I graduated with high honours from the University of Toronto with a

Bachelor of Applied Science in Mechanical Engineering. I have a

keen interest in problem solving, especially with regard to the design

of creative and innovative solutions to real world problems. There is

seldom greater satisfaction than witnessing design work come to

fruition. The following depicts my preferred design work.

DAVE WAKNIN

Engineering Portfolio

408—2200 Ward Street

Montreal QC H4M 2R1

Canada

1-514-833-2091

dave.waknin@mail.utoronto.ca

DAVE WAKNIN

Table of Contents

Multidisciplinary Projects

1.1 Table Tennis Serving Machine (Demo Video Here) ............................................... 3

1.2 3D Printer: Filament Feeder 1 ..................................................................................... 4

1.3 3D Printer: Filament Feeder 2 ..................................................................................... 5

International Project

2.1 Scaffold Bracing Device ............................................................................................... 6

Finite Element Analysis Projects

3.1 Wrench Design ............................................................................................................. 7

3.2 Truss Support ............................................................................................................... 8

3.3 Tensile Member ............................................................................................................ 9

Additional Designs

4.1 Pressure Test Canister Redesign .............................................................................. 10

4.2 Redesign of a Can Opener’s Spur Gears ................................................................. 10

4.3 Design of an Electric Pencil Sharpener Gear Train ............................................... 10

Letters of Recommendation

5.1 Dr. Peter Weiss ........................................................................................................... 11

5.2 Dr. Mathew Mackay .................................................................................................. 12

N.B. Table of Contents is hyperlinked (clickable) to the corresponding pages.

3

Mult id isc ip l inar y : Table Tennis Ser v ing Machine

Design Features For mechanical and coding simplicity, the barrel rotates only about the vertical axis

The maximum velocity and feed rate were set to match the typical human reaction time for competitive gameplay

The fixed height and vertical angle of the barrel have been set, based on kinematics, to achieve the maximum velocity distribution for diverse gameplay situations

Firing mechanism is composed of two independently rotating wheels directly driven by DC motors for consistent launch velocity while avoiding unintended spin on the ball

Barrel and firing mechanism rest on a lazy Susan and are rotated by a servo motor

Hopper is independently supported to minimize the polar moment of inertia of the firing mechanism and is set directly above the axis of rotation of the barrel to remain inline while it rotates

The hopper possesses an agitator, powered by a DC motor, to maintain constant feeding

A cam mechanism is utilized to feed and push (low pressure angle) a single ball into the barrel per rotation and is powered by a stepper motor for controllable feeding rates

Conclusion and Final Notes

In order to view an initial demonstration video of the machine in action,

please click here. After the initial testing and demonstration, improvements

were to be made. However, due to financial and time constraints, the design

modifications were simply stated in the final report.

Context and Project Requirements The problem statement of this term project (winter 2015) was to design any

embedded system that required the use of a microcontroller. My responsibili-

ties involved the mechanical design; that is, the firing, aiming, feeding and

loading mechanisms. I also established the required motor specifications and

helped in motor selection. Lastly, I was charged with machining and assembly.

Approach Design a simple and reliable, yet competitive, machine with only a single axis

of rotation, but that can later be adapted to a more complex two-axis design

with minimal modifications.

4

Mult id isc ipl inar y : 3D Pr inter - Fi lament Feeder 1

Design Features The filament is fed into the extruder via a drive gear; the gear

possesses striations to increase feeding force and minimize filament slippage

A stepper motor allows for accurate and controllable movements

The drive gear is directly driven by the motor for simplicity

A bearing, supported by a pivoting arm, forces the filament against the drive gear for accurate feeding while minimizing friction

Interference fit between the filament and drive gear is adjustable via springs and bolts supporting the bearing’s pivoting arm

The pivoting arm has a hole to guide the filament into a polyether ether ketone (PEEK) thermal break between the cold-end and hot-end

Feeder is composed of aluminum for its ease of machining and high heat transfer abilities to avoid premature melting

An aluminum heat sink is used to increase heat conduction away from the filament, thus further avoiding premature melting

A fan is added to the heat sink for more effective cooling

A Pico hot-end is used for fast, accurate and reliable deposition

Conclusion and Final Notes

All discussed components are designed from scratch apart from the

drive gear, motor, heat sink, fan and hot-end. A second filament feeder

design for the same project is depicted in the following page.

