1. ME312 - Mechanical Design3A
Group 2
Striving for Eggcelence
Egg Lifting Device – Design Report
JonathanSmith,Campbell Simpson,JackLucas,Andrew
McKenna,AhmadSheikh,Max Brown
12/15/2014
2. Introduction
The following report shows the progression of our group’s design from
receivingthe originalbrief tothe detailsof the finalised design. First, the
initial brief was read with all constraints taken into account then a PDS
(ProductDesignSpecification), whichhighlights the crucial specifications
for the design, wascreated.Thislistof tenimportantareasrelatingto the
product allowed a list of specific requirements to be produced. The
Statement of Requirements and the PDS were then used as a tool to
generate creative and effective designs solutions which fit in with the
guidelines.
After long discussion it was realised that any ideas the group came up
withcouldbe separatedintofourcategoriesof design. Using comparison
tables and a Pugh Matrix, we quickly decided on the most favourable
being a self-contained driving and lifting mechanism.
Each member of our group was then assigned the task of creating their
own concepts so that we had a wide range to choose from. Various
different options were picked as suggestions for each part of the design
i.e. a suction-cup, claw, pincer and net, to be used as the mechanism to
pick up the egg. Then each of these options was put into another Pugh
Matrix to assess the strengths and weaknesses of each concept on a
ratingscale.Whicheveroptionachievedthe highest score was then used
to help the process of creating the final design to take further. This was
done forall partsof the design,the egg collection mechanism, the lifting
mechanism and the driving mechanism.
Each group memberthencame upwithand presentedadesign(usingthe
components decided on from above) which they felt would most
effectivelyaccomplishthe taskinhand.These conceptswere discussed in
detail and were then combined to finalise our design.
This final concept was then sketched by hand and then drawn in detail,
using both pencil and CAD (Computer Aided Design) software. Material
properties andcontrol systems were researched and various suggestions
were producedforboth.Againusingcomparison tables, we were able to
choose the best materials and motors for the job, while sticking to our
£300 budget.
Finally, with all of the components decided on, and their function
described in detail, a conclusion was written, summarising the project.
Initial Brief
“To design a device that is capable of lifting a raw egg from one location
and depositing it safely in another location. The entire device must be
located at least 1m from the egg initially. After the device has initially
liftedthe eggitmustthendepositthe eggsafely to a position located 1m
to its side and 1m above the initial location. Finally, the device must
withdrawatleast 1m horizontally from the location in which the egg has
been deposited.”
3. Project Plan
Our groupwas briefedontheirdesignspecification-todesignanegglifter- onweek2inthe first semester of third year mechanical engineering. Work was
splitupbetweenthe 6group members;witheachtaskbeingassigned to the members according to their specific strengths and weaknesses e.g. the most
artisticteammember was to produce our drawings. We created our own deadlines for work to be completed by the group so that we did not fall behind
and have to rushour work onthe final day-creatingasub-standarddesign.The firsttwoweekswere spentbrainstormingonthe mosteffectiveandcreative
way to lift the egg. Week 4 was used to create a statement of requirements and week 5 to generate a PDS (Product design Specification) to fuel our
creativityandhelpus arrive at our final goal of an innovative design. By week 6 we had put all of our ideas on paper with each group member coming up
withtheirown specificdesign,producinganannotateddrawingof theirconcepts.Byweek7,a Pugh Matrix was usedasa tool to select the best design and
work began on perfecting this design while creating better, more detailed drawings. Material properties were researched before we finally chose the
correct materialsforeachcomponentwhile staying withinour£300 budget. We thencollected all of the information and put together a report before the
final presentation in week 12. We aimed to have completed all of our tasks by the start of week 11, to leave time to reassess our work and perform any
necessary tweaking.
Task Week1 Week2 Week3 Week4 Week5 Week6 Week7 Week8 Week9
Week
10
Week
11
Week
12
BrainstormingIdeas
Statementof Requirements
PDS
ConceptGenerationTables
Final ComponentSelection
DesignGeneration
Selectionof Final Design
DetailedDesignDrawings
Calculations
Material Selection
Comprisingreport
Costings
Create final Presentation
4. Statement of Requirements
We mustdesignadevice thatwill liftaraw eggfrom an initial location
and deposititinanotherlocationthatis1m above andto the side.The
device mustbe capable of starting1m from the egg.The device mustbe
capable of liftingthe eggsafelyandina controlledmotion,andbe
structurallystable throughoutall motion.The workingenvironmentof
the device isnotknownand sothe device mustbe capable of operating
on multiple surfacesandareas.Ourbudgetis£300 for the whole project.
Product DesignSpecification
Performance
1.1 The device mustbe able to lifta rawegg fromone locationand
deposititsafelyinanotherwithoutbreakingit.
1.2 The device mustbe able to collectthe eggfroma startingpoint
1m away horizontally.
1.3 The device mustbe able to liftthe egg1m verticallytoa new
positionanddepositthe egg
1.4 The device mustbe able to move 1m awayfrom the final position
of the egg
1.5 The device mustbe able to operate ateverystage without
physical humaninteractionwiththe egg
1.6 The device mustbe structurallystable andsecure atall times
1.7 The device mustmove at a safe controlledspeed
1.8 At nopointin the processshouldexcessforcesbe appliedtothe
egg
Environment
2.1 device mustoperate indoorsatroomtemperature
2.2 The device mustbe able to operate onvarious commonindoor
surfaces(wood,carpet,linoleumetc)
Life in Service
3.1 The device shouldlastaminimumof 12 weeksandstandupto
multiple roundsof testingincludingmultiple demonstrations
3.2 No componentsshouldhave excessstressonthem, risking
damage overtime
Maintenance
4.1 The devicescomponentsmustbe easilyaccessible for
replacement,repairormodification
4.2 The device mustbe easilycleanedandmaintained(cleanedof
any eggwaste)
Ergonomics
5.1 The device musteasilycontrollable
5.2 The device musthave a control systemable tobe operatedby
onlyone groupmember
5.3 The device mustbe lightweightenoughtobe movedtothe
demonstrationareaeasily
5.4 The device mustbe easilydismantledandreconstructedif
necessarytoreach demonstrationarea
Quality
6.1 The device mustbe createdusingsolidmaterialsthatwill neither
deteriorate norfail withrepeateduse
6.2 The device mustbe well finishedwithnoloose fittingsordefects
5. 6.3 The device mustbe constructedina way where itwill notfail,
structurallyormechanically
6.4 Motors and electrical componentsmustbe chosenthatwill
reliablypowerthe actionsof the device
6.5 No partsof the machine shouldbe underexcessiveloadsono
componentsdeteriorate betweenfirstconstructionandfinal
testing
6.6 The device’sperformanceshouldnotdiminishovertime
Materials
7.1 The materialsmustbe cheapenoughto stayunderbudget
7.2 The materialsmustbe durable andstrong enoughtocomplete
the task at hand
7.3 Where possible,the device mustbe made of readilyavailable
materialstocut costs
7.4 No loadbearingmaterialsshouldbe of lowquality
7.5 Where possible,componentsshouldbe boughtdomestically,orif
possible,pickeduplocallyinordertocut emissionsin
transportationandcosts in delivery
7.6 All materialsshouldbe checkedfordefectssotoavoidfailure
Target Cost
8.1 The device mustcost under£300 to manufacture
8.2 Whereverpossible,componentsandmaterialsshouldbe taken
fromreadilyavailablesourceswhichthe teammembersalready
have access to, to cut costs
8.3 Manufacture shouldbe done byteammembersor labtechnicians
withinthe universityinordertokeepcostsdown
8.4 For any specialisedparts,the bestprice shouldbe foundwith
extensive researchintothatarea
Safety
9.1 The device musthave nosharp edgesthatcould cause harmto
the personmovingit
9.2 The device mustbe electricallysafe(humaninteractionmustbe
lowvoltage)
9.3 The device mustnotproduce harmful emissions(asitisoperating
indoors)
9.4 The device mustmove at a safe,controlledspeed toavoid
crashingintoanythingandcausingany damage
9.5 The device mustbe structurallystable atall times asto avoid
fallingandharminganyone oranything
9.6 Anyautomatedcomponentsshouldbe poweredbyelectrically
safe,testedcomponentstoavoidfire orelectrocutionrisks
Weight & Dimensions
10.1 The device mustbe lightweightenoughtobe movedto
the demonstrationareaeasily
10.2 The device mustbe able to reachthe demonstrationarea,
therefore be small enoughtofitthroughdoors
10.3 If the device isrequired tobe assembledonsite,all
separate componentsmustbe small enoughtofitthroughdoors
and make itto the demonstrationarea
10.4 The device mustbe small enoughtooperate indoors,ina
small room
10.5 The device mustbe lightenoughtobe poweredbythe
chosenmotors
6. ComparisonTables
The followingpagesdemonstratethe conceptgenerationstage of ourdesign.Itwasclearfrom our initial conversationandpreliminaryideasthatdeciding
on our type of designwasof paramountimportance.Eachcategory isshownbelowthenfollowingthis, aweightingandratingtable concludesourideal
category.
