David,
In my mind a redesigned wheelchair needs these key features:
Low cost of manufacturability, high level of durability, easy of repair if necessary, light weight, folds flat for easy transport/shipping to far places, flexibility for multiple types of terrain, and ability for gear reduction for going up hills easier.
I would look at a simple folding chair (the kind that comes in a bag) as a starting point for the frame work of the unit, with a nylon type seat/sling in the middle to support the rider. Since some of these folks may be in the chairs 24/7 comfort also has to be critical. A frame structure like a bag-chair will also allow it to be light weight, fold up flat, and can be extremely durable if the structure/connection points are designed properly.
The points where the wheels attach (wheel ends/spindles for lack of better words) can be made of a glass filled reinforced nylon (Nylon-66) or similar low cost but high strength material. I would incorporate a molded in place wheel spindle/axle with quick disconnect wheels for easy shipping and maintenance if necessary.
The wheel assembly is where the critical feature of the wheel chair comes into play. A simple conventional wheel can be designed for use in areas that rocky/uneven terrain isn’t an issue. But for areas where the terrain is an issue I would design a composite/plastic wheel that has a secondary wheel on the outside that is slightly smaller, has a handle/knob on it (like a suicide knob for lack of better words), and is gear reduced through a one-way clutch mechanism for climbing hills. I would incorporate an anti-roll back feature into the gear reduction/one way clutch to help climb hills or use as a brake coming down hills.
I would also try to incorporate as many off the shelf parts as possible, like common tire sizes, tubes, bearings, or other parts in order to keep the cost low and help with replacement parts in the future (think of small block Chevy……parts from the 60’s work all the way through the 90’s if you need to MacGyver something together in the middle of Haiti).
As for cost I would think you could engineer it here, have the components made by a low cost country (China), and final assembly in the states. The seat can be made for less than $1 - 2 in fabric, $3 - 4 for the rods for the structure, $3 - 4 for the rod ends, $7 - 8 each for the wheel ends/spindles ($15 total), $10-15 each for the wheels ($30 total), and $15-20 for the gear reduction mechanism ($40 total). Add in a few $$ for odds and ends and you could have something for less than $100………..probably half that number when you get into the 100K volume number.
Like you said earlier………..you need to think totally out of the box and take as many ideas as possible and melt them together into something spectacular.
And when you get frustrated and think it might be a monumental task take a look at the web site below:
http://www.bodynbobsled.com/
Almost 20 years ago Geoff Bodine (former NASCAR driver) was approached by the USA bobsled teams looking for help. They told Geoff about how they competed on old equipment that they had to buy second hand from the European teams. Geoff set forth on a mission to design and build the best equipment here in the US for our men and women competing for our country. After almost 20 years the US men’s bobsled team won the gold medal at the Olympics in a Bodine bobsled, finally fulfilling Geoff’s vision and goal he had been working for over the last 18 years.
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