proceedings - rochester institute of technologyedge.rit.edu/edge/p18025/public/tech_paper.docx ·...

Multidisciplinary Senior Design ConferenceKate Gleason College of Engineering

Rochester Institute of TechnologyRochester, New York 14623

Project Number: 18025

ZOOM TOTS @ RIT: AN ASSISTIVE MOBILITY DEVICE

Austin GoddardComputer Engineering

Alaiya TuntemekeElectrical Engineering

Kathryn CyrBiomedical Engineering

Solomiya Vysochanska Mechanical Engineering

Brady SweeneyIndustrial Engineering

Allison CrimElectrical Engineering

AbstractA local physical therapist contacted RITs senior design program needing a motion device for a

young patient of hers who has Cerebral Palsy. The purpose of this motion device is to allow the child to explore their environment with minimal parent involvement. The team developed a system that incorporated adjustable child seating, various levels of controls for navigation and power steering to satisfy the needs of the customer. This paper outlines the planning, design, and manufacturing of this system.

Background/MotivationCerebral Palsy (CP) defines a group of permanent movement disorders with symptoms appearing

in early childhood. Symptoms include: stiff/weak muscles, poor coordination and tremors, which stem from abnormal development or damage to the part of the brain that controls movement (Figure 1). Babies and young children especially have trouble with sitting up, crawling, and walking, and may end up using a powered wheelchair as they age to move around. Currently, there is no cure for CP, but therapy, surgery, and medications may help. About 1 in 323 children is born with CP and it is the most common motor disability in early childhood1.

Figure 1: The effect of Cerebral Palsy on brain development

Copyright © 2018 Rochester Institute of Technology

Proceedings of the Multidisciplinary Senior Design Conference

Our MSD team is focusing on solving the problem of children with CP having limited mobility. Our aim is to modify a childrens ride on car to allow the children to open up their cognitive, social, and motor development. Having a sense of independence is extremely important for the mental health of a child with CP. Those living with CP say that “needing someone in your personal business 24/7 gets tiring and can have a negative impact on your self-esteem. I can’t express enough how much better I feel when I accomplish a task without assistance2.” Our car will provide the independence that a child with CP needs to move around their world with limited supervision that would otherwise be impossible. We are specifically designing a car for a young boy we will refer to as “A”. Even though A is our main client, we have designed a built a car that can be adjusted to other children once A outgrows it.

A’s car will be primarily used in his own home, as well as in his school. This will not only benefit A, but also allow his parents and teachers to multitasks while A has the ability to move around without their help. Without the car our MSD team has made, A and other children that use this car, would have needed constant hands-on supervision by their caretakers in order to move. This may have caused some delays in development, since A wouldn’t have been able to independently learn from his environment.

Our customer provided some requirements in order to make sure the car we make fits their vision. The most important requirement was that this car was safe for both the child and adult. Other requirements, such as the car is adjustable, reliable, and easy to use, drove our team’s list of engineering requirements. The biggest requirement our team had to meet was that the car was able to be remotely controlled by a supervising adult, and conforms to ASTM and ISO safety standards for children’s toys. These, as well as other engineering requirements such as controls the child is able to use are available and not too much weight is added to the car, were met within our limited budget.

Description of DesignDesigning this system required many considerations to take into account in order to satisfy the

needs of the customer. In order to solve the problem of limited mobility in children with Cerebral Palsy, the system was designed to allow for various levels of control and customization. Implementing these levels of variability required a design that utilizes the flexibility that software can provide coupled with a robust and well thought out mechanical design. The main systems in this design are adjustable child seating, various levels of controls for navigation and power steering.

Adjustable seating and Control TrayIt was important to provide a comfortable and safe seating for the child, so we chose a standard

car seat. A car seat provides a secure attachment of a child to the seat, and straps for the purpose of attaching the car seat into a standard car. The straps are known as the LATCH system and are required by law in all car seats. The figure below explains the requirements for the LATCH system in vehicles. There are three anchors in total, two lower anchors (in blue) and one anchor for a strap that goes over the seat (in red).