The rest of thissectionfollowsthe same layoutbutforsolutionstoeachof the necessarycomponentsinourdesign.Thereisacomparisontable,describing
each optionthenawaitingandrating table todecide onour ideal component.
Categories of Design
Category Advantages Disadvantages
Flying
(reachingthe egg
by air,pickingit
up,reachingthe
desiredaltitude by
air and depositing
the egg)
Device isinone assembly;all functionsare achievedby
the same machine
The machine isextremelymanoeuvrableandadaptable to
changesinthe testenvironmentcomparedwiththe
environmentthathasbeenplannedfor
Designisambitiousandoriginal;itmaybe scoredmore
highlybymarkers
Device will be difficulttoprogram
Device will be difficulttomake,several motorswill be
neededandveryspecificcomponentswill be required
Entire device will have tobe keptverylightweight.The
grabbingpart for example mustbe keptaslightas
possible
The weightof the egg itself mayseverelyalterthe
control of the device
One mistake incontrol (acrash) will be devastating
Stationary
(stationarybase,
arm extending
horizontally,
pickingupegg&
liftingtodesired
height)
Easy to construct,most componentswillbe large and
easyto tinkerwithbyhand
There will be nosize or weightrestrictions
Control will be relativelysimple,withonlyaselectionof
forwards/ backwardsmotorsrequired
Balance will have tobe considered,inordertoreachout
the full distance the device maybecome unstable
Momentson the device maybe large and counter
weightsmaybe required
The device will have tostandverytall
The device maybe unstable duringcertainpartsof the
process
The device maybe veryheavyand difficulttotransport
Driving & Self
ContainedLifting
(reachingthe egg
Entire device will be one assembly
Device will be able toadaptto changesinenvironment
such as positionof egg
Control maybe complex,withprogramming requiredfor
several partsof the processall containedwithinthe
same machine.
7. ComparisonTable of DesignCategories:Each columnhas a multiplierinordertoweightthatcomparisoncategoryaccordingto itsimportance.Eachvalue isgiven
independentlyof sum of thatcolumn,soeach designcategoryreceivesthe correctscore.(1 beingverypoor,rangingto4 beingexcellent)
Category Power
Methodand
Source [2]
Build
Complexity
[2]
Ease of
Operation[2]
Aesthetics[1] Egg Safety [3] Stability[2] Dexterity[2] Adaptability
[1]
Total
Flying 1 1 1 4 1 1 4 3 26
Stationary 4 3 4 1 3 2 1 1 39
Driving & Self
ContainedLifting
3 4 3 3 2 4 4 4 49
Driving & Separate
Lifting
2 2 2 2 2 3 2 2 32
by drivingover
land,pickingup
the egg then
raisingitup and
depositingit,all as
part of the same,
portable assembly)
Device will be verymanoeuvrable
The Device shouldbe reasonablystableasitisnot
requiredtoreachout
Requiredcomponentswillbe easytocome by
The device will needtobe keptlightweightinorderto
complete the full task,movingandelevating
Powerwill be requiredtooperate the drivingof the
machine onthe flatas well aselevatingthe egg
The device maybe top heavy,drivingaroundwithtall
componentsrequiredforthe elevationprocess
Driving & Separate
Lifting
(reachingthe egg
by land,takingit
back to a separate,
stationary
assemblywhich
will achieve the
requiredaltitude)
Simple control asthe separate partsof the jobwill be split
up betweenmachines
No weightconstraintswill be required
No size constraintswillbe required
Parts will be bigandeasyto alterby hand
Designmaystruggle tobe withinconstraintsof the
designbrief asitmay notbe able towithdrawa metre
fromthe egg
There will be anewcomplexityaddedwiththe transfer
of eggfromone machine to another
A part of the assemblywill needtobe at the desired
heightbefore the demonstrationbegins
The egg may be damagedinthe transitionbetween
machines
8. Component Concepts – Egg Grabber
Concept Advantages Disadvantages
Suction Cup No hardsurfacesincontact
witheggshell
Ideaismore original and
unusual thansome others
Requiresahighpowersource
to maintainvacuum
Egg may drop if a tightseal is
not created
Closing Net No hardsurfacesare in
contact withthe egg
There are noconcentrated
forcesactingon the egg at any
point
Ideaisoriginal
The net will require an
innovative systeminorderto
close upthe openendonce
the egg isinside
The net maybe difficultto
place accuratelyoverthe egg
The net maybe difficultto
re-openonce the egginin
position
Claw Control will be relativelyeasy
Componentswillbe simpleto
make
There will be asmall number
of hardpointsof contact
withthe egg
It may be veryeasyto crush
the egg by accident
9. Cage Egg will be secure
Pickingupand depositingof
the egg will be easy
Ideaisoriginal
Conceptshouldlookgood
Componentwill be difficult
to manufacture
Egg may rattle aroundinside
cage and be damaged
Componentsmaybe
specialisedanddifficultto
acquire
Scoop Componentissimple to
construct
Control of the componentis
simple withonlyupanddown
motion
It may be difficulttopickegg
up withoutjustpushingit
away
Egg may fall outeasily
Egg may rattle aroundand be
damaged
10. Pincer Easy to control withtwo
forwardsandbackwards
motors
Verymanoeuvrableand able
to accuratelycollectthe egg
Versatile atpickingupthe egg
independentof howitis
sitting
Hard pointsof contact may
damage the egg
Control of the motorsmaybe
difficultastheyneedto
move slowlyandnotcrush
the egg
Spoons Correctlyshapeddevice will
cup the egg nicely
Egg will be secure
Egg may fall outof spoon
Control of the motorsmaybe
difficultastheyneedto
move slowlyandnotcrush
the egg
Badlyshapedspoonsmay
cause a stressconcentrator
on the egg
Forks Simple control
Easy to construct
Cheapto manufacture
Easilyacquiredcomponents
Egg couldfall out easily, any
vibrationsortiltingmaybe
problematic
Unoriginal idea
Egg may be difficulttopick
up,forksmay simplypushit
away whentryingtoget
underit
12. Component Concepts – Driving
Advantages Disadvantages
Wheels:frontwheel drive,front
wheel steering
Stable
Cheap
Easilypowered
More complex thanseparate steering
and drive systems
Will require aspecificsteering
system
Drive and steeringsystemwillneed
to be appliedatsame wheel
Wheels:rearwheel drive,frontwheel
steering
Relativelysimple control
Stable
Cheap
EasilyPowered
Specificsteeringsystemwill be
required
Possibilityof badtraction
Large turningcircle
Wheels:4 wheel drive,frontwheel
steering
Extremelystable
Can deal withdifferentterrain
More powercan be delivered
Susceptibletobreakagesandfailure
Difficulttoconstruct
Veryreliantongooddifferentials
All motorswill needtobe
synchronised
Drive and steeringsystemwillneed
to be appliedatsame wheel
13. Wheels:powered(Forwardsand
Reverse) wheel oneitherside with
free torotate casterwheelsfor
