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Expedition: MANTA Multipurpose Aquatic Navigator and Trash Annihilator

Daniel Diazdelcastillo

Alexander Ly

Nicholas Philips

Aryaman Sinha

Elisabeth Wagner

Faculty Advisor 1: Dr. Tein-Min Tan

Faculty Advisor 2: Dr. M. Ani Hsieh

Department of Mechanical Engineering and Mechanics

Drexel University

ASTM STUDENT PROJECT GRANT PAPER

Submitted: June 18th, 2017

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Table of Contents Abstract ................................................................................................................................................... 3

1 Introduction .................................................................................................................................... 3

1.1 Background ............................................................................................................................. 3

1.2 Stakeholders and Needs ......................................................................................................... 3

1.3 Problem Statement ................................................................................................................. 4

2 Methods .......................................................................................................................................... 4

3 Design Description .......................................................................................................................... 5

3.1 Specifications .......................................................................................................................... 5

3.2 Concepts.................................................................................................................................. 5

3.2.1 Hull Design ...................................................................................................................... 5

3.2.2 V-Wing Design ................................................................................................................. 6

3.2.3 Conveying Design ............................................................................................................ 6

3.2.4 Compaction Design ......................................................................................................... 6

3.2.5 Wireless Communication Design .................................................................................... 7

3.2.6 Trajectory Tracking & Motion Planning Design .............................................................. 7

3.3 Concept Evaluation ................................................................................................................. 7

3.3.1 Hull Design Selection ....................................................................................................... 7

3.3.2 V-Wing Design Selection ................................................................................................. 8

3.3.3 Conveying Design Selection ............................................................................................ 8

3.3.4 Compaction Design Selection ......................................................................................... 9

3.3.5 Trajectory Tracking & Motion Planning Design Selection ............................................... 9

3.3.6 Wireless Communication Design Selection................................................................... 10

3.4 Embodiment .......................................................................................................................... 10

3.5 Detail Design ......................................................................................................................... 11

3.5.1 Hull Detail Design .......................................................................................................... 11

3.5.2 V-Wing Detail Design .................................................................................................... 12

3.5.3 Conveyor System Detail Design .................................................................................... 13

3.5.4 Shredder System Detail Design ..................................................................................... 14

3.5.5 Trajectory Tracking & Motion Planning Detail Design .................................................. 14

4 Discussion ...................................................................................................................................... 15

5 Summary & Conclusion ................................................................................................................. 17

6 Future Work .................................................................................................................................. 17

7 References .................................................................................................................................... 17

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Abstract

Herein, the design of an autonomous surface-skimming vessel, termed the MANTA (Multipurpose

Aquatic Navigator and Trash Annihilator), is detailed. The MANTA is designed to capture marine

debris, store it onboard, and bring it to land for waste management. This paper summarizes the

development of the MANTA, from the concept development phase to prototyping and testing.

Section 1 describes the identified potential stakeholders that would benefit from the use of this

design, the needs of the device, and the project’s problem statement. Six subsystems of the design

concept were originally proposed to divide the work structure, which composes of a hull, v-wings,

conveying system, compacting system, controls, and power system. Several design concepts were

proposed for each subsystem and weighed via decision matrices to choose a concept for the final

design. Thorough and detailed analyses were performed on these concepts to check if these

concepts were feasible. The results of our prototype development and testing are detailed. Finally,

future areas of work are presented to improve the ongoing capabilities of the MANTA.

1 Introduction

1.1 Background

Marine debris, commonly referred to as floatables, are defined as any solid material that is disposed

of or abandoned into the marine environment [1]. Marine debris are found in water resources across

the world and consist of waste items such as plastics (bottles and wrappers), polyesters (clothing),

paper products, and metals. Over time, these wastes are broken down into smaller macroscopic

fragments, affecting marine life and ultimately the food supply chain. Plastics account for the

greatest proportion of pollutants, and without improvements in waste management infrastructure,

the cumulative quantity of plastic waste available to enter the ocean from land is predicted to

increase by an order of magnitude by 2025 [2].

