A Journey by Bike… trial and error

Posted: September 12, 2015 in Uncategorized

After realizing that the Continually Adjustable Bike Transmission (CABT) model was just too cumbersome to be appealing, I could not let the idea go. I still thought the problem of an expanding chainring system should be solvable, but it would take a new approach.  As my wife will gladly tell you, I am often guilty of over thinking things and making them more complicated than they need to be. So, I ditched the CABT design and started over from scratch.

I tried to think of the simplest way to get the gear segments both to be adjusted (i.e., change radial position) and  to lock into that new position. First, I decided that having gear segments slide along straight arms radiating from the center of a circle was the simplest way to for them to change radial position. (This is far simpler than my use of spiral-shaped gear segments being moved by a pin sliding within them, which thereby changed their radial position).

The other problem was how to allow them to lock into position while engaging the chain, and unlock and change position when the bicycle’s rider wishes to change gears. I got rid of the threaded screws that changed the position of the gear segments in the CABT model. I went through several designs for the locking mechanisms and tried building and testing them, using simple materials and working in my garage.

Initially, I thought the gear segments could be locked by means of a toggle which fit into a notch on the edge of the radial arms. I tried simple pivoting brackets, and an elaborate scissoring mechanism:

sketch 1

Toggle locking mechanism

The another design involved having pins pinch the radial arms when depressed by the force of the chain:

sketch 6

Pin locking mechanism

Neither of these seemed like they would work sufficiently well, and they were too complicated. So, I thought it would be most feasible to have a pin perpendicular to the plane of the base plate serve as a locking mechanism.  I thus had to figure out a way for this pin to move in and out as directed by the rider:

sketch 2

Perpendicular pin locking mechanism

Next, I tried a design inspired by clothespins:

sketch 3

Clothespin-inspired locking mechanism.

After that, I tried having the toggle swivel when making contact with the control plates, which would raise the locking pin from its notch:

sketch 4

Swiveling toggle locking mechanism

As many designs as I came up with and tried to build, they all seemed too complicated and/or heavy to be commercially feasible:

button-pin photo

Not it either!

It wasn’t until I thought of putting the locking notches within the groove along which the gear segments slide that I made the step which led to VECTr in its current design:

sketch 5

The penultimate design

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