My first major design element is the front hub for the large wheel. Nearly every other design uses a fixed hub with the pedals tied directly to the axle and hub. This accomplishes two things, 1. the design is simple and inexpensive, and 2. provides integral braking via the pedals. This was the first version of a "fixie." My design was going to be different. For several weeks I researched internal gear hubs like this 14-speed monster.
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| Schematic of a gear box Rohloff Speedhub (14 speed) |
Bicycle hubs are designed to have a fixed axle (connected to frame) and a driven shell (connected to gears). I couldn't think of a good way to modify one for use on a penny farthing.
Amazingly and expensively, someone makes an internal gear hub designed for unicycles. (Note: this was the point that I realized unicycle parts would directly apply to my design). Have a look here to see it http://www.unicycle.uk.com/unicycle-parts/hubs-bearings/kris-holm-schlumpf-geared-unicycle-hub.html
With enough cash, problem solved, right? Not quite. The two gear ratios for this hub are 1:1 and 1:1.55. With a 48" front wheel, I did not need a higher gear. Without the ability to downshift, the internal gear hub wouldn't work.
So, I abandoned a geared hub and went with option #2, a freewheel. More on that in my next post.
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