Stair Climbing Wheelchair Using PA-17-POT Actuator

Individuals with limited or no leg mobility often require mobility devices capable of navigating terrain with rough surfaces, minor stairways, individual steps, and snowy conditions. Although wheelchair solutions are available on the market, they often do not adequately address these challenges or are too expensive for many users who need affordable solutions. The CMD (Collapsible Mobile Device) project aims to provide wheelchair users with essential mobility solutions at an affordable price by developing a wheelchair attachment heavily inspired by contemporary snowmobiles. In this article, we will cover highlights of the stair climbing wheelchair project by Team CMD that uses our PA-17-POT actuator!

Challenges of Using Wheelchairs

Arshak Petrosyan engaged in a detailed discussion with stakeholders Aaron and Emmanuel, focusing on the daily challenges they encounter as university students. These primary challenges include the difficulty of operating wheelchairs in adverse weather, navigating bumps and stairs, and the prohibitive cost of these devices. Notably, high-end wheelchairs can exceed $8,000 CAD, while existing stair-climbing variants may cost over $50,000 CAD. To address these challenges, the ideal solution would include:

• Stair climbing capabilities to overcome the most common obstacles faced by wheelchair users.
• Self balancing to ensure the wheelchair seat balances itself and automatically adjusts based on the stair angle for comfort and safety.
• Winter weather functionality to handle conditions such as the Canadian weather.
• Affordable price points that reduce financial barriers and promote greater accessibility.

Forming Team CMD

To address the issues described by the stakeholders, a group of Engineering students from the University of Waterloo formed Team CMD. The CMD (Collapsible Mobile Device) is a student-led fourth-year design project with the goal of providing wheelchair users an affordable future that offers the freedom and comfort to navigate any terrain.

Nigel Fernandes - CEO & Business Department Manager

Abhi Gupta - CTO & Electrical & Controls Department Manager

Mohamed Moustafa - Software Department Manager

Arshak Petrosyan - CMO & Powertrain Department Manager

Avinash Yarram - Chassis & Dynamics Department Manager

Together, they are committed to revolutionizing the concept of a wheelchair, turning it from a barrier into a symbol of freedom, independence, and inclusivity. 

Designing and Manufacturing the CMD Project

The CMD works as an add-on for traditional wheelchairs, enabling users to handle rough terrain, small bumps, and stairs in winter conditions. It keeps the user safe and comfortable for a full day on a single charge without needing to exit their wheelchair. The device functions allow users to attach and detach it as necessary to overcome outdoor obstacles. This prevents the need to purchase a new wheelchair and helps keep the size and weight to a minimum. The chassis was constructed from square aluminum tubing as a strong but lightweight solution, with extensive force and motion analysis performed to ensure effective design and structural integrity.

CAD Designs and Schematics

The software that was most used and helpful during the design process was Solidworks for all the mechanical designs and finite element analysis (FEA). For electrical work, a software called RapidHarness helped organize all the electronics and lay out an electrical harness for the building while KiCad was used for all electrical schematics.

Finding The Right Linear Actuator

Since the CMD will require outdoor suitable ingress protection ratings, heavy duty capabilities, and positional feedback, the PA-17-8-2000-POT Industrial Linear Actuator was found to be the best fit for the application. This model has a brushed DC motor that operates at 12 VDC, includes Potentiometer Feedback, and comes with an 8" stroke rated to handle 2000 lbs of force.

Our BRK-17 Heavy Duty Mounting Bracket allows for secure mounting in the installation process. The actuator is used to tilt the wheelchair seat so that the user can be parallel to the ground when traversing stairs. To do this, a dump truck mechanism as illustrated below was implemented.

Microcontroller Selection and Programming

The team originally planned for the STM32 Nucleo board as their microcontroller, however, they ended up using the Arduino Mega 2560 since Arduino support is significantly more available and aligned with the team’s skill set. The software was developed using C programming language to allow users to easily control the device with two analog sticks. This frees the user’s hands to pilot the intuitive steering mechanism, as well as to ensure the user remained safe and balanced during stair climbing using sensor feedback. The sensors were connected to the microcontroller with sufficient current supply and GPIO ports to accommodate them.

Electrical System Protection and Fuses

The team’s battery capacity calculations led to choosing a 35Ah, 12V battery from Fortress Scooters, providing more than the necessary power for extended use. Being connected in parallel to each other increased the overall operation time of the device. 

Given that the CMD is high-powered and draws high current from the lead acid batteries, there is a risk of current surges damaging essential electrical components. Therefore, every major electrical component linked to the batteries is first connected to a fuse rated for the correct current value. Additionally, an emergency disconnect switch was installed as a safety feature, allowing the user to immediately stop the current flow to all of the CMD.

Testing and Final Results of the CMD

The CMD project has not only been a significant learning experience, but also a trigger for identifying areas for design enhancements. Some design decisions were driven by time limitations, while others were influenced by a restricted budget. Ultimately, the actual amount spent was $2611.44, which is $940.90 less than the initially projected cost for the CMD.  

The current CMD prototype is unable to navigate curved stairs. However, with continued development, the next version from Team CMD will address this limitation by incorporating two smaller tracks, enhancing its ability to maneuver stairs and bypass obstacles. For more details on the CMD project, check out the PDF capstone report and the website link to Team CMD below:

Stair climbing wheelchair Waterloo Final Capstone Report.pdf

https://cmd-business.webflow.io/

IN SUMMARY

Our PA-17-POT offers heavy duty capabilities with positional feedback suitable for many applications including the tilt adjustments of stair climbing wheelchairs. Thank you to Team CMD from the University of Waterloo for sharing your amazing projects!

We hope you found this as informative and interesting as we did, especially if you were looking for inspirational ideas for upgrading wheelchairs. If you have any queries or wish to discuss our products further, please do not hesitate to contact us! We are experts in what we do and will be happy to assist however we can.

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