Adam Nolte, Alicia Li, Victoria Li, Jessica Ordax
Individuals that are dependent on a wheelchair for mobility often have trouble walking their dogs. The goal of this project was to create an easily removable wheelchair attachment to facilitate dog walking. The Wheelchair Dog Walker (WDW) device consists of two hinged, rigid Dog Guides that extend from metal pipes mounted underneath the wheelchair’s armrests. The leashes thread through the Dog Guides and run alongside the chair, terminating at Leash Locks attached near the wheelchair’s handles. The WDW restricts the dogs’ movements to the sides of the wheelchair, allowing the user to walk their dogs while minimizing entanglement issues. Empirical testing proved the device does not have a risk of tipping the wheelchair. The device gives the wheelchair user the ability to walk two dogs without holding the leashes, and prevents the dogs from tangling with each other or getting in the way of the wheelchair.
The client is a young man in his early twenties who loves participating in triathlons, playing musical instruments, and walking his two dogs. The client has severe cerebral palsy, a congenital disorder that affects muscle tone and movement. While he demonstrates normal intellectual ability by communicating via a computer system controlled with a head switch, the client displays symptoms of spasticity and has limited physical mobility. The client cannot move his wheelchair autonomously and depends on his assistant to push him.
The client would like to walk his two dogs with the aid of his assistant. Currently, the assistant must push the client’s wheelchair while simultaneously holding the leashes of both dogs. As a result, in order to ensure safety of the client, the assistant cannot control the dogs effectively; the dogs get tangled with each other and get in the way of the chair.
Although there are commercial devices designed to walk multiple dogs, including several that attach to wheelchairs, none of the existing and patented devices provide the necessary features to address the client’s needs. The proposed Wheelchair Dog-Walker design will be a custom device that incorporates a rigid buffer region that will control the radius of movement of the dogs and a retractable dual leash system with added features of removability and hands-free operation.
The client needs a device to attach to his wheelchair so he can walk his two dogs with the aid of his assistant. Currently, his assistant pushes the chair and holds on to both of the dog’s leashes simultaneously. The goal of this project is to design such a device that will be low profile, easily attachable and removable, hands free, and rigid enough to prevent the dogs from getting entangled with each other and with the wheelchair.
Design and Development
The WDW is shown in Figure 1. It consists of a pair of Leash Clamps, Leash Locks, Rigid Dog Guides, Hinges, and Connector Pipes.
The Leash Clamps (Fig. 2) are used to connect the Leash Locks (Fig. 5) to the wheelchair. They are each secured tightly around the attachment points of the chair and have rubber lining to prevent slipping. The two ends are clamped around the corresponding pipe on the wheelchair and fastened using a 3/16” hex wrench. They will typically be left on the chair at all times. The two clamps are slightly different due to the asymmetry of the chair. On the left side, the clamp attaches such that the Leash Lock Connector is vertical (Fig. 3), while on the right side the Leash Lock Connector is horizontal (Fig 4). A thumbscrew is inserted to secure the horizontal clamp to the leash lock (Fig. 7).
The Leash Lock features an HDPE enclosure that clamps around a Flexi-durabelt mid-size retractable leash. A retractable leash was chosen because it allows the operator to let the dog away from the chair if the dog needs to reach a grassy area to relieve itself. T-wedges and T-slots were cut in the enclosure panels to ensure they are always lined up correctly (Fig. 9). The sides of the Leash Lock are lined with rubber to prevent the leash from slipping within the enclosure. The leash is held firmly in place with four 3” 5/16 bolts with matching nylon nuts (Fig. 9). The bottom two bolts hug the leash tightly to prevent downward slipping. The locking button is a standard E-stop button and can easily be pressed downwards to lock the leash in place. This works by aligning the bottom of the button with the trigger on the retractable leash. To unlock, the button is simply twisted in the clockwise direction. The leash threads from the leash lock through the hinged-rigid dog guide.
Hinges are used to attach the dog guides to the wheelchair (Fig. 10). They are made of aluminum, and the Dog Guides are welded to the hinges. The hinges rotate about a shoulder bolt. A Stop Wedge limits the angle of rotation. This ensures that the dog guides cannot become parallel with the wheelchair, thus inhibiting the dogs from crossing in front of the wheelchair’s path. The other side of the Hinge is a Connector Pipe Insert. This provides the attachment point to the wheelchair. It slides into the Connector Pipe (Fig. 11) and is pinned in place.