support
EasilycontrolledandPowered
Easy to make
Cheap
Verygoodturningcircle
May be difficulttoensure the castors
are alignedandthe assemblyisnot
wobbly
May struggle withdifferentterrain
(carpetor unevenfloor)
Motors will need tobe synchronised
withone another
CaterpillarTracks: independently
driven(forwardsandreverse motors)
leftandright
Extremelystable
Verysimple control
Verygoodturningcircle
Durable
Good on differentterrain(lotsof traction)
Controlledmotion
Heavytracks may provide lowcentre of gravityandstable
base
Slow(thoughthisisa small negative)
Slipmayoccur betweentracksand
drivingwheels
Difficulttoturn while onthe move,
stationaryturningmaybe the only
option
Heavyand cumbersome design
May require more powertodrive
heavierconstruction
Tracks may be difficulttoconstruct
WheelsandPulley:unpowered
wheelsandpoweredexternal pulley
Simple tocontrol
Easy to power
Cheapcomponents
Onlyone directionisavailable
withouthumaninteraction
Pulleymustbe heavyinordertodrag
entire assemblyalong
May notfitdesigncriteria(not
startinga full metre away)
15. Component Concepts – Lifting Method
Concept Advantages Disadvantages
Pneumatics Simple
Easy to control (onvs off)
Easy to generate alotof liftingpower
Legsdo not needtobe at full extensionwhile
driving
Difficulttocompressair
May require inbuiltcompressor
Extra weightwill be addedwithcanisterand
pump
Regulatorwill be requiredtoensure the correct
amountof pressure isused
All legsmustbe connectedtoensure equal
pressure oneachsupport
Hydraulics Verypowerful liftingmethod
Easy to control
Simple
Couldmake a bigmess if a leakage occurs
Difficulttoactuate
Will be veryheavytodrive around
Possiblyveryexpensive
Screw Cheap
Stable
Easy to operate
Simple tocontrol
Easy to have a controlled,slowlift
Complex asyou may have tocoordinate several
screwsto liftthe machine inunison
Difficulttocreate componentswhichwill allow
free screwrotationwithoutconflicting withother
componentsaroundit
Designmayhave to include heavyfeettoensure
stabilitythroughoutthe demonstration
Legswill have tobe at full heightevenwhen
drivingaround andnot inuse
16. Rack and Pinion Simple toconstruct
Simple tocontrol
Reasonablylightweight
Notas creative asolution
Couldbe flimsywhenreachingsuchahighheight
Legswill have tobe at full heightevenwhen
drivingaroundwiththe legsnotinuse.
The Feetwill have tobe extremelyheavyto
ensure stabilitythroughoutthe demonstration.
Pulley Simple tomake
Lightweight
Cheap
Simple tocontrol
Basic components(suchasstring)
Easy to source components
Legswill have tobe at full heightevenwhen
drivingaroundwiththe legsnotinuse.
The Feetwill have tobe extremelyheavyto
ensure stability throughoutthe demonstration.
Unstable
Possible large loadonthincables
Spring Easy to source components
Easy to create enoughforce to liftentire assembly
Isn’tfullyextendedwhendriving
Springhas to be compressed1metre
Expansionmustbe controllable
Springof such a large size may be expensive
Dampenerswill be required
17. ComparisonTable of LiftingMethods:Each columnhasa multiplierinordertoweightthatcomparisoncategoryaccordingtoitsimportance.Each value is
givenindependentlyof sumof thatcolumn,so eachdesigncategoryreceivesthe correctscore.(1beingverypoor,rangingto5 beingexcellent)
Category Available
Lifting
Power[2]
Power Source
Complexity[2]
Leg Build
Complexity[2]
Ease of
Operation[2]
Aesthetics[1] Egg Safety
(Smoothness
of Lift) [3]
Stability[2] Total
Pneumatics 5 2 2 4 5 3 3 46
Hydraulics 5 1 1 3 4 3 4 41
Screw& Motor 3 4 3 5 3 4 3 51
Rack and Pinion
& Motor
3 5 5 5 2 4 4 58
Pulley&Motor 2 4 4 5 1 5 2 50
Spring 5 4 1 3 4 1 1 35
18. Final Components
From the comparisontables,we canconclude thatthe ideal designforthe taskwill be aself-contained,drivingandliftingmachine withapincermechanism
for pickingupthe egg,a Rack andPinionforachievingthe desiredaltitude and twopoweredwheelsateitherside withfreelyrotatingcasterwheelsaround
for support.
19. SuggestedDesigns
All groupmemberswere nowfree togoaway andcome upwitha final designastheysawit,utilisingthe componentsdecideduponinthe comparison
tables.Thisresultedinthe conceptsasshownbelow.
Concept 1 -
• This concept has 2 driven wheels and 2 free wheels
• The base has a slice taken out to allow the claw to
reach the floor and pick up the egg.
• The lifting mechanism has 2 gears on ether side of
the pole to allow for stability when lifting
• The claw closes by use of a small motor
• This design is controlled by using a wired control
devise which is lead away from the base and to the
operator’s hand
• There will be switches to control each motor (turn
on, off and reverse
• The 2 wheels will be individually controlled to allow
for turning
20. Concept 2 –
Thisconceptis self-contained,andthe lifting
mechanismsitsontopof the bodyin the centre.
The liftingusesarack and pinionmethod,withthe
motor attachedto the large gear at the back of the
pincerarm.
The pinceris a 4 arm design,with2lowerarmsto
supportweightand2 movingupperarms to
stabilise the egg.
The wheel setuphas2 drivenwheelsatthe front
using2 independentmotors,and2 fullyrotational
wheelsatthe rear. The device canbe turnedby
alteringthe movementof the 2 frontmotors.
The base isa solidsquare plate tocreate a low
centre of gravityfor balance andstability.
The functionof the designisto drive upto the egg
and pickup the eggonto the pincer,andthen
drive tothe newlocationandstopall wheel
motion. The pincerandegg will thenbe lifted
usingthe rack and piniontothe requiredheight.
21. Concept 3 –
Thisconceptis reallyintwohalves,the drivingpartof the designis
all containedwithinthe box atthe bottom,where the majorityof the
weightwill be.The otherhalf isthe clawandextendablearm,
attachedto a frame that sitson top of the drivingbox.Thismeans
the frame and egggrabber assemblycanmove upthe 4 legsalone,
leavingthe majorityof the weightonthe groundaspart of the
drivingbox.
Thisconcepthas 4 legs,all withteethupthemand4 motors,
synchronisedin ordertoliftthe frame andgrabberassemblyup
smoothlyandstably.
The pinceris extendable asshowninthe detailedviewof the rack
and pinion,containedwithinthe centre of the frame.Thispincer
extendsalongthe upper,horizontal partof itsarm, as shownbythe
arrows inthe drawing.
Thisextendableideaistoallowgreatercontrol whenpickingupand
depositingthe egg,sonotto solelyrelyondrivingthe entire machine
intothe exactlycorrectposition.
The extendablearmanglesdownsothe pincermaypick upthe egg
fromground level.The suggestedclosingmechanismforthe pinceris
showninanotherdetailedview,usingatinymotorand a screw.
