Final Report for the Automatic Manual Wheelchair

Transcription

1 AMW Enterprises Final Report for the Automatic Manual Wheelchair Prepared for: Dr. Emeka Oguejiofor, FEC, P.Eng Paul Doiron, P.Eng 10 April 2017 Group 3 (AMW) Brett Ferrari Justin Graham Liam MacDonald Brett Reede Carli Spears Zack Tarr St. Francis Xavier University P.O Box 5000 Antigonish, NS B2G 2W5 i

2 Abstract The Automatic Manual Wheelchair [AMW] is a project designed to fill a void in the current wheelchair market. The current wheelchair market has two main branches: automatic and manual wheelchairs. Automatic wheelchairs are great for long distance travel but are very expensive and lack the portability of manual counterparts and become useless when the batteries die. The AMW encompasses the best aspects of both types of wheelchair. The lightweight portability of manual wheelchairs as well as the driving ability of automatic wheelchairs. It also features the ability to switch from automatic to manual propulsion for circumstances that require. Research was conducted using active and former wheelchair users to determine viability of the AMW. To achieve the result involved months of brainstorming, design and research into different parts and controls. The final prototype involves two direct current [DC] motors mounted directly to the axels powered by two 12 Volt batteries (24V total). The speed and turning are controlled using an analog joystick wired through an Arduino microcontroller and motor controller unit. This microcontroller unit gives the wheelchair precise turning and braking capabilities. The wheelchair can the be switched into manual powered mode using two circuit breakers placed under the seat. Throughout this project many different aspects of engineering were incorporated to progress the AMW and reach our final prototype. Electrical, Mechanical and Civil engineering along with bits and pieces from other disciplines were used for calculations, theory and design on the AMW. i

3 Acknowledgments Dr. Frank Comeau, Ph.D., P.Eng. and the St. FX Engineering Department Helped the group order motors and provide the necessary skills to conduct the project Paul Doiron, P. Eng. Recommended the undertaking of the Automatic/Manual Wheelchair project Steve MacDonald As the campus machinist he allowed use of the machine shop and gave the group technical advice Craig Seaboyer Gave the group electronic parts, and technical advice Cameron Turner Helped with the installation of electronic components on the wheelchair and provided said components Gary Matty, Dillon MacMillan, and Nolan O Reilly Wheelchair users who expressed the need and interest for an engineering solution of the automatic and manual wheelchair ii

4 Contents Abstract... i Acknowledgments... ii Contents... iii List of Figures... iv List of Tables... iv List of Abbreviations... iv 1.0 Introduction Purpose of the Report Background Information Research Conducted Technical Design Arm Rests Battery Plates Back Rod Wheel Attachment Microcomputer and Joystick Analysis Analysis of Battery Plates & Bolts Analysis of Arm Rest and Back Bar Financial Analysis Demonstration of Prototype Conclusion and Recommendations References Appendices iii

5 List of Figures Figure 1: Arm Rest... 3 Figure 2: Battery Plates... 4 Figure 3: Spacer for Back Rod... 5 Figure 4: Sheave for Wheel Attachment... 6 Figure 5: Compression Pin and Spacer... 7 Figure 6: Battery Plate Analysis... 8 Figure 7: Battery Plate Calculations... 9 Figure 8: Battery Plate Bolt Calculations... 9 Figure 9: Armrest Analysis Figure 10: Armrest Pipe Buckling Calculation Figure 11: Back Bar Calculations Figure 12: Back Bar Deflection Figure 13: Arduino Microcontroller Figure 14: Circuit Demonstration List of Tables Table 1: Financial Analysis List of Abbreviations AMW Automatic Manual Wheelchair iv

