jude varun liam - jedg

Jude Gonzales (gonzaj6)

Varun Ramanathan (ramanatv)

Liam Smolenaars (smolenal)

Abilarsh Vijiananthan (vijianaa)

ENG 1P03: Engineering Profession and Practice

Group 2, Tutorial 17 December 5, 2017

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1. Table of Contents

1. Table of Contents 2

2. Introduction 4 2.1. Background Information 4 2.2. Current Garbage Disposal Process 4 2.3. Refined Problem Statement 4 2.4. Objectives and Constraints 4 2.5. Commercial Products 5 2.6. Patents 5

3. Conceptual Design 6 3.1. Brainstorming 6 3.2. Design Alternatives 6

3.2.1. Preliminary Alternative 6 3.2.2. Secondary Alternative 6

3.3. Design Evaluation 7

4. Final Design 8 4.1. Description 8 4.2. User 8 4.3. Construction 9

4.3.1. Materials 9 4.3.2. Mechanical Assembly 10 4.3.3. Electrical Assembly 11

4.3.3.1. Main Components 11 4.3.3.2. Motor Driver 11 4.3.3.3. 10 Watt LED 12 4.3.3.4. Master Switch 12 4.3.3.5. Custom PCB 12 4.3.3.6. Joystick 13 4.3.3.7. Limit Switch 13

4.3.4. Software Design 13 4.3.5. Mechanical Testing 14 4.3.6. Electrical Testing 15

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4.4. Safety 15 4.4.1. Low-Voltage Cutoff 15 4.4.2. Slow-Blow Fuse 15 4.4.3. Floor Limit Switch 16 4.4.4. Hot Swappable Joystick 16 4.4.5. Metal Finishing 16

5. Discussion of Feedback from Design Reviews 16 5.1. Design Review 1 16 5.2. Design Review 2 17

6. Conclusions 17

7. References 18

8. Appendix A 19

9. Appendix B 20

10. Appendix C 23

11. Appendix D 31

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2. Introduction

2.1. Background Information Cerebral palsy, also known as CP, is a disability that causes permanent movement disorders. Though the signs and symptoms of this disease can vary amongst people, almost all the time the symptoms are noticed during childhood. The only method of diagnosis that has been researched at this point is observed the development of the child as they grow. Children with cerebral palsy would show signs such as not rolling, not crawling or not sitting up. These are possible methods of diagnosing children with cerebral palsy. The product described in this report was designed specifically for a user who has cerebral palsy, although the device would likely be beneficial to a much wider audience. The device is an electromechanical arm that attaches to a wheelchair, is controlled with a joystick, and can lift garbage cans and recycling bins. The device allows the user to be more independent in the household chore of bringing waste to the garage or the curb.

2.2. Current Garbage Disposal Process Currently, F.M. is not able to be a part of the garbage disposal process. Someone else has to remove the garbage bag, tie the bag, put the bag in the correct disposal area and then place a new bag into the garbage bin.

2.3. Refined Problem Statement Create a device that allows the user to lift garbage and recycling bins while exerting minimal effort.

2.4. Objectives and Constraints There are three main objectives for this product’s design: ease of use, safety, and durability. In order to ensure that GIGO is easy to use, it incorporated software features that would make it easier to interface with the arm, as well as the use of a joystick. A joystick ensures a similar interface that F.M. has used before, for the wheelchair. This will enable a quicker learning curve for F.M. to learn how to use our device. Exponential mapping of the joystick is implemented so F.M. would not need to push the joystick to either of the limits to reach the maximum power of the actuator, as shown in Appendix A, Figure 1. Many safety features are included and are explained in depth in section 4.4 of this report. Briefly, they are low voltage cutoff, a fuse, the floor limit switch, the hot-swappable joystick, and the metal finishing. A final objective that was met was the durability of the product. Unlike many of the other projects, GIGO was created with aluminium and nuts and bolts. This ensures structural rigidity and long term durability.

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2.5. Commercial Products There are not many commercial products that provide a similar experience to GIGO. There are a few robotic arm type products that are commercially available. However, they are extraordinarily expensive, hard to control, and have low load capacities. For example, there is a product called Jaco, by Kinova Robotics. It’s the most similar product to GIGO that could be found, but it costs $35,000 - $50,000 and can lift a maximum of 1.6kg. The GIGO arm can lift over 10kg, and costs only $228.55. Of course, the Jaco has 6 degrees of motion and the GIGO only has one, but this is the closest commercial product available.