Whenthe egg iscollected,the fourliftingmotors(poweredbya
batterypack heldinthe centre of the frame) startdrivingthe frame
and grabberassemblyupwards,toreachthe desiredaltitude.
The two drivingwheelsare positionedoneitherside of the driving
box withfourcaster wheels,one ateachcornerfor support.All
batteriesandmotorsfordrivingare containedwithinthe assembly
at the bottom.
22. Concept 4 –
There are twoparts to thisdesign;the drivingpartisa simple four
wheeledvehicle withfrontwheeldrive where the pincerwill be
there to pickup the egg.The secondpart of the designis3
extendable armswhichare arrangedina triangle formationwhich
will liftthe entire unitmore than1 metre off the ground.
The three extendablearmswhichall have arough bottomon them
for grip,iscontrolledby3 individualmotorswhichwillsupplythe
necessarypowertoliftthe unitfromthe ground.
The pinceris extendable andcontainstwoindividual pincers.One
whichgripsthe egg at itstop and one that gripsthe eggsat the
bottomprovidingthe eggare inthe uprightposition.
The main advantage of havinganextendablearmisthat it when
the egg isliftedadistance of one metre verticallythe armcan
extendoutfromthe containeddesigntosafelydeposititsloadof
an egg.
There will be twoseparate small motorswhichwill be usedtoclose
and openthese individual pincerswiththe helpof twoscrews.
The whole designwillbe poweredbyabatterypack storedwithin
the base of the drivingunit.Thisshall be locatedinthe centre of
the designasto try and make the structure as stable aspossible
whenairborne
23. Concept 5 –
Thisconcepthas a rectangularbase andmost of itsweightwill be
concentratedatthe frontof the device
It has 4 wheels.The base sitsontop of the wheels.The fronttwo
wheelsare connectedtoindependent motorslocatedunderneath
the body.The tworear wheelsare free tomove inanydirection.
The device hastwo racks locatednearthe frontof the base that
standvertically.
Connectedbetweenthe tworacksisthe liftingdevice,fromthe
centre of whichthe claw extendsforwardspastthe base of the
device.
The side of the racks containingthe bitesfacesinwardssoboth
racks are facingone another.Connectedtoeachrack isa worm
gear.These gearsare poweredbythe motorlocatedon the lifting
device whichcausesittorise vertically.
The arm connectedtothe pincerisnot extendable.
The pincerhas twoarms that are curvedina waythat allows
themto grab the egg fromunderneathapplyingpressuretothe
underside aswell asthe sidesof the eggand holdit securely.
The inside of the arms containa soft,shock-absorbingmaterial to
aidin safelymanagingthe egg.
The closingmechanismof the pincerheadhasone motor.It is
connectedtoa gear that turnsone arm of the pincer.Thisgear
alsocausesthe opposite armto close throughthe turningof an
additional gear.Botharmswill close atthe same speed.
24. Concept 6 –
Thisconceptis fullyself-contained
There are fourwheels,andthe fronttwowheelshave
independentdrivemotorstoallowforwardandreverse
motionforboth wheels
The pinceris 2 arms attachedto a central cog drivenbya
small motor,and thisisattachedto an arm whichfeaturesa
loweredfrontsectionsothatthe pincerscan pickup from
groundheight.There isalsoa rack alongthe lengthof the arm
to allowextensionof the armtowardsthe pickuplocation
The rear of the base is fairlylarge toencompasspossibleradio
technology,andtoallowforadditional weighttobalance the
momentscausedwhenthe pincerisatmaximumheight
The front of the base isa beamstructure tominimise weight
The liftingof the pincersisthrougha pulleysystemupa1-
metre pole,poweredbyamotor at the rearof the vehicle
The insidesof the pincerscontainsasoftmaterial toact as a
shock-absorber
25. Final Design
To create the final design,the six conceptswere discussedtoconsiderthe advantagesof
each part of each concept,andthese advantageouspartswere takenoutfromthe
concept. We combinedthese to create adesignthatwe feltcontainedthe bestof every
concept.
It was decidedthatasingle rackand pinion,suchas fromconcept2, was all that was
necessarytoprovide the liftingforthe accumulative weightof the pincerandegg. This
wouldminimise complexitythatwouldbe causedfromcombinedlifting,asitwouldnot
be requiredtosynchronise liftingwithmultiplemotorsactinguponmultiple rackand
pinions. Italsoreducesriskof failure due tolesscomponents. Stabilitycouldstillbe
ensuredbytakingappropriate dimensionsof the central rack. The gearchosento move
up the rack was a worm gearas showninconcept 5, as thiswouldprovide highertorque
and be lesslikelytoslipthanastandardcog gear.
The pincerdesignisto be deep,cupshapedpincersthatare curvedina way to allowthe
weightof the eggto be supportedfromunderneathtoreduce the pressure requiredon
the sidesof the egg to liftit,takenfromconcept5. This helpsreduce the force required
to act upon the eggfor stable liftingtoprevent damage beingcausedtothe egg.
The pincerarm was takenfromconcepts1 and 3, whichwouldbe forthe arm designto
lowertoground level atminimumheight. Thiswaschosentoensure that the eggcan be
takenfromall heights, toimprove the flexibilityof the design. Itisalsoto be extendable
as showninconcept3. Thisallowsthe pincerstobe movedouttowards the eggat a
slowandstable speedtopreventthe eggbeingdamagedormovedif impactedbythe
pincerarm at a highspeed.
26. The wheel designwaschosentobe similartoconcept3, involving2independantlydrivenwheelsateitherside of the midpointof the base toprovide a
forwardand reverese force tobothsidesof the base. Thisallowsthe device toturncompletelyonthe spotandmove inany direction. Extrafullyrotational
wheelsare tobe placedat the front andrear of the base to provide stability.
The base waschosento be of octagonal shape. A circular shape wasinitiallyconsideredasfromconcept1 but thiswassimplifiedtoanoctagon due to the
manufacturingcomplicationsof acircle. Anoctagon isalso more astheticallyunique.
27. Final Design – Revision
Aftersome considerationregardingmaterialsandcontrol inthe sections
to come,we decidedtorevise ourfinal design.Whenlookingfurtherinto
manufacture we decidedtogoaheadand solve some problemsbeforewe
came to them.Firstly,we have mountedthe liftingmotorabove the worm
so to allowthe arm togo as low as possible,withouthavingtocuta hole
for the motorto sit in.
Secondlywe have simplifiedthe angledsectionof the armby achieving
the drop inelevationwithtwooverlappingbeams,boltedtogether.
In thisarea,it isalsonoticeable thatwe have done awaywiththe arm
extensionmechanism.Thisisbecause withfurtherresearchintocontrol
and motors(coveredinthe followingtwosections),we have come tothe
realisationthatwe will be able todrive the machine accuratelyenoughto
collectthe eggsafelywithoutanarmextensionmechanism.Thisdecision
will make the entire assemblyfarsimplerandmake the arm far lighterto
lift.
Our final designrevisionisof the pincer.Here,the size of the proposed
motor hasbeenmore accuratelyconsidered andthe cogdiametershave
beencalculatedtoallowaslowclosingmotionaroundthe egg.Inorderto
reduce bendingmomentsonthe pincers,anadditional supporthasbeen
addedat the bottomand the curvedsectionshave beenrevisedinshape
to alloweasiermanufacture.
30. The drawingon the leftshowsthe base assembly,includingwheels,motorsandbatterypack.(Scale 1:5)
The drawingon the rightshowsthe pillarandrack assembly,alongwithaplate forconnectionwiththe base assembly.(Scale 1:10)
31. Material selection
In thissectionisshownhowthe needsof certaincomponentswere
identifiedandsuitable materialswere analysedinordertochoose the
ideal material foreachcomponent.All materialswere judgedonthings
such as price and availabilitywhiledifferentmaterialswerejudgedon
more specificcriteriasuchasstrength,density,frictionco-efficientand
malleability.
