Proceedings of the Multi-Disciplinary Senior Design Conference Page 5

Proceedings of the Multi-Disciplinary Senior Design Conference Page 5

Project Number: P16012

ALL-TERRAIN WALKER

Angelica Hambrecht
Mechanical Engineer / Justin Kibler
Mechanical Engineer
Maxine Laroche
Industrial & Systems Engineer / Nathaniel Watts
Mechanical Engineer

ABSTRACT

Walking a hiking trail or along some rough terrain has its risks especially for people with motor impairments. To mitigate this risk, walkers have been used as assistive devices to support the user as they walk. There are even some with special features so that these users have more freedom to go where they like. Even with all these special features, finding a simple, accessible walker that is safe enough for people diagnosed with conditions that limit their physical abilities such as Multiple Sclerosis or Cerebral Palsy can be difficult. In this paper, the process by which the All-Terrain Walker was developed and designed is illustrated. Unlike common walkers, the All-Terrain Walker is designed with MS and CP patients in mind and thus allows them to walk on rough terrain. In addition, the device has a hand drive system attached to the wheels which allows users to go over obstacles safely and has modified wheels and braking systems that makes the walker simple and durable. This paper also discusses some of the major risks and challenges the team faced and any recommendations that can be useful for a second iteration.

BACKGROUND

Multiple Sclerosis and Cerebral Palsy are both conditions that affect the motor skills and even brain function of many people around the world. Essentially both ailments attack the nervous system but each has different effects on the body. According to the National Multiple Sclerosis Society [1], about 2.3 million individuals are living with MS nationwide. Although the cause of this disease is unknown, it forces the immune system to attack the brain and spinal cord which interferes with signals to and from the brain. This essentially causes symptoms, such as tingling sensation, fatigue, or paralysis, that are unique to each person of various ages. Over time these symptoms can worsen or new symptoms can surface while some patients experience calm periods with no symptoms. There are currently no definite cures or therapies to slow down or stop the disease [2].

Cerebral Palsy is a neurological disorder that appears in infancy and permanently affects body movement and muscle coordination though symptoms are not entirely visible until the child is three years old [3]. As of 2008, about 1 in 323 children are diagnosed as having the condition [4]. Symptoms include stiffness of muscles, spasmodic reflexes, or unsteady gait where a foot or leg is dragged while walking. There is also no cure for the disorder but unlike MS this disorder is not progressive and will not worsen over time. In the end, these conditions can severally impact a person’s mobility [3]. By using assistive devices, people with one of these disabilities can walk wherever they want with confidence while remaining safe. With this information in mind, the purpose of this project is to develop a walker catered to these users that will allow them to walk on terrain likely seen in a hiking trail.

PROCESS

When assigned this project, the team was introduced to Karrie, a 35 year old MS patient, and Tobi, a 15 year old CP patient. As stakeholders of this project their insight greatly impacted the basic requirements and overall design of the walker. Upon meeting with them various requests and expectations were highlighted. The walker had to be durable enough to traverse rough terrain as well as overcome standard sized objects, such as a curb, without tipping. In addition, the walker should be light enough so the user or their aid can move it easily. It is required that the walker have folding capabilities so that it may be carried and put away for storage. The completed walker and all of its features must be safe enough so that no danger come to the user during operation. These requests and more were formed into customer requirements and are further translated into engineering requirements to serve as building metrics for the project. As seen in Fig. 1 below, the requirements were ranked to illustrate their importance to the customer and the project. The main sponsor for this project was Al Sigl and the team was given $3,000 to complete the project.

With these deliverables, as well as gathered benchmarking ideas from other competitors, various design concepts were considered. Industrial design students, Kurtis Unruh-Kracke and Tatiana Ferrucio Ferreira, were a great asset to the design selection process and offered valuable insight on ergonomic and aesthetic concepts such as the walker’s shape and how the user should best interact with the walker. They also provided preliminary sketches and models. These inputs were debated alongside the customer and engineering requirements and a morphological table was developed to illustrate what design concepts were feasible and acceptable.

The first topic discussed during this process was what material to use to make the walker. Almost every walker on the market used aluminum as it is a light material that can be easily purchased and fabricated into various shapes. However, these types of walkers are not meant to be used outdoors under rough conditions for prolonged periods of time so strength and durability became an issue. Fortunately, the team was able to gather some insight from RIT’s Baja team [5], a competitive racing club that create off road vehicles that are capable of surviving courses with rough terrains and jumps. It was suggested that a thin tubing of steel could be used to grant the strength and durability needed while still being light enough for everyday use. The team then spent further time selecting the type of steel that would be able to support a 250-pound user as well as be affordable. Another crucial discussion helped to determine the method by which a user would walk over obstacles. After meeting with our clients several times and even witnessing a demonstration in which one of them used their current walker at Mendon Ponds Park, it was evident that a unique feature would be needed to assist the user over obstacles. It was noted that when used over gravel, mud, or other uneven terrain, the walker would slide unsteadily and the wheels would not turn over the terrain as the user walked. In addition, the user spent most of their time dragging the walker rather than guiding it along the path. Lastly, going downhill was a great safety hazard as the user did not have the strength to support themselves and needed some assistance to make it down without losing balance. These are important observations the team considered throughout the design of the walker.

