mechanisms, fabrication, and crash course...
TRANSCRIPT
Mechanisms, Fabrication,
and
Crash Course Tips
Patrick Jung & Zoe KlesmithWith much appreciation to
Kyle Saleeby, Dr. Rich Simmons, Dr. Tom Kurfess, Dr. Chris Saldana,
and former Head TA C.J. Adams
Some content based upon material created by:
Dr. Andrew Semidey & contributions from Alexis Noel and Hannes Daepp
ME2110 | Fall 2019
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This Lecture
2
Crash Course:
1) a rapid and intense course of study
2) an experience that resembles such a course--Merriam-Webster Dictionary
Not comprehensive
Inspire and engage
Reference slides
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Announcements
1. Announcements on homepage of website
2. FAQ Page http://2110.me.gatech.edu/QnAs
3. Introductory Project Presentation this week http://2110.me.gatech.edu/sites/default/files/documents/Studios/me2
110_fall_2019_studio2_introductoryproject.pdf
4. Due by end of your studio section this week:– Completed Tray Assembly
– Motor Coupler
– Mechatronics Tasks 1-7 (Groups A or B)
5. Homework 4 Due Monday 9/23 at start of lecture– Bring your motor coupler (w/ your initials) to lecture if not already
given to TA
3
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Individual Project
4
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Design Process – How to utilize CAD during conceptual
design and prototyping
Discuss material selection for ME2110 machines
Joining and fastening methods
Provide fabrication tips with available tools
Apply lessons learned & avoid common mistakes
Learning Objectives
5
1.
2.
3.
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Mechanical DesignIndividual project and final competition
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Successful Design
Terrible Ideas Great Ideas
Bad Construction
Good Construction Reliable Performance
High Scoring Potential
7
Other critical dimensions: Execution, Timing, Communication & Reporting
win the
competition
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Design Process
8https://www.google.com/search?q=design+process&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiQ99WJ05XgAhUrhOAKHd4
CCVsQ_AUIDigB&biw=1660&bih=875#imgrc=I2Ez6g6_VE9LeM:
What is the fundamental problem?
Not CAD
Prototype & CAD, then test
(order depends)
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Iteratively Building Robots
❖ ME 2110 projects are time consuming – Ideas must work
– Construction must be feasible with available tools
– Construction needs to be well executed
❖ Choose tools to match your skillset – aim to
make manufacturing efficient & error-free– Design for Manufacturing (next lecture)
– Invention studio tools expand fabrication capability, and can
improve quality and efficiency
9
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CAD and Conceptual Design
10
❖ Locate and orient subsystems and parts
❖ Enhanced visualization
❖ Fast concept generation by combining existing
concepts
❖ Documentation
❖ File sharing for co-operation and communication
❖ Detailed design can proceed from conceptual models
❖ CAD models easily evaluated with engineering tools
(e.g. FEA)
❖ Leads directly to rapid prototyping processes for
fabricating parts (Invention Studio)
Adapted from: E. Bamberg, "Principles of Rapid Machine Design", 2000.
Why incorporate CAD in your design process?