*Modulusof rupture isan acceptedcriterionof strengththoughitisnot a
true stress.
Recommended material
White Pine woodseemsto be ideal for the base of the device. Due to its
good strength to weight ratio it should be able to support the lifting
device andpowersource withminimal weightaddedtothe structure as a
whole. Additionally, the fact it is easy to work and machine, glues and
finisheswell and is cheaper than the stronger white oak means it would
be best suited to the task.
BaseRequirements:Strong,Lightaspossible,loadbearing
Possible
materials
White Pine
wood
Structural Steel Aluminium White Oak
wood
characteristics Strongand
cheap.Easy to
machine and
shape.Very
goodstrengthto
weightratio.
Moderately
durable- needs
to be treated
with
preservatives.
Durable,resilient
and strong.
Denserthan
woodand more
costly.
Low density,
highstrength,
malleable and
easyto
machine.
Workable by
handand
machine.Rot
resistant,used
for boat
building.
Numerical
Values:
Density:400
ElasticModulus:
8.55GPa
Ultimate Tensile
Strength:
40MPa
Modulusof
rupture*:
59MPa
Density:8000
Elastic
modulus:200GPa
Ultimate Tensile
strength:400MPa
Density:2700
Elastic
modulus:69
GPa
Ultimate
Tensile
Strength:110
MPa
Density:600-
900
Elastic
modulus:12.15
GPa
Modulusof
rupture*:
105MPa
32. WormGear Requirements:Strong,stiff,lowfriction
material Nylon6 Structural Steel Polyoxymethylene(POM)
Characteristics VeryStrongand
abrasion
resistant.Low
frictionco-
efficient.
Excellentwear
resistance,
good
toughness,
hardnessand
lowdensity.
Verystrongand
stiff.Higher
densityand
higherfriction
coefficient
whendry.
A thermoplasticwith
highstiffness,low
frictionanda high
strengththat isinjected
moulded.
Numerical
Values
Density:1150
Elastic
modulus:2-
4GPa
frictional
coefficientv
steel:0.35
Ultimate tensile
Strength:45-
90MPa
Yield
Strength:45MPa
Density:8000
Elasticmodulus:
200GPa
Kineticfrictional
coefficient(Steel
on Steel):0.6
Yield Strength:
250MPa
Density:1410-1420
Elasticmodulus:2.9-
3.5GPa
Kineticfrictional
coefficienton steel:0.21
Compressive strength:
31MPa
Recommended material
Nylonwormgearsare oftenusedinsmall electricalappliancessince they
are cheaperthanmetal gearsand require nolubrication.Furthermore,
the lowdensityandabrasionresistance of nylonmake itanideal material
for thispurpose.Steel,althoughstrongerandstifferthanNylon,isalso
heavier,more expensiveandwouldrequirelubricationtoreduce the co-
efficientof frictionbetweenthe gearandthe rack. POMis slightlydenser
and has aroundthe same stiffnessasNylon.Itmayhowever,notbe as
available toacquire.Therefore,we intendforthiscomponenttobe made
fromnylon.
33. Rack Requirements:lowfrictioncoefficient,gluesandjoinswell
Material Stainless
steel
Nylon POM Aluminiu
m alloy
Brass
characteristics Strongand
stiff,Higher
friction
coefficient
than nylon
and pom.
Could
require
lubrication.
Denserthan
nylonand
pom.
Strong
and stiff
but notas
strongas
steel.Has
a lower
density
and lower
friction
co-
efficient
Strong
and
stiff
also.
Notas
strong
as
steel.
Stronger
and stiffer
than
Nylonand
POMbut
lessso
than steel.
Alloy
made
from
copper
and zinc.
Low
friction
coefficien
t and
malleable.
Recommended material
Racks can come in the formof solid racksor flexible racks.If a flexible
rack is useditwouldneedtobe attachedto the side of the central pillar.
It wouldoffernostructural supportandpossiblyrequire athickerpillaror
a strongermaterial.Itwouldhoweverbe cheaper. Italsoappearsthat it
wouldbe difficulttogetracks of the rightsize.To acquire a steel rackat a
lengthovera metre inlengthwouldbe costlyandtake upa large part of
the budget.However,asteel rackiswhat we intendtouse as it isstrong
and has a low frictioncoefficientwithnylon.
Pillar Requirements:Strong,lowdensity,gluesandjoinswell
material Steel Aluminium
alloy
wood
characteristics Strongand stiff.
More dense
than
Aluminium.
Notas strongas
steel butless
dense.
Lessdense than
bothsteel and
aluminium
while offering
goodstrength
to weightratio.
Recommended material
Since the purpose of the pillaristo supportthe rack thismeansthe
material useddependsheavilyonwhatmaterial ischosenforthe rack.
Since the rack is to be made fromsolidsteel,thislendsitself towood
beingusedsince lesssupportwouldbe requiredandthe weightof the
structure will be minimised.SteelandAluminiumwouldbe more
expensive also.
34. Recommended material
Since the pincerarms are to be a more complicatedshape thanother
components,thiswillneedtobe takenintoaccountwhenchoosingthe
material.Additionally,the densityof the material isimportantasheavy
arms wouldcause a largermomentandput a largerstrain onthe
structure.Initiallydifferentwoods,metalsandplasticswere considered
until the ideaof usingrigidfoamthat iseasyto carve came to the fore.As
thismaterial wasreadilyavailable tousandits lowweightofferedagreat
advantage,modellingfoambecame the chosenmaterial forthis
component.
Recommended material
Styrofoamandotherrigid,close-celledfoamsdon’tprovidethe `cushion’
that we desire fromthiscomponent. Aswe are usingrigidfoamtoform
the pincerarms, itis possible thatnoadditional`cushioning’material
wouldbe required.If,however,itisrequiredthenbubble wrapwouldbe
our chosenmaterial foritsshockabsorbingproperties,versatilityand
availabilityata lowprice.
Pincer ArmsRequirements: workable,easytoshape,goodtensilestrength
material Mildsteel Aluminium wood Plastic Modelling(close
celled) foam
Characteristics Ductile
and
malleable.
Strong
and
dense.
Very
malleable
and very
ductile.
Lessdense
than steel
and less
strong.
Can be
carved
or cut
into
shape.
Good
strength
v
weight
ratio.
Malleable,
lowcost and
easyto
manufacture.
Rigidfoam
structure that
has verylittle
weight.Very
cheapand
readily
available.
Inner pincer armsRequirements: shockabsorbing,glue well.
material Styrofoam Low density
foam
Bubble wrap
Characteristics Lightweight,
buoyantusedfor
insulation.Rigid
and close celled.
Low density
and soft.
Shapesto
thingsit
comesin
contact with.
Trapped
pocketsof air.
Sock absorbing
material used
to protect
fragile objects.
35. Lifting arm Requirements:strong,lowdensity,workable
material Steel aluminium wood Plastic
Characteristics Strongbut
dense.
Workable.
Strongand
lessdense
than steel.
Malleable
and ductile.
Good
strengthto
weightratio
thoughnot
as strong as
steel or
aluminium.
Easy to
shape and
cut.
Lessstrong
than steel
or
aluminium
but
stronger
than wood.
Lessdense
than metal
alloys.
Recommended material
Althoughthiscomponenthastobe strong,a large part of the load applied
to thiscomponentisitsownweight.Thisgiveswoodandplastican
advantage.Aluminiumwouldbe betterthansteel foritsmalleable
qualitiesandbecause steel ismore dense.Due topossible budget
constraints,a type of woodwitha lowdensitysuch aspine or basswood
that iseasyto shape and readilyavailable wouldbe more ideal thana
plasticcomposite.
