Time and time again, one of the most exciting developments that we’ve been seeing with 3D printing has been in disrupting traditionally manufactured products with products that users are capable of manufacturing on their own for much cheaper than what they would otherwise retail for.  Among other reasons, this dramatically brings the cost of goods down since there is little overhead in terms of marketing, shipping and the cost of manufacturing the parts through traditional processes.    
When combined with how easy it is to share these open source product designs, it becomes clear just how powerful this notion can be - especially for niche-specific medical products that are oftentimes not covered by insurance and are very expensive for what they are.  
More recently, this example of open source product design was demonstrated by Boston-based Kate Reed, an avid unicyclist and street performer and her partner Nathaniel Tong, a competitive fencer and entrepreneur.  Together, the two developed a wheelchair hack that won the 2015 Best Product category on Hackaday - the Hand Drive wheelchair attachment.
The attachment - which aims to be an affordable replacement to the otherwise expensive lever-powered wheelchairs that retailed for up to $10K - was developed to be used with existing wheelchair designs.  Originally, the pair were going to focus on redesigning an entire wheelchair, but soon determined that they could accomplish what they needed to do just by simply hacking existing wheelchair designs for an average of just $40 per unit.  
“The Hand Drive wheelchair attachment can be attached to any wheelchair and allows it to be powered in a rowing motion,” explains the designers.   
“This motion is better for your back, as it uses bigger muscle groups, and it keeps your hands cleaner. Because of our price point and the adaptability of the Hand Drive, all wheelchair users now have access to a lever-powered wheelchair.”
Of course, developing a polished product like the Hand Drive didn’t come without it’s fair share of design challenges, but the designers were able to implement all of the necessary features into an aesthetically-pleasing design that’s capable of being 3D printed on most 3D printers using Autodesk's Fusion 360 CAD software.  Among other features, the lever system includes a dual-ratchet mechanism for propulsion - a system that involves a spring-powered action to move the chair forward and a handlebar brake that can disengage one ratchet and engage the other to make the chair move backwards.  
In order to make sure that their system would work for a variety of different users, the team developed multiple prototypes to test their system in action.
“So far we have been through five major prototypes and dozens of sub-prototypes,” they explain.
“It's been a long process but we finally feel like we are getting somewhere significant. We now have three final stages of the Hand Drive, one with a single double ratchet, one with three double sided ratchets, and one with planetary gears incorporated into it. Although we have gotten each design to a high level of functioning, we are still working and still trying to improve our designs.”
In total, the team’s finished design is made from just six 3D printed parts, an aluminum pole, a bicycle brake assembly and some fastening hardware - not bad considering that they originally thought that they would have to redesign an entire wheelchair to achieve the same result.  
Currently, the designers are looking to gain feedback from users to improve upon their design and make it as accessible as possible for users at all ages and income levels.  
“We never want to lose sight of our goal to make the Hand Drive affordable and accessible for all,” they said.
“Wheelchair user statistics inform us that wheelchair users are very unlikely to have jobs and, partly as a consequence, are substantially more likely than the remainder of the population to live in poverty. At all ages, income levels for mobility device users tend to be low. If we can pull this Hand Drive off we can significantly improve the quality of life for many- at a price point they can handle, and with the personal satisfaction of building their Hand Drive themselves with their own specifications.”
Those interested in finding out more about the Hand Drive - including source files and assembly instructions - can head over to Hackaday.  

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