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Risks and Drawbacks with CAD
11
❖ Biggest Drawback: Loss of hands-on experience
❖ Need to make sure concepts are physically realizable
❖ Limiting assumptions can stifle creativity
❖ Cannot test unmodeled effects or validate assumptions
❖ Physical tests can lead to lots of learning
You need to balance Physical Testing with the
Design Process and CAD
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Other Sources of Standard Parts
13
Mechanism Inspiration:
❖ 507 Mechanical Movements
http://507movements.com/
Other Sources of Standard Parts:
❖ ServoCity
https://www.servocity.com/
❖ SDP/SI
https://shop.sdp-si.com/catalog/
❖ MISUMI USA
https://us.misumi-ec.com/
– Application Library:
https://us.misumi-ec.com/us/ideanote/
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ROBOT DESIGNDO’S AND DON’T
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Wire Management
❖ [Do] Wire Management– Cables and wires
– Strings
What can catch wires?– Zip tie ends
– Lose duct tape
– Bolts and screws
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Wire Management Methods
1. Wire harness
1. Spiral cover
1. (Cleanly cut) Zip ties
1. Duct tape
1. Twisties
16
Balance successful
functionality with
clean design
https://www.amazon.com/Tesa-adhesive-wiring-original-
ISOBAND/dp/B00XPDVER2/ref=sr_1_6?keywords=wire+harness+wrap&qid=1550078407&s
=gateway&sr=8-6
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MyRio Indication Feedback
❖ [Do] Realtime Feedback from MyRio
❖ Basic LED Feedback – Built-In LED status / state indicators
– On / off combinations
– Flashing protocol
❖ Advanced LED Feedback– External LEDs connected to MyRio (add resistors!)
– External LED / LCD screen (digikey, adafruit, sparkfun)
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Selectable Functionality
❖ [Don’t] Live programming of MyRio– Modifying code each round
– Re-uploading code for different home zone
– Drop your computer in the competition
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Selectable Functionality
❖ Modular and movable design– Pegged limit switch
❖ DIP Switches– Digikey, Amazon
❖ SPST (Toggle) Switch)– Easier to mount and solder
– Cheap, robust
❖ Push button with LED feedback– Mechatronics kit
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https://www.google.com/search?q=dip+switch&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiyofrwhbjgAhXJct8KHRiFCikQ_AUIDigB&biw=1546&bih=873&dpr=2#imgrc=VBWkt5Lk6aCK5M:
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Auxiliary Sensors
❖ [Do] Checkout other sensors!
❖ Light-sensitive diode
❖ Ultrasonic range finder
❖ Potentiometer, encoder
20
https://www.google.com/search?q=light+sensitive+diode&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjpms75hrjgAhWBUt8KHfiQATcQ_AUIDygC&biw=1546&bih=824#imgrc=HWP-2Spom-BTMM:
https://www.sparkfun.com/products/13959
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Fabrication Common Materials
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Common Materials – Wood
❖ Natural Wood– Hardwood vs Softwood
– Stay away from softwoods, such as pine, as they
tend to warp
– Hardwoods, like poplar or oak, are easy to work with
and more dimensionally stable than pine
❖ Manmade Wood Products– Manmade wood products are more dimensionally
stable then natural products
– Avoid MDF (medium density fiberboard) as it does
not hold nails or screws well and is not as strong as
other manmade materials
– Plywood is good for large flat members (such as a
base)
▪ Stick to sanded plywood or birch plywood (best)
▪ OSB is a rough material and hard to work with
Poplarhttp://www.boulterplywood.com/photogallery/wood%20names/poplar.jpg
Birch Plywoodhttp://tablerosferrandis.sharepoint.com/siteimages/birch.jpg
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Common Materials – Plastics
❖ PVC (Polyvinyl chloride)– Mainly for rods and pipes
– Easy to work with
– Readily available
– Rigid or flexible
❖ HDPE (High-Density Polyethylene)– Mainly used for flat sheets
– High strength to weight ratio
❖ Plastics can be used as linear or
rotational bearing surfaces– Plastics have low coefficient of friction against
most other materials
– Avoid metal-on-metal or wood-on-wood moving
joints
PVChttp://www.jayplastindustries.com/product/hose-pipe.html
HDPEhttp://www.tapplastics.com/product/plastics/cut_to_size_plastic/hdpe
_sheets/529
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Common Materials – Metal
❖ For products requiring a long
lifetime (i.e. not your robot!)
