For the TEK Design Project (11), our team has been tasked with developing and integrating accessibility modifications to our target’s mobility scooter.
Dwarfism is a condition caused by a genetic mutation that results in diminutive stature, restricting mobility in situations where height is a critical factor. This project aims to assist an adult woman possessing this disability by implementing a series of modifications to her accessibility scooter. The proposed solution is expected to accommodate ergonomic seating on the device, storing/removing the rain cover, and propping up the user’s feet. As the client anticipates moving out of her current residence in the foreseeable future, the goal is to provide more universal support of quality-of-life.
Priorities:
Secondary requests:
As a preliminary guide, the client was requested to provide product information for her accessibility scooter. From this, the voltage ratings for the DC motor and rechargeable battery were determined to inform measures for simplifying the device’s power supply process. Currently, it is anticipated that the voltage from the lift will need to be stepped up to that of the 24 V motor.
Beyond this, our team investigated the operation of the lifting mechanism to edify the approach to modifying the rain cover.
The lift on the back of the car uses a line that leads directly from the battery terminals to the hydraulics pump. Right off the bat, we need to check that there is a fuse or some implementation of a safety device to ensure that there’s no potential for a violent short circuit. Secondly, we will need a step-up device to jump the voltage from the battery from 12 to 24 volts because this is the voltage that the mobility charges on. The astute minded have caught that the batteries would charge while the car is off, which would kill the battery on the car. So, to prevent this, behind the voltage stepper would need to be a relay connected to a fuse that is only active while the engine is running.
In this segment of the concept design, the objective was to address the difficulty of removing the rain cover from the mobility scooter.
For the first design, it is proposed to put tie-down holes in the client’s rain cover to affix it to the lift via carabiners that loop into four hooks. This will require drilling into the base to enable the insertion of eyebolts to attach said hooks.
The second design entails creating a structure that is reminiscent of a children’s play tunnel, the base of which is a solid platform that the scooter can be parked onto. Additionally, there is a vertical zipper located 90 degrees away from the opening to create an exit point.
For this portion of our design, we wanted to integrate a folding stair mechanism that allows the user to hook a set of folding stairs onto the scooter for better accessibility to reach the seat.
In the first stage (upright position), the stair is in its folded position, where it is hooked onto the scooter.
In stage two (unfolded position), the stair will be unhooked in its unfolded position, where there will be two support bars to set the stair at a specific angle. These support bars will have a static revolute at one end, and a sliding revolute at the other end.
For this concept design, our team wanted to implement an elevated foothold for the user in order to provide more support when maneuvering the mobility scooter.
On the first image, we have a desk-drawer style footrest that will slide out whenever the user wants to use the scooter. It will have a stopping and lock mechanism in order to set it in place while the footrest is in the extended position.
On the second image, we have a storage container style footrest, that doubles simply as a footrest and a storage crate.
Despite deviating from our original decision matrix, we still plan to utilize all of our decisions; however, we plan on combining some of these ideas.
Our team’s choice for overall concept design is split into three sections.
For our first section, we decided to merge the footrest and sliding stair designs for a more compact and efficient design. After analyzing and measuring different parts of the mobility scooter, we realized that our original folding stair design would not be practical given the dimensions of the scooter. Therefore, since the chair can rotate and lock at a 45-degree angle, we meshed the slider stair design into the footrest crate near the base of the scooter.
For our second section, we decided to do some slight modifications to an already existing part for the scooter. There is a canopy that covers the mobility scooter whenever it is resting on its lift, in order to prevent weather damage. In order to combat the struggle of removing and replacing this cover, we decided to implement a drawstring where the current elastic is and create a folded seam which will attach to a beam on the lift, in order to guide the canopy on and off the lift.
For our final section, we plan on adapting an electrical relay system in order to efficiently charge the mobility scooter while it is attached to the vehicle. In order to prevent the car battery from dying, there will be a relay implemented to prevent any power flow while the car is not running. We will wire the charger from the car’s battery in its on state to the scooter, in order to make sure it is charged whenever the scooter needs to be in use (i.e. public outing).