Context and Project Requirements Within a term project (winter 2014), the task was to design a

filament 3D printer for use by hobbyists. As part of my

responsibilities, I was charged with the extruder design,

specifically the feeding mechanism. The main requirements

involved high speed and accuracy as well as low cost and low

energy consumption.

Approach 1 Design a simple, yet high performing, extruder feeding

mechanism with the minimal amount of components to

minimize size, weight and cost while increasing reliability.

5

Mult id isc ipl inar y : 3D Pr inter - Fi lament Feeder 2

Design Features Bowden principle decreases inertia, momentum and vibration of extruder

A stepper motor allows for accurate and controllable movements

Unlike a typical drive gear, a screw-drive has all of its teeth in contact with the filament at once, creating a larger force and minimizing potential slip

The screw has threads removed in two sections so that it can be properly supported within the housing; it rests on two bearings to minimize energy loss via friction and to avoid heat buildup

Feeder is composed of aluminum for its high heat transfer abilities to avoid premature melting as well as due to its corrosion resistance to avoid impurity deposition on the filament

Two aluminum heat sinks are used in order to cover the entire back area of the feeder, thus maximizing the contact area and increasing heat conduction to further avoid premature melting

Fans are added to the heat sinks for cooling via forced convection

Interference fit between the filament and screw is adjustable via the springs on the outer bolts

Filament tube is composed of PTFE for low friction and high thermal resistance

A Pico hot-end is used for fast, accurate and reliable deposition

Conclusion and Final Notes

All discussed components are designed from scratch apart from the motor, heat

sinks, fans and hot-end. In addition, in retrospect, only four bolts and springs

would be necessary as opposed to the eight used in this design. The fans are also

excessive and the heat sinks would be sufficient. Lastly, the Bowden extruder

(feeder 2) was selected for the final proposal, as opposed to the previous

extruder (feeder 1).

Approach 2

Design a feeding mechanism for a Bowden-

type extruder to minimize size and weight,

while modifying it to alleviate some of the

disadvantages possessed by this type of

extruder.

6

Internat ional Project : Scaffold Bracing Device

Context and Project Requirements As part of a final year project (fall 2014 - winter 2015), in collaboration with Peking

University as well as the National University of Singapore, a means of securing planks

and ladders to a scaffold was to be developed. The solution was to be a single design

that is reusable and does not pose safety concerns. Due to the high variability in

component dimensions, no state of the art solution was feasible. I was charged with

leading the design process for the University of Toronto’s candidate design. The main

concerns were repeatable and efficient use while being capable of withstanding the

working conditions.

Approach Validate the clients claim that no viable off-the-shelf solution exists

Conduct brainstorming, blue sky thinking, functional decomposition, function-means-tree, TRIZ and design methods to establish candidate designs; the decided upon design was analogous to a cargo lash with a ratchet

Determine optimum lashing pattern to minimize material use and installation time

Explore different types of lashing devices such as wire ropes and webbing

Evaluate different types of metals (plain steel, galvanized steel, stainless steel and Monel) for wire rope designs, aramid fibers (Kevlar, Nomex, Technora, Vectran and Twaron) for webbing designs and the possibility of other solutions (SparkGard, Ponsa fire retardant coating and BioThane webbing)

Determine most practical and efficient tightening mechanism (worm and wheel, ratchet and pawl, turnbuckle, rack and pinion, over-center buckle)

Determine best combination of lashing material, lashing device and tightening mechanism

Conduct economic and life cycle analyses to determine viability of final design

Conduct appropriate tests (stress versus strain behavior, tension required to avoid slippage, creep analysis, ease of installation, FEM simulations and heat tests) to validate theoretical calculations, initial assumptions and design feasibility

Design Features Design is reusable and possesses a lower environmental impact than current system

Relieves safety concerns possessed by currently used system

Reduces installation time and therefore also reduces cost

Design had insufficient creep resistance and temperature resistance

Conclusion and Final Notes It was concluded by all participating universities that, based on the unique working

conditions at Sembawang Shipyard, the currently used wires are the optimal design for

securing the planks and ladders to the poles. As a final note, it was recommended to the

academic supervisor that the project be abandoned midway; however, due to its

educational purposes, the project had to be pursued.

