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ASME - Robots for Relief Student Design Competition
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Midterm Project Report
Presented to:
Sebastian Y. Bawab, Ph.D.Colin Britcher, Ph.D.
Associate Professor of Mechanical and Aerospace Engineering
Frank Batten College of Engineering and Technology
Old Dominion University
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In Partial Fulfillment of the Requirements for:
MAE 435 - Project Management and Design II
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By Mechanical Engineering Students:
Ryan Kenny
Rosalyn Lopez
Mark Sodusta
Michael McDermott
Aaron Fuentes
Austin Priest
Advised By:
Thomas Alberts, Ph.D.
TABLE OF CONTENTS
1) ABSTRACT……………….……………………..……………….………….…………...1
2) INTRODUCTION………….…………….……………..………………………………...2
3) CHASSIS………………………………………………………………………………….3
A. INTRODUCTION
B. COMPLETED METHODS
C. PROPOSED METHODS
4) TRACKS…………………………………………………………………………………..4
A. INTRODUCTION
B. COMPLETED METHODS
C. PROPOSED METHODS
5) DRIVE TRAIN…...... 7
A. INTRODUCTION
B. COMPLETED METHODS
C. PROPOSED METHODS
6) PAYLOAD MECHANISM……………………………………………………………...... 8
A. INTRODUCTION
B. COMPLETED METHODS
C. PROPOSED METHODS
7) ELECTRICAL……………………………………………………………………………..10
A. INTRODUCTION
B. COMPLETED METHODS
C. PROPOSED METHODS
8) CONTROL SYSTEM……………………………………………………………………...12
A. INTRODUCTION
B. COMPLETED METHODS
C. PROPOSED METHODS
9) RESULTS…………………………………………………………………………………..12
A. MATERIAL SELECTION
B. DESIGN
10) DISCUSSION………...………….….…..…………..…………………………...... …………...13
11) REFERENCES……………………………………………………………………………….....15
LIST OF FIGURES
Figure 1………………..Course Schematic, Page 3
Figure 2………………..Chassis Isometric and Front Views, Page 5
Figure 3………………..Track Arm Detailed View, Page 7
Figure 4………………..Track Arm Rotation System, Page 9
Figure 5………………..Payload Hopper, Page 10
Figure 6………………..Electrical Schematic, Page 12
APPENDICES
Appendix 1……...Gantt Chart
Appendix 2……...Budget Analysis
Appendix 3……...Budget
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1. ABSTRACT
The goal of this project is to develop a scaled down prototype robot capable of transporting humanitarian aid to areas affected by natural disasters such as the Philippines after Typhoon Haiyan hit. The ability for the robot to complete this task will be measured by how well the team competes in the ASME Student Professional Development Conference. The design that was decided upon features an articulated track system in which four independent motors give the vehicle its driving capabilities. A gravity-fed hopper system was designed to deliver the humanitarian aid and an Arduino based control system was developed to actuate all of the electronic components. Each track will have the ability to rotate a full 360 degrees to assist with climbing over and traveling through obstructed areas. The payload storage will consist of a square-shaped funnel with a sliding hatch operated by a dc motor. A Playstation®3 controller will be used to operate the robot via bluetooth and manipulate the entire drivetrain and all motors used for the payload dispensing mechanism. A 3D printed model of the chassis will allow us to look into the finite element analysis to ensure the integrity of the design.
2. INTRODUCTION
In the last 50 years there has been an increase in the need for an all-terrain, amphibious vehicle that has the ability to deliver a payload safely to its destination. The necessity of a disaster relief robot is even more critical in developing countries where roads are not paved and infrastructure is not well established. A disaster relief robot must have the ability to climb over obstacles and cross water without contaminating its' payload. The purpose of this project is to design and build an unmanned variable-terrain vehicle that will navigate a closed course while maximizing humanitarian payload capacity and minimizing energy consumption. Combining different terrains, such as sand and water, create many issues in the design of a small amphibious vehicle.