Summary ofrecommendedmaterials
The base shouldbe made of wood.We have plannedforusingwhite pine
wood.The rack will be made fromsteel andthe wormgearnylon.Wood
has beenchosenforthe pillarsoa minimal amountof weightwillbe
addedto the structure by the component.The pincerarmsshouldbe
made fromrigid,close celledfoamwithbubble wrapattachedtothe
inside of the armsif required.The liftingarmsitself will alsobe made
fromwoodbecause of its excellentstrengthtoweightqualities.A low
densitysoftwoodlike basswoodwouldperformwellforthiscomponent.
36. ConstructionMethods
The base we will constructbycuttingout the cornersfroma wooden
blockusinga circular sawingtool.The frontpart of the base will be cut
out usinga jigsawtool. The wormgear and rack shouldbe orderedinthe
correct sizessono additional workwillbe required.The motorswill be
screwedtothe underside of the base andare connectedtothe wheels
throughthe drive shafts.The wheelswill be rubbercoatedandmade
fromplastic.The batterypack is alsoscrewedtothe underside of the
base towards the back endof the device.Usingthe jigsaw,a rectangular
hole will be cutoutfrom the centre of the base.The rack and pillarwill be
gluedtoa metal rectangle thatwill be screwedintothe underside of the
base.The rack andpillarwill be gluedtogetherusinganadhesive.The
liftingarmisbrokenintotwoparts to make it easiertoconstruct.Starting
withtwowoodenbeams,sectionswill be cutoutusinga jigsaw to create
the desiredshape.The circularshapeswill be cutoutusinga hole saw.
The two parts of the arm will be boltedtogetherattwopoints.The
pincerswill be shapedwithahighprecisionknife andconnectedtothe
gearsat the endof the liftingmechanismusingsmallaluminiumbars.The
bubble wrapwill be attachedtothe close celledfoamusinganadhesive.
The liftingmotorwill be attachedtothe back of the liftingarmat the
same side as the counterweight.Itwill be screwedinplace usingmetal
platesandsupports.The liftingmotorwill be connectedtothe wormgear
and keepitinplace.
37. Control Selection:
One of the firstthingdecidedforthe designwashowitshouldbe
controlled.A fewcontrol methodsdiscussedwhere manualcontrol
(crank/leveretc.),wiredsemi-automatic,wirelesssemi-automatic, fully
automatic(sensorsandself-correctingfeedbackloopi.e.completestask
withoutuserinput) andcombinationsof the fouroptions.Manual control
didnot showour competencyandwasunderwhelmingsowasnotan
option.Fullyautomaticcontrol wastoo complicatedandwouldneed
heavyprograming,some sortof egg recogniserdevice andwould
probablybe difficultconsideringthe costandconstructiontime
constraint.Itwas decidedthatthisoptionwouldshowextreme
competency,however,wouldnotlikely be the bestoption.Itseemedthat
the device shouldbe controlledeitherthroughwiredorwireless
communication.Afterdoingsome researchitseemedpossibletodo
eitherone.Itcame downto the benefitsanddisadvantagesof eachtype.
Wireless:
Advantages:
Showedcompetency
Wouldbe reallyimpressive
Wouldnot be confinedbywiresrunningtothe user
User would not have to be moved and could control the egg lifter
from a phone/wireless controller
Electronics can be confined to device and hidden to improve
aesthetics
Disadvantages:
Group wouldneedtolearnprogramingtocontrol the device
More potential problems/complications
Likelytobe more expensive thanasimple wiredsolution
More complicatedthata wiredsolution
Multiple powersourcesorvoltage stepperswillbe neededto
supplymultiple devicese.g.microcontroller,motors,wireless
communicatoretc.
Wired control:
Disadvantages:
Notas impressive aswireless
Notas aestheticallypleasingaswirelessaswill be shownand
strungto the user
Needsmanual inpute.g.switchingswitches
May needmultiple powersuppliesdependingonmotorselection,
howeverthiscanbe solvedbyusingmotorsof same voltage
Controllerwillneedtomove alongwiththe egglifter
38. Advantages:
Simplerwiringandcontrol drawingsthanwireless
Can be sourcedby one supply
Easierto control
Can me modifiedeasilyviahardware changesinsteadof
programming
Lessexpensive
Lesspossibilityof thingsgoingwrongandreliable
Physical tactile feedback
Componentsreadilyavailable
It was decidedthatthe egglifterwouldbe controlledbywiredswitches
and physical inputbythe controllersomewayawayfromthe device due
to simplicityandcost.
Power Source selection:
There were three mainwaystopowerthe device.Through solar,fixed
powersupplye.g.wall supplyandthroughaportable batteryfixedtothe
lifter.Solarwouldnotprovide enoughelectricityandafixedsupplywould
meanthat the device wastetheredinanotherplace otherthanthe user
and the componentswouldhave tobe A.C.compatible.The bestoption
was to use a batteryplacedonthe device tosupplypowerasbatteries
are widelyavailable andcame readilyindifferentconfigurations.This
meantthat the device couldmove aroundfreelyandstillhave sufficient
powerto run.The batterypack wouldhave tobe as small as possible so
wouldonlyprovide enoughcurrentforthe motorsto operate andno
more.
Motor Selection:
In orderto generate movementinourchosendesignsatleast4 motors
are required:two forthe wheels,one forthe armliftingandone forthe
clawmechanism. The drivingmotorsaswell asthe liftingmotorwould
have to produce a hightorque inorder to move aroundthe full weightof
the entire design.The drivingmotorswouldneedvariablespeedcontrol
so that the liftercanreach the eggwithprecisionandnotknock itaway.
The claw motorwouldhave to be small,slowandlightweightinorderto
ensure eggsafetyandadd as small a momentaspossible actingonthe
39. arm. Possible motors include DCbrushed/brushlessmotors,DCgeared
motors,servermotorsand steppermotors.Normal dcmotorshave too
highan rpm and notenoughtorque sowhere excluded.Steppermotors
where somewhatbulkyandcouldnotreachthe desiredspeedsand
wouldrequire multiple powersourcesforcomponents.Servoswouldalso
needmultiple powersupplies(forthe microcontrollerandthe servo),
wouldonlybe suitable forthe claw(due toonlytuningacertainnumber
of degreesandback) andwouldalsoneedtobe programedso these were
alsoexcluded.Gearedmotorscouldbe usedineverypartof the device
and couldalsobe run from a single powersupply.Almostanyspeedcould
be achievedandtheycouldrunwithoutbeingprogrammed(through
switches). Theycanalsobe reversedandhave hightorque.
Therefore gearedDCmotorswhere chosentorunthe egglifter.
Aftersome researchitwasevidentthatmostgearedmotorsrun
efficientlyat12v soonly12v gearedmotorswhere selectedsothatthey
can be runof a single 12v batterypack withouthavingtobe adjusted.
Motor Requirements:
Claw:
Thismotor isto close the pincerextremelyslowlysowe canvisuallyjudge
whenthe eggis securelyheldbutnotyetbeingcrushed.We estimate
that for 10 secondsbetweenfullyopenandmeetingthe surface of the
eggwe needthismotortorotate at 2-4rpm (assumingthata fractionof
one rotationwouldclose the pincers).There are nospecifictorque
requirementsforthismotorapart fromit shouldbe able to supportand
close the pincers(whichat2rpm wouldnotbe a problemforanygeared
motor).The motor mustbe small enoughtofitonto the backendof the
clawand lightweight.Itshouldalsohave an
offsetoutputshaftsothat itallowsroomand is
not inthe way of claw operation,ascan be seen
inthe final conceptdrawings(right).