2.6. Patents Patents allow the owner to protect the work which they have completed for a set period, allowing for exclusivity of a product. There are many patents related to cerebral palsy as well as accessibility aids. However, patents are public and expire, which can allow other companies and individuals to utilize them. Patent US4149532A, a cerebral palsy arm-and-hand brace is a patent for the stability of the patient’s arm. The device does this by reducing and dampening of spasms in the arm. It also allows for finer control of the arm and hand. However, this patent is less valuable for practical use in our project as we are designing a solution for a specific task. The concepts behind the patent is useful in understanding the issues that people with cerebral palsy face and acknowledging an existing solution. [3] Patent US4523781A, Gripping aid for the manually disabled is a patent for people with arthritis or similar ailment that reduces the movement of the hand and fingers. The mechanism is based upon two hinged half shells which clamp on a smaller object such as a knife or a fork. The user can utilize various objects with this device depending on their use case as shown in Figure 2. This device would be useful for eating as it requires less gripping force, making it easier for F.M. to use utensils to eat food such as ice cream or lasagna. [1] Patent US9364364B2, Simple prosthesis for manually-challenged persons is a similar implementation of Patent US4523781A in the above paragraph in the sense that it is attached to the hand and allows for the manipulation of an object that requires fine movements to use with a hand to be used with limited hand capabilities. It is an elastic material with a grid or mesh like pattern, allowing an object to be slid in and used as shown in Figure 3. This requires significantly less gripping force as the object will be slid into the mesh multiple times in order to grip on the object. However, this requires a longer setup time in order to effectively use the device and not have the object fall out. [2] Patent US4944766A, Gripping device is another iteration of the previous two patents. Like Patent US9364364B2 and US4523781A, it allows a user without precise control of their fingers to control something like a fork or knife. Unlike the previous two patents where the object was held rigidly, this device allows for the movement of the object being used. This allows for greater movement of the device, but it requires some ability of hand movement in order to achieve this greater range of motion. [4]

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Patent US4708570A, Universal container grabber apparatus for a refuse collection vehicle is an apparatus which can securely grab a round container. It uses two grabbing arms which are attached to another moveable arm. An apparatus used for reaching and gripping would be useful as an attachment to the wheelchair in order to manipulate the garbage can. This would be controlled by a joystick as F.M. is easily able to use a joystick to control her wheelchair. [2]

3. Conceptual Design

3.1. Brainstorming The problem that the group decided to approach is the garbage disposal. The brainstorming process was branched into four categories of safety, usability, reliability and cost. These categories were split into headings which are ways to achieve the objective of the heading. Safety breaks down to using non-hazardous materials and not causing physical strain. Usability comes down to intuitive controls. Reliability came down to the ability to withstand forces. The main way to achieve a low cost is by using inexpensive materials, since that is really the only cost. Under each of headings, actual materials and means were thought of in more detail. Refer to Appendix B, Figure 1 for the brainstorming chart.

3.2. Design Alternatives

3.2.1. Preliminary Alternative The first design alternative is shown in Appendix B, Figure 2. This design uses a four bar linkage, made out of aluminum, to achieve linear vertical translation while the 3D printed hook remains vertical. To move the four bar linkage, an electric linear actuator will be used. At the end of the four bar linkage, a 3D printed hook is attached. This hook will be used to attach onto a plate that will be attached to the garbage can. This will allow the user to pick up and move the garbage can. This mechanism will utilize basic control system components such as a battery, an Arduino, a motor controller, and limit switches. A joystick will be used to control this mechanism, since this is an interface the user is already familiar with.

3.2.2. Secondary Alternative The second design alternative is shown in Appendix B, Figure 3. This design resembles a miniature forklift which mounts to the front of the wheelchair. An electric linear actuator is used to move the fork tines up and down. The fork tines will be mounted to a pair of vertical rods, allowing them to slide up and down while maintaining rigidity in all other axes. This mechanism will use similar control components as the first design alternative: a motor controller, an Arduino, limit switches, and a joystick interface. The garbage cans would need to be sloped on the bottom for the fork tines to easily slide under.

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3.3. Design Evaluation There were various metrics which were considered when evaluating our design alternatives. The metrics that were decided upon were it must be reliable. Reliability was determined to be works consistently or => 95% of the time. It has to be safe, as in would not cause harm to F.M., the people around her, or her environment. It has to be easy to use, defined as requiring about 15 minutes to learn how to effectively use the device. It also had to be low cost, which was determined to be around $80-100. Following this criteria, it was determined that both design alternatives would be equally safe as they would extend about the same distance from the wheelchair and would have relatively the same safety. The arm would be more reliable as it would just be mounted to the side of the wheelchair and it was slightly off, it would still be fine as it would be counteracted by the movement of the wheelchair for the first design alternative. The second design alternative would require the rods to be placed in the same position every time or else it would not line up with the pipes from the garbage can, thus decreasing reliability. Ease of use for the device would be easier for the first design alternative as it would require less usage of the wheelchair joystick compared to the second design alternative. There is also more precision with the joystick for the first design alternative due to the exponential mapping on the joystick. Initially, it was thought that the first design alternative would not cost significantly more compared to the second design alternative so at the time it was scored similarly. Taking all this into consideration, JVAL decided to go forward with the first design alternative.

