Team RLNT< here with another update on our progress in developing the Wheelchair Hill Assist Device! The Wheelchair Hill Assist Device will operate by attaching to the wheelie bars of a manual wheelchair. The device will feature a motor and battery system, which when activated will provide a boost to the user's pushing force. This additional force assists the wheelchair user in ascending steep ramps or inclines with ease, effectively reducing the physical effort required by the user by a minimum of 50%. The device will feature a controller that manages the power output, ensuring a smooth and controlled experience. Refer to Figure 1 below for a flowchart of our design.
Figure 1: Flowchart of device process.
Our team has made significant strides in advancing our project since our last post. To gain a deeper understanding of the project's evolution, here are the tasks recently completed:
Completed Tasks
Task 3.1 - Measure distances between wheely bars and the closest surfaces in vertical and horizontal directions to optimize device location.
The team found there to be three major wheelie bar dimensions: the wheelie bar's inner diameter, the distance between the wheelie bars, and the height of the wheelie bars from the floor. These key dimension locations can be seen in Figure 2 below, with the values for each wheelchair listed in Table 1. These differing dimensions pose a challenge to the adaptability of the device. Team RLNT< will need to use an adjustable mounting style to accommodate this challenge.
Figure 2: Major wheelie bar dimension locations.
Task 3.2 - Select a battery with 10,000 mAh at 36 V.
The team was unsure about voltage selection, so they reached out to Les Hickman, a local scooter mechanic and the owner of Sonic Scooters in Kemah, Texas. Les donated a battery rated for 36 [V] and 10,000 [mAh]. The team then input the maximum weight of the user, wheelchair, device weight of 136 [kg], the slope of 4.76°, and a ramp height of 100 feet (30.5[m]) to capacity equations to confirm the battery viability.
Task 3.3 - Calculate static force analysis of the wheelchair with the user and device’s weight to select a motor.
Team RLNT< then used the free body diagram below in Figure 3 along with a summation of forces, when considering gravity and friction, to calculate a minimum pushing force of 137.55[N].
Figure 3: Free body diagram of use.
Task 3.4 - Perform dynamic analysis to find the velocity and acceleration output of the device to define the rpm required to calculate motor power requirements.
Using the force of 137.55[N], possible torques are calculated using basic torque equations for different wheel and rim radiuses. Table 2 shows the different possible torques. Assuming the device and wheelchair should travel at an average walking speed of 3 [mph] (1.34 [m/s]), the different angular velocities are calculated for each radius by using angular velocity equations. These values are shown in Table 3.
Task 3.5 - Convert force analysis using power equations to search for motor parameters.
Team RLNT< calculated the minimum motor power output of 184.5[W] using power equations that involve the previously found torques and angular velocities. These values can be seen below in Table 4. Using this value, the team is considering purchasing a motor rated for 350[W].
Task 3.6 - Conduct stress concentration analysis using motor parameters to select the material of the adaptor fastener.
Team RLNT< used the maximum weight of the device (51[lb]), and the required pushing force of the motor (31[lb]) to find the worst-case resultant force of 60 [lb]. This force was applied to the smallest wheelie bar diameter, which has a cross-sectional area of 0.44 [in²] resulting in a stress of 135[lbf/in²].
For the work period of October 28 - November 11, Team RLNT< has completed the following progress:
Task 3.7 - Conduct heat transfer analysis using battery and motor parameters to determine minimum thermal conductivity to select material for the device's shell.
Team RLNT< selected ASA filament for its UV resistivity and its yield strength of ASA is 4380 [lbf/in] when printed in the weakest direction at an inlay of 25%. Thermal analysis was performed to confirm the validity of the ASA filament.
Although progress has been made, significant tasks still need to be completed. The tasks currently in progress are as follows:
In Progress Tasks
Task 4.1 - Finalize the material of the device shell and select fasteners.
The team has selected ASA as the shell's material but is currently in progress of selecting device fasteners.
Task 4.2 - Use the power of the motor and battery voltage/charge to select the motor hub.
Task 4.3 - Re-evaluate analyses in Milestone 3 to confirm that the design satisfies the parameters.
Task 4.4 - Model CAD of wheelchair hill assist device shell, electronics, and assembly.
A CAD model of the initial prototype design can be seen in Figure 4 below. This CAD file needs to be updated to be more accurate in dimension. Part 1 is the shell that will encase the electrical components. Part 2 is the motor hub. Part 3 is the horizontally and vertically adjustable bars discussed previously.
Figure 4: An initial CAD model of the Wheelchair Hill Assist Device.
Task 4.5 - Create a Bill of Material (BoM) for the device.
Task 4.6 - Create standard operating procedures (SOP) for device assembly.
Task 4.7 - Submit critical design review to finalize the design of the device.
The team is expecting to finalize the major milestone of designing the Wheelchair Hill Assist device within the next month. Team RLNT< is currently ahead of schedule and plans to continue on their aggressive progress by prioritizing their Capstone 1 course load. Since the team anticipates encountering issues with wiring the device, Team RLNT< plans to have a meeting with Les Hickman of Sonic Scooters within the next week to discuss the compatibility of the electronic components they are proposing to use. If the team is unable to wire the device and Les is unable to offer assistance, the team will consult other industry professionals.
All equations mentioned in this blog post as well as sample calculations can be found in the appendix of the attached document below. This Written Progress Report document outlines the most recent progress made by the team more in-depth.
Thank you all for your unwavering support! As we move closer to the prototyping phase, we eagerly anticipate sharing more updates to our project. Stay tuned for exciting developments!
It sounds like you are making progress. Keep up the great work! Can't wait to see the prototype!