I bought the donor 2003 H-D 883 Sportster on December 31, 2010. On the next day, January 1st 2011, I began tearing it apart and started the reverse engineering process. I measured the parts I would keep and design around, like the engine, frame and a few others. The unneeded parts were donated to a moto club co-op in San Francisco, CA.
Six months later I had a rolling prototype, the SC3 Adventure, which consisted of the Sportster motor and the frame with some minor mods, a custom designed billet Aluminum swingarm, a KTM 525 front end, a small tracker gas tank, 18” rear wheel and 21” front wheel both with knobby tires, and a hand modified seat that looked pretty bad. The bike worked well, proving the concept and geometry.
I spent the first few months on the CAD system laying out the 2-D architecture side-view before designing and machining any parts. I nailed down the critical geometry: wheel base, rake, trail, rider position, foot controls and handlebar position, and instantaneous force center related to swingarm length and angle. All are key to the bike performing well on road and off.
Once the architecture was set, I began design engineering the components in 3D CAD solid modeling. I quickly had a complete solid model assembly of the entire bike along with fully documented detail drawings of every part and a complete Bill of Materials (BOM) down to the last nut, bolt, and washer.
The bike evolved over the next three years, consisting of refining and adding features like improved suspension, a larger gas tank for longer range, a better seat, a lighter and higher performance exhaust, better brakes, repositioned foot controls, a wind screen, hand guards, and a few other more minor details.
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