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4. Final Design

4.1. Description GIGO is a robotic arm wheelchair attachment that provides the user with the ability to lift things up and down. Though this arm potentially has many potential applications, the one it was primarily designed for was providing the user with a means of taking out garbage cans and recycling bins and bringing them back in. The arm allows the user to lift up the bin without having to exert any manual force, because it uses an electric actuator. The device features a 3D printed mating system to make it very easy for the user to attach the arm to a bin. A red cone-shaped hook is attached to the arm, and a corresponding blue receptacle is bolted onto each bin. The user simply needs to align the tip of the red cone within the opening of the blue receptacle, and then as the arm raises, the cones will self-align. These two parts can be seen in Appendix C, figure 0. The name of the device originates from a saying in computer science: garbage in, garbage out. It means that nonsensical input data, or “garbage”, will always produce meaningless output. However, JVAL interpreted this literally, since the product is used to take garbage cans in and out of the house. This was abbreviated to “GIGO” for simplicity.

4.2. User The device must first be set up by a personal support worker. To set up the device, the following steps must be followed: ▪ The arm attaches to the side of the wheelchair using hooks ▪ The battery attaches to the control box with Velcro ▪ The joystick attaches to the arm rest with Velcro ▪ The battery and joystick plug into the control box ▪ The large blue switch turns on the device ▪ The small switch turns on the LED ▪ Pulling the joystick back raises the arm, pushing it forward lowers the arm When the user needs to take out the trash, a personal support worker will set up the device and turn it on. The user must first drive their wheelchair and align the cone mating system. Then the user will be able to use the joystick to lift up the garbage bin, travel to their destination, and place it down. This process is repeated to bring the bin back indoors.

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4.3. Construction

4.3.1. Materials The following materials are required to reproduce the GIGO arm. Several items were available for free due to the fact that this is a course-related project. For example, all the 3D printed parts were printed at Mills Library, free of charge. The ATtiny85 microcontroller was ordered from Microchip Technology Inc. as a free sample, which is a service available to engineers and students.

Item Name Quantity Cost Source

Motor Controller 1 $13.99 Amazon

Rust-Oleum Rubber Coat 1 $12.00 Amazon

10 Watt LED 1 $0.89 Banggood

JST RCY Connector 1 $0.15 Banggood

Linear Actuator 1 $39.99 Banggood

Aluminum Structural Tubing 4 $40.00 Canadian Tire

Fasteners 1 $8.99 Canadian Tire

10 Watt LED Driver Circuit 1 $2.50 Ebay

LiPo Battery 1 $7.99 Hobby King

Cone Mating System 1 $0.00 McMaster Lyons

Joystick Extension & Housing 1 $0.00 McMaster Lyons

ATtiny85 1 $0.00 Microchip

Arduino Protoshield 1 $2.99 RobotShop

Female 0.1” header pins 1 $2.88 RobotShop

Joystick 1 $26.91 RobotShop

Male 0.1” header pins 1 $2.50 RobotShop

Master Toggle Switch 1 $3.78 RobotShop

24k 1/4W Resistors 1 $1.00 Sayal

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2A Slow Blow Fuse 1 $2.50 Sayal

330 OHMs 1/4W Resistors 1 $1.00 Sayal



Blank PCB 1 $1.00 Sayal

Female DIN Connector 2 $4.50 Sayal

Fuse Holder 1 $2.50 Sayal

Limit Switch 1 $3.50 Sayal

Male DIN Connector 2 $4.50 Sayal

Mini 1PST Toggle Switch 1 $1.22 Sayal

Project Enclosure 1 $7.99 Sayal

Subtotal 206.26

Tax 26.29

Total 228.55

4.3.2. Mechanical Assembly The main mechanical assembly is simple in design, but deceptively complex to fabricate. Ideally the four joints should use ball bearings, but due to monetary constraints, simple bolts were used. The long arm pieces are made from ¾“ by ¾” by 3’ hollow aluminum square tubing. The aluminum tubing was specified as being 3’ long, but in reality, one of the tubes was ½” longer than the other. This meant the longer tube had to be cut to match the length of the shorter one. The end was then ground on a disc sander to produce a smooth and squared surface. Two ¼” holes were then drilled approximately 15mm from each end of one of the square tubes. The exact distance from the end of the tube does not need to be exactly 15mm, as long as it is the same on both tubes. To guarantee this, the second square tube was clamped onto the first square tube, and another pair of ¼” holes were drilled using the first two holes as guides. A drill press was used for all the holes, to ensure they are as straight as possible. The drill press also makes it easier to drill aluminum, since more feed pressure can be achieved when compared to drilling by hand. A centre punch was used to mark the location of each hole before drilling, to prevent the drill bit from wandering. Cutting oil was also used to cool the workpiece and the drill bit. After drilling, all holes were deburred using a chamfering bit and a hand drill. For the vertical pieces of the four-bar linkage, 1.5” by 1.5” aluminum angle was used. The angle was bought in a 4’ length, but less than half of this was actually used. A 20cm and 30cm piece of angle was