The Connector Pipes (Fig. 11) are mounted underneath the armrests of the wheelchair (Fig. 12). They consist of an aluminum pipe that slides through two aluminum Pipe Clamps. The Pipe Clamps are attached to the wheelchair using the same mechanism as the Leash Clamps. A Rotation Stopper is bolted through the back Pipe Clamp to prevent the dogs from rotating the connector pipes. The Connector Pipe insert end of the Hinge slides through the pipes such that the Pin Holes in the Hinge (Fig. 10) align with the Connector Pipe Pin Holes (indicated by the red lines in Figure 11). A Stabilization Pin (Fig. 13) is inserted through the aligned holes to hold the hinged-rigid Dog Guide in place.
The Dog Guides (Fig. 14) are thin-walled aluminum pipes that each have an opening for the leash to thread through. The leash is threaded from the Leash Lock under the armrest through the Leash Hole and out the open end of the pipe.
The clasp that attaches to the dog’s collar is wider than the opening of the Dog Guide so it cannot slide back up the pipe.
The Dog Guides are the main functional component of the device. They provide rigidity to the leash, which maintains the dogs at a safe distance from the chair and, if multiple dogs are walking, keeps them separated from each other. They also provide the operator with added leverage when making turns, allowing the dogs to be gently steered in the direction the wheelchair is going (Fig. 15). The dog guides are hinged to provide the dogs more freedom on the walk.
The final device was tested for efficacy and safety. To test the device effectiveness, a series of maneuvers were conducted by the client. First, the dogs were turned along a tight radius and the dog guides easily steered the dogs together with the chair. Next, the chair was stopped and the leash was let out so that a dog could get to a grassy patch to relieve itself. Finally, the leash was retracted and the leash effectively brought the dog close to the chair.
To test for safety, a quantitative analysis was done to asses the risk of the device failing due to strain of the dogs and the dogs causing the chair to tip over. The max force that the dogs could pull with was measured with a force sensor and the maximum force needed break the leash locks and tip the chair was assessed with both theory and experiments. It was found that the device would not fail for forces the dogs were capable of producing and that the chair could not tip.
Discussion and Conclusion
The WDW fulfilled the project goals outlined at the beginning of the project. Specifically, it provided a safe, removable wheelchair attachment that enabled the client to walk his two dogs with the aid of his assistant. The WDW successfully prevented the dogs from entangling with each other or getting in the way of the client’s wheelchair, while still enabling the leash length to be adjusted. Moreover, it is durable, lightweight, and compact, allowing it to be easily attached and removed from the client’s wheelchair. Finally, it has an effective, easy-to-use locking system that enable the client’s assistant to push the wheelchair without the need to hold on to the leashes.
Currently, our client and his assistant use our WDW regularly and with great ease. They are very comfortable with our product because we used an attachment mechanism familiar to them. They were also exposed to our device at least once a week while we made minor adjustments and so were comfortable with our device for sometime before delivery of the final product.
During the design of the WDW, the most difficult challenges arose when we were building the leash locks and the hinges. It was difficult to maintain the utility of the built-in retracting mechanism of the leashes, but also have the leashes close at hand. After multiple iterations we finally developed a casing that holds the leashes in place and attaches to the client’s wheelchair handles bars. We decided on a push-button mechanism where you press the big red button down to lock the leashes and twist to the right to release them.
Moreover, as we began designing the connector pipes (inspired by a previous group who worked with our client) and the dog guides we decided that we wanted to minimize the number of separate parts so that the device could be as strong and stable as possible. We decided to attach the connector pipes to the dog guides via a custom hinge. We designed and machined the hinges ourselves and then had the dog guides welded to them. The hinge itself only allows for horizontal movement up to a limited angle. This ensures that the dogs have some degree of self-autonomy during the walk, but not so much that they can wander off and get in the way of the chair.
The final device was modified to minimize safety hazards that posed potential threats to the client, his assistant, or his dogs. The edges and corners of all the pieces of the WDW were filed down to be smooth and rounded in order to eliminate the risk of cutting the users. The device was also attached at a height that prevented the dogs from tipping the wheelchair. Thus, the WDW met all design specification, project goals, client needs, and safety targets.
Furthermore, although the device was designed specifically with the needs of our client in mind, a similar device with a modified attachment system could easily be implemented. For example, the position of the leash locks could be altered such that they could be controlled by the person in the wheelchair.
We would like to thank our client and his assistant for accommodating us throughout the project, and for working cooperatively and closely with us throughout the semester. It was a truly inspiring and rewarding experience working with them and their energetic dogs. We would also like to thank Nancy Curtis, our client’s physical therapist for her constructive feedback and recommendations that helped improve our device. We would like to extend a special thanks to our professor, Dr. Laurence Bohs, without whose support and inspiration we could not have succeeded in completing our project. Finally, we would like to thank the Duke University Machine shop staff, Steve Earp and Greg Bumpass, for their patience in helping us learn and use the various mechanical machines in the shop.