Figure 2: LATCH anchor positions in a standard vehicle.

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Proceedings of the Multi-Disciplinary Senior Design Conference

Using the LATCH system as our basis, we added three anchors in our car base, and a frame constructed from 80/20 to prevent the car seat from tipping over. Figure 3 shows the car seat mounting. After testing, we found that the car seat was able to move sideways a little. To limit the sideways motion, we attached tubes, which were being used for the child control tray, very close to car seat.

Figure 3. Car seat mounting system.One of the important requirements for the system was that some vehicle controls be physically accessible to the child. This meant that the child controls needed to be within arms reach of the child. Because the age of the child, we knew he would grow drastically within the period we expected the child to use it. Therefore, the location of the child controls needed to be flexible to account for different sizes of the child. To achieve these goals, PVC tubing was used. The figure below shows the resulting tray (black plastic). The PVC tubes were painted blue for a polished look. The height of the tray is controlled by two tubes, where the inner tube can slide in and out of the outer tube. A small hole was drilled in the outer tube, and several holes were drilled in the smaller tube. A thin rod (show as a gray circle in the image below) can be used to secure the height of the tray. The tray also slides in and out of the car seat to allow the child to be comfortable strapped in or removed.



Figure 4. Child control tray system.Because we ended up choosing two levels of control for the child, two different trays were manufactured. Each tray can be easily removed and interchanged simply by pulling the tray up to remove it from the lower tubing assembly.Various Levels of Control

The final design includes three control methods, one for the parent and two interchangeable control methods for the child. Having two interchangeable controls for the child, a wiimote steering wheel and a joystick, allows the car to be adapted to the child’s capabilities. The parent control, the Playstation 4 controller, allows for the parent to intervene and take control of the vehicle to assist the child if they become stuck or safely stop the vehicle if necessary.

The specific controllers were selected to be easily interfaced with the car as well as being easily replaceable. This led to the decision of using game controllers since they can be easily found and purchased and the drivers to interface with them are readily available. In addition, the Raspberry PI microcontroller was selected due to the operating system having bluetooth and usb adapters built in and ready to work with the controller drivers. The controls were then easily interfaced through a Python program to control the various motors being used to control the car through a PWM (pulse width modulated) driver attached to the Raspberry PI.

To coordinate these controls, the software was broken down into four sections, each running on a separate thread to allow them to work simultaneously. The first three threads are dedicated to each control method. These three threads monitor the connectivity of the control and handle the raw inputs from the controllers and puts them into a standard output which can be used to control the vehicle. Monitoring connectivity and status is important as the vehicle requires the parent control to be connected to ensure that the parent can intervene if necessary.

The standardized outputs generated from the control threads are placed in a priority queue which is fed into the main thread. By utilizing a priority queue, this ensures that the parent actions are serviced first which is important if the parent is trying to use the emergency stop.

The main thread determines which controls should be reflected in the cars movements. If the emergency stop is active no movements can be made, also if the parent has recently controlled the vehicle the child controls are rejected to avoid conflicting inputs from the child. In addition to normal control and emergency stop, the parent can select two speed levels which limits the max speed of the car.

To maintain ease of use, the wiimote and joystick can be swapped out and will automatically pair, however this was not feasible for the parent controller. A pairing mode was added to remedy this. It is accessed through entering a specific input from the joystick which allows for the pairing of a new PS4 controller which, once paired, will auto reconnect as the original controller does. This allows for easy replacement of the various controllers if necessary.

Power SteeringThe decision to add a power steering system to the car was chosen based on the need for a

customizable level of control for the parent/child. As it was, the car that was provided to the team was not accessible to a young child or a child with a disability because of the force required to turn the steering wheel. In the original GoBabyGo! Design, the car could only be steered by the child if they possessed the strength required to turn the wheel. In most cases, a child under the age of three does not possess this strength regardless of their abilities. Implementing a power steering system in this vehicle improves upon the childs ability to explore their environment more thoroughly which is the purpose of the project.