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cut and ground square. Holes were then drilled approximately 18cm apart, 15mm from the edge. These pieces are shown in Appendix C, figure 1 & 2. On the shorter piece of aluminum angle, two holes were drilled on the other face to attach the 3D printed cone. A pair of 3mm holes were drilled on the shorter aluminum angle as well, to bolt on the LED. This is shown in Appendix C, figure 3. The four pieces of the four-bar linkage were then bolted together, using four ¼” - 20 bolts of length 1.5”, two washers, and a ¼” - 20 nyloc nut. Nyloc nuts were used to prevent the nuts from loosening when the device operates. An exploded view of one of the bolts is shown in Appendix C, figure 4. These bolts were tightened to 18 inch-pounds; a specification that was determined by experimentation. It was found that if the bolts were tighter, the actuator struggled to move the linkages, and if the bolts were looser, there was too much backlash. The actuator was then clamped to the arm tubes and mounting holes were marked with a centre punch. These holes were then drilled with a 7mm drill bit, and M8 threads were tapped. The actuator mounting brackets were then bolted on using M8 bolts. Nuts were not used to avoid having bolt ends protruding from the arms, which could get caught on clothing and would be unsightly. Finally, the limit switch and the control box were bolted on. The limit switch was bolted as close as possible to the end of the arm, using #2-56 screws and nuts. The control box was bolted to the long aluminum angle using M8 bolts, with M8 threads tapped into the aluminum. The joystick was glued into a 3D printed enclosure, which can be seen in Appendix C, figures 10 & 11. This protects the wiring, and creates a more professional looking device. The 3D printed joystick extension, seen in Appendix CC, figure 12, was coated several times in a black rubber spray to make it easier to grip. Then it was placed on the joystick, and held tightly in place by a friction fit.

4.3.3. Electrical Assembly

4.3.3.1. Main Components

The electrical assembly uses four main parts: a battery, a motor driver, a microcontroller, and a joystick. The device was initially tested using an Arduino Uno, but this is not a good choice for a deliverable product. The Arduino Uno is a development board, and is not meant to be installed permanently in a product. Originally an ATmega328 (the microcontroller used in an Arduino Uno) was going to be used, but it was also not an ideal choice because it has many more IO pins than necessary. For the final product, an ATtiny85 microcontroller was chosen because it has exactly the number of IO pins needed, and is therefore the most compact choice. The ATtiny85 has two PWM capable outputs, which is exactly the number required to control the chosen motor driver. It also features an internal clock, so an external crystal oscillator is not required, reducing the part count. An ABS plastic project enclosure was used to house most of the electronics. The enclosure had to had several holes drilled in it to mount all the switches, connectors, and the fuse.

4.3.3.2. Motor Driver

The motor controller used is an L298n, which is a dual H-bridge circuit capable of supplying 2 amps per channel at 12V. While the second channel is not required, this motor controller was chosen because it includes an internal linear 5V regulator. The regulator is just a simple 7805, which can easily supply

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100mA without a heatsink. This provides power to the microcontroller and its corresponding logic-level circuitry, which is all very low power. In fact, the microcontroller and its related circuitry draws only 38mA of current. Most of this current is from the on-board indicator LED. To control the motor driver, two PWM outputs are needed, which can be called ‘A’ and ‘B’. To rotate the motor in the forward direction, input A receives an 8-bit PWM signal at approximately 490Hz and input B is pulled low. To run the motor in the opposite direction, input A is pulled low and the PWM signal is sent to pin B. To brake, the two inputs are both pulled low, which shorts the motor leads without drawing any power. This is not required, because the actuator has enough friction to prevent being forced in either direction.

4.3.3.3. 10 Watt LED

For the 10W LED, a driver circuit is required. All LEDs require current limiting to ensure the current does not exceed the specified forward-current rating. For small LEDs, a single resistor can be used, but for a 10W LED, a resistor to limit current would be very inefficient as it would need to dissipate a lot of heat. An off-the-shelf 10W LED driver circuit was sourced for only $2.50, and it was glued in the main control box. There is a small SPST toggle switch inline with the LED driver, which allows the user to turn the LED on and off by flicking the switch.

