Front Hub - Build from Scratch

I'm building the front hub from scratch. It will be substantially based on the Nimbus drift trike hub, just resized for the application. It took some time to get through the rusty parts of my 3D CAD skills and make a complete model of the hub body and axle. Below is a really cool "photo" of the hub body next to the original part. This comes from eDrawings on iOS. After modeling the part, you can use their augmented reality feature to represent the part in the real world. As you can see, it is much larger than the original. 

Once complete, I will have it anodized to match whatever color scheme I choose for the bike. 

Front Hub - Modify or Build New?

My first approach to making the hub wide enough was to modify it. It needed to grow in width and the number of spoke holes needed to increase. The width has to increase by 2-4 inches (50-100mm). I envisioned parting the existing hub and using a tube to stretch it. The tube was to be welded to the hub pieces. The spoke holes required a different type of added part, the spoke ring donut. After machining the existing old flange down below the spoke holes, a new flange ring would be welded along the perimeter. The rendering below shows original hub pieces (gray) and the new pieces (red).  

I'm sure this would work, but a local machinist suggested that I would do better to make a new hub from scratch. 

Front Hub - The Freewheel

After abandoning the geared hub, I elected to pursue another modern hub configuration. The freewheel or freehub would allow a rider to coast without pedaling. A different braking means is now needed but more on that later.

Amazingly, someone sells a unicycle hub with a built-in freewheel. Freewheel on a unicycle!? I don't ride them, but it sounds dangerous. Still, I bought one with the intention of using it as-is or making modifications. Roger at unicycle.uk.com suggested that the width (bearing to bearing distance) needs to be 150-200mm. The stock hub is 100mm. I believe the theory is that a narrow hub would put the spokes in a nearly vertical orientation and the lateral strength would be insufficient. Here is the hub after disassembling all bearings, the axle, and the pawls. 

It's pretty simple. Next step, how do you "stretch" this design?

Front Hub

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.

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.