Each year, the American Society of Mechanical Engineers (ASME) has a student design competition. In this year’s competition, entitled “Robots for Relief”, students must design a 25 cm X 25 cm X 30 cm relief vehicle capable of spanning a ramp, traveling through water and sand, and upstairs of various heights to deposit relief aid into a designated hole at the end of the course. The scoring of the competition is based on the amount of payload delivered, the time taken to complete the course, and the energy capacity of the robot.
The robot’s design must keep both the payload and all sensitive electrical components safe and dry while traversing the course. A chassis design with four articulating tracks on each corner of the vehicle was determined to be the best method for the robot to be able to travel through all of the obstacles. Elongated tracks eliminated the need for waterproofing all electronic components. A track design gave the operator more control over the vehicle and also combined the mechanics required to climb the stairs and cross the water.
3. CHASSIS
3A. INTRODUCTION
The chassis makes up the main frame of the robot. It houses the drive train, as well as, the payload funnel mechanism. Because the chassis provides the basis of support for the robot, it must be fabricated out of a material capable of withstanding the stresses the robot will encounter while navigating the competition course.
3B. COMPLETED METHODS
The chassis of the robot was designed based on the competition requirements to maintain overall dimensions of 25cm x 25cm x 30cm. The chassis was modeled using an angled design in SolidWorks (Dassault Systemes Corp, Waltham, MA) with 8mm square solid extruded aluminum fitted for bushings and an 8mm diameter axle to create the assembly.
A 3D model was printed using Acrylonitrile Butadiene Styrene (ABS) plastic to perform the finite element analysis tests which proved that an aluminum chassis would be more practical than one that is 3D printed.
3C. PROPOSED METHODS
Due to an unexpected backup at the machine shop, the chassis will be cut and welded together out of aluminum stock by members of our team with welding experience.
4. TRACKS
4A. INTRODUCTION
The ability of a tracked vehicle to move efficiently over loose or rough terrain is directly related to how the weight is distributed from the suspension through the tracks and onto the driving surface [1]. Known as the mean weight distribution, it's optimization alongside the specific shape ratio determines the success of vehicle maneuverability [2]. As most materials wear, they tend to stretch which can have negative effects on the handling capabilities of the vehicle, therefore most tracked vehicle designs include a tensioning system to ensure that the tracksremain on the drive sprockets [3]. A significant advantage of track propulsion systems is their ability to climb shear obstacles that are much higher that the vehicle itself. A mathematical model was developed to predict the size of track necessary to climb stair-step style obstacles [4]. Independently driven tracks must actuate drive motors to move the treads with equal velocity so the vehicle can be driven in a straight line. This is done through a closed loop power control module that regulates the specific voltage into the drive motors on each side of the vehicle [5]. A control system is often necessary to take input from the environment the vehicle is encountering, and provide feedback to the suspension.
4B. COMPLETED METHODS
After multiple track tensioning systems were considered, including a scissor-lift type device, and an ‘up-and-over’ system, a simple screw-in-slot was designed and will be manufactured accordingly. These designs will be used instead of a traditional track tensioning system due to the rules for the ASME student design competition which preclude the use of springs. The front and rear sets of tracks were designed to rotate simultaneously to create the climbing feature. Research was also done on belt materials and suppliers. A 3-ply rubber belt was chosen from McLeod Belting Company of Chesterfield Virginia. The raw material has already been ordered and cut to the appropriate length of 497mm.
After realizing that the wires connecting the motors for the tracks to the robot would become tangled as the arms rotated, a wireless relay was integrated into the plates making up thearms that held the tracks. This wireless relay would also need its own energy source which required that we take some of the trusses out of the arm plates to make room to mount batteries and the XBee microcontroller into each rotating arm.