The process of designing the power steering system was started by observing the original makeup of the donated vehicle. In order to implement power steering, the steering column was taken apart to study the motion needed to turn the wheels. It was discovered that in order to properly turn the wheels with the existing setup, an arc motion with adequate force needed to be created. Initially, a design using a bevel gear was proposed because the team members had a misconception about the cost of a custom bevel gear. After meeting with Dr.Alfonso Fuentes-Aznar, a subject matter expert in gears, the team chose to go in another direction with the power steering design.

The final design for the power steering system resulted in a slot and pin design that was compatible with a servo. In searching for servos that would work with the system, it was important to find one that had adequate torque and was an appropriate size. In considering servos to purchase, the main metrics used were cost, voltage requirements, potential turning speed, and maximum degrees of rotation. Based on what was needed for this design, the M-785HB Servo Gearbox was chosen. With a cost of

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$139.98, a voltage range of 4.8V-6V, a maximum speed of 1.63 seconds/60°, and a maximum turning radius of 404°, this servo was an appropriate choice for the system. After choosing this servo, it was determined that it would perfectly fit into the existing axle which made it even better for mounting. A preliminary drawing of the power steering system is shown below. It shows the servo recessed into the axle, a slot attached to the gear and a pin attached to the moving steering rack. As the servo turns, the slot will push against the pin, moving the steering rack which in turn moves the tires.

Figure 5. Preliminary Servo DrawingIn order to make the steering system, two parts were manufactured. These parts included the slot and a metal plate for mounting the servo to the axel. A drawing of the slot is shown below. The slot was manufactured using a mill to cut the slot and a deburring tool to grind the outer part to a rounded part. The slot was made with aluminum that was found in the scrap pile of the machine shop. This saved the team money because aluminum can be expensive.

The second part that was manufactured was a metal plate used to secure the servo in place. This metal plate was made of aluminum and the only change made to it was drilling holes into it to secure the servo. A shoulder bolt was used as the pin for the design because it was easily secured to the steering rack, but had a smoot area that would easily glide in the slot.

Figure 6. Slot DrawingThe finalized assembly of the power steering system was tested using a power supply and the PWM hat on the raspberry pi. The plate used on the system was very secure and completely eliminated any movement of the servo even when the maximum torque was being applied. A picture of the power steering assembly is shown below.



Figure 7. Final Power Steering AssemblySupporting Feasibility Evidence

A large part of delivering a working product to the customer is proving that the system will be safe and functional. Throughout the process of design, it is very important to follow proper methodology to make design decisions. Tools like morph charts, Pugh charts and decision matrices were used to choose components and discern the most feasible idea was.

Equally as important as the feasibility testing are the tests that were completed for the final product. Before the car was designed, the team created a list of test plans based off of engineering requirements for the system. Testing these parameters allows for the team to feel comfortable with the safety and functionality of the product before it is used by the customer.

The initial phase of design required the team to look into a myriad of components, ideas, and solutions to solve the main problems that were being addressed by this project. The team used four different methods to discern between options so that the optimal parts were chosen for the design. The first method to come up with groups of solutions for each of the main problems is called a morphological chart. This chart provided designers with all of the potential decision for each of the main concerns in the project in a visual for. The morphological chart is shown below.

Figure 8. Morphological ChartFollowing this process, several combinations of the above options were complied. These groupings of parts were generated to act as comparisons to existing solutions to our problem. Using these solutions, the team was able to use a pugh chart to figure out in what ways were our solutions better and worse that existing solutions. The pugh chart is shown below. This chart was instrumental in the team feeling

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comfortable that their choices were best. The pugh chart shows the major criteria that the team found important to a successful design.

Figure 9. Pugh ChartAfter these choices were made, each individual component was evaluated to find the best specific product that would work on the car. This stage is when technical details were factored in to the design. Decision matrices were used for this process. An example of a decision matrix is shown below. This matrix was made to decide which microcontroller to use.