Numerous collection techniques have been employed by municipalities and countries around the

world to clean waterways and curb the amount of pollutants entering the water. In addition to

affecting marine life, waterways are epicenters of industrial, commercial, recreational, and

residential activity, and they can be impacted by the abundance of floating debris on the surface of

the water. Current cleanup programs consist of skimming vessels and static receptacles that are

costly to operate and maintain, energy inefficient, operate only during warmer seasons, and rely on

human operators to manually collect the debris from waterways. Education and civic engagement

programs are often touted as the best way for prevention, but unfortunately, there is an

overwhelming lack of initiative to fully engage in proper sorting and disposal techniques. Today’s

methods are not enough to combat the overwhelming task of routinely cleaning up debris from

water environments, and are an ineffective use of the resources and technologies available to

engage in full remediation.

1.2 Stakeholders and Needs

Stakeholders in the Philadelphia area were interviewed to identify needs for the product. The

Philadelphia Water Department (PWD) is the main stakeholder for this project. As described by PWD

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representatives, the current methods used within Philadelphia are manned vessels: one is a pontoon

in which people onboard can use nets and bags to collect trash, and the other—the “R. E. Roy”— is a

large vessel that collects trash into a debris bin as it maneuvers. These two methods are user-

operated, and thus one primary need expressed by the PWD is for the product to be unmanned and

capable of acting autonomously. Additionally, the PWD expressed that it would be necessary for the

vessel to identify patterns in debris presence (e.g. where do debris commonly appear, what are the

precedent weather conditions, etc.). Lastly, the product needs to be more cost-effective—as

measured in cost per pound of collected trash—than the current employed methods.

1.3 Problem Statement

The problem statement for this project is to design a vessel—termed the MANTA (Multipurpose

Aquatic Navigator and Trash Annihilator)—that autonomously collects debris within a defined space

in a body of water. The vessel should also track and record environmental conditions during debris

collection and be more cost-effective than the current solutions.

2 Methods

Stakeholder needs, primarily those of the PWD, were used to create product specifications and to

evaluate concepts for the device. Each concept was vetted through a strict engineering design

process. Decision matrices were used to decide on all major functionalities of the product in which

each concept was scored in regard to how well it meets product specifications.

Concepts were first sketched using pen-and-paper. Upon refinement of design ideas, SolidWorks, a

computer-aided design (CAD) software, was used to draft a 3D model of the product. This allowed

for proper scaling of the product and was later used to determine size, placement, and fit of

components.

To meet design needs, the final concept was modelled as a system with six subsystems: four (4)

structural subsystems and two (2) electronics subsystems. The structural subsystems were: hull, v-

wings, conveyor, and shredder. The shredder subsystem has been removed from the current

prototype due to safety concerns, cost, and time constraints. The electronics subsystems are

controls and power distribution, in which the former is composed of the sensors and

microcomputers that control the vessel’s path-following algorithm, collect data on debris collection,

and communicate information to and from the user, and the latter is composed of the components

that supply power to the vessel.

For the development of the structural subsystems, mathematical hand calculations were performed

to size each component (e.g. waste bin sizing). ANSYS, a finite element software, was used to verify

hand calculations with both finite element methods (FEM) and computational fluid dynamics (CFD).

SolidWorks was used to model the components with the determined dimensions and ensure proper

fit. To construct the prototype (in its current state), 80/20 aluminum, a T-slot aluminum building

system, and carbon fiber layup techniques were used.

In regard to the controls subsystem, several sensors were utilized, such as accelerometers and GPS

receivers, to simulate data exchange and control between a Raspberry Pi, Arduino Uno

microcontroller, and a home-base computer. Programming languages Python and C were used to

communicate between these devices. An iRobot Create was used to simulate the path-planning

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algorithm of the MANTA. Waterproof motors were obtained to test differential drive capability. For

the power subsystem, total power demands required by the motors and all electronics were

considered to determine the necessary power supply. Batteries with the necessary power supply

were obtained.

