MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Mechanical Design

Ian Mackenzie

November 17, 2007

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Ian Mackenzie

I Involved in FIRST since 1998

I Member of team 188 from 1998-2002

I Recruiter/organizer for FIRST Canadian Regional in2003

I Lead mentor for team 1114 in 2004, created SimSwervecrab drive system

I Planning committee member for Waterloo Regionalsince 2005

I Head referee at Waterloo Regional, Toronto Regional,Wonderland

I Currently planning committee chair for WaterlooRegional and mentor for 1114

I Scheduling algorithm developer, inspector, gamedesigner, Lego League referee, webmaster. . .

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Outline

General PrinciplesSimplicityDisassemblyMultifunctionalityTheoryIterationWeight

How To. . .Power TransmissionChainsMotorsCAD

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Simplicity

I Simplicity is the key todurability

I To come up with a complexsolution to a complexproblem is hard; to come upwith a simple solution to acomplex problem is evenharder

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Design for Disassembly

I Access holes

I Common tools

I Think twice about glue,welding etc.

I Think about how hard itwould be to remove a partfor repair

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Multifunctionality

I Figure out where you can useone part or mechanism formultiple tasks

I One arm to pick up a balland hang from a bar

I One rod as both a pivotand a structural member

I One shaft for both armsand wheels (OK, maybe not)

I Can save weight andcomplexity

I Careful of conflictingrequirements

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Theory

I BREAKING NEWS: Theoryactually works

I Calculate gear ratios

I Determine whether a motorhas enough torque

I Calculate forces and torqueson joints

I Swerve drive kinematics

I Work-energy arguments

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Qualitative Theory

I Self-locking mechanisms

I Directions of forces ortorques

I Rate of change offorce/stress/torque etc.

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Iteration

I Design is iterative!

I Rethink old ideas

I Eliminate leftovers

I In the early stages, it is oftena good idea to throw outdesigns and redo them fromscratch

I Every time you restart, youknow the problem a lotbetter

I As my Grade 9 mathteacher used to say,“Expand, then simplify”

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Weight

I FIRST has a weight limit

I Very easy to exceed theweight limit without noticing

I Drilling holes can only getyou so far

I Think twice before usingsteel parts, large bolts, orthick plate

I Lighten parts as you go

I Weight is bad; weight uphigh is much worse

I Consider alternate materials:Lexan, nylon, HDPE/LDPE,or wood

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Outline

General PrinciplesSimplicityDisassemblyMultifunctionalityTheoryIterationWeight

How To. . .Power TransmissionChainsMotorsCAD

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Power Transmission

I Common problem: how to transmit power between ashaft and something attached to it

I GearI SprocketI Wheel

I High stresses, so easy to break

I Often hard to fix

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Power TransmissionSet Screws

I “Set screws inhale audibly”. . .

I Weak

I Prone to coming loose

I Sometimes the only choice for small shafts

I Use a dimple on the shaft

I Use Loctite or similar to slow down loosening

I Check/tighten every match

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Power TransmissionPins

I Stronger than set screwsI Fairly easy to use

I Can be tricky to get holecentred

I Weakens shaftI Hard to remove

I Tapered pins can be used,but they’re hard to findand tricky to use

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Power TransmissionKeys

I Very strong

I Does not significantlyweaken shaft

I Keying shaft requires specialcutter

I Can buy standardpre-keyed shaft

I Still need some way to holdgear and key from slidingalong shaft

I Often a good idea to haveset screw hold key in place

I Can have some backlash ifnot done properly

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Power TransmissionBolts

I Often underrated

I Very simple and easy to build

I Very strong

I Easily disassembled

I Most often used to attachsprocket/gear to wheel

I Can also be used betweensprockets/gears

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Chains

I StrengthI Switch to 3/8”?I Power argument: P = Fv

(power = force × velocity)I Power P is a constantI We want to reduce the

tensile force FI So. . . ?

I TensioningI Sprung tensioner or simple

block/rollerI Reduce backlashI Reduce probability of

chain becoming derailed

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

MotorsMotor Curves

FP801-005 Motor

MOTOR PERFORMANCE

0 50 100 150 200 250 300 350 400 450 500 550 600

Spe

ed (r

pm)

0

400

800

1200

1600

2000

2400

2800

3200

3600

4000

Effic

ienc

y (%

)

0

10

20

30

40

50

60

70

80

90

100

Pow

er O

ut (w

atts

)

0

40

80

120

160

200

240

280

320

360

400

Cur

rent

(am

ps)

0

10

20

30

40

50

60

70

80

90

100Constant Voltage: 12.0 V

Torque (oz-in)

Current (a)

Power Out (watts)

Efficiency

Speed (rpm)

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

MotorsMultiple Motors

I Only way to increase actualpower in drivetrain

I “But won’t the motors fighteach other?”

I As long as each motor isnot running faster thanfree speed, it iscontributing power

I Some motors mightcontribute more powerthan others

I Need to (roughly) matchmotor speeds if usingdifferent motors

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Computer Aided Design

I Usually used for complexand/or high-precision parts

I Not just a drafting tool – usefor design as well!

I See how parts go togetherI Check clearances between

componentsI Calculate mass of

subassembliesI Visualize mechanism

motionI Edit, restructure, and

redesign parts andassemblies

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Computer Aided Design

I Get familiar with a CADprogram before the buildseason

I InventorI SolidWorksI Pro/ENGINEER

I Think about “design intent”I Make sure you can modify

the design easily (becauseyou will)

I Use version control for CADfiles

I Peace of mindI Allow sharing of dataI Subversion, Autodesk

Vault

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Resources

I Mechanism Galleries, workshop presentationshttp://www.firstroboticscanada.org/site/resources

I White Papers, image galleries, discussion boardshttp://www.chiefdelphi.com

I Subversion (free, high-quality version control system)http://subversion.tigris.orghttp://tortoisesvn.tigris.org

I SDP/SIhttp://www.sdp-si.com

I McMaster-Carrhttp://www.mcmaster.com

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Resources (cont.)

I Boston Gearhttp://www.bostongear.com

I Use BostSpec 2 to search for gears (need to create freeaccount)

I Canadian Bearings (find local store)http://www.canadianbearings.com

I Metal Supermarkets (find local store)http://www.metalsupermarkets.com

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Questions?

I ian.e.mackenzie@gmail.com

MechanicalDesign

Ian Mackenzie

General Principles

Simplicity

Disassembly

Multifunctionality

Theory

Iteration

Weight

How To. . .

Power Transmission

Chains

Motors

CAD

Resources

Questions

Exercise

Exercise

Some ideas of things to look for:

I Simple solutions to complex problems

I Disassembly

I Multifunctionality

I Theoretical calculations required

I Physical principles

I Why a certain method of power transmission was used

I Chain design

I Why a certain material was used

I Why a certain type of component was used

I Why a certain type of structure was used

I Design tradeoffs (usually weight and something else)

I Why pneumatics used instead of motors, or vice versa

I BONUS: Design leftovers