Allez: One Arm Wheelchair Drive
January 2016 - July 2016
Product Design, Mechanical Design

Individuals with hemiplegia currently do not have effective mobility solutions. We designed and prototyped a modular one arm wheelchair drive attachment for manual wheelchairs in order to increase the independence of our users.

The Challenge

A common condition that arises as a result of stroke is hemiplegia, weakness of one side of the body. Currently, there aren’t very good mobility solutions for individuals with hemiplegia. If people were to propel themselves with their strong arm in a manual wheelchair, they’d just move in circles! Right now, individuals either: propel their manual wheelchairs with their arms and steer with their foot, propel and steer with their foot, or use commercially available one arm drives that physical therapists don’t recommend to their patients because they don’t work all that well.

User/Market Research

We began our project by trying to understand the needs of our users and other stakeholders. Our team spoke with physical therapists, rehabilitation engineers, caretakers, and individuals with hemiplegia in order to first determine points of tension with current mobility solutions. Additionally, from our research into existing commercially available one arm drives, we were able to narrow the scope of our solution to focus on controlling only one of the front caster wheels as that was all that was needed to control the direction of the wheelchair.

Dual-rim Drive Chair

Lever Drive Chair

Neater Uni-Chair

Prototyping

For our first iteration, we wanted to integrate a footplate that attached directly to the front caster wheel. However, when we tested our first prototype, we learned that we needed significantly more force to keep the wheel pointed in the desired direction.

Render of Rev A design with a modular footplate

For our second iteration, we moved to an electromechanical solution with an actuator assembly coupled to the front caster wheel. We did some calculations as to how much force was needed to turn the wheel on a high friction surface in order to size our servo. To more easily troubleshoot our prototype, we opted to simplify our footplate mechanism by implementing a joystick instead.

Render of Rev B design with actuator assembly

Closeup of gears on wheelchair

Rev B assembly

Based on our testing, we found that we needed a stronger servo. Due to the angled design of the caster fork, the caster wheel flipped 180 degrees when a user moved backwards. This “flip” made it very difficult to calibrate direction input to actuator movement. For our third iteration, we implemented our footplate mechanism and rebuilt our actuator assembly using a stronger servo.

Rev C design overview

How It Works

A user rotates the electromechanical footplate with their strong foot to indicate the direction they want the chair to go. A Hall effect sensor in the footplate reads the position of the rotated plates; there is a change in magnetic field when the magnet rotates with respect to the sensor, which is stationary on the bottom footplate. An Arduino then translates that rotation into a desired position for an actuator assembly that is coupled to the front caster wheel.

Animation of actuator assembly and footplate mechanism

User Testing

In collaboration with Rancho Los Amigos National Rehabilitation Center in Downey, CA, my team tested our prototype with inpatients and physical therapists. It was essential for us to receive feedback from individuals who could be potential users and integrate their feedback into subsequent iterations of our one arm wheelchair drive.

Video compilation of product testing

After testing, we also considered potential directions our project could go. Ideas we had included adding a case to better protect against items from getting caught between the gears and a fail-safe disengage mechanism in the event of device failure.

Case to isolate gears

Fail-safe mechanism, engaged

Fail-safe mechanism, disengaged

What Else?

Allez means “go” in French. We designed our one arm wheelchair drive to be another potential mobility solution in order to increase the independence of individuals with hemiplegia. My teammates and I also all fenced on the Caltech Fencing team at one point in our undergraduate careers. Stephanie fenced foil, Auggie fenced sabre, and I fenced epee (the best weapon). The command of “allez” begins the bout.

In May 2016, our one arm wheelchair drive was selected as one of six finalist projects from over 90 submissions to the RESNA Student Design Competition! My team presented our project at the RESNA Conference and Developer’s Forum in Washington DC in July 2016.

Final one arm wheelchair drive design

Representing Caltech at the RESNA Conference

After the competition, in the spirit of the scientific process, we, the RESNA Student Design Competition finalists, wanted to see how many engineers and occupational therapists you could fit into an elevator selfie. The answer: 13, with room to spare!

RESNA Student Design Competition finalists 2016