In this upcoming blog post, we are excited to bring our readers up to speed on the latest developments in our "Wheelchair Hill Assist Device" project. We aim to provide a clear and comprehensive overview of how our project has evolved, highlighting the refinements we've incorporated to address the unique challenges faced by manual wheelchair users. By sharing these updates, we hope to keep our readers engaged and informed as we continue to work towards creating a more accessible and user-friendly solution for individuals relying on manual wheelchairs.
According to the World Health Organization (WHO), more than 65 million people use a wheelchair [1]. The use of these wheelchairs can be cumbersome and physically demanding for the user, especially when considering traversing wheelchair ramps. One of our group members, Jakob, has a sister who is physically disabled. Jakob's sister spends a large portion of her time in a manual wheelchair and often complains about the functionality of the wheelchairs she has available to her. Some of her complaints include that individuals who use manual wheelchairs struggle to get up wheelchair ramps, especially if the ramps do not adhere to the handrail regulations in the Americans with Disabilities Act (ADA) code as shown in Figure 1. Handrails enable manual wheelchair users to take a break while navigating the ramp, allowing the user to regain the energy necessary to get to the top. Handrails are required to be on both sides if the vertical rise is greater than 6”. The maximum slope of a ramp adhering to ADA standards is 1:12, or 4.76°, with a 30” max rise per run. Syvanna is on disability assistance and does not have the option to purchase an electric wheelchair due to the average wheelchair costing $7,000 [3]. Besides the cost, electric wheelchairs often have their own set of problems. Electric wheelchairs can weigh up to two hundred and fifty pounds, and often loading them in a vehicle is a near-impossible task.
Fig.1: ADA Ramp Requirements [4].
The main goal of the device is to help the client climb up wheelchair ramps in manual wheelchairs by decreasing the energy expenditure by at least 50%. The wheelchair must remain 100% operable regardless of if the device is on or off. The device should be attachable and detachable, and it must be done by someone who is not disabled within a fifteen-minute time frame. A potential location of device attachment is the wheelie bars at the back of the wheelchair. The wheelie bars are used to prevent the user from tipping over in the backward direction. Please refer to Figure 2 for the location of the wheelie bar. The battery of the device must be rechargeable with a 110-volt power cable with a USB-C type charger, and include this charging cord with the product [5]. The device's wiring harness must not get tangled with the wheels.
Fig. 2: Diagram of Maximum Tilt Angle and Wheelie Bar Location.
In the design of our product, we expect to encounter many physical constraints. The device, the user, and the wheelchair have a maximum weight of 300 pounds. The device should be compatible with both of the client’s manual wheelchairs and one additional wheelchair, with the potential to adapt to more wheelchairs. The battery lifespan needs to allow the device to climb at least 100 vertical feet of ramps at a 1:12 ratio with or without guard rails. The device should not increase the overall degree of tilt by more than 5° when going up wheelchair ramps, as seen in Figure 2. The device should have an ingress protection rating of IP63 as shown in Figure 3, which ensures the device is dust-tight and protected against sprays of water [6]. The weight of the device should be kept below 51 pounds as according to OSHA, this is the maximum weight a single non-disabled person can lift [7][8]. The device must remain at least 5°F below the electronics and shell material’s maximum operating temperatures. A potentiometer or adjustable controller must be programmed with the wheelchair hill assist device that is adjustable between 0 and 12 volts. These constraints can be found below in Table 1.
Fig. 3: Ingress Protection Rating [6]
Table 1: Table of Project Constraints
Constraint | Quantification | Comments |
Max device weight | 51 [lbs] | |
Weight of assembly | 300 [lbs] | User, chair, and device |
Water and dust resistance | IP63 Rating | |
Adaptability | 3 or more wheelchairs | |
Battery life | 100 total vertical feet of ramps at 1:12 ratio | Combined feet throughout the testing period |
Temperature | Within 5°F of the maximum operating temperature of electronics | |
Stability | 5° of rotation past the normal direction | |
Controller | 0 - 12V potentiometer and switch | |
These constraints present several challenges to team RLNT<’s project, primarily related to the design and functionality of the device. The weight maximum requires the team to select and utilize lightweight materials, while simultaneously balancing structural robustness. The IP63 constraint will require materials to be selected that can withstand environmental conditions while also maintaining functionality. Compatibility with at least three wheelchairs requires the team to consider how the device will attach to the wheelchair and introduces complexity in achieving an adaptable fit. The requirement for a battery lifespan capable of climbing 100 vertical feet poses a challenge in selecting energy-efficient components in order to optimize power consumption. Keeping the temperature within 5°F of the maximum requires heat dissipation strategies for the device. Ensuring the device does not exceed 5° of rotation past the normal direction poses the challenge of engineering dynamic and load analyses on the chair. Selecting the controller introduces project complexity due to the compatibility and user interface of the device.
To address the key physical challenges in the team’s design, the team proposes a technical analysis plan to develop and refine the conceptual design before execution. The distances between the wheelchair wheelie bars and the closest surfaces to optimize device location selection. This analysis will help determine the optimal position for the device on the wheelchair, ensuring that it does not hinder the device's stability, functionality, or overall performance. The team will finalize the motor, battery, and drivetrain selection by performing a static and dynamic analysis of the wheelchair when considering a range of user inputs. The static analysis will help the team determine whether or not the motor and battery selection is sufficient to provide power for navigating wheelchair ramps while handling the combined weight of the user, wheelchair, and the device. The dynamic analysis will determine the device’s power through the conversion of force analysis in order to search for motor parameter requirements. Dynamic analysis will be used to find the velocity and acceleration output of the device when attached to the wheelchair being operated by the user. A force and torsion analysis on the motor on the wheelchair’s wheelie bar will be completed in order to find what material is required for the production of the device.
Other than the physical challenges of the problem, the team anticipates having minimal electrical knowledge to be a challenge. The team needs to research possible ways to simplify the required electric work to streamline the design process of the motor, battery, drivetrain, and switch. The team will measure the success of completion through device testing after the prototyping phase.
For more comprehensive information on the project and the updates that have been made to it, refer to the Project Proposal below.
Stay tuned for an insightful glimpse into our project's progress and the positive impact it will make!
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