike seat on the handle bars. I typically use the lowest assist level, and wish I could go half. The bike could easily be a fixed gear, plenty of power even for hills, I rarely need to shift it. 

Here are some updated pics...


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