Figure 10. Microcontroller Decision MatrixThe final source of discernment for the decision making process was the use of subject matter experts. Consulting these experts helped most when the tools used above were not suited for providing a clear solution. Combining all of these strategies resulted in design that all of the team members felt confident with.

The final source of confidence for the success of this project was the test plans. These tests were written based on the engineering requirements created at the beginning of the design process. A table of the results of these tests are shown below.

Test Final choice Goal Results

Wireless Remote Range PS2 controller >30 ft 70ft

Battery Life Included battery 30-60 mins

Charging Time Included battery

ImpactNo bumper added

RC Field PS2 controller 360 degrees 360 degrees

Servo Torque Slot and Pin Steering works Steering works

Test Final choice Goal Results



Controls Reach Child trays 8-10 in

Adjustable within child’s reach

Seat Fitment Car seatA wide range of 1-3 year olds can fit

The car seat fits a wide range of children

Control Force 30-100 grams

Remote Controls Available PS2Working remote control

Remote can do all directions and e-stop

Speed Pre-sets In ProgrammingMultiple speed options

50% of max speed and 80% of max speed

Ease of Securing Child Car Seat <60 seconds

Cost Given Budget <$500 $465.71

Ease of Use

Clear manual and easily cleaned cleaned

Car Seat Mounting Strength 8020 bar >450 N

Passed all testing

Figure 11. Testing Chart

Results/Conclusion

The final product produced is a base of a fisher price power wheels car where steering is powered by a servo, the child is in a car seat, and the car is controlled via a raspberry pi by joystick(on board for child), wiimote(on board for child), and PS4 controller(wireless for parent).

Figure 13. High ¾ angle of the front of the car

Figure 14. Undercarriage of car as seen from front

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The customer was positive at the systems demo. The customer was very happy with the safety of the vehicle, the speed of the vehicle and the customization of the controls, and very impressed with how the car looked. They requested improvements be made to the ease of use of the joystick(in the demo it had a lot of travel distance before actuation), shortening of the control tray to ease the child's reach to the controls. These improvements will be made before customer hand off.

Our most major concern and unexpected result is the size of the car. The car is larger than expected which makes it difficult to get through normal sized doors. It is too wide to roll through and the car seats height makes it difficult to get through a door when turn to its side. The only way to mitigate this is removing the car seat to make it easier to get through the door, which is a 1-2 minute process to remove and replace. Another more minor unexpected outcome is that we needed 2 child control trays, one for the joystick and one for the wii wheel. 1 control tray was preferable because of the added complexity of having 2 trays for the user to keep track of and swap, and unplug and replug the usb cord for the joystick. But it was ultimately decided that both were necessary when we had the joystick and wheel and our control tray all together, there was no way to put both side by side, and front and back would have limited visibility and reach for the control that was further away. So we were forced to make a second control tray, luckily we had spare material to replicate the first tray and the fittings were cheap so it did not impact to budget much.

In terms of requirements and team goals, the project was a success. The car is on schedule to be delivered on time. Due to the numerous donations which total to a value of hundreds of dollars, we have kept the project under budget. The car has also passed every test of our specifications we have been able to perform.

References/Acknowledgements Stakeholder List

o Main Sponsor: MSD/Roosevelt Children’s Centero Laird Plastics for the sheet of ABS plastico Fisher-Price for the caro Kathryn Cyr for the Wii remoteo Sara and Kelly from Rochester Step by Step Developmental Serviceso RIT MSDo A and A’s Parentso Art Northo Leah Talbot

[1] https://www.cdc.gov/ncbddd/cp/data.html [2]https://cerebralpalsynewstoday.com/2017/10/17/cerebral-palsy-and-affect-on-mental-health/


https://cerebralpalsynewstoday.com/2017/10/17/cerebral-palsy-and-affect-on-mental-health/

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