3 Design Description

3.1 Specifications

From the need statements, competitive benchmarks and existing systems that clean debris up from

water resources were assessed during the concept development phase of the vessel. Industry design

and compliance guidelines were also considered. Key specifications from stakeholders from the PWD

were focused on improving their current methods of water cleaning. The limitations of these vessels

are common with commercial skimmer and aquatic harvesters: they require human operators, are

expensive to maintain, and have a limited operation schedule due to constraints such as weather

conditions, water conditions, and available budget. Improvements were requested by the PWD for a

device that can operate beyond their current six (6) month window, while maintaining the current

debris collection rates. There is also concern for the work crew, as the difficulty of manually of

collecting the debris has worker safety concerns. The water department also expressed desire for a

modular platform that could be used for environmental monitoring, underwater mapping, tracking

trends of debris flow, and be adaptable for possible further configurations as deemed necessary for

operation.

Governing standards for the design and operation of this vessel are clearly defined by boating

regulations on the Schuylkill River, while the design is adapted from industry standards. Launching

the vessel would require a permit granted by the PA Fish and Boat Commission while also being

conducted under supervision from representatives of the PWD. The ASTM F41 committee provides

guidelines for the design of Unmanned Maritime Vehicle Systems, and, in particular, standards for

Unmanned Surface Vehicles. These standards were obtained to use as a reference for considerations

in the design of the vessel’s structural and control systems, and to ensure the device is in compliance

with design codes and other operating guidelines. ASTM Standards consulted include:

1. F2541-06 - Standard Guide for Unmanned Undersea Vehicles (UUV) Autonomy and Control

2. F2545-07 - Standard Guide for Unmanned Undersea Vehicle (UUV) Physical Payload 3. F2594-07 - Standard Guide for Unmanned Undersea Vehicle (UUV) Communications 4. F2595-07 - Standard Guide for Unmanned Undersea Vehicle(UUV) Sensor Data

Formats

3.2 Concepts

3.2.1 Hull Design

The hull of a vessel displaces water to allow the watercraft to float. Numerous kinds of vessels with

different shapes, dimensions, and construction materials were considered in the design decision

making process. Several tools were used to analyze and verify the buoyant forces needed in the

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design of the hull. The first step in the design was to determine what shape would be optimal for the

application and configuration of the vessel. The second step was to determine the general vessel size

and the necessary buoyant force to keep the entire vessel afloat. The preliminary mass of the system

was determined via hand calculations based on inputs from all other components, such as the wings,

conveyor, shredder, and weight of the collected trash. A safety factor of 1.5 was then incorporated

in this resulting value to ensure margins for error. The third step was creating a CAD model, and then

using ANSYS to verify the forces and loads that were calculated using hand calculations.

3.2.2 V-Wing Design

The v-wing is the structure that channels debris from below the water to the surface and onwards

towards the mouth of the vessel. The efficiency of the vessel is increased as the width of the v-wing

increases because more space would be traversed per distance traveled (compared to a narrower

wing or no wing at all). The two design criteria that were considered for the v-wing were the size and

the configuration. The size calculation involves determining the optimal angle, length, depth, and

structural configuration to mitigate stresses and avoid failures on impact. A failure mode effects

analysis (FMEA) was conducted for the v-wing to determine the failure modes and the size of the

wing that is optimal for the design. Additionally, a comparison was made to the wings of the R. E.

Roy, as the vessel would have a scaled wing size to have similar or better-traversed displacement

efficiency.

3.2.3 Conveying Design

To collect and convey the debris from the surface and into the vessel, several common mechanical

systems and configurations were considered. The first option considered was dependent entirely on

the flow of water, as debris would be funneled into a basin within the hull of the structure as the

vessel traverses the surface. The second system considered was a pump system to directly vacuum

debris into the vessel from the waterline, and deposit it directly into the vessel receptacle. A third

system considered was using a bucket on an elevated rail system powered by an actuator to raise

the debris from the water’s surface and dump the collected load into the receptacle, a system

similar to what is utilized on the R.E. Roy. The final concept considered was using an inclined

conveyor system to propel debris collected from the surface of the water at the mouth of the vessel

and convey the collected load into the vessel. To evaluate all of these concepts, a scoring system as

well as FMEA’s were created for each concept to establish a baseline and identify the optimal

configurations when considering safety, capacity, power requirements, maintainability, and

procurement of components.