4.3.3.4. Master Switch

A larger SPST toggle switch is used as the master power switch, and is directly inline with the battery. This switch features a built-in blue LED, which has been wired to turn on only when the switch is in the on-position. The switch also has a safety cover which makes it harder to turn the device on accidentally, and very easy to turn off in an emergency.

4.3.3.5. Custom PCB

There is a small custom PCB which contains the microcontroller and a few passive components. The board has two parallel 4-pin female headers to allow the microcontroller to be plugged in and removed easily for reprogramming. There is a resistive voltage divider to lower the input battery voltage to a level the microcontroller can read. The microcontroller has a built in 10-bit analog to digital converter (ADC) but it can only read a maximum voltage of 5V. Therefore, a voltage divider must be used to lower the battery voltage to an appropriate level. The divider is comprised of a 430Ω and 750Ω resistor. This produces a voltage drop across the 430Ω resistor that will not exceed 5V so long as the input voltage is nominally 12V. The voltage of the battery can then be calculated in software so that the microcontroller can monitor the battery and prevent over-discharge. For maximum accuracy, the voltage divider was calibrated using varying known input voltages and, and the microcontroller logged the analog input values. The calibration table is shown in Appendix C, figure 5. This data was then graphed, and a linear equation was generated. This graph can be seen in Appendix C, figure 6. The linear equation is as follows:

(x) 0.0131862(x) 0.0326896V = + In this equation, ‘V’ represents the actual battery voltage, and ‘x’ represents the value read by the microcontroller’s ADC. The ADC has 10 bits of resolution, which means there are 1024 different levels that can be detected. This means the resolution of the battery voltage reading will be equal to

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V(1024)/1024, where V(1024) is the equation above at the maximum acceptable input voltage. This works out to a resolution of about 0.0132V, or 13.2mV. This resolution is more than adequate for preventing over-discharge. The board also contains a second voltage divider which uses two 10kΩ resistors to provide 2.5V to the second analog input pin. This is the same pin used by the joystick. The purpose of this voltage divider is to prevent the analog input from floating if the joystick is disconnected, which could cause the arm to move unpredictably. The joystick contains a 25kΩ potentiometer which is in the middle position when at the joystick is neutral. This corresponds to a 2.5V signal, which is why the voltage divider uses two equal resistor values.

4.3.3.6. Joystick

The joystick uses a 4-pin DIN connector. This provides a connection to +5V, ground, and two signal wires. While only one signal wire is used, the second is available for future expansion. The joystick currently only has one axis being used, but the second axis could easily be used to add another feature, such as a second degree of motion.

4.3.3.7. Limit Switch

The final electrical component is the limit switch, which is mounted at the end of the arm. This switch was selected because it is entirely metal, and unlikely to get damaged if it were to slam into something like the floor or a wall. Two wires run from the switch’s common terminal and the normally closed terminal to the control box. At the control box, the actuator is wired such that the limit switch is in series, and if the switch is pressed, the actuator is prevented from moving the arm any farther down. However, the arm must still be able to rise back up while the limit switch is pressed. For that, a 1n4004 bypass diode is placed across the switch. So when the switch is pressed, the motor cannot continue in the downward direction, but the diode still allows the arm to move back up. The downside of this is that the diode creates a voltage drop of about 0.7V, which is typical for any silicon diode. However, this is only the case when the switch is pressed, and once the arm rises enough to disengage the switch, the diode becomes inactive. There are also two limit switches built into the actuator with similar bypass diodes. The three limit switches (two internal, one external) and their corresponding diodes can be seen in the bottom right corner of the electrical schematic, in Appendix C, figure 7. A photograph of the inside of the control box can be seen in Appendix C, figure 8.

4.3.4. Software Design The program is very simple, having only 121 lines of code. A block diagram of the code can be found in Appendix C, figure 9. First, the microcontroller reads the analog input pin corresponding to the joystick. This value is then mapped exponentially using the following formula:

(|x|/x) |x| )/(m )y = * ( p p−1 The variable ‘y’ represents the value to be sent to the motor, ‘x’ represents the input value, ‘p’ represents the exponent, and ‘m’ represents the maximum value that can be sent to the motor. Since the microcontroller has an 8-bit PWM capability, the ‘m’ value is 256. Several different values for ‘p’ were tested, and the best value in terms of user-friendliness was 2. This formula was determined through some experimentation using the Desmos graphing calculator. The function serves three main purposes: turn a