For each design parameter, we selected the elements that would best help our client and stay robust over time. In turn these options will increase the convenience of the mobility scooter for our client to the point she can use it anytime she wants.
The footrest combining with the stairs allows for direct and easy access to the seat, prompting natural movements to get seated.
Charging will be easy as plugging in the scooter before driving, so it can charge on the trip. The tripping hazards for our client and her neighbors is non existent for this solution.
The rain cover will be easy to pull over the scooter. With one side unzipped it will simply pull straight over, without excessive reaching for our client.
Steps: After initial measurements, we decided that we could efficiently integrate the footrest and folding step into one another. We knew that the most important aspect of this scooter was its accessibility, so we had to let go of some other good ideas to make room for the primary design aspect. After a post measurement, we realized that we could take advantage of a preexisting bracket that swivels with the seat. This Bracket would allow a permanent footrest to swivel with the chair. This would give our client the room to turn around the stairs to sit down and a place for them to rest their feet; two birds, one stone. The step that folds down for our client would need two accomplish two things: descend from below the top step, then extend outward as well. This would be accomplished with multiple binary links attached to the outside of both steps and an industrial strength sliding drawer assembly, respectively. Of course, a locking mechanism would need to be added so the stair would not randomly fall.
Charging: It’s important to us and our client that their scooter is fully charged when they need it, so we are integrating a passive charging system into their car, which allows the car to charge the 24 Volt Scooter Battery ONLY when the engine is running. To achieve this, the following modifications will be made to the existing electrical system attached to the mobility scooter lift affixed to the rear of the car. Running away from the positive lead that runs directly from the battery to the lift (which, has a 30 Amp fuse) would be a 12 volt relay rated for 20 Amps. This relay would be flipped by a fuse that is only active when the car is on, like a phone charging port. The relay would consume 0.96 Watts from the 90 that are available to phone charging to keep the relay flipped and the scooter battery charging. Once this relay was flipped, the 12 volts coming from the battery would be stepped up to 24 volts then fed into a CC/CV Buck converter to supply a steady 2 A supply at 24 volts. Then, this would output to the scooter battery to be charged.
Canopy: We ended up taking a closer look at the canopy and found some differences with our initial understanding of the design. The existing elastic band was only attached to half the canopy, a buckle system is sewn onto the other half, and the lift may not be high enough for the previous idea of a pully system. So after reconsideration, it was decided that we should remove the elastic band, expand on the buckle system to loop around the entire canopy (making up for the elastic), and sew on two zippers on one end to help take apart the canopy for removal and covering.
Framework: There is minor damage to the mobility scooter lift on the back of the client’s car that needs heated and hammered out.
When conducting structural analysis, developed stresses and deflections are of salient interest to ensure safety for human use.
Toward this end, a series of three simulations on the lid, upper stair, and bottom stair, respectively, were tested. In all three cases, the selected material was 6061-T6 Aluminum alloy, the bottom of the base was fixed as ground, and the loadings were a 150 lb distributed loading (~667 N) and the gravitational force. Moreover, each revolute at the platforms and arms were configured as a pin with translational lock, and the sliders were established as roller/slider fixtures. Otherwise, the global interaction was treated as contact. Finally, the mesh quality was set to high at a moderate density.
Ultimately, the greatest von Mises Stress observed was 54.51 MPa on the bottom stair, 33.77 MPa for the top stair, and 7.354 MPa for the lid, none of which exceeded the material yield stress of 275 MPa. Furthermore, the maximum deflections were 1.123 mm for the bottom stair, 0.2874 mm for the top stair, and 2.792 mm for the lid, all of which negligible for our purposes. This suggests the system is very rigid and should be sufficiently sturdy for use by the client.
It’s very important that modifications to the canopy don’t ruin the integrity of its weatherproofing.
Canopy Material Selection:
Zippers- We chose a size #10 molded tooth zipper made with DuPont Delrin® acetal resins using a locking slider. Size #10 zippers are used for projects such as boat covers and tents. Delrin molded tooth zippers are UV and corrosion-resistant. The locking slider will resist unzipping when pulled perpendicular.
Buckle System- The final material hasn’t been decided, but we are considering nylon or a higher-strength and more expensive polyester webbing for the strap.