Liftingmotor:
Thismotor mustproduce large amountsof torque in orderto elevate the
entire armincludingthe cradledeggtothe desiredheight.Itmustalso
rotate quicklyenoughtoreachthe correct elevationinareasonable
amountof time.We estimate for20-30 secondsto the 1m heightwe
wouldneedamotor rotatingat 2000 – 3000 rpmdue to usinga worm
gear.Each rotationof the gear leadsto a 1mm increase inheightof the
40. arm. Thismotor doesnothave a size requirementaslongas itfitsthe
designanda worm gearcan be sourcedof large enoughsize toexpand
overthe motor edge. Itwouldprobablybe
necessarytoinclude asmall spurgear (andlower
the worm diameter) tolowerthe effect of friction
betweenthe wormgearandthe rack (lefttopand
bottomimage).The speedwouldnotbe affected
inthiscase as longas the spur gearspitch
remainsat 1mm.
Drivingmotor:
The drivingmotorsmustproduce a hightorque,inorder to move around
the full weightof ourentire design(max 10kg).The motorsmustalso
have variable speedsinbothforwardsandreverse directionsinorderto
accuratelynavigate tocomplete the taskinhand.Theywouldbe
operatedusingpulse widthmodulation(rapidon andoff switchingof the
motor) whichwouldallowforvariable speeds withconstanttorque. Soto
travel 1m a 10cm diameterwheel will have toturnjustover3 times.If
thistookabout 10 secondsthenthe wheels shouldturnat
18rpm. The motorspeedshouldhoweverbe approximately
50rpm (un-geared) fora2.5-50rpm range (assuming5-100%
p.w.m.range). Thiswouldallowforslow,precise movement
while manoeuvringandfastermovementwhendrivingstraight. This
motor couldalsobe attacheddirectlytothe wheel givenenoughtorque.
Final motor selectionlist:
The motors where chosentomeettheirrequirementsatminimal cost
and theirspecificationsare asfollows:
Claw Motor:
Rated Voltage: DC12V
Gearbox
Diameter
40mm
Rated Current: 0.06A
DC Motor
Diameter:
32mm
Output Speed: 2RPM
Overall
Size(Approx.):
54 x 52mm
Max.
Width*Height)
Output Shaft
Diameter:
5mm Weight: 90g
Price: £7.78
Source: http://ebay.eu/1z9J6B6
41. Lifting Motor:
Rated Voltage: DC12V Diameter: 35mm
Rated Current:
0.52A(2.85 at
max efficiency)
Overall Size: 47 x 96mm Max.
Width*Height)
Output Shaft
Diameter:
6mm
Weight: 234g
Price: £20
Max torque: 0.88Nm(stall) Rated torque: 0.294Nm
Rated RPM:
2633rpm at max
efficiency, 12V
Efficiency: 64.9%
Sorce: http://www.maplin.co.uk/p/61-mfa-large-single-ratio-motor-gearbox-n98bn
Driving Motors:
Rated Voltage: DC 12V
RatedTorque 1.289Nm
Rated Speed: 50 RPM
Shaft Size: 15 x 6mm L*D
Motor Body Length: 62mm
Thread Diameter: 2.5mm
Total Length(Included Pins): 85mm
Rated Current: 0.5652Amps
Weight: 200g
Motor Body Diameter 37mm
Price: £11.19
Source: http://ebay.eu/1yPGRE4
All motorsmay change accordingto nextsemestersdesign
requirements/changesaswell asaccordingto availabilityandshipping
time butat the momenttheyare all suitable forthe egglifter.Anyother
motorswill be as close tothese as possible.
42. Circuit Diagrams:
Circuitsone,twoand three showhowthe motorsmightbe wired.Circuit
one showsa voltage dividerwithafixedmotorspeedaswell asa stepped
downvoltage.Thiswasnotneededsince all the motorswhere the same
voltage socouldbe run off one supply.Circuittwoshowsa variable
voltage dividerwithavariable speedmotor.Againthisdesignwasinitially
thoughtto be usedbut since the onlyvariable speedmotorsinthe
systemwhere the drive motors(usingpwm)thiswasnotneeded.Circuit
3 showshowthe drivermotorscouldbe wiredusingpwm. The pwm
componentistoa standalone device thatsendsavariable pwmpulse
throughitsoutputsvariesviaa turn knob.Thiscomponentcan be bought
for around£5 and meansthat noprogramingisneeded.Inthissolution,
as the motor speeddecrease sodoes the torque.All motorsare reversible
viathe double pole double throwswitcheswhichcanbe wiredas shown
inthe physical representation.The switchesputthe motorinforward,off,
and reverse states,controlledbythe three switchpositions.The full
circuitdiagramshowshowall the motorswill be wiredtoa single power
supply.All switcheswill be wiredawayfromthe eggliftertoacontrol
board inthe user’shand.The diodespreventbacke.m.f fromthe motor
reversal.Itwasestimatedthatthe batteryshouldprovide atleast3amps
at all timeswhenneededandonly1or 2 motorswouldbe on at anygiven
time.The supplywouldprovidepowertothe pwmcomponentaswell.A
batterypack of at least2.5amp hourbatteryis neededtoprovide a
constantmaximumcurrentof 3Amps to anydevice thatmay drawfrom
it.The motorswill notdrawmore than3 amps.The batterypack couldbe
a Ni-MH batterypack as these are easilyrechargeable,small,and
relativelylightbutwouldcostaround£20. Alternatively10AA alkaline
batteriescouldbe wiredupinserieswhichwouldbe equivalentbutnot
be rechargeable.Thissetupwouldcost£10. Since the egg lifteris
designedonlytobe usedonce includingtesting(30mins-1hr) buying
batteriesandwiringthemupwould be suitable.
43.
44. Motor Placement & Wiring
These diagramsshowourdesignforthe layoutof the electronicsinthe
machine.
On the left(fromtopto bottom),the firstdrawing(at1:3) showsthe arm
assembly,showingthe placement of the wire runningalongthe arm,the
liftingmotorabove the wormgearand the pincerclosingmotorat the free
endof the arm.
The seconddrawingshowsthe base at 1:5 and the pillar/ rack
assemblyat1:10. The planviewatthe bottomof thisdrawing showswhere
the wire will come throughthe base andcoil,while the viewfrom
underneath(positionedabovethe planview) showsthe placementof the
drivingmotors,the batterypackand the wiring.
The third drawingshowsthe pincerassemblyat1:1 and where the
motor will be placedinitalongwithwhere the wire willhave toreachin
orderto reach the supplypins.
On the right,youcan see the full assemblyof the machine withthe same
colourcodingapplied.
Thisdrawinghighlightsapossibleissueforthe design,the prospectof
havinga wire coiledontopof the base.Whenmanufacturingthe machine,
a systemmayneedto be put inplace inorder to allowthe wire tosmoothly
coil and uncoil asthe arm climbsanddescentsthe rack.
Blue – Motors
Red– Wires
Green– BatteryPack
46. Final Considerations
Lift Locking
There may be an issue withthe liftarmafterhavingreachedits
destinationheightwherethe wormgearmaybeginto slipandstart to fall
back down.Obviouslyitwouldbe preferable forthe gripperarmtolockin
place and notsliponce the motor that rotatesthe worm gearstops
rotating.We couldimplementalockingsystemsuchasa solenoidwitha
rubberstoppermountedunderneaththe liftarmtoactivate andextend
itsarm ontothe centre pole tolock the arm in place once itreachesthe
desiredheight.Howeveritmaybe the case that the worm gearprovides
enoughof a frictionforce to stopthe arm from fallingbackdownonce it
reachesthe desiredheight,howeverwe wouldnotknowthisuntil we
complete testing(dueinsemester2) onthe liftdesignandmayneedto
implementalockingsystematthat time.Itwouldbe preferablehowever
if we couldsave on weightandnot have to addextracomponentstothe
liftarm.
