Crankin' It - Mid-Mounted Crank Drive
For years now, I have been considering a mid-mounted freewheel crank drive.
Running a geared reduction motor through the 7 speed freewheel sprocket, or freehub cassette.
Most any bike could be converted, adding less than 10lbs of motor hardware. (Battery additional.)
Typically, this involves using a geared reduction motor connected through the front chainring.
A big improvement over most any type eBike drive!
With a 11-34T 7spd freewheel you can have the equivalent of a 7 speed motorcycle, with +300% the torque at low speed.
Great low speed torque and high speed assist ... right to 30mph(?) ... from the same motor!
An important option is a 2 chainring freewheel crank.
This allows motor power without pedals being turned ... much safer!
There is the variable of matching motor to pedal speed.
The size of the 2 chainrings can be varied, and / or voltage adjusted, to match your rhythm.
The next stage option is a freewheel sprocket, instead of a fixed sprocket on the motor, this allows easy pedaling when motor not engaged.
My project motor is the Unite MY1018z gear reduction motor.
I've poked-prodded-tested and tried this model for ~20,000 miles.
As a demonstration,
I graphed the speed and torque available from running the motor through the 7 speed sprockets.
MY1018z motor @24V w/9T sprocket
At 24V Low gear (34T) will give you great power-acceleration till 7mph, great for the worst hills.
Then, there are a variety of optimal hill climbing, or acceleration, choices till about 16mph.
Of note is that a 34-13T would limit maximum speed to the "legal" 20mph.
I just finished purchasing the individual components and will continue to post build reports.
Crank Drive - Parts-n-Such
SunRace 13-34T MegaRange - $16.99 shipped
DNP Epoch 7spd 30-32 to 11T Freewheel - $34
Upgrades EZip w/44T Front Sprocket to near 30mph pedal assist (90 crank rpm)
More sizes - 11- 28,30,32,34T - $32
Quality ACS Freewheel for freewheel crank! $16.50
BCD not specified ... might bolt directly to certain chainrings?
Also available _ more components, from Staton-inc.com
Freewheel Cranks - Choices ... >$32
450w 24v, gear reduction motor, standard 1/2" x 1/8" chain (MY1018Z) - $95 + shipping
The "silent" motor (well ... not real loud)
XYD-16 motor w/mounting bracket - $108.89 - Will try to find working link