Mountain Bike Builds (2D)

I had a lot of parts left over from adding mid-drive motors to our two trikes.  Timing belt pulleys, bearings, shafts, freewheels, some cheap motors, HV80 controllers, etc.  So I decided to go back to our old mountain bikes, which were temporarily abandoned in favor of the more stable and comfortable recumbent trikes, and see what I could do to add 2-stage belt-reduction electric crank-drive assist to them.  Worked out surprisingly well, using the cheap parts (like narrow plastic pulleys and Turnigy motors, perhaps $300 total per drive).  Hopefully we can attack the slickrock in Moab this fall.  Some Pix:

I had built a gas-assisted (30cc 4 stroker) mountain bike 12 years ago.  I used it for canyoneering (hide the bike at the end of a long canyon, do the technical descent, motor back to the car at the head of the canyon after a long day).  Deep sandy back-roads in Utah gave it a workout, but it made it (after letting air out of the tires).  However, the engine was noisy and riding was quite awkward.  So I decided to remove the gas engine, and install a lighter/smaller/quieter electric drive with a timing-belt 2 step (~18:1) reduction system.

A 5mm pitch by 15mm wide first stage belt has proved adequate (no skipping at all).  Surprise to me: I haven’t been able to break the cheap and lightweight plastic pulley. 

Second stage required 8mm pitch to avoid skipping on hard full-power up-shifts.

The big 10S 20Ah lipo battery I originally made for the bike is a bit heavy, high, and far back for anything but mild roads.  Kind of kills the maneuverability.

A smaller battery (12S 8Ah) on the cross bar feels better.

My wife’s old mountain bike, similarly converted.  This second bike-build has the motor, gearing, and battery lower down and it rides a lot better.

 Tiny Turnigy 6374 (~2hp) Motor and 8mm pitch 2nd stage belt.  48V 8Ah battery below.

First stage (5mm pitch, 15mm wide HTD belt), HV80, and crank drive.

Top View.

Have to be careful with these.  Easy to do unanticipated wheelies.  Can’t wait to hit the slickrock…….