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linear set of data into an exponential set for any possible exponent, preserve the sign of the input, and ensure the maximum, minimum, and zero values of the input are equal to the output. This is shown in Appendix A, figure 1. Since the “zero” position of the joystick corresponds to 2.5V on the analog input, the ADC will see a value of around 512 when the joystick is inactive. Therefore, a second mapping must be done before the value is mapped exponentially. This takes the range of data from the joystick, which has a value from 0 to 1023, and maps it from -255 to 255. To accomplish this, a function built into the Arduino language called “map” is used. Next, the program checks if the newly mapped value is positive or negative. If it’s positive, the value is sent through a PWM output to the motor driver’s first input pin ‘A’ and the other pin ‘B’ of the driver is pulled low. If the signal value is negative, then pin ‘A’ is pulled low, and the absolute value of the signal is sent through a PWM output to the motor driver’s pin ‘B’. If the value is zero, both ‘A’ and ‘B’ are pulled low. Finally, the microcontroller checks the battery voltage. To do this, the analog reading from the battery voltage divider is put through a formula to convert it to the actual battery voltage. If this value is below 10.5V, the program enters a loop that cannot be exited unless the voltage rises above 10.5V. In this loop, the actuator is disabled and a constant “beep” is played. If the voltage is above 10.5V but below 11.1V, the actuator remains usable, but the device will beep rapidly five times, and repeat this at 20-second intervals. One problem that arose during the design was that the microcontroller did not have any remaining PWM outputs to connect a speaker for auditory alerts. A visual LED could be used without a PWM output, but this is not ideal because another length of wire would be needed to get the indicator to a location that could be seen by the user. Instead, an innovative solution was used, that did not affect the total part count. Rather than having a separate components to produce sound, the motor in the actuator could be used as a speaker. Through experimentation, it was discovered that a PWM signal with a duty cycle of less than 10% simply produces an audible whine without moving the actuator. This was taken advantage of as a means for alerting the user when the battery is low. The only downside to this solution is that the actuator becomes disabled while a tone is being played. However, the solution was reliable enough to be implemented in the final deliverable product.

4.3.5. Mechanical Testing During assembly, a couple tests took place to ensure the device would be reliable. Before the actuator brackets were installed, a piece of scrap aluminum with double the thickness as the arm tubes was tested. Two 7.1mm holes were drilled, and then M8 threads were tapped. Then an M8 bolt was tightened with a spacer until the threading in the aluminum broke. For the two holes, the threads failed at 76 and 78 inch-pounds. The formula can be used, where ‘P’ is the clamping force in pounds, ‘T’ is /(K )P = T * D the torque (76 inch-pounds), ‘K’ is the dry friction constant (0.2), and ‘D’ is the nominal diameter (0.28 inches):

(76 in lbs) /(0.2 .28 in) 1400 lbsP = * 0 = Assuming the arms will only withstand half of that, since the material used for the test was twice as thick as the arms, the material should withstand 700 lbs. Then using a safety factor of 2, it is safe to assume the fasteners will be able to withstand 350 lbs. But since there are two of these M8 bolts holding the bracket

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on, the number goes back up to 700 lbs. Of course, the actuator is not pulling on the bolts at a 90º angle; in fact, the actuator is pulling at an acute angle. However, this was just done as a very rough test to get an idea of whether the threads would be strong enough. The actuator is rated for about 170 lbs, so it is safe to assume the threads will hold under extreme conditions. The second test was to determine an appropriate amount of torque on the four joint bolts. This was determined through experimentation until the mechanism felt rigid enough, without being so tight that the actuator struggled to move. This was found to be approximately 18 inch-pounds. This number does not need to be very accurate, but the important thing is that all four joints are tightened to the exact same torque specification. A “click”-style torque wrench was used to meet these specifications.

4.3.6. Electrical Testing Once the device was fully assembled, it was tested for functionality. First, the master switch was tested to ensure the indicator LED worked. Then the small toggle switch was turned on to verify the 10 watt LED was working. Then the joystick was used to move the arm up and down, which worked well. However, it was discovered that the joystick had to be moved very far to reach its limits, which could be difficult for the user. To fix this, the code was tweaked so that the input domain is reduced, allowing the motor to reach full speed without having to move the joystick to the absolute maximum positions. Next, the limit switch was tested to ensure it stopped the arm from moving down, but still allowed the arm to move up. Finally, the low-voltage cutoff was tested by using a precision variable power supply to adjust the input voltage. When the voltage reached 11.1V, the device remained functional, but emitted an audible “beep” every 20 seconds. When the voltage reached 10.5V, the arm became locked out, and the device just beeped constantly.

4.4. Safety

4.4.1. Low-Voltage Cutoff LiPo cells should never fall below 3.5 volts to prolong their overall life. The device includes protection features to notify the user when the battery needs to be changed. There is a “warning” and a “cutoff” level in the program: → The warning level is 3.7V/cell and causes 5 short beeps every 20 seconds → The cutoff level is 3.5V/cell and prevents the motors from running while beeping constantly

4.4.2. Slow-Blow Fuse There is a replaceable fuse inline with the main power switch. The actuator draws about 1.5 amps under heavy load, so a 2 amp fuse should blow under extreme conditions. The fuse will also blow if the wiring gets damaged, which helps prevent a fire.

