LEVI ONE - AN ATTEMPT AT ACCESSIBLE DESIGN
Bachelor Thesis Documentation 2021 Sina Julia Spring Freiburgstrasse 732, Oberwangen b. Bern +41 78 611 04 36 sina@springs.ch
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In a nutshell This project deals with the late effects of manual wheelchair use and their prevention, as well as with the inadequacy of available solutions. With an environmentally friendly and elegant object, the aim is to establish an easy access to design without losing functionality. Natural materials and a soft design vocabulary are combined with a non-medical look to create a sign of equity in design. The name “LEVI ONE” consists of two parts. The first one, Levi, is an hommage to the lever-propelling technique. The second one is the beginning of a numbering system, defining this project as the first developmental stage on the way to completion.
Starting Point In our everyday life we all use aids. Be it a spoon to eat our morning cereal, a stool to reach something higher up or a pair of scissors to cut paper. However, in the world of the disabled aids tend to become even more apparent and omnipresent because they are a necessity. The prime example obviously being the wheelchair. Having seen my grandfather struggle heavily in the realm of aids on his journey with Parkinson and witnessing a decline and subsequent rise in my mother’s health and mobility, I felt the need to be part of changing this situation. One of the most prevalent aids to this day is the wheelchair. Despite it being well-known and well-used, it does still harbor some room for improvement. The aspect that caught my eye was the way users propel themselves in wheelchairs and how those movements impact their bodies. I quickly realized that for a casual stroll or afternoon hike, a person in a wheelchair uses much more force and is subjected to the elements in a way more intimate manner. Born out of all these factors was the idea to design an add-on for manual wheelchairs that allows the user to self-propel using levers instead of the traditional handrims.
Available Products Wanting to alleviate the symptoms of prolonged manual wheelchair use as well as make the use of a wheelchair more efficient and practical on rougher terrains, I started researching what was already on the market. The two biggest players seemed to be Grit and Wijit.
Grit came to existence through an MIT project. It is a standalone outdoor wheelchair using a transmission similar to that of a bicycle. It is threewheeled to provide more stability on rough terrain, has two very long levers to allow different grip angles and to make usage of leverage.
Wijit is a set of wheels that are put on any standard wheelchair. They use a gear transmission inside of the lever handle to allow the user to use less force for the same distance as in a typical wheelchair.
Project Idea I wanted to provide an alternative to the products already on the market by allowing the user to install the add-on to their already existent wheelchair, since outdoor vehicles like the Grit Freedom Chair are quite expensive and often not covered by insurances, as well as giving them the option to remove the lever without removing the wheel and keeping their original wheels intact. I believe that this adds the benefits of flexibility in how to use a wheelchair as well as keeping the costs lower. A big problem in the disabled community is the lack of access to environmentally friendly options for people’s specific needs. A lot of aids are made from plastic and compound materials and together with medical waste due to medically necessary interventions, this leaves a lot of people with a feeling of guilt and helplessness. So, I wanted to provide a more sustainable option, using only renewable and recyclable materials like wood and metal.
Target Audience My product is meant to appeal to people that enjoy being outdoors in a casual nature. Someone that wants to go on an independent stroll in the woods or that wants some mechanical assistance to make up for a lack of upper body strength. Someone that enjoys simple design and cares about sustainability.
Aesthetics Moodboard
First Approach The Add-On that I want to design is meant to be used in rough terrain. The lever system is supposed to alleviate shoulder, wrist and elbow pain and prevent the complications that cause this. The tyres that will be used have a high friction tread to allow for more grip. This does also cause higher resistance. Exerting force on a lever is easier than on a typical wheelchair handrim, however there will still be a lot of effort needed to propel the wheelchair. Thus, I was searching for solutions and started researching how gears work, what kind of transmissions there are and especially how different bike systems work.