4C. PROPOSED METHODS
The tensioning assembly will be examined to determine the forces it is able to withstand before losing functionality. Custom designed treads have been selected based on their pliability and traction in sand and on wet surfaces. Once the treads are assembled, they must be installed on the tracks and tensioned so that they do not slip off the drive sprocket during operation.
5. DRIVE TRAIN
5A. INTRODUCTION
A tracked drivetrain system meets the competition requirements of the robot to be capable of navigating through water, sand, and able to climb steps of varying heights. Individually pivoting tracks powered by stepper motors were designed to have a minimum length of 205 mm and maximum width of 22 mm to climb the stairs and travel through the water without exceeding the dimensions of the competition rules.
5B. COMPLETED METHODS
Due to the size constraints of placing the motor in between the track plates, the 20mm diameter brushless, 3 watt DC motor was ordered. With a low-profile design and a maximum load rating of 8 mNm, this motor was best suited to drive the tracks. A custom mounting bracket was made to fit the small size of the motors.
Based off the CAD drawing, a list of stepper motors was compiled to operate the drive train on the axles based on the space available in the robot chassis. The size of the motor would have to be a National Electrical Manufacturers Association (NEMA) 14. Since the space is limited within the chassis and weight has to be put into consideration, each motor weighing around 60 grams, the drivetrain was limited to two motors which will use spur gears to rotate the front and rear axles connected to the robot’s track arms.
5C. PROPOSED METHODS
While the Nema 14 motors and spur gears were ordered, the axle and motor mounts will be custom made using aluminum.
6. PAYLOAD MECHANISM
6A. INTRODUCTION
Materials considered for the design of the delivery mechanism must have properties to protect the vehicle from harsh conditions such as wind, rain, temperature, and/or mechanical damage [6]. If the cargo becomes contaminated, the aid could cause illness and/or death [7]. A delivery mechanism needs to be compatible to the type of aid being delivered [8], as well as, able to be strategically integrated into the robot to prevent excess bulking which hinders the vehicle’s maneuverability [9]. The payload system must be made of a material that can endure rough terrain and withstand dynamic, reversible loading [10].
6B. COMPLETED METHODS
The method chosen to deposit the material was a trap door at the exit of a funnel located within the center of the chassis. This system was chosen over several other designs due to its ease of operation and its predicted use of small amounts of electricity. A sliding door release mechanism can allow for a high mass-flowrate through the opening, reducing the amount of time needed to unload all of the contents. The payload mechanism will be hand loaded using a sliding latch door located at the top of the hopper.
6C. PROPOSED METHODS
Due to the complex design of the payload system, both the top and bottom funnels will be 3D printed. Also, because of the competition size restrictions of the robot, the side of the bottom funnel will be used to mount the dc motor being used to operate the trap door to dispense the payload, and the top funnel will be used to mount the Arduino microcontroller.
7. ELECTRICAL
7A. INTRODUCTION
The electronic components consists of a 12-volt, nickel-metal hydride (Ni-MH) rechargeable battery pack, XBee Explorer microcontroller, host shield, and four 3.6-volt batteries which will all be mounted within each track arm. The XBee Explorer system is an easy to use and operate component that will provide a radio signal to and from the Arduino microcontroller at a low power and can be used in simple or complex networks [14]. The XBee explorer creates a serial connection between the Arduino Mega and the Arduino Pro Mini utilizing a point to multi-point network.
7B. COMPLETED METHODS
An Arduino compatible code and setup platform were developed to create and test the multi-functional capabilities of the robot’s control system. Actual motors to be used on final design were not used with this test set up. Each button was assigned an operation based on its digital or analog nature. The purpose of this test setup was to test the reliability and strength of the connections. A new battery holder for the four 3.6-volt batteries and top and bottom mounting plates were created using SolidWorks and are in the process of being fabricated using Delrin and ABS (Acrylonitrile butadiene styrene).
7C. PROPOSED METHODS
The previous Arduino code will be restructured to include the XBee microcontroller, Explorer host shield, additional batteries and actual NEMA 14 motors. Testing on the system as a whole will be conducted to familiarize the group members with the controls.