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4.4.3. Floor Limit Switch A limit switch is attached to the bottom of the arm, which gets pressed when the arm hits the floor. When the switch is pressed, the arm cannot move down any further, but remains able to move back up. This prevents the user from damaging the arm or tipping the wheelchair backwards.

4.4.4. Hot Swappable Joystick With the joystick connector wired to the microcontroller, the device will work just fine. However, if the joystick were to come unplugged, the analog input of the microcontroller would be floating, which means it could receive unpredictable values. This means the arm could move sporadically, potentially causing damage to the device or its surroundings. To solve this, a pair of high-value resistors pull the joystick input pin to 2.5V, so if the joystick is disconnected the pin will not be floating. This prevents undesired operation if the joystick is accidentally unplugged, or the device is turned on before the joystick is connected.

4.4.5. Metal Finishing All the edges and corners of the aluminum parts have been ground and filed to remove burrs and sharp edges. This prevents clothing from getting snagged or skin being cut when handling the device. Since the mechanical components are mainly made of aluminum, there is no risk of rust or corrosion. Even if the materials were prone to corrosion, the device will never be exposed to harsh environments because it is not meant to be waterproof.

5. Discussion of Feedback from Design Reviews

5.1. Design Review 1 There were many useful suggestions made in the first design review, and almost all the ideas were implemented. A common suggestion was that the arm could be used for more than just garbage bins if there were different attachments. This is certainly a valid suggestion, but it is beyond the scope of the project due to time constraints. However, several potential ideas were brainstormed such as an attachment to lift shopping bags or laundry bins. One of the OT students suggested adding a rubberized coating to the joystick to make it easier to grip, because the plastic alone is very smooth. After researching potential solutions, a product called Rust-Oleum Flexidip was used. Several coats were used to achieve a very grippy coating. One concern that was brought up was the potential for garbage bins to fall over if the user makes an error. A simple solution for this is to mount the blue receptacle cone at the top of the bin to lower the center of gravity. If this is not enough, a ballast weight (such as sand) can be added to the bottom of the garbage bins to lower the center of gravity even more.

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Another suggestion was to make the control system removable. For this, velcro was used on the bottom of the joystick holder to allow it to be held securely on the wheelchair tray, while still being removable. There were a few other concerns, such as the total weight of the system. This was minimized as much as possible by using aluminum, and the final product is light enough for the support worker to easily lift. One suggestion that was not implemented was the ability for the arm to extend in a telescopic manner. This was deemed unnecessary because the arm is already quite long, and adding the ability to extend would nearly double the cost and severely increase the complexity.

5.2. Design Review 2 One potential flaw was pointed out: when using the cone mating system, the garbage could rotate side to side when the wheelchair turns. One suggested fix involved replacing the cones with pyramids, which would serve a similar function without being able to spin. However, this would involve reprinting all the parts, which would take too much time. Instead, the rubber spray used on the joystick was used to coat the inside of the blue cone receptacle. This creates a lot of friction, which prevents the garbage can from being able to rotate once lifted up. Another interesting comment was regarding the length of the arm. One reviewer asked why the arm was so long. This conflicts with another reviewer’s comment from the first review session that the arm should be able to extend. This suggests that the length is a potential source of debate, and could be a matter of the user’s preference. For the prototype, the stock length of the tubing (3 feet) was used, simply to reduce the build time. One reviewer was concerned that the metal had sharp edges. This is not the case, as the edges have been filed to remove burrs and sharp edges. Given more time, the entire metal mechanism could be coated in the rubberized spray. The final suggestion was to include a mounting system to attach the device to the wheelchair. The problem with this suggestion is the fact that there is minimal information available about the user’s wheelchair, as it is customized. However, if the user chooses to use the product, JVAL will work closely with them to design a mounting system that works excellently, rather than attempting to include a mounting system based on minimal information that likely would not work. However, to show a general idea of how the device could mount, a CAD rendering of an adjustable hook mounting system is included in Appendix D, figure 1 & 2. The hooks would be able to slide up and down the aluminum angle and then be tightened in place in the desired position. Finally, a reviewer suggested adding an LED to the end of the arm to help the user line up the cones in the dark. The reviewer pointed out that many people take out their garbage in the evening, so it would be very helpful to have a light. To fulfill this suggestion, a super bright 10 watt LED was added, with a toggle switch on the control box to turn it on and off.

