What it does
ASCEND is an affordable and easy-to-assemble accessory that can be retrofitted onto existing manual wheelchairs. It aims to mitigate the challenge that wheelchair users face when climbing an incline.
ASCEND was first conceptualized when I was helping to push a wheelchair user up a ramp. While ramps can be easily traversed by an able bodied person, it is actually a significant obstacle to a wheelchair user. These include safety hazards like rolling backwards or tipping over, physical fatigue from working against gravity, or even emotional distress from feeling powerless or asking for help. The idea for a device that could be retrofitted on manual wheelchairs to address these invisible issues and empower wheelchair users with the ability to tackle inclines safely without excessive physical strain or assistance from others was then born.
How it works
ASCEND uses the principles of a ratchet and pawl mechanism to allow for mono-directional motion. When ASCEND is engaged for use in navigating an incline, the slanted edge of the spring loaded rotor and stator teeth are able to slide past each other for forward motion. If the wheelchair user releases contact with the wheels, the spring in the rotor forces the vertical edges of the rotor and stator to contact and prevents backwards motion. The wheel is hence constrained to only move forward. This eliminates the need for wheelchair users to constantly propel their wheelchair upwards or be in constant contact with the wheels. They are now able to tackle the incline with significantly less exertion and danger. For use on level ground, the rotor can be put into a disengaged position and the wheels would be free to roll forwards and backwards as usual.
The design process started with me trying to climb a ramp in a wheelchair unassisted to understand the issue first-hand. Rolling backwards was a major problem as the quick onset of fatigue made it hard to keep constant hand contact with both wheels to prevent rollbacks. In designing ASCEND, the following requirements had to be fulfilled. 1) Forward motion must be allowed while backwards motion must be stopped. 2) Compatibility with existing manual wheelchairs. 3) Intuitive and simple design to cater to all wheelchair users. A ratchet and pawl mechanism was chosen for its simplicity and efficacy in mono-directional rotation. ASCEND underwent a few iterations during the design process. First, the number of teeth on the stator was increased from 4 to 12 to minimise distance between teeth and hence whiplash if the user releases contact. Next, the radius of curvature of the teeth surface was increased to allow a smoother rotary action. FEA was conducted to determine the maximum load that ASCEND could take without irreversible plastic deformation and the number of rotor teeth was reduced from 4 to 3 to minimise raw material usage. A simple push and pull action to engage or disengage ASCEND was then adopted for ease of use for wheelchair users before arriving at the final variant.
How it is different
While motorised wheelchairs do exist, it may not be affordable or accessible for all. The price, duration of use and hidden maintenance costs contribute to the impracticality of obtaining a motorised wheelchair in most instances. ASCEND is an affordable and feasible alternative to navigating inclines without any motorised parts. It can be manufactured by machining or 3D printing with low cost due to its small size and simple design. ASCEND is designed to be retrofitted on to most existing manual wheelchairs and hence eliminates the need for designing and manufacturing a completely new wheelchair platform. It can also be assembled and installed with minimal tools and knowledge to make it accessible to almost everyone who needs it.
My goal for ASCEND is for it to enhance and maximise wheelchair mobility. Additional functions like assisted braking on downslopes, kinetic energy recovery and storage system to provide short power assisted boosts on inclines are some examples that I am working on for a second generation prototype. The simplicity of ASCEND provides a versatile platform for modifications and new functions that can be added in the future. In time, I hope to make ASCEND an all-in-one accessory to solve most, if not all of the mobility problems that wheelchair users face in their daily lives.