3.2.4 Compaction Design

Note that the development for a compaction system has been removed from this prototype due to

safety concerns, cost, and time constraints. This section has been kept in this report for future

pursuits beyond the timeline of the senior design sequence.

Two methods of compacting the collected debris from the water’s surface onboard the vessel were

conceptualized for implementation through the use of a motorized shredder or a compactor

comprised of a linear actuator. The main purpose of the compaction system is to reduce the size of

the collected debris so that a greater capacity and greater operational run time could be achieved.

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This would allow the device to operate in continuous operation with less oversight from an operator

who would have to unload debris at more intervals. The device would also be to complete longer

cleaning cycles by being able to traverse larger areas while collecting more debris. The shredder

would operate continuously by having multiple cutting knives that would be mounted to a drive

shaft coupled to a motor. The shredder would pulverize debris into smaller pieces as it is funneled

into the vessel from the conveyance system, and an orientation would be chosen to efficiently

funnel the debris into the receptacle. The compactor system would operate by having all of the

debris funneled directly into the receptacle, and an actuator mounted on either the side or above

would compact the debris horizontally or vertically depending on the available space. To evaluate all

of these concepts, a decision matrix and FMEA were created for each concept to identify the optimal

configurations when considering safety, capacity, power requirements, maintainability, and

procurement of components.

3.2.5 Wireless Communication Design

The MANTA is an autonomous device, and thus needs two-way communication between a computer

and a “home base” computer to: (1) provide an initial input of a geofence, which is used to mark the

boundaries of the device’s motion; (2) send data to the home base computer for reliable monitoring

of environmental and physical conditions; and (3) act as a stipulation in case of emergencies so that

the observer can take over the command of the device via remote control. Bluetooth and Wi-Fi were

the two chosen methods of wireless communication due to their range and speed of data

communication.

3.2.6 Trajectory Tracking & Motion Planning Design

It is desirable that when the device is within its set geofence, it implements a trajectory tracking

motion to collect waste. Trajectory tracking is concerned with the design of control algorithms that

drive a vehicle to reach a point and follow a time-dependent reference. There are a few constraints

that have to be considered in order for this to work: (1) the time constraint, i.e. the system must be

able to reach its destination in the least amount of time, and (2) control input; that is, due to motor

voltage restrictions, there may be limitations on the voltage supplied to the system.

For under-actuated systems such as the MANTA, trajectory tracking is complicated because most of

these systems are not fully feedback-linearizable and they exhibit non-holonomic constraints. The

classical approach for trajectory tracking of under-actuated vehicles utilizes local linearization and

decoupling of the multivariable model to steer the same number of degrees of freedom as the

number of available control inputs, which can be done using standard linear control methods.

3.3 Concept Evaluation

3.3.1 Hull Design Selection

A catamaran hull design was chosen because it provides greater stability and a wider span compared

to all other hull options. Since debris is being collected toward the central part of the vessel, the

middle section of the vessel needs to be clear of any other structure to prevent obstruction during

debris collection. Two kinds of catamaran pontoon styles were considered in this prototype. One is a

triangle design and the other is a trapezoidal design in which the bottom of the pontoon is nearly

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flat. The decision factor between these two options was the amount of water displaced while

maintaining a small draft height. In other words, the device needs to have less of its pontoon

structure in the water because the vessel may be operating in shallow water. The nominal empty

weight configuration would have low draft height, but there would be a larger draft height or depth

with the expected max weight of the collected debris. If the triangular design was chosen, the

pontoons would need to be much taller, wider, and longer compared to the trapezoidal design in

order to meet the same water displacement needs. Ease of manufacturing was also considered as

having a design that involved less material and smaller space would be ideal from a size and cost

perspective.

3.3.2 V-Wing Design Selection

A fixed-wing option, but manually adjustable orientation by a user was selected. This wing design is

also made to be removable for transportation purposes. The drawback to any fixed-wing option is

that it makes the system very inefficient: When traveling in various bodies of water, certain sections

of streams or rivers could be narrow, or there may be obstacles requiring a vessel span reduction.