8. CONTROL SYSTEM
8A. INTRODUCTION
A Bluetooth connection will be made with the Arduino and a Playstation®3 video game controller. The controller was a better option as compared to a radio frequency (RF) and Wi-Fi™ due to having a better connection quality. A Bluetooth dongle is a compact antenna that allows direct, immediate contact with the board. Anupright, or vertical RF antennae, took up meaningful space, and limited the means of communication available for the microcontroller to use.
8B. COMPLETED METHODS
A PS3TM controller paired with a Bluetooth® dongle was selected as low cost, higher quality alternative to a multi-functional RF controller. An Arduino program was written and successfully tested to establish an optimal connection between controller and dongle.
8C. PROPOSED METHODS
Testing and potential troubleshooting of new Arduino program with new XBee system and NEMA 14 motors will be conducted to ensure proper functioning of all components.
9. RESULTS
9A. MATERIAL SELECTION
In order to ensure the structural integrity of the robot, general purpose aluminum 6061 was selected for the chassis, axle, track arm plates, and track supports. This material is lightweight and is strong enough to withstand the obstacles throughout the course. The material is also easy to obtain, easy to weld, and has good machinability. The funnel and hopper uses Acrylonitrile butadiene styrene (ABS) plastic. ABS is both strong and flexible and is also one of two types of plastic that can be 3-D printed, the other being Polylactic acid (PLA) plastic. Delrin was chosen as a lightweight, corrosion-free alternative to aluminum 6061, its high machinability, non-conductivity, and high strength characteristics make a perfect solution for the battery cover, funnel and hopper doors.
9B. DESIGN
SolidWorks was used to primarily design the robot. Custom designed parts were made around the dimensions of purchased parts such as the motors. After finite element analysis was performed on multiple parts, the designs of the parts were made thicker to allow for stability.
10. DISCUSSION
The purpose of this project is to design and build a variable terrain robot capable of climbing stairs, crossing water, and delivering a payload of relief supplies to a determined location via remote control. This simulates an environment similar to one found after a natural disaster, like a typhoon or tornado, where people in need are in dangerous or cramped spaces that would be difficult and hazardous to access. Robotic aid creates the capability to safely transport supplies to these areas, helping people that may have had to wait hours or even days for relief. This project is focused on developing technologies for a scaled-down prototype of a robot that can complete these tasks.
Several limitations were observed during the project. Insufficient CAD experience amongst team members limited the part-modeling process. One included part-modeling due to the team’s lack of experience with CAD software. This meant that high volumes of workload had to be completed by a few team members, while the rest of the group learned to use the software. This resulted in a couple of weeks where there was a backlog of modeling work, while not much other work was able to be completed at that time. Another limitation includes the need for a small motor to fit the design’s dimensional requirements that is powerful enough to carry a large payload while minimizing energy consumption. Another limiting factor was the maximum capacity of the batteries available. Many 12 volt NiMH batteries had large milliampere/hour ratings which affected the total performance of the robot. The accuracy of the 3D printer is another limiting factor when designing small, intricate parts for the tracks. Based on the prototype, the 3D printer has a difficult time accurately creating parts that are one to two millimeters thick.
By the end of the Project Design and Management II in the spring of 2015, the team will have completed the robot and will be able to compete in the ASME Student Design Competition. This includes having a complete robot capable of navigating the competition course (Figure 1), depositing the granular supply, and returning to the loading area. The final chassis material will be chosen and constructed after testing. Motors and other parts will be selected, purchased, and incorporated into the vehicle as they are received. Testing and optimization of the robot’s functions will occur at least a month prior to the competition in April using a reconfigurable testing course to be constructed. The final design will take the finite element analysis into account to ensure the robot will be safely tested. Sufficient time will be spent developing operator proficiency with the robot on a prototype course.