Research Often, a transmission has multiple gear ratios (or simply “gears”) with the ability to switch between them as speed varies. This switching may be done manually (by the operator) or automatically (by a control unit). Directional (forward and reverse) control may also be provided. Singleratio transmissions also exist, which simply change the speed and torque (and sometimes direction) of motor output. Bicycles usually have a system for selecting different gear ratios. There are two main types: derailleur gears and hub gears. The derailleur type is the most common, and the most visible, using sprocket gears. Typically there are several gears available on the rear sprocket assembly, attached to the rear wheel. A few more sprockets are usually added to the front assembly as well. Multiplying the number of sprocket gears in front by the number to the rear gives the number of gear ratios, often called “speeds”. Hub gears use epicyclic gearing and are enclosed within the axle of the rear wheel. Because of the small space, they typically offer fewer different speeds, although at least one has reached 14 gear ratios and Fallbrook Technologies manufactures a transmission with technically infinite ratios.
Initial Research I happened upon gear hubs and upon freehubs. Gear hubs would allow me to provide a higher torque on the wheels. After researching similar products like the Wijit I concluded that a gear ratio of 1:2 would be a good starting point. The reason why I started to look more into gear hubs rather than typical bicycle derailleurs is that they could be easily adapted to where they wouldn’t need a chain at all. With what I have in mind for my project and especially for how the product is suppose to function and be attached to an existing wheelchair, there is no space or method to utilise a bike chain.
Findings A bike relies on circular motions from pedals which by way of a bike chain put the back wheel in motion. Lever-propelling a wheelchair doesn’t utilise circular motions but rather seesaw-esque motions. Furthermore, the levers will be attached pretty directly to the hub of the outdoor wheel, thus making it impossible to add some kind of “in-between” transmission tool like a chain. Through my research I came across a multitude of bicycle gear hubs that could be used for my project and Sturmey Archer was one of the most common names to pop up. In a local sportswear resale shop I acquired a used back wheel with a Sturmey Archer gear hub. On Ricardo I also bought a Sachs Torpedo Jet Gear Hub which is supposed to be sent to me. The Sachs hub features a coaster brake, which at first I thought would be a really great addition.
Problem Solving One of the first problems that I identified was the fact that to allow the best possible manoeuvring, you need to be able to drive backwards. Hand in hand with that goes the fact that locomotion by levers needs some kind of mechanic where the levers engage and disengage with the hub so as to not just rock back and forth but actually propel forward.
Findings To solve both these problems, I immediately thought about ratchet wrenches. A ratchet is a mechanical device that allows continuous linear or rotary motion in only one direction while preventing motion in the opposite direction. Ratchets are widely used in machinery and tools. The word ratchet is also used informally to refer to a ratcheting socket wrench. To fully utilize this attribute I will need to find a way to switch between ratcheting direction from the handle. On typical ratcheting socket wrenches there is a little switch located on the head of the tool. This is obviously nota good solution for what I want to use this system for, since users might not have the mobility to reach this far down and the hub might be dirty from using the wheelchair outdoors. It would also disrupt the flow of driving, which is not wanted. At first, I thought that the ratchet system in combination with a gear hub featuring a coaster brake would be a perfect solution. That way, the user could just switch ratchet directions and thus activate the brakes. This would however make it impossible to drive backwards, since a ratchet mechanism only has two directions. A coaster brake is a special rear hub for a bicycle, which performs two functions: It allows the bicycle to roll without forcing the pedals to turn. This is the “coaster” part. It is similar in function to a freewheel , but uses a different sort of mechanism to accomplish it. It is also a brake, operated by turning the pedals backwards.
A new Approach? At first, I thought about just using a fixed transmission where the gear ratio stays the same. After researching many different gear hubs and especially after finding out about continuously variable planetary gear hubs I became open to the idea of including multiple gears and a gear shift in the final product.