❖ Hard to alter design
❖ Time consuming to shape
❖ Usage only recommended for long,
thin parts
❖ Stick to aluminum (5000-6000
series if you buy online)
❖ Sheet material can be cut to shape
on Waterjet
Aluminum rodshttp://www.alumaloy.org/
Aluminum machininghttp://www.fabricatingandmetalworking.com
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Standard of Quality
❖ Devices in the Trash Can– Dumpster outside
❖ Devices in the scrap bin– Break down components
– Take out screws and nails
❖ Begin early
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FabricationJoining and Assembly
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Joining – Common Methods
❖ Nails– Shear Strength only
– Easy and fast, but not very accurate
❖ Screws– Shear Strength and Tensile Strength
– Needs pre-drilling
– To draw 2 parts together, you can’t have threads bite
into both parts
– Counter-sinking may be used to ensure a flat surface
❖ Nuts and Bolts – Good for metal or plastic joining
– Must oversize the bolt hole to draw the parts together
❖ Rigid Joints require 2 fasteners– 1 fastener makes a pin joint
❖ Soldering– Don’t let electrical connections plague your builds!
Youtube - Soldering Video
Nailshttp://www.commonnail.com/co
mmonnails/ironnails.html
Screwshttp://www.norfolkhardware.com/
Nut and Bolthttp://upload.wikimedia.org/wikipedia/c
ommons/2/2f/M4_Inbusschraube_focu
sstacked.jpg 27
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Joining - Nails
28https://www.google.com/search?biw=1660&bih=826&tbm=isch&sa=1&ei=f61RXKmsO9CIggemr6CYDQ&q=joining+wood+with+nails&oq=joi
ning+wood+with+nails&gs_l=img.3...6154.6581..6722...0.0..0.58.246.5......1....1..gws-wiz-img.NGx_1qQfWoo#imgrc=66GAUkAYSMZiLM:
Only resists shear
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Joining - Screws
❖ Drill pilot hole first
❖ Fasten with screws– Transfer punch / one at a time
– Don’t drill 4 pilot holes, then fasten with 4 screws
– Difficult to precisely align
29https://www.popularwoodworking.com/wp-content/uploads/PWE150322_QAfull.jpg
Checkout
popularwoodworking.com!
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Joining - Screws
❖ Screws– To draw 2 parts together, you can’t have threads bite
into both parts
30
https://www.nmri.go.jp/eng/khirata/metalwork/basic/bolt/ind
ex_e.html
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Joining - Wood
❖ Combination of:– Wood Glue
– Screws
– Nails (rarely)
❖ Wood glue is amazingly strong– https://www.thegeekpub.com/4314/glue-vs-screws-which-one-is-
stronger/
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Joining – Wood Glue
32https://www.thegeekpub.com/4314/glue-vs-screws-which-one-is-stronger/
Glue 2 withstood 590 lbs
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Joining – Wood Glue
❖ Wipe joint with cloth– Remove saw dust
– Gorilla glue? Use damp cloth
– Yellow glue? Use dry cloth (water weakens joint)
❖ Spread glue evenly over surface
❖ Clamp together– Some advise slightly moving the joint
❖ Wipe away excess glue
❖ (Optional) Drill pilot hole and fasten with screws
while clamped
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Joint and Link Fabrication
❖ Pin Joints
❖ Link Fabrication– Lasercut (plastics/wood)
– Waterjet (wood/metal)
Links
Pin Joint
Exploded View
NutJam Nut
Washers
Bolt
Bushing
or Sleeve
Bearing
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Joining - Enforcing Constraints
Rotational Constrainers Translational Constrainers
Flange Bearinghttp://www.micromech.co.uk/dir_suppliers/spyraflo_gfx/flangemount.jpg
http://vipdictionary.com/img/SSHinge.jpg
Pillow Block Bearinghttp://www.vxb.com/ball-bearings-images/ucp.jpg
Turntable / Lazy Susanhttp://ecx.images-amazon.com/images/I/71TgDkqXx1L.jpg
Hinge
Drawer Sliderhttp://www.edirecthardware.com/img/products/643/643-3832_GRP1.jpg
Linear Bearinghttp://3.imimg.com/data3/YP/BT/MY-4165859367/linear-ball-bearing-2-500x500.jpg
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You wanted… You got…
Common Fabrication Mistakes
36
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Use
Corner
Clamps……and
Squares
Common Fabrication Mistakes
37
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vs.