Depending on whether or not the system is cleaning would determine if the wings need to be re-

positioned. Specifically, if the vessel is travelling to the cleaning destination, the wings would ideally

be folded flush with the side of the vessel to reduce drag and increase longevity of the vessel. Once

the vessel reaches the destination of cleaning, the wings would then unfold, and the debris

collection can begin. With a fixed wing, however, the vessel would constantly be in “cleaning mode”

since the wings cannot be folded without user interference. Still, construction and testing of the

component would be simplified and independent of any other system on the vessel. It would be

simpler to test, build, and modify if any issues were to occur.

3.3.3 Conveying Design Selection

A conveyor system was selected against the other debris conveying options for numerous reasons: it

mitigates capacity concerns by running in a continuous loop, has easy controllability when integrated

into the control system and with other subsystems, and provides the simplest path for ease of access

when funneling debris into the next subsystem. A conveyor also reduces the amount of water

entering the vessel, as the belting surface is cleated to secure the debris as it is conveyed and also

funnel water out of the system. With a static conveyance system that depends entirely on the flow

of debris against the vessel, limitations were identified when meeting the necessary capacity needs

to make the device commercially feasible, and keeping the debris contained within the basin before

it would reach the shore for its ultimate disposal. With the vacuum pump collection system,

limitations were found with the tubing diameters commercially available and power requirements

for such a system. The size of debris commonly collected, such as plastic bottles had a larger

diameter than that of the tubing sizes available. This risk allowed for debris to potentially get lodged

if its dimensions were too large, creating potential power issues by increasing demand and causing a

loss of suction pressure. With the bucket system, capacity was analyzed, and it was determined to

be more inefficient when collecting debris compared to the conveyor, as the bucket could not

continuously intake waste if it were on a direct path against a large amount of debris.

Maintainability was also a concern as there would be more moving parts, stricter lubrication needs,

and more corrosion considerations that would have to be assessed.

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3.3.4 Compaction Design Selection

A shredder was selected as being the most optimal approach to meet capacity demands by

compacting debris to a smaller degree and being more adaptable when compared to other systems

to meet the vessel’s space constraints. The compaction system with an actuator required a large

elevation that vessel had to meet, as the stroke size would heavily dictate the size of the system and

how much force is available to output from the cylinder onto a piece of debris during compaction.

Impacts on other subsystems were considered, as the conveying system would also have to meet

the elevation and power requirements. The output force of the cylinder was also analyzed, as and it

could require additional power sources such as hydraulics, pneumatics, or electric power, as well as

a controller. A shredder provides a simpler design configuration, as a only a motor coupling is

required to power the knives and revolve them about a shaft to pulverize the material. This

configuration requires less space, could be tied into the power and control system easier, was

comprised of more maintainable and cheaper components, as well as is assembled of fewer

components. As mentioned previously, due to safety concerns, cost, and time constraints, the

shredder has been withheld from the design in this stage of prototype development and is reserved

for a future improvement.

3.3.5 Trajectory Tracking & Motion Planning Design Selection

For efficient user control of the MANTA, the device’s path of motion needs to be bounded by the

user interface inputs, specifically user or external system selected GPS coordinates. Geolocation

allows users to trace the area that the user wants the system to clean, in which it creates a visible

fence boundary that the vehicle’s motion will be bounded by. The GPS coordinates can be sent

directly from a mobile application of the user or remotely through a computer interface.

The GPS coordinates sent to the vehicle itself has numerous options. The user could manually trace

the area in a body of water or there could be preset shapes boundaries that the user may use to

confine the cleaning boundary. Basic present shapes include but not limited to squares, rectangles,

circles, ovals, hexagons, etc. Within each shape boundary the user also has options to determine the

GPS boundary condition point spacing. This will determine the precision with which the user can

decide the vehicle’s boundaries. The user has full control of the vehicle telling what time of day to

start and return the vehicle. The GPS coordinates are sent to the vehicle via GPS transmitter, 3G, Wi-

