The birth of a new species
a.k.a. making the ObliqO
I had to build a full-scale mock-up to effectively present the initial concept. It was first designed in SolidWorks and then assembled using welded tubular steel and MDF boards for the footplates. It clearly showed the angled wheels and the pivoting footplates, as well as giving a first impression of the overall size.
I conceived the first prototype as an experimental piece, where several manufacturing processes and technologies were tested. The wheel had a diameter of 12 inches. Skateboard bearings were chosen, because they are readily available and inexpensive, as well as being suitable for the range of loads involved.
Aluminium alloy was the choice for the framework, because of its high strength-to-weight ratio and stiffness. I turned most metal parts on the lathe and used a milling machine and other metalwork machinery.
The main component for the stator was cut on a CNC milling machine, and then bent. I used a very large aluminium tube for the linkage bar, simply because no other suitable size was available in the short term, drilling massive holes through it to save weight.
Coasting a few meters was enough to understand that the principle was valid and further efforts should have been put into refining the design.
After the completion of the first prototype, I considered the use of exotic materials, like Carbon Fibre Reinforced Composite (CFRP), because of its outstanding strength-to-weight ratio, neglecting its very high cost. It goes without saying that this version would be inconvenient to manufacture and I intended it as a conceptual exercise to see how far the design process could be pushed.
The second prototype was the result of a completely different approach. After a long and arduous research, the choice of wheels fell onto standard 16 inch bicycle rims and tires. I chose 28 millimeters tires: among the slimmest available on the market. The whole prototype was created as a rig which could be fully tested so the ergonomics could be modified and investigated. For example, the distance between the footplates and their height could be varied in discrete steps, by simply undoing few bolts. All the components were designed to be fabricated in the shortest possible time, rather than using elaborate processes. I neglected weight this time and I made the whole structure using steel bars and pop rivets. I chose nylon for the rollers and increased their diameter, while their number was reduced from four per wheel to three. An adjustable ridge was added to their external side, for tactile feedback on the feet. I used special care in the design of the hinges. Then a problem arose.
The new tires required a tube. Tubes require valves. Valves usually have stems. Stems tend to stick out of the rims. Now, my rims were running on rollers: there was no space for valve stems in my new prototype! The last detail to be designed was a special, custom-made valve, to be installed in the place of the standard Schrader valve.
The construction of the second prototype was much more rapid, given that the wheels were bought from a specialized shop and most of the materials were once again available in the workshop. In just over a month the rig was ready for testing.
Six nylon rollers were turned on the lathe and all the parts for the frame were easily cut from steel bars or sheet, drilled and assembled using pop rivets. The hinges had to be welded and some of the holes in them threaded. I cut the two footplates out of 6mm plywood and a thin strip of sandpaper was stack onto them as grip-tape.
The construction of a working ball valve took longer than expected. The valve had to be turned on the lathe out of nylon, with accuracy in the range of 5 hundredths of a millimeter. I tried several different solutions for the inner ball. At first, a 5mm steel sphere was employed. Leakages were difficult to avoid, so, after several trials, I tried a rubber ball instead. It worked reasonably well: these valves held the pressure for several months.
The overall weight of the prototype was considerably higher than that of the previous one. Nevertheless, its performance proved by far better. The wheels were rolling much more smoothly and the whole structure felt more solid. This prototype was used to refine the propulsion technique. I adjusted the width and height to the most comfortable and efficient position, as well as the angle of the ridges on the footplates. These were used as constraints for the design of the following prototype.
In the third and final prototype, several different aspects, matured along the design process, took physical form. I intended to emphasize the purity and harmony of the design, as well as improving technical features of the vehicle.
Aluminium alloy was once again used for essential components in the structure, although I decided to make use of plywood for more of the structural parts, because of its flexibility and lightness. The four load-bearing nylon rollers were further increased in diameter and given an asymmetrical profile, in order to better support the oblique wheel. The two top rollers, in contrast were reduced in size and ball bearings were not used for them, since the force they have to withstand is modest.
With the experience of the CNC cutting process in mind, I designed new aluminium parts for a shorter manufacturing time. I initially came out with an idea for a deck to be CNC-machine cut out of a single plywood block, but it proved too complex to fabricate. In the end I decided to go for a much simpler, flat plywood deck, with a supporting aluminium ridge.
All the aluminium parts went through a hard-anodizing process, in order to make them scratch-resistant. The plywood components were dyed and then coated with a hard layer of clear epoxy resin, which was then sanded smooth. I had to order special, non-drilled rims. These rims have no holes for spokes, which helps improve the neat look of the prototype. The fastener used were polished stainless steel socket head bolts, with self locking nuts, ranging from M4 to M8. Depending on their position, they have a countersunk or button head.
This prototype was exhibited in several exhibitions (One Off at Kingston University, D&AD at Olympia and New Designers at the Business Design centre) before being tested extensively (see video below). The results helped me make all the improvements for the current prototypes, which are under manufacture as I write. But this is another story.
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