Frame
Lacks
Lateral
Support
Adding
Cross
Member
Increases
Stiffness
Common Fabrication Mistakes
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Common Fabrication Mistakes
39
❖ Building without a plan (‘cut and try’)
❖ Assembling skewed or slanted frames
❖ Open-loop structures
❖ Fasteners that must be tightened 'just right’
❖ Using duct tape as a fastener
❖ Using mousetraps as hinges
❖ Overuse of string – String tangles and snags
– Requires proper management to be used effectively
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FabricationMachines and Resources
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Rapid Prototyping – Laser Cutter
41
How does it work?
• Lasers
• Accuracy of 20 microns
• Can cut through 0.5” wood
When to use laser cutter:
• 2D cuts of wood, some plastics
Common materials NOT ALLOWED:
• Polycarbonate (Lexan), PVC
• Most rubbers
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Rapid Prototyping – Laser Cutter2D to 3D Wood Fabrication
42https://www.google.com/search?q=laser+cut+bendable+wood&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiQoJ2C08fdAhUmTt8KHd5kAjcQ_AUIDygC&biw=1118&bih=676#imgrc=p266zv8a8KMTGM:
https://www.google.com/search?biw=1118&bih=676&tbm=isch&sa=1&ei=14-iW6C5Kqqc_QaUkYbICw&q=laser+cut+wood+gears&oq=laser+cut+wood+gears&gs_l=img.3..0i24.27396.28362..28883...0.0..0.51.233.5......1....1..gws-wiz-img.......0j0i30.DO78RL64VG8#imgrc=zciSYmJToLucQM:
https://www.google.com/search?biw=1118&bih=676&tbm=isch&sa=1&ei=SJCiW7aKA427ggfigIf4DQ&q=laser+cut+wood+robot&oq=laser+cut+wood+robot&gs_l=img.3...2844.3755..3882...0.0..0.50.262.6......1....1..gws-wiz-img.......0j0i67j0i24.DDoMB7_on4c#imgrc=xlazkNF0oe8EXM:
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Laser Cutting
Benefits
Very Small Kerf
“Non-Contact” Cutting
Precise, Repeatable
Relatively cheap
Drawbacks
Relatively thin materials
2D Constrained design
Limited materials (non-Chlorine)
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Laser Cutting
Focused
beam heats
material
OR
Gas-
Assisted
Gas blows
away melted material
Material is
burned or vaporized Image [2]
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Types of Cuts
Raster Vector
Cut
Vector
Engrave
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Types of Cuts
Raster
Vector
Cut
Vector
Engrave
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Power Density
Power of a laser matters far less than power density
[W/m2]
50W @ 6mm Spot
Diameter50W @ 0.6mm Spot
Diameter
100X Higher Power
Density!
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Power Density for Common Materials
Process Power Density (W/mm2) Process Rate
Cutting thin plastic
(0.07 – 0.13mm)
30-70 380 – 760 mm/min
Hard Wood Engraving 70-110 100mm/min (1.5-3mm deep)
Tissue Removal 10-100 N/A
Cautery 5-10 N/A
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Design for Laser Cutting
Considerations
3D -> 2D Components
Carefully plan joints, shear load
Kerf of Laser
Consider Aesthetics:
Illumination, Light, Opacity
Disadvantages
Design for Assembly
Difficult to hide fasteners
Shear, Brittle Fracture (Acrylic)
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Laser Ablation
UV Laser, lower wavelength
Minimum spot diameter limited by wavelength of light
Allows for higher power density with extremely small spot size
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Rapid Prototyping - 2D to 3D Design
Assembling 2D shapes into 3D geometries
51
Finger Joints and T-nuts
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Rapid Prototyping – Finger Joint
52https://en.wikipedia.org/wiki/Finger_joint#/media/File:Boxjoint.png
Finger joints are used for structure and rigidity
Load-bearing
• Generally, finger joint width is thickness of material
• Wider is ok, application specific
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Fastening with Acrylic
T-Nuts
Attachment Only
Nut width = thickness of acrylic
Finger Joints
Load Bearing (somewhat)
Joint width = thickness of acrylic
Image
[3]
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Fastening with Acrylic
Recommend combination
of T-Nut with finger joints.