6 1.0 Introduction 1.1 Purpose of the Report The design and analysis of an automatic and manual wheelchair is the purpose of this report. The report includes details about the overall design process, research conducted, analyses performed, and the fabrication of the added wheelchair parts. The report is intended for Dr. Emeka Oguejiofor and Mr. Paul Doiron. The design, titled the AMW (automatic manual wheelchair) is a Drive Med wheelchair powered by two independent motors with the capabilities of being both automatic and manually powered. 1.2 Background Information The main problem with the current wheelchair market is the lack of lightweight, cost efficient, portable, automatic and manually powered wheelchairs. Automatic wheelchairs are heavy. Their weights can range from 100lb to 400lb (Themed Supply Guide, n.d.). They are also expensive, their prices can vary from $1620 to $ depending on the capabilities of the chair (CostHelper, n.d.). Due to their weights and the inability to fold, automatic wheelchairs are difficult to transport. Manual wheelchairs are more cost efficient, lightweight and portable in comparison to automatic wheelchairs. However, between 60 to 70 percent of manual wheelchair uses develop shoulder pain due to constantly having to operate their chair (Sosnoff, 2011). 1.3 Research Conducted Once the design topic was confirmed, research had to be performed to see what was needed and what improvements could be made upon the wheelchair. Throughout meetings, it was discussed what features could improve the AMW and if they would be beneficial to society. It was the consensus that the wheelchair would need two motors which would run on 12V each, therefore requiring two 12 V batteries. Multiple parts were searched for online and compared on their prices and dimensions. When beginning this project, it was important to prove that there was a need for the product that our group wanted to design. Part of this process was to interview 1

7 several people who use or have used a wheelchair to find out their opinions on what could be improved upon. The first contact made was Dillon MacMillan who became a paraplegic after a car crash in He is currently living in Halifax and works as a welder, as well as training for the Canada Games to be a member of the wheelchair racing team. He owns three wheelchairs; a manual, standing and racing wheelchair. When Dillon was approached, his first issue was the cost of each wheelchair and the trouble to need to switch between them throughout his day. Nolan O Reilly is a fourth-year finance major at St. Francis Xavier University and he was in a wheelchair for two months due to breaking both of his heels in April The chair that Nolan was confined to was a standard manual wheelchair, since an automatic wheelchair was too costly for a student. Nolan mentioned he had trouble maintaining endurance to travel long distances which restricted him to staying home. He recommended a lightweight automatic wheelchair that has foldability and would not be as costly. 2.0 Technical Design 2.1 Arm Rests The original arm rests that were mounted to the wheelchair were simplistic in nature but damaged from a previous owner. New arm rests were manufactured similar to the original using the attached CAD drawing in Appendix 2. The design was altered a total of three times due to the manufacturing process to reduce the complexity of the design and allow for easy construction. This included the removal of a bent bar concept for a basic post and lintel design. A further change was made to use a C-bar for the lintel part as it is lighter and stronger than a rectangular bar of the same weight. C-bars were also readily available in the St.FX machine shop allowing for easy access to materials. 2

8 Figure 1: Arm Rest 2.2 Battery Plates Battery plates were not a part of the initial design as the original batteries were to be placed on the back plate. This idea was abandoned once the size of the motors were determined and how they would needed to be attached. The battery plates used a simple cantilever design and could take the load of much higher than that placed on them. Calculations for the plates can be found in section 3.1 of the report along with calculations in Appendix 2 and a photo in Figure 2. 3

9 Figure 2: Battery Plates 2.3 Back Rod The back rod was the fourth design of the motor mount system placed on the back of the wheelchair assembly. Originally it was designed as one long piece of aluminum that would support the battery and motor. This idea was modified to allow for fold-ability of the wheelchair by using two cantilevers. These would allow for roughly 40% folding before the two motors would interfere with each other. Once the wheelchair s motors arrived it became apparent that the motors were unable to be mounted in the method originally intended. A rod was used instead of a plate as the motors had mounting holes already bored into the mount. A spacer was added to each bore hole to assure a secure 4

10 fit between the rod and the motor. The CAD drawing of the back rod can be found in figure Appendix 3 along with a photo of the spacer in Figure 3. Figure 3: Spacer for Back Rod 2.4 Wheel Attachment The attachment of the wheel to the motor was the most difficult and crucial part of the design project. The original design included the use of beveled gears and a movable motor that would allow for the detachment of the motor when possible. This design seemed impractical due to time constraints therefor other designs were considered. The use of a system of gears was considered to increase the rotational velocity of the wheels. This concept was disregarded due to the complexity and time constraints. Thus, the drive shaft was connected directly to the wheel s axel through a sheave placed over both the axel and the drive shaft. This can be seen in Figure 4 below. This connection does not allow for the motor to be disconnected but this issue is solved using breakers in the electric circuit. 5