Findings Before I found out about CVPs I was looking into Kick-Shift gear hubs. I had extensively researched a Sturmey Archer gear hub with featured three gears, a coaster brake (because at that point I still thought that would work for my project) and kick-shift. This means that shifting gears is done by pedalling back just a little and the coaster brake is activated by pedalling back harder/further. I thought that by utilising a ratchet mechanism, the user could simply switch ratchet directions, slightly pull back on the levers to change gears and then switch back to the forwards ratcheting direction and keep on moving. This would have allowed a more dynamic driving experience because the transmission ratio could be adjusted according to the terrain. We do however run into the same problem as with the coaster brake, the user would not be able to drive backwards which would make smooth manoeuvring almost impossible. I then began searching for other gear hub solutions that would allow me to use multiple gears. Obviously, a normal gear hub without a coaster brake could do this too, but I wanted to see what else was on the market. I happened upon CVPs, which allow stepless manual shifting, even under load. Specifically, I found the brand Enviolo. A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while the vehicle moves at varying speeds. On Tutti, I found a used wheel with an Enviolo NuVinci gear hub.
Experiments Finding a manual and/or an explosion drawing of the gear hub was pretty difficult and I was unable to find detailed images of the insides of the hub. When I started to take the hub apart to “switch” the input and output ring (since the hub is meant for a bicycle and there it only needs to be usable from one side) I happened upon a big hurdle. In order to properly upon the hub, Enviolo uses (and sells..) a special tool. I tried different ways to open the hub without said tool and ended up building an own version of the tool. Even with that, I was not able to open the hub. Because of that, the next step was to go to a local bike mechanic to see if they have this tool. The first shop that I visited did not have it. The second shop had it and opened the hub for me, however I could not actually access the gearing and would have had to use heavy machinery to cut the hub open.
Overhasty Since I didn’t have the special tool at home I decided to already start on building a connection from the two hub sides to the future lever. A lot of welding, turning, milling and sanding later I had two separate connector pieces. One attaching directly to the otherwise unused sprocket (no more chain used) and the other simply sitting on the axle for stabilization, containing a ball bearing.
Realization Once the hub was open, I noticed that there were two ratcheting mechanisms and only one of them could be accessed without breaking apart the whole hub.
Second Approach My first approach with the bike hubs inevitably failed. The weight of the hubs wouldn’t have been supported sufficiently, the design would have ended up being very clunky and heavy as well as frankly, rather ugly. The only way to address these problems was to go back into my research of transmissions and go from there.
Research Inspired by the NuVinci gear hubs, that use CVP’s (continuously variable planetaries) I decided to look further into planetary gear systems. They allow for a transmission of force around a single axle. Compared to traditional bike gearings that need multiple gear sets connected via a chain, a planetary has three types of gears circling around one point.
Gearset I decided to use the planetary carrier as the power input but at first, I wanted to have the ring gear fixed and use the sun gear as the output. After calculating the number of teeth needed on the individual gears for a good speed increase and setting the diameters of all the parts based on having the sun gear big enough to have a hole in the middle, I went to geargenerator.com to get functioning, two-dimensional gears.
CAD Based on the illustrator file of the gearset I designed on geargenerator. com, I started building my planetary gearset. The biggest challenge turned out to be the connection between the gearset and the wheelchair. Finding a way to keep one part of the gearset fixed in a position turned out to be rather tricky.
Difficulties At first, I just started modelling and after I had the whole thing mocked up, I realized that it would not work out like that. If I used the sun gear in the middle of gearset to connect with the handrim of the wheelchair, it would be nearly impossible to keep the ring gear fixed for the transmission to work. I had chosen this setup because it provided the biggest increase in speed, but I had to switch it up. Taking a step back made me realize that I should just go with what seemed the easiest construction, which was still using the carrier as the force input but fixing the sun ger instead of the ring gear. This still provides a substantial increase in speed whilst also allowing for a simpler and thus sturdier build. In this newer version, it is very obvious how much simpler the construction of just the gearset itself already is. The sun gear is also the bottom of the gear set and has a hole in the middle with a hexagonal dent for the bolt of the wheelchair axle to fit into, keeping it from turning with the wheel. The ring gear also forms the side wall and half the top, keeping the six planet gears from falling out. Its sides wall directly connects to the wooden connecter which connects to the wheel via the handrim. The carrier closes of the gearset and has a “neck” for the lever to grab onto.