Add epoxy for permanent
joints.
Image
[4]
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Rapid Prototyping – T-Nuts
55
• Match nut to thickness of material
• Wide-head bolts are better
T-nuts are used for fastening
Not load-bearing
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❖ Laser kerf and fitting tolerances:https://alliance.seas.upenn.edu/~medesign/wiki/index.php/Guides/Las
erCuttingFits
❖ T-slots with captive nuts:– Trade-off between process time (tapping holes) and assembly time
(more parts)
Rapid Prototyping – Combination
56
http://www.instructables.com/id/How-to-Build-your-Everything-Really-Really-Fast
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Rapid Prototyping – Finger Joints
57
http://www.instructables.com/id/How-to-Build-your-Everything-Really-Really-Fast
http://3dbizcenter.com/category/how-does-3d-printing-work/
http://www.instructables.com/id/How-to-Build-your-Everything-Really-Really-Fasthttp://www.instructables.com/id/How-to-Build-your-Everything-Really-Really-Fast
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Rapid Prototyping – 3D Printers
58
How does it work?
• FDM, SLA, SLS, DLP
• FDM accuracy 150 microns
• Uses PLA (other materials available)
When to use 3D printers:
• Complex 3D geometries
When NOT to use 3D printers:
• To make boxes
• To make 2D shapes
For more general tips and guidelines, see:
https://www.3dhubs.com/knowledge-base/3d-printing-stl-files-step-step-guide
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Rapid Prototyping – Boxes
59
• Warped
• Time-consuming
• Inaccurate
measurements
• Expensive
• Flat edges
• Fast
• Accurate
measurements
• Cheap
3D Printing Laser Cutting
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Rapid Prototyping – Waterjet
60
How does it work?
• 50,000 PSI with garnet
• Accuracy of 80 microns
• Can cut through 6 inches of steel
When to use waterjet:
• 2D cuts of most materials
• Wood, metal, plastic
When NOT to use waterjet:
• Cutting soft woods, glass, foam
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Rapid Prototyping – Trade-offs
❖ ‘Build it now and tinker until it all fits together and works’ vs.
‘Design (CAD) it now and let a machine make it for us’
❖ Trade-off involving Time and Effort:
upfront design / CAD build and tinker
61
CAD: ~15 hours
Manufacture: ~3 hours
Assembly: ~15 minutes
Ex: Sanding End Effector Prototype
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Summary
❖ Use mechanisms to achieve capable designs– Use materials that are appropriate for desired properties (strength-weight
ratio, friction, etc.)– Constrain mechanisms to achieve reliable performance– Re-purpose household items to match functionality
❖ Select materials that are easy to work with– Low quality materials mostly produce low quality results
❖ Choose an efficient, straightforward primary manufacturing strategy that matches your experience & skills– Most foolproof manufacturing methods do not rely heavily on manual
skills: waterjet, laser-cutter, 3-D printer, CNC, etc.