11 Figure 4: Sheave for Wheel Attachment Modifications were also made to the axel attachment to the wheel to make a rigid attachment. This was done using a large aluminum spacer and compression pins to secure the wheel to the axel. This allows the point of rotation to be between the axel and the frame and not the axel and the wheel. The pin and aluminum spacer can be found in the appendix in Figure 5. There were two compression pins used to secure the axel and wheel and reduce the stress in each pin. 6

12 Figure 5: Compression Pin and Spacer 2.5 Microcomputer and Joystick Different methods were considered for conversion from automatic to manually powered. One idea was to implement friction clutches on each wheel. This idea was discarded due to only being able to convert from automatic to manual when stationary. Another method of conversion was to disconnect the batteries and push the wheels while still attached to the motors. The initial idea for speed control was two levers mounted on each arm rest to control the rotational velocity of each motor. As well, the original braking mechanism was to attach bicycle brakes at the bottom of each wheel to allow the user to stop. Both ideas were discarded and replaced with a microcontroller. 7

13 3.0 Analysis 3.1 Analysis of Battery Plates & Bolts Figure 6: Battery Plate Analysis When conducting the analysis of the battery plates, it was assumed that the plates took on the form of a cantilevered beam. The maximum value of Poisson s ratio obtained was 0.33 which was used to determine the maximum load that the Aluminum 2014-T6 could withstand, this resulted in approximately N. When compared to the 24.25N force that the battery plates withstand, this only gave a Poisson s ratio of

14 Figure 7: Battery Plate Calculations The battery plate was bolted to the wheelchair with two M3x6mm Cap Head Bolt Pk10 s which will split the N force between them. Using data on the selected bolts it was found that the maximum shear force at the thread of the bolts are kn/m 2 and the maximum shear force at the full bolt is equal to approximately kn/m 2. The force used to find the real shear force in each bolt was N and that resulted in a shear force of kn/m 2 which is well before the max shear forces at either the thread or full bolt. This ensures that there will be no shearing taking place due to the batteries. Figure 8: Battery Plate Bolt Calculations 9

15 3.2 Analysis of Arm Rest and Back Bar When analysing the arm rest it can be broken down into two main parts. The first part is the aluminum 2014-T6 C-bar which constitutes the top of the arm rest. Aluminum was chosen for the arm rest parts as it does not rust like steel and it is much lighter then steel. The group determined that the most likely force that this bar would undertake would be the vertical forces that a person would exert when exiting or entering the wheelchair. The C-bar could withstand a PCritical of about 250 kn this means that the two C-bars could handle a 300lb person constantly entering and exiting the wheelchair. Figure 9: Armrest Analysis The second part of the arm rest is the two aluminum 2014-T6 pipes that hold the C-bar in place. The group found that it would take around 37.5 KN to make one of these pipes buckle. This shows that the two pipes on each arm rest could easily handle a 300lb person entering and exiting the wheelchair. 10

16 Figure 10: Armrest Pipe Buckling Calculation The back rod unlike the arm rest only has to handle the two motors that are mounted on the.75in diameter aluminum 2014-T6 bar. Figure 11: Back Bar Calculations The forces and moments that the two motors exert are relatively small. The reason such a large bar was chosen was in case someone was to accidently step on the bar or if the wheelchair crashed the bar would withstand those forces and keep the motors aligned. 11

17 Figure 12: Back Bar Deflection 3.3 Financial Analysis Table 1: Financial Analysis Parts Project Cost Actual Cost Wheelchair $ $40.00 Motors $ $0.00 Batteries $93.98 $0.00 Microcontroller $31.63 $0.00 Joystick $39.99 $0.00 Fuses $11.38 $0.00 Metal $3.15 $0.00 Misc. $7.99 $7.99 Total $ $ Demonstration of Prototype For the first demonstration, video footage was taken of two small scale DC motors being powered and controlled by the Arduino microcontroller. The video shows the rotational velocity of the two motors varying with respect to the current position of the digital joystick as it is randomly pointed in different directions. When the joystick is 12