Connector For the ring gear to have a connection with the wheel, I had to come up with a connector that does not obstruct the user or make the wheelchair much wider. The first version was based on the assumption that most handrims are connected via three or six points to the rim of the wheel. I decided on a three-part design, leaving most of the wheel unobstructed and visible. The design was supposed to be sleek and simple. The three identical parts would be CNC milled from multiplex wood and receive triangular inserts made from a wood of choice. The problem was that this connector was completely flat and thus, didn’t fit onto a standard wheelchair wheel.
Regrouping After acquiring a used wheelchair, a second problem arose. This particular model had four instead of the expected three or six connector bolts. I decided to completely upend my design and make it with four “arms” instead of three. The second version of the connector was still very similar to the first one, I chose to do another flat one again to see how the shape worked with the wheel and to be able to measure how much I had to lift the middle of the connector to conform to the shape of the wheel.
Finalization Once again, I also chose to connect the individual pieces only with wood and wood glue. Since I wanted to keep the whole project as sustainable as I possibly could, I wanted to abstain from mixing materials and connecting parts irreversibly. In the future I would like to look into tannin-based glues to connect the wooden pieces, since the glue keeps them from becoming firewood at some point. This second version showed me that the general design worked how I wanted it and it visually appealed to me. So, I started on version three, which would address the shape of the wheel and finally be able to be fitted to wheel.
Lever The last missing part of my project was the one connecting the user to the product: the lever. The idea is that the lever uses a ratchet system in order to allow the user to self-propel with a continuous motion. I wanted to use natural materials that are nice to the touch since one of my main motivations for this project was the fact that traditional handrims are cold and uncomfortable to the touch and I wanted to set an example with my product of how accessible design can be more user oriented and still remain stylish.
Aesthetics Moodboard
Looking back and forward At the end of a tumultuous semester I can look back on a lot of research and gained knowledge, a lot of work and mistakes, a lot of learning and growing. Most things didn’t go according to plan and so I’m left with what isn’t a finished product but a solid base of a prototype. I can confidently say that this project gave me the opportunity to learn a lot about accessible design, inclusive deisgn, disability and ableism. What lies ahead for me is trying to get this project to the next level. I want to try and get into contact with the research department of Paraplegikerzentrum Nottwil, I want to get a focus group to test the haptics of the prototype and critique the dimensions. The hope is to find a partner firm to further develop my vision and make it into a viable product.
Thanks to: My gratitude goes out to my mentor Andreas Saxer for expert advice and critical feedback. Further thanks goes to Gabrielle Alioth for helping me write a conclusive thesis and keeping my english in check. A big thank you to my father for providing me with the tools and machines I needed for my first approach and for serving as a sounding board for all my technical questions. In addition, I am very grateful to Andrea Schürmann for our long discussions as well as mutual criticism and support. Thanks to Tim Frank, Res Wallimann and Renato Rüfenacht for helping me with material questions and providing workplace banter. Many thanks to Johannes Maria Runge for helping me with editing my video and for believing in me. Last but not least, my thanks goes out to Joël Reinmann and Martina Häusermann for helping me with scenography and colour space.
Appendix The Different Patterns of Wheelchair Propulsion and their Negative Impacts [It is] documented that more than 46% of persons with quadriplegia and 36% of the paraplegic population had significant shoulder pain, with chronic inflammatory and impingement syndromes as the most common diagnoses. The repetitive forces experienced by the shoulder joints of persons with [spinal cord injuries] during wheelchair propulsion are likely contributors to the increased incidence of shoulder pain in this group. 1 In this text, the different patterns of manual wheelchair propulsion via handrims will be explained and compared as well as the medical implications of utilising these long-term. The last chapter will explain the difference in pushrim and lever propulsion and why that is of importance.