From this information it was finally determined that a posterior design should be implemented. This means the walker is used from behind the user in order to promote better posture and prevent the risk of the walker pulling the user forward. Taking away from the basic “A” shape design of the Generic Rollator used by the clients, the device would have a wide base to support the user while using as little material as possible. A ratchet system made from 3D printed material will assist the user over obstacles and rough terrain. A seat and a pair of handle bars will provide support to the user during the walk. Braking handles are installed on the handle bars and the ratchet system to stop the walker when needed. This gives the user more control. A foldable footrest is installed under the seat to secure the user’s feet when using the ratchet system. The four wheels to move the walker are fitted with treaded mountain tires to withstand rough conditions.

Once a basic design concept was agreed upon it was important to evaluate its effectiveness and feasibility using detailed calculations. A Finite Element Analysis was performed to determine the effective strength of the frame. By performing this analysis, the team was able to identify key variables, see Fig. 2, that would play a part in the size and shape of the basic design and analyze the effects when changed.

FRAME

A 0.065” thick 1” outer diameter steel material was cut and bent to create handle bars and the basic frame work that connects the front wheels to the walker’s body. The final design utilizes push button hinges on the front legs so the user can fold it to carry or store in a car. Metal shims were machined for each end of the hinges to secure them to the legs of the frame. For stronger support, 0.188” thick 1.375” outer diameter steel material was cut and bent to form the main body of the walker. Except for the handle bars, all the frame material was welded together to form the walker’s main body. A cloth backrest is fitted on the frame above the seat to provide support to the user while they are seated. It has a simple sleeve design that slips through the detachable handle bars.

Static load testing will determine if the newly fabricated frame can safely hold a maximum user weight of 250 pounds. Foldability and setup testing was also be performed to evaluate the amount of time needed to fold the walker.

After these tests were performed, the frame was sent for powder coating to prevent rusting and other damage. A maximum incline test and obstacle test will be performed to determine at what angle the walker will tip and if it can successfully and safely go over standard sized obstacles.

HANDLE BARS

The handles are composed of the same 0.065” thick 1” outer diameter material used to fabricate the majority of the frame and slides into the 0.188” thick portion of the frame. Several holes at 1” incriments were machined on the length of the tubes so the handle bar height may be adjusted to the user’s liking. An adjustment screw can be placed in one of the holes to lock the handle bars in position. The handles are also fitted with ergonomic rubber grips to achieve the best comfort for the user’s hands. Braking handles are also installed to stop the walker when the user wished. It was ensured that the distance from the midpoint of the handle grip to the brake handle was in compliance with ISO-7176-3. Though originally designed to have an arch, preliminary feasibility tests identified that there was a risk of over bending and issues with effectively adjusting the handle height. As a result, the handle bar design was changed to a more conventional shape.

RATCHET SYSTEM

Through communication with the project’s main client it was determined that uphill and downhill obstacles were a major challenge, especially for those suffering from Cerebral Palsy or Multiple Sclerosis. It was important that the user feels secure and has complete control of the walker during the ascent or decent. Through benchmarking and research, it was determined that some sort of assistive device would be required. After some research, it was determined that a mechanical gear and ratchet system would be incredibly helpful. The original concept and models for this design are credited to a high school industrial design team in Cambridge, MA [6]. The ratchet system was 3D printed on a highly precise 3D printer using PLA which is a high strength, high durability plastic. Due to time constraints, only one hand drive system could be installed as a proof of concept. However, the design still requires one drive for each side.

The final design of the ratchet system is made up of a hand lever and a casing that holds a planetary gear system. The handle is used as a lever arm that allows a user to operate the ratchet system and move the walker forward. Brake handles, which are connected to the walker’s braking and rotor system, give the user the ability to stop the walker when needed. The casing is at the base of the ratchet system and attaches to the wheel spokes. Inside, 3 small planetary gears work together with a bigger sun gear to reduce the amount of force needed to move the walker.

BRAKING SYSTEM

Hydraulic disc brakes are some of the most reliable and durable brakes for smaller applications such as this. Two sets of hydraulic calipers were mounted to the frame using custom machined brackets that precisely line up the brake pads with the brake rotors. The rotors are mounted on each of the hubs of the rear wheels. The wheels were custom made in order to accommodate this braking system. Two sets of brake handles are connected to each of the calipers, One set is mounted on the main handles of the walker and the other set is mounted on the hand drive arms. This ensures the user will always have brakes handles within reach. The hydraulic brake setup is a variable force system meaning the user can easily apply as little or as much force to the brakes as they need to. The brakes have the capability to instntly completely stop the wheels with very little force on the handles.

WHEELS

The are two different sets of wheels and tires on the walker. The front wheels are 12” and the rear wheels are 20”. The large diameters allow for superior maneuverablity over rough terrain and obsticles. They are both fitted with mountain bike treaded tires for improved traction and stability. The rear wheels were customed spoked at Park AveBike shop to accommondate the disc brake hub needed for the braking system. The front wheels are mounted on casters which allow 360 degrees of movement. This allows the user to easily turn in any direction while moving or while stationary.