Fi, Bluetooth and/or radio communication with satellites. The path of the vehicle as it adjusts to the

optimal path based on the obstacles it faces is sent back to the user interface. Other sensors, such as

anemometers and pressure sensors, exist to determine water conditions and if conditions are in

favor for vehicle operation. Sensors to measure the tidal and wind conditions will also adjust the

propulsion and motor speed to utilize the environment to move the vehicle and save power. The

vessel has onboard sensors and a monitoring system to aid the vehicle user on status of trash

cleaning as well as any issues encountered, such as collisions with boats or other obstacles. The data

from the sensors reading water condition (flow rate, wind etc.) would communicate with the motors

to control the speed of the vessel. Algorithms incorporating sensor data on obstacles, repeated

obstacles, static boundaries, environmental conditions and the like would be utilized to control the

rudder placement or differential motor speeds to direct the vessel to the optimal path.

Camera vision would be the primary system to detect and where solid debris is located. The camera

and its software would recognize the debris from a long distance away but there would be a very

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broad area, which it recognizes as the debris field. As the vessel gets closer to the debris field, the

camera and software would better identify the debris field and objects in the water. This

information would be used to create an optimal path of the system to clean up the debris in a short

amount of time. There would be preset paths the system can follow based on the debris field

region. The vessel’s software would compute the optimal path to perform the task. User inputs can

also override the automated path optimization and a user can choose their preferred cleaning route.

3.3.6 Wireless Communication Design Selection

Bluetooth technology is useful when transferring information between two or more devices that are

near each other when speed is not an issue, such as telephones, printers, modems, and headsets. It

is best suited to low-bandwidth applications such as transferring sound data with telephones (e.g.

with a Bluetooth headset) or byte data with handheld computers (e.g. transferring files) or keyboard

and mice.

Wi-Fi is better suited for operating full-scale networks because it enables a faster connection and

has better range from the base station. The drawback with Wi-Fi communication is that due to its

high bandwidth, it consumes more power than other methods of communication.

Wi-Fi was chosen as the suitable communication medium because the device would be out in open

bodies of water and thus require fast decision-making capability. Of the two, Wi-Fi is the only one

applicable to the needs of the MANTA. Additionally, although the power consumption is greater

than other mediums, the amount is negligible to other systems that draw power, such as the

motors.

3.4 Embodiment

All four original primary structural subsystems (hull, v-wing, conveyor, and shredder) were designed

using 3D CAD modeling in SolidWorks. Hand calculations using standard analysis assumptions were

verified with ANSYS Simulation tools. Fabrication plans were assessed with on-campus and external

resources to gauge capability in building the scaled prototype.

The first step was creating a detailed design of the vessel in 3D, and generating a bill of materials

with predominantly commercial off the shelf (COTS) components and custom structural weldments

and assemblies. The catamaran pontoon structure was modeled in 3D and was used to create a

fiberglass mold to fabricate the pontoons out of carbon fiber. The frame and the wings were

developed using 80/20 T-slot Aluminum with the appropriate fasteners. Chicken mesh was used for

the faces of the wings. The conveyor subsystem was assembled with standard hardware from

vendors such as McMaster-Carr, Grainger, Fastenal. Structural support members and metal

enclosures that could be easily fabricated at a reduced cost rather than purchased from suppliers

were fabricated at the campus machine shop.

The detailed CAD model is presented in Figure 1.

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Figure 1. Detailed CAD Model

During the development of this senior design project prototype, time and budgetary constraints

resulted in a modified design, reflected in the CAD model below:

Figure 2. Modified CAD Model for Prototype

3.5 Detail Design

All analyses and final design specifications for the detailed design phase of the senior design

prototype are presented below.

3.5.1 Hull Detail Design

A final analysis of the pontoon design was completed using a MATLAB script, which encompasses all

the parameters established for the component weights. The script incorporates propulsion forces,

drag, and overall buoyant force of the pontoons. Figure 3 shows an example of a produced graph

from the MATLAB script, in which the pontoon drag is plotted as a function of velocity. To operate at

a top speed of 2.5m/s, the pontoons would need to produce a drag of 7 kgf based on max normal

load, which would be 2 in. to 3 in. in the water. An example of analysis via hand calculation was

presented in Figure 1 in the plot labeled “Pontoon Depth in Water VS Water Displaced.” This graph

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shows the amount of displaced water based on the geometry and depth of the pontoon in the

water.