❖ Plan & design your device layout & construction thoroughly– Design for Manufacture, Design for Assembly, Design for Disassembly– Secure & store all components in a well-defined device location– Use strain relief (secure wires) to avoid loose electronic connections– Remember that design is iterative: prototype and test thoroughly
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Individual Competition
❖ Triggering -> One action– No ”additional energy”
– Clean, repeatable
❖ Things that get you DQ’d…..– Damage to the track (Scratches, WD-40, etc…)
– Not triggering
– Projectiles (including unintentional rubber bands)
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Appendix:Good Examples
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Good Examples: Blue’s Clues (Spring 2015)
❖ Chelsea Silberglied
Armaan Velji
Opeyemi Olaleye
65
• Constructed primarily from 2-D laser-cut plywood components
• DFA/DFD: Slotted parts assemble/disassemble easily; reinforced with screws & brackets as necessary
• Result: Ability to minimize manufacturing effort - majority time spent in planning & design (CAD), and testing
• Performance: 4th round (within top 30/74)
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Good Examples: Top Gun (Spring 2015)
Chris Healy, Zach Archbold, Randy Long, & Sahas Singh 66
Sidewalls for secure storage,
boxing, & aesthetics
Quality materials & assembly
Good usage of space & absence of hair triggers
Laser-cut precision
components: storage
shelf, side walls, &
victim pusherClean decals for simple
visual appeal
• Performance: 4th round (within top 30/74)
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Good Examples: The Shady Mammals (Summer 2015)
67
Hoang Dang, Andrew Hanna, & Reagan Wilkerson
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Good Examples: The Shady Mammals (Summer 2015)
68
• Performance: 1st Place
Victim Retrieval
Linkage
Rubble Sweeping
Linkage
Weight with
Pulley System
Motor 1
(Wheel and
Axle)
Motor 2
(Spur
Gears)
Constraints (Pivots
and Support)
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Good Examples: Ghost Squadron (Fall 2015)
William Neidecker-Gonzales, Hannah Orr, Abheer Bipin, & Darren Maguire
• LED display for aesthetic appeal
• Waterjet use for metal components
• CAD: Cardboard-Aided-Design
Example: Torpedo deployment arm
1. Prototype in cardboard & test
2. Trace/Modify in CAD package
3. Manufacture (e.g., waterjet, lasercut)
4. Assemble & run
Performance: 3rd Place
1/2
1/2
3/4
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Good Examples: WoodFellas (Fall 2015)
• Example of good planning & great
carpentry skills
• Tools: table saw, drill press, waterjet,
metal shop, general assembly
• Secure location for ALL components (use
provided mounting holes if possible)
• Avoid fabricating necessary/important
parts if they are hard to make and
affordable elsewhere (e.g., some gears
are cheap on Amazon)
• Design with construction in mind (DFA)
• Use structural cuts (e.g., Dado cut)
• Performance: 2nd Place
Robert Lineberg, Nolan Hall, Jason Hunyar, & Shen Yoon
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Good Examples: Average Joes (Summer 2016)Reed Morris, Kyle Brantley, Nick Maniscalco, & Alex Ullrich
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Good Examples: Average Joes (Summer 2016)
• Laser cut parts provided:
Precision
Spare parts
Ability to make mirrored subsystems
• Minimized snag/rough points for all string
driven systems
• Used manual prototyping / rough builds to
validate concepts, then created CAD
models to produce final parts
• Performance: 1st Place and Best In Show72
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Laptop
Arduino &
Electronics
Mounting Platform
AmigoBot Base
Air Supply
Launcher
& Reloading
Mechanism
Camera
Non-ME 2110 Example: Ramblin’ Wrecking Bot
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Non-ME 2110 Example: Ramblin’ Wrecking Bot
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Mechanical Design & Construction
❖ Primarily laser-cut plywood and 3-D printed parts
❖ Launching Mechanism– Solenoid valve attached to PVC
pipe– Servo-actuated gimbal provides
2 DoF
❖ Reloading Mechanism– Servo-controlled barrel– Custom laser-cut plywood parts
with 3D-printed spacers/braces
❖ ME2110 Projects have different requirements – use resources wisely
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