The Four Main Techniques Before explaining the different ways of how to self-propel a wheelchair, the distinctive phases of propulsion must be explained. There is a push phase in which there is contact between the user’s hands and the pushrims and afterwards there’s the recovery phase in which the hands return to their starting point.2 How long these individual phases last is determined by the propulsion pattern, the speed the manual wheelchair user (MWU) is going at, whether there is an incline or decline in the terrain they’re on as well as what kind of properties the surface on which they are moving has. The four prominent propulsion patterns are characterized by how the hands of the MWU move, specifically by how the third metacarpophalangeal joint moves (more commonly known as the third or middle knuckle3). 4 1 2 3 4
(Sara J. Mulroy 1996) Page 187 (Medical 2020) (Okafor, Sinkler and Varacallo. 2020) (Michael L. Boninger 2002) Page 718
The most common pattern seems to be the single looping over propulsion pattern (also known as SLOP).5 The SLOP pattern is characterized by the hands rising above the pushrim during the recovery phase.6 There is another pattern where the hands rise above the pushrim during recovery, the double looping over propulsion (DLOP). It begins with the hands rising above the pushrim after pushing, then crossing over and dropping underneath during recovery. The next pattern is supposedly the healthiest considering shoulder pain and injuries since it lowers stroke frequency.7 It is called the semicircular pattern and is recognized by the hands falling below the pushrim during recovery. The fourth pattern, which is most used on inclines, is the arc pattern. During recovery the hand follows the pushrim back to the starting point. It yields the highest efficiency, but it also has the highest stroke frequency, which makes it the worst pattern to use long-term.
5 6 7
(Michael L. Boninger 2002) Page 721 (Sean D. Shimada, et al. 1998) Page 213 (Hyde and Fontein 2018) Page 49
Possible Improvement and Injury Prevention through Lever Propulsion This study was primarily interested in the impact of LEVER [wheelchair] propulsion on the muscular demands of the push phase. This is the phase of the propulsion cycle when the downward force exerted on the pushrim results in a superiorly directed joint reaction force at the shoulder. It is this vertical force that places the shoulder at risk for impingement of the subacromial structures on the overlying acromion. Alternative propulsion modes (e.g., LEVER system) that reduce the intensity of muscle activation for the primary muscle groups would decrease the likelihood of fatigue and reduce the susceptibility for impingement.8
8
(Philip Santos Requejo, et al. 2008) Page 576
Disclaimer This appendix could not be finished in a timely manner and thus, remains as a first draft.
Bibliography Hyde, Alli, and Jane Fontein. “Manual Wheelchair Propulsion: Technique for Efficiency and Upper Extremity Health.” Canadian Seating & Mobility Conference. Toronto, ON: Canadian Seating & Mobility Conference, 2018. 48-50. Medical, Sunrise. Education in Motion: Manual Wheelchair Propulsion. 12 November 2020. https://www.sunrisemedical.com/education-in-motion/resources/manualmobility/manual-wheelchair-propulsion (accessed February 27, 2021). Michael L. Boninger, MD, Aaron L. Souza, MS, Rory A. Cooper, PhD, Shirley G. Fitzgerald, PhD,Alicia M. Koontz, MS, ATP, Brian T. Fay, MS. “Propulsion Patterns and Pushrim Biomechanics in ManualWheelchair Propulsion.” In The Archives of Physical Medicine and Rehabilitation Volume 83.5, by The Archives of Physical Medicine and Rehabilitation, 718-723. Pittsburgh, PA: The Archives of Physical Medicine and Rehabilitation, 2002. Okafor, Lauren, Margaret A. Sinkler, and Matthew Varacallo. Anatomy, Shoulder and Upper Limb, Metacarpophalangeal Joints. Treasure Island FL: StatPearls Publishing, 2020. Sara J. Mulroy, PhD, PT, JoAnne K. Gronley, MA, PT, Craig J. Newsam, MPT, Jacquelin Perry, MD. “Electromyographic Activity of Shoulder Muscles During Wheelchair Propulsion by Paraplegic Persons .” In The Archives of Physical Medicine and Rehabilitation Volume 77, by The Archives of Physical Medicine and Rehabilitation, 187193. Downey CA: The Archives of Physical Medicine and Rehabilitation, 1996 Sean D. Shimada, PhD, PhD Rick N. Robertson, MD Michael L. Bonninger, and PhD Rory A. Cooper. “Kinematic characterization of wheelchair propulsio.” In Journal of Rehabilitation Research and Development Vol. 35, by Department of Veterans Affairs, 210-218. Pittsburgh, PA: Journal of Rehabilitation Research and Development, 1998.