6. Conclusions GIGO, produced by JVAL is a unique solution to the problem of moving garbage around the apartment and outside to a bin for F.M. to use. We designed this keeping in mind what F.M. currently used in her day to day life and her limited movement of the hands. With this knowledge, we developed a robotic arm

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which we determined to be most effective in accomplishing the task we had set by comparing them to the metrics which we had set. In order to evaluate the final prototype, the metrics used were the same ones used for evaluating the design alternatives: ease of use, reliability, cost, and usability. The product incorporated exponential mapping with the joystick in order to ensure a quick learning curve, as it would be similar to the joystick used on her wheelchair, both in shape and function. As this would be the only method of interfacing with the product, it would ensure that the user would be capable of easily using the product. GIGO’s reliability is strong as the construction of the product is very robust. The cost was fairly expensive compared to other groups at over $200, however the utility of the product justifies the cost, as it has the potential to solve many other issues besides just the garbage task. There was lots of feedback given by various other students and OTs during the design review, as explained in section 5. The key points taken from these reviews were adding a rubberized coating to both the joystick and the inside of the attaching cones, considering what should happen if the user makes an error in operating the device, and the length of the arm affecting the turning radius of the wheelchair due to the narrowness of the hallways. As many of these concerns were addressed as possible, given the time constraints. There are many benefits to the device which will aid both F.M. and the PSW in their usage of the device. For F.M, the joystick has been extended and coated with a rubberized coating which will help her to better grasp the joystick to move the arm around. The mating cones have also been coated with the same rubberized coating to increase the amount of friction, preventing the garbage from rotating side to side. For the PSW, the device is lightweight and quick to set up. The battery and joystick simply plug in, and are held in place with Velcro. To turn the device on, a simple toggle switch must be flicked, and the device is ready to use. Through our many design iterations, JVAL believes that it has created the best design for moving garbage cans around the house and yard. GIGO is a lightweight, user-friendly device which will allow F.M. to be more independent.

7. References [1] H. Brody, “Gripping aid for the manually disabled,” US4523781A, 18-Jun-1985. [2] F. T. Smith and F. P. Smith, “Universal container grabber apparatus for a refuse collection vehicle,” US4708570A, 24-Nov-1987. [3] T. E. Terry and L. J. Hoyt, “Cerebral palsy arm and hand brace ,” US4149532A, 17-Apr-1979. [4] B. R. Williams, “Gripping device,” US4944766A, 31-Jul-1990. [5] F. A. Williams, “Simple prosthesis for manually-challenged persons,” US9364364B2, 14-Jun-2016.

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8. Appendix A

Figure 1: Exponential Mapping of Joystick

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9. Appendix B

Figure 1: Brainstorming Chart

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Figure 2: The first design alternative.

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Figure 3: The second design alternative.

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10. Appendix C

Figure 0: The cone mating system. The arm is on the left, and a garbage bin is on the right.

Figure 1: The shorter vertical bracket.

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Figure 2: The longer vertical bracket.

Figure 3: The shorter bracket with the 3D printed cone and LED attached.

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Figure 4: Exploded view of a bolt connecting an arm tube to a vertical aluminum angle.

Figure 5: The battery voltage divider calibration data.

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Figure 6: The battery voltage divider calibration plot, with the equation shown.

Figure 7: A simplified electrical schematic of the device (excluding inactive parts).

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Figure 8: Photograph of the control box internals.

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Figure 9: A simplified block diagram of the program.

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Figure 10: A CAD rendering of the joystick enclosure.

Figure 11: The physical joystick, in the 3D printed enclosure.

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Figure 12: A CAD rendering of the 3D printed joystick extension.

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11. Appendix D

Table 1: Raw Notes From Design Review 1

Use a larger cone for bigger garbage bins Could make arm go vertical so can permanently stay on wheelchair Different attachments (future expansion)

Allow tilt movement? (to dump garbage) Adjust length of entire arm (telescopic) Add grippy coating to joystick, plastidip, tape, silicone

Easy to remove control system (velcro?) Weight too high? Different attachments to lift different objects What to do if garbage falls? → Could add ballast to bottom of garbage can to lower C.G. What if garbage can not aligned to cone?

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Table 2: Raw Notes From Design Review 2

Pyramid instead of cone to prevent rotating → Using plasti dip Attaching to wheelchair? → Clamping system Improve aesthetics, ask F.M. Very universal in picking up garbage cans Seems easy to use More testing

Enlarge cone Mini LED Lights on cone Turning, doorways → Check upright length Gives more independence compared to other groups More colourful Padding on edges

Worry about garbage can tipping from total weight Why so long? → Can make shorter, currently in this state for ease of assembly Mounting to wheelchair? → Do not have specific specs Sharp edges → Cover in rubber Turning around corners → Put upright Using familiar joystick Learning curve more natural Have options instead of waiting (for mounting)

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Figure 1: A rear view of a potential mounting system.

Figure 2: A side view of a potential mounting system.

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