Figure 3. Pontoon depth vs water displacement results

The calculations show that for roughly every inch of draft of pontoon in the water, there would be

10 kgf of displaced water. In the normal max load condition, this leads to a total of 20 to 30 kg of

mass, or 20 to 30 kg of displaced water. Another method of analysis was to verify the buoyant forces

utilizing CFD modeling. This determined the stresses, drag, and buoyant forces that the designed

pontoon would have.

After verifying that all results met our needs, manufacturing began. The pontoons are made of

carbon fiber because carbon fiber and the equipment needed to perform vacuum bagging

techniques are currently in possession. Vacuum bagging allows for a high quality finish, which

ensures no holes—causing leaks—throughout the formed structure, given that a generous amount

of epoxy is applied. The two pontoons are parallel to each other and are secured with a cross beam,

which ensures that the two pontoons are always parallel to each other.

3.5.2 V-Wing Detail Design

The compiled FMEA in Figure B3 was used to analyze the v-wings. All major concerns were verified

and mitigated by having thick beams, ensuring that the components of the wings are strong enough

to withstand the worst failure modes. These failure modes happen at max speed and max load

conditions. Figure B9 shows an example of a hand calculation determining the drag of the wing from

the mesh as a function of velocity. Based on the operational velocity of 2.5 m/s, there would be a

drag force of about 0.3 kgf from the mesh. The mesh is spaced out in 0.25” blocks. CFD was used to

verify that the hand calculation results were correct. An ANSYS CFD Fluent model was completed

and is presented in Figure 4. These results verify the results of the hand calculations.

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Figure 4. Wing Mesh CFD Simulation

The final wing design is shown in Figure 3. The overall wing size is 3 ft long and 12 in. below the

water with a 0.25 in. mesh. The frame labeled as top, bottom, and side beams are welded together.

The wing is symmetrical on both the left and right side of the vessel as shown in Figure 5.

Figure 5. Final Wing Design

3.5.3 Conveyor System Detail Design

Debris collected from the water’s surface is transported into the vessel through the use of a

conveyor system. The CEMA Belt Conveyors Handbook [3] was referenced as the main design

reference because it outlines the process and necessary calculations for designing a conveyor

system. Anticipated debris that would be collected by the vessel were analyzed and material

properties organized in a excel spreadsheet to calculate the anticipated loading of the debris while in

operation. A specified capacity for the conveyor was defined at 500 lbs/hr, and calculations were

made for the belt tensioning requirements that are necessary based on the configuration and

orientation of the conveyor system, as well as determining the power requirements for the motor.

The conveyor system is comprised of two 20 in. pulleys and an 18 in. wide belt. The conveyor belt is

submerged 6 in. below the water line and is inclined at a 30º angle to convey the collected debris

into the subsequent compaction subsystem. The pulleys are supported by pillow-block bearings. The

upper pulley is the main drive pulley, which has a drive shaft coupled with a 1 HP/90VDC motor that

is mounted in the main body structure. Figure 6 shows the main system elements.

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Figure 6. Conveyor System Design

3.5.4 Shredder System Detail Design

The shredder has been removed from the MANTA in this phase of the design process due budgetary

and time constraints with the development of this prototype. This section has been kept in to

indicate work for future development beyond the timeframe of this senior design project sequence.

3.5.5 Trajectory Tracking & Motion Planning Detail Design

For design simplicity, the movement pattern of the MANTA was designed to take a “Roomba”

approach. In this algorithm, the MANTA continuously moves forward until an obstacle is detected by

a mounted camera, and upon detection, the MANTA turns and rotates in a sequence of steps until

the object is cleared from its path. The vessel is propelled by two BlueRobotics T200 DC Thruster

Motors.