7

Fini te Element Analys is : Wrench Design

Design Features Adopted a Warren Truss design to the wrench’s handle to efficiently reduce its weight

At critical locations, struts were utilized; otherwise, material was completely removed

Minimized stress concentrations by filleting all internal corners and avoiding geometric discontinuities

Conclusion and Final Notes

The mass of the wrench was decreased from 2.20 kg to 0.985 kg (55 %

reduction). In hindsight, a final vertex sizing should have been implemented at all

locations of relatively high stress to confirm that the weakest locations have not

changed.

Context and Project Requirements As part of an individual Finite Element Analysis report (winter 2014), the goal

was to redesign a wrench in order to optimize its strength-to-weight ratio. The

mass of the wrench was to be minimized, without altering its periphery, while

also maintaining a safety factor of at least 2 against yielding when subjected to

a specified load.

Approach Study initial stresses and strategically remove mass from locations of low

stress

Employ mesh convergence analysis at locations of highest stress via vertex sizing in order to maintain simulation accuracy while reducing computation time

Avoided further mesh analyses by maintaining initial locations of highest stress as weakest points throughout design process (without vertex sizing)

Balance structural rigidity throughout specimen to allow for most uniform distribution of elastic energy storage

8

Finite Element Analys is : Truss Suppor t

Design Features Aluminum was selected for its high specific modulus and titanium for its high specific strength

Given the asymmetrical state of stress, circular rods were selected as they do not warp under torsional stresses and do not possess stress concentrations (corners)

Since the deflection constraint was more difficult to meet than the yield constraint, locations of higher stress are designed with aluminum to limit deflection and locations of lower stress are designed with small amounts of titanium to minimize mass

Context and Project Requirements

The objective of this Finite Element Analysis assignment was to design a

truss (stage support) as light as possible and stiff enough to resist a

maximum deflection of 1 inch, while supporting its own weight (B) and

a force of 500 lbf (C). The truss is pivot supported at its back-end (A). A

safety factor of at least 2 against yielding and deflection is required. The

structural design of the truss is restricted to that shown on the left. The

design parameters involve material and cross section selection; cost is

irrelevant.

Conclusion and Final Notes

Due to the large length to cross-sectional area ratio, the rods can be considered

slender; therefore, only axial stresses are relevant and the cross-sectional shape is

not. The final design possessed a safety factor of 2.4320, a total deformation of

0.99195 inch and a weight of 4.3157 lbm. This deformation was approximated

and validated via Castigilano’s second theorem. As a final note, since the rods are

thin and the truss is intended as a stage support (potential interaction with

fireworks), magnesium was not considered due to its high flammability.

Approach Initially simulate the entire structure with rods of the same cross section and

material for a consistent comparison of stresses and deflections

Test hollow cross sections as they have larger moments of inertia per unit weight and should diminish both bending stresses and deflections

Survey available materials on ANSYS for highest specific modulus and highest specific strength (importing materials was not allowed)

Rods with high stress are designed with high specific modulus material and rods with low stress are designed with high specific strength material

Adjust radii of rods in groups based on stress level and iterate process to meet constraints

9

Finite Element Analys is : Tens i le Member

Context and Project Requirements The goal of this Finite Element Analysis report (winter 2014) was to design a tensile

member with the maximum strength-to-weight ratio. The initial component was a slab of

PMMA (shown on right). The constraints are as follows:

A minimum of 0.25 inch of acrylic must remain between adjacent cutouts

The loading holes must be a maximum of 1 inch from the loading edges

The width and height through the center of the plate must remain 6 inch

Approach Optimize computation time by considering a 2D model, a quarter specimen (two planes

of symmetry) and a mesh convergence analysis

Use vertex sizing to refine the mesh at critical locations to improve accuracy yet minimize computation time

Two potential methods to increase strength-to-weight ratio: designing internal cutouts to distribute the stress or simply removing as much unstressed material as possible

Since it is difficult to uniformly distribute stress within the member via cutouts, the width of the structure was reduced to remove excess material

Design Features All edges and corners are filleted to eliminate stress concentrations

The maximum distance from the hole to the loading edge (1 inch) was chosen to maximize the amount of energy absorption prior to failure

All unstressed material was removed to optimize the member’s strength-to-weight ratio (the removal of the corners was accepted despite the first constraint)

An oval cutout was placed along the stress chains to distribute stress along the member while minimizing weight

The dimensions of the oval have been changed and iterated to provide the highest strength-to-weight ratio

Conclusion and Final Notes Stress chains follow the path of least resistance and therefore do not distribute well as

they simply go around cutouts and maintain high stresses near boundaries. However,

internal cutouts can decrease weight while increasing structural elasticity thus decreasing

the stress on the loading holes by allowing the rest of the structure to absorb most of the

strain energy. The strength-to-weight ratio of the tensile specimen increased by a factor of

5.75 between the initial slab and the final design.

10

Pressure Test Canister Redesign

Addit ional Designs

During my summer research internship at McGill University

(summer 2014), as a side project, I was tasked with

redesigning a test pressure system to achieve lower

pressures of 0.100 Torr. It was believed that a hi-vacuum

pump was needed. I had the flexibility of changing most of

the design and buy a new pump (2000 CAD budget). Before

buying a new pump, I decided to research the canister

(bottom-half section on left) which was much cheaper to

change. The assumption was that the current pump may be

able to achieve such pressures but the canister design is inhibiting it. Based on research and tests, I

determined that PVC is not suitable for low pressures since it outgases and does not form a good

vacuum seal to itself (PVC cement) or to metal fittings. The new canister was composed mostly of scrap metal collected

around the lab welded together; Teflon tape was used on fittings to eliminate leaks and the clearance present in the

collimator and piezoelectric pin holes were sealed via epoxy. The final design was to be made wholly of aluminum. The tested

design achieved a pressure of 0.070 Torr with less than 5 % of the allotted budget as a new pump was no longer needed.

As part of a group assignment (winter 2014), in which we dissected a can opener, I was

tasked with redesigning its gear train to produce 50 % more torque (original design is

depicted on left). The number of teeth on the larger gear was increased from 52 to 78. It

was also possible to reduce the number of teeth on the pinion, however this was not done

so as to avoid undercutting. Furthermore, it was

important to maintain the center-to-center

distance so as to comply with the housing dimensions. In order to do so, the

module of both gears had to be reduced. The tooth profile was also changed to a

stub tooth with a pressure angle of 20 degrees. This profile minimizes the size of

the pinion’s dedendum to maximize its strength while also avoiding a new shaft

design. To support the additional torque requirement, the thickness of the larger

gear was increased. The final design is shown on the right.

In this assignment, the task was to design the powertrain of an

electric mechanism and choose an accordingly sized motor.

The exploded view to the left is that of an electric pencil

sharpener. The design consists of a planetary gear train so as to

achieve an effective ratio of 9:1 while remaining compact. The

planet carrier is the output of the gear train and acts as the

sharpener via the conical loft at its center. The motor chosen

was a 75 W brushless DC motor; it is rated to have an output of

1620 rpm and a torque of about 0.442 Nm. With the effective

ratio of 9:1, the output would rotate at 180 rpm with a torque of about 4 N∙m, which is necessary to shear off excess wood

from a pencil. The motor has been modeled as a cylinder for simplicity reasons.

Redesign of a Can Opener’s Spur Gears

Design of an Electric Pencil Sharpener Gear Train

11

Letter of Recommendat ion: Dr. Peter Weiss

12

Letter of Recommendat ion: Dr. Matthew Mackay