Design of the second prototype took place almost concurrently with the first, with initial ideas paving the way for a “mark .” prototype, which was then further refined using computer simulations, input from my supervisors, and further testing.
Design of the second prototype addresses several key issues found in the first, as well as adding some extra features. While the design underwent many fundamental changes, critical measurements – backrest to crank distance, crank height and backrest to leg rest distance, were monitored closely, and kept constant or changed according to their needs.
Mechanisms for adjustment were improved and added, with the second prototype featuring adjustable crank height and leg rest distance, as well as the crank to cyclist distance adjustment, which also allows breaking of the bike in two for storage or transportation. Quick releases were used instead of bolts and holes for the centre adjuster and crank height adjustment, making it quicker and easier to adjust, and reducing movement in the frame.
Instability issues have been tackled by increasing the space between the rear wheels, and adding a camber, changes which also created a larger space behind the cyclist allowing for the installation of a storage rack.
Problems with the steering have been fixed by adding mounts for a steering compensator, and changing the location of the axis of steering.
The second prototype is built using only parts from scrap bikes, cut at home into the requisite dimensions. Using scrap bikes allows prototypes to be developed very cheaply, and stay within the budget given by RMIT. The bike will be welded together by RMIT technical staff in the next month, and then sand blasted and spray painted for a nicer finish.
Now that design of the second prototype is completed, some work on costing needs to be done. Factors to be considered include the cost of raw materials, a comparison of different materials (steel, aluminium, titanium), different manufacturing models – i.e. using refurbished second hand bikes, new bikes or a scratch built frame, labor (welding, cutting, grinding, etc.) costs, as well and transportation and other overhead costs.
Once the work on costing has been done, its insights can be fed back into the design process in order to drive optimisation of future iterations.
Other work to be done includes my academic requirements – writing the thesis and preparing for myoral defense, as well as making a plan for work to continue next year while I am overseas.
Photos:Top left – testing handcyclesRight -The first prototype Bottom left – Computer Aid Design comparison of the first and second prototypeBottom- cutting up parts for the second prototype