In defining the movement region for the MANTA, the MANTA uses an integrated system of

accelerometers and a GPS sensor to restrict itself to a preset geofence-bounded region. A user uses

the developed web application to select four coordinates that create the device’s geofence. Once

this boundary is set, the user begins the program, and the MANTA moves in the aforementioned

pattern until all points within the defined geofence have been covered. To improve the accuracy of

the device’s GPS tracking (which is often skewed due to noise and environmental conditions that

affect satellite strength such as weather and local blockages, e.g. trees), a Kalman filter, which is a

type of filter that takes an input from numerous sensors to provide an accurate future estimate, is

implemented. In this case, accelerometers and GPS are used as the sensor inputs to estimate what

its position will be in the future. This new location is theoretically more accurate than what would be

obtained through a single sensor output alone because of multiple sensor integration. A simulation

of this methodology is shown in Figure 7.

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Figure 7. Geofencing simulation

4 Discussion

Numerous modifications were made to our design due to cost and time constraints. As mentioned

previously, one major subsystem that was removed from structures development was the shredder

component of our system. The removal of this component allowed for increased focus on the

development of the other integral parts of the MANTA to ensure completion in the senior design

timeframe. Likewise, in regard to controls system development, the obstacle detection feature has

been postponed to future work because it was not as deemed necessary as other components at

this stage of the prototype. Testing of this prototype included functionality tests of all mechanical,

electrical, and controls subsystem components in order achieve the main goal of corralling and

collecting debris from waterways. Simulated tests were conducted in the Drexel University

Recreation Center Pool to integrate the conveyor and thruster propulsion motors with an RC

controller to corral pieces of plastic debris. A final demonstration test was conducted at FDR Park in

South Philadelphia. Images of the final prototype and of testing are presented in the figures below:

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Figure 8. Final prototype testing

Figure 9. Functionality test using RC Control at FDR Park in Philadelphia, Pennsylvania

All development of the structure has given the team a better understanding of the engineering

design process. As concept evaluation progressed into detailed design, 3D models, stress analyses,

and controls simulations were of increasing importance to ensure that each subsystem can operate

or be manufactured as planned. Success during the detailed design phase also required extensive

project management work, and collaboration and decision-making were significantly more

important as project complexity increased. With these new insights, the device can be tailored in the

future to better suit the needs of stakeholders. Overall, the development of the current MANTA

prototype is completed.

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5 Summary & Conclusion

There is a need in the market for a device that cleans waste from water autonomously. Current

methods of waste cleanup are static or manually operated, which are costly to maintain, energy

inefficient, and only operate when weather permits. The MANTA is designed to be a surface-

skimming vessel that collects debris autonomously, eliminating the need for manual operation and

cutting costs in the process.

Specifications of the MANTA are aimed toward meeting the needs of stakeholders and collecting

debris more cheaply and more efficiently than current competitors on the market. Modifications to

the design were made as necessary given cost and time constraints. The structural subsystems that

were chosen to be developed to accomplish this goal were a hull, v-wing, conveyor, and—in the

near future—a shredder. The controls system incorporates an autonomous algorithm to maneuver

and collect debris. With updated specifications, the current prototype of the MANTA is completed,

and will soon be able to collect and contain more debris—without manual operation—than its

competitors.

6 Future Work

With all current steps of prototype development completed, the goals for the future are to complete

the movement algorithm of the MANTA and integrate the updated controls system with the

structure, further develop the design of the shredder and implement it into the structure, and to test

the updated system in both an environmentally controlled pool and the Schuykill River.

Furthermore, to extend the capabilities of the MANTA, work will be done to implement sensors that

track environmental conditions, such as preceding precipitation, weather, and current flow, to

provide data to users on where and how debris tends to collect.

7 References

[1] “What Is Marine Debris?" NOAA Marine Debris. NOAA, n.d. Web.

[2] J. Jambeck, R. Geyer, C. Wilcox, T. Siegler, M. Perryman, A. Andrady, R. Narayan and K. Law,

“Plastic waste inputs from land into the ocean", Science, vol. 347, no. 6223, pp. 768-771,

2015.

[3] Belt Conveyors for Bulk Materials, 5th Ed. Rockville, Maryland: Conveyor Equipment

Manufacturers Association, 1997