Braking System
An issue mayarise withthe drivingsystemascurrentlythere are
no brakesdesignedtobringthe vehicletoa halt,hence the drivingand
handlingof the systemisnotlikelytobe veryprecise.The systemmay
continue toroll once put inplace whichisclearlynotideal as there needs
to be a degree of accuracy to the placementof the egg.Toeliminate this
there mayneedto be a brakingsystemimplementedtoincrease the
accuracy of the driving.One exampleof howthiscouldbe done wouldbe
to have twosolenoidswhichare mountedonthe underside of the chassis
nextto the twomaindrive wheels.The solenoidwouldextendandstop
the wheelsfrommoving(throughfriction).Thiswouldallowustostop
the vehicle whenitisina particularspotand keepthe brakesheldonto
stopit fromrolling(thiswouldbe especiallyusefulforwhenthe lifting
procedure takesplace).Itcouldalsobe the case howeverthatthe weight
of the vehicle itselfmaycause a frictionforce highenoughthatthisissue
couldbe disregarded,howeverthisisagainsomethinge cannotfully
understanduntil the testingstages.
Gripper Issues
It needstobe takenintoconsiderationthatthe pincergripwill
needtobe manufacturedaswell aspossible because the consequences
of the pincerbeingfaultywouldbe catastrophic.Nothaving enoughgrip
withoutbreakingthe eggetc.We have chosento go witha double pincer
griphence there will be twomovingcomponentsthatneedtobe
controlled.Inthe lifting,we willneedtobe aware of theirweight soto
avoidlarge momentsonthe arm. We will alsoneedtobe aware of how
the gripperwill actuallyoperate (asbothof these armswill needtoclose
at the exactsame speed andhave a veryslowrpm) also bothof these
arms needtocome togetherwhichrequiredsome precision.
Runner on Gripper Arm
The surface of the liftarm that will contactthe flatside of the
rack may generate averyhighamountof friction.Thismaycause an issue
whenthe wormgear istryingto rotate andliftthe arm that it maynot
provide enoughtorque toovercome the frictioncreatedbythe two
surfacesrubbingagainstone another(technicallythe frictionwill be
causedby the weightof the grippercausinga small rotationinthe gripper
47. arm by creatinga momentaroundit).One easywayto get aroundthis
wouldbe to addin a runnerwheel tocontact the centre pole. Thiswill be
free torotate hence decreasingthe frictionwhenthe armisascending.
Thiswouldeasilyeliminate the issueof frictionandismostlikelytobe
implementedintoourdesignasitwouldalsobe verycheapand effective
to introduce.
Do we need an extension (Decided)?
Originallywe have designedthe systemtohave asmall extension
arm to allowitto easilyextendandallowforalongerreachingdistance.
Howeverwe discussedwhetherornotthiswas particularlynecessaryand
whetherornot itcouldbe omitted.If itwere tobe omittedthenwe
woulddecrease the numberof motorswe wouldrequireandsave weight
on the liftarm (the mostcrucial piece of the device thatrequiresalow
weight).We eventuallydecidedthatwe wouldomitthe extension,but
we wouldputmore effortintoour drivingmechanismstomaintain
accuracy (as the arm wouldhave extendedslowlyanditmaybe more
difficulttodothiswhile driving).Therefore itisveryimportantforthe
speedof the motorsto be veryvariable betweeninchingforwardtowards
the egg,to drivingthe 1m distance requiredwithouttakingtoolong.
Rack & Worm Size and Friction
A potential issuemayarise withtryingtoobtainthe correct size
of rack (needstobe justover1m in length) withawormgear whose pitch
will matchthat of the rack. Anotherconsiderationwill be howquicklythe
liftingprocesswillbe carriedout;as for a worm gear,1 rotation= moving
vertically1tooth.If we assume thateach toothis1mm inlengthandwe
wantthe lifttotake no longerthan30 secondsto reach the desired
heightthenthe motormustrotate at 2000 rpm. That speedof rotation
however(approx 33revsor33 mm per second) isrelativelyfastbut
generallyfasterrotationtendtomeanlowertorque whichcouldgiverise
to more problems.The rackand worm systemshouldworkwellif all parts
are properlysourcedandpiecedtogetherhowever, butif we struggle in
manufacturingandthe rack doesnot live uptocurrent expectationsand
whatwe have researchedthenwe dohave otherpotential backupideas
for lifting(e.g.apulleysystem).
It seemsdifficulttopurchase acombinationrackand wormgear
to fitour needssoitis likelythatwe will buyindependentcomponents
and combine them.The mainproblemwiththisislikelytobe a friction
factor far toohighfor our motor.While thismayentirelyeradicatethe
needforthe liftlockingmechanism,the staticfrictionmayactuallybe too
highto be overcome bythe liftingmotor.Orif thisis possible,itmayburn
the motor outwitha slowedmotiondue toexcessive kineticfriction.A
possible solutiontothismaybe to insertanintermediatespurgearto
connectthe worm gearto the rack. Howeverif the wormgearand rack
are compatible andthe armcan climb thenthiswill notneedtobe
addressed.
48.
49. Conclusion
Group 2 thoroughlyresearched every option that they felt was available
to come up with an effective design within the £300 budget. Pugh’s
design methodology was used through the process in order to find the
best performing pieces on each part of the design. Concept generation
tables were used extensively during this process with the assigned
weighting system concluding upon the best results. Detailed drawings
were done by hand along with using CAD programmes in order to
properlyshowwhatthe prospective designwill look like. Materials were
extensively researched for properties and to make sure that we kept
within the £300 budget.
The group had a weekly meeting during the timetabled Monday slot,
where eachmemberwasassignedtheirownindividual taskinaccordance
withtheirskill set which had to be completed before the next week e.g.
create CAD drawings.We setour own deadlines to ensure that work was
completedontime andwe metoutside tutorialsandusedsocial media to
communicate anynewideasandgive additional help to group members.
Attendance wasgenerallygoodduringMondayTutorial sessionshowever
a couple of group members were unfortunately unable to attend these
lectures due to illness and work commitments. However the rest of the
groupmemberswere still able to get into contact with then through text
or social media such as Facebook and work was always completed on
time. On one occasion an absent group member was put on
speakerphonesothat they could still participate in a group discussion. It
can be concluded that the group worked well as one cohesive unit to
produce what we believe is an innovative product which is highly
functional and creative at the same time.
Parts List
Component Suggested Source Estimated Cost (£)
Pincer Independently 0
PincerConnectors eBay– AluminiumFlat
Bar
2
Cogs RS POMGear 12.32
PincerMotor eBay– GearedMotor 7.78
Pins eBay– Steel M8 6
PincerMotor Casing eBay– Al T Profile 2
Arm Beatson’s/
Independently
2.04 / 0
Arm Bolts Ross Castors 0.5
Worm Gear RS Worm Gear 8.68
LiftingMotor Maplin 19.99
Base Independently 0
CasterWheels CyberMarket 21.82
DrivenWheels Ross CastorsGV 6.6 + D
BatteryPack We Sell Electrical 6
Wires The Tool Box Shop 2.32
DrivingMotors eBay 22.38
SpeedRegulator(p.w.m.) RS 3.89
DPDT Switches Maplin 11.16
Rack Beltingonline 61.32
Pillar Beatson’s/
Independently
4.24 / 0
ConnectorPlate Beatsons’s/
Independently
6.08
Screws Screwfix 4.49
Total (Estimated) Cost £211.61
53. Appendix 3 - Motor Calculations:
The requiredtoque forthe drivingmotorandthe liftingmotorwhere calculatedasshown:
No calculationisrequiredforthe clawmotorasany gearedmotor
undera fewhundredrpmshouldbe able toclose the claw.
