Tischer's 1hp Electric Bike #2

2015-10-15
I decided to build a second electric bike, this time a 27.5" mountain bike. My goal for this bike was to reduce weight, and improve braking, since I'm often on dirt trails towing a 70lb trailer bike.

I'm now using the Bafang BBS02 750 watt mid drive motor with a 400whr battery, double the capacity of my first conversion. Using identical batteries (200whr), this bike was 6 lbs lighter than the first, largely due to the aluminum front fork and hydroformed aluminum frame. This bike also uses an 11-34 cassette which is lighter, stronger and has less friction compared to my previous bike's Nexus 8 speed Internal Gear Hub; I do miss the ability to shift while stopped, but I always worried about the IGH stripping gears.


Fuji Bike frame with 27.5" wheels.

The cassette is a 9 speed 11-34 with a 42 tooth chain ring. This matches the gearing I had fine tuned on my previous bike (Nexus 8 speed 12.4-38 equivalent with 46 tooth chain ring). The gearing allows for 32mph without pedaling in the highest gear, and enough torque to pull the front wheel off the ground in 1st.



The aero bars really help on long rides by transferring your upper body weight off your rear end, it's also nice to duck out of the wind when facing a strong head wind.




One of my first TIG welding projects was the battery box.




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Slide on Battery lid




Turnigy 6S 10Ah batteries.
These are designed for RC airplanes and drones, so they are light weight and compact compared to the RC car batteries I was previously using. I also like the XT90 plugs on them which are available with a precharge (anti-spark) connector.




I added peel and stick felt to prevent any rattling.




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Chain line with the Lekke Bling Ring

I have mixed feelings about the Lekke Chain ring. Rocks are often getting wedged between the chain ring and motor because the chain ring face is so open and there is not much clearance around the motor. When this happens, it makes a horrible grinding sound. I also had my chain fall off a few times, so I added a chain guide.



Chain guide and 42T Lekke Bling ring




I stuffed the excess Bafang wiring (Banfang bundle) in the aero bar.




The grip shifter allows rapid gear shifts up or down. With all the power on tap with the electric motor, I often shift 4-5 gears at once, and it's time consuming to have to click an index shifter one gear at a time. It's also nice to row from 9th to 1st in one swoop.

I'm also using a magnetic brake switch with my Avid brake handles The brake switch kills power to the motor. I'm only using one brake switch so I can use one brake to hold the bike on a hill until the motor starts turning. The Bafang brake handles included in the kit are huge and feel loose and sloppy.




I went with 180mm front disc which required spacing off the caliper.




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