18 pointing completely along the positive Y-axis, both motors are turning at their maximum velocity in the forward direction. When pointed completely along the negative Y-axis, they turn backwards at their maximum velocities. When a turn is commanded by the joystick, the motor on the side of the desired turn is slowed depending on the angle of the turn. This allows the chair to turn gradually or, at its most extreme, completely stop one motor and turn about the contact point between the stopped wheel and the ground. The microcontroller makes this possible through conditional computer logic. It outputs specific amount of current to each motor depending on the value it reads from the joystick. This demonstration proved that the code intended to control and steer the wheelchair was completely sound. For the second demonstration, video footage was taken of the prototype being powered by a DC power supply. The motors that were acquired to run the wheelchair had few specifications, so the purpose of this demonstration was to acquire figures for the motors. It was discovered that the motors needed to pull approximately 5 amps of current each to start. This was a problem because the motor controller being used was not rated to take a load that large. This demonstration showed why the motor controller failed. For the third demonstration, video footage was taking of the wheelchair being driven by a person. Since ordering a new motor controller that had the capacity to run the wheelchair would have taken too much time; proving the wheelchair s ability to function with a person seated needed to be achieved without the microcontroller. The batteries were hooked up to the motors through a breaker switch. The wheelchair was steered using a friction brake on each wheel. In this demonstration, the wheelchair travels 50 feet in 6.8 seconds, reaching a peak velocity of 16 km/h. This proved the wheelchair could operate under the weight of a person. Combining the three different demonstrations of the prototype proved that the motor controller was the sole reason the wheelchair was not fully functioning the day of presentations. The joystick clearly controlled the rotational velocities of each motor and the wheelchair operated at high speeds carrying the weight of a person. 13

19 Figure 13: Arduino Microcontroller The prototype s performance was beyond satisfactory. The wheelchair could easily surpass the targeted maximum velocity of 8 km/h, which is the average maximum velocity of automatic wheelchairs on the market. With the motors, tightly mounted, it was only slightly harder to operate while in manual mode then without the motors attached. Without the controllers, the automatic mode of the wheelchair only goes forward. The performance of the prototype would have been much more impressive if an adequate motor controller was used. The prototype did not have a long life due to the lead-acid 12 volt batteries only having 7.2 Amp*hours of charge. One could easily fix this problem by using superior batteries. The prototype lost all folding ability due to the size and orientation of the motors. One could regain folding ability by possibly using beveled gears to attach the motors to the shaft of the wheels. This would allow the length of the motors to run out the back creating room to fold. 14

20 Figure 14: Circuit Demonstration 5.0 Conclusion and Recommendations In conclusion, the motors, batteries, wires, and the armrests were effectively installed and mounted to the AMW prototype. The wheelchair could work even without the microcontroller. A top speed of 16 km/h was achieved which is much faster than the average electric wheelchair speed of around 8 km/h. To further put this speed into context our wheelchair would break the speed limit of some dirt roads and parks in Canada. Some areas that could be improved on our wheelchair would be: 1. A microcontroller that can handle more than 24 volts 2. Larger wires could be installed in the wheelchair so there is no fear of the wires overheating after an extended period of use 3. The pins that connect the wheels to the motors could also be larger to help resist the wear and tear of constant use. In addition to applying the skills that were taught in engineering, the group also had to gain experience in the manufacturing for parts. Before this project the 15

21 manufacturing of parts was almost completely foreign to most of the group members. The group was able to learn how to effectively use various machines such as the; band saw, drill press, the art of tapping, and an understanding of how lathes work. An appreciation was gained for the difficulties and effort that is required to turn a CAD drawing into a working prototype as well as the importance of adapting and changing ideas when met with an obstacle or problem. The group learned the value of ordering parts as soon as possible to have the maximum amount of time to trouble shoot or fix any problems. One way that the Design II course could be improved in the future is letting the students know exactly what kind of resources and personnel are available to assist them in completion of their projects. Informing the students of this from the start would save a great deal of time and allow them to fully understand what projects they can create. 6.0 References Sosnoff, J. (Winter 2011). A new approach to solving an old problem for wheelchair users. Synergy. Hibbeler, R.C. (2011). Statics and Mechanics of Materials, Pearson Prentice Hall, United States of America. How much does an electric wheelchair weigh? (n.d.). Retrieved from How Much Does a Wheelchair Cost? Costhelper.com. (n.d.). Retrieved from 16

22 7.0 Appendices Appendix 1: Wheel Chair Design 17

23 Appendix 2: Arm Rest 18

24 Appendix 3: Back Rod 19

25 Appendix 4: Battery Plate 20