SECME Mousetrap Car Originally prepared by: Brad Nunn BSIE Purdue University Program Manager - Citrix 10/1/2005 UPDATED: September 2011.

SECME Mousetrap Car

Originally prepared by: Brad NunnOriginally prepared by: Brad Nunn

BSIE Purdue University Program Manager - CitrixBSIE Purdue University Program Manager - Citrix

10/1/200510/1/2005

UPDATED: September 2011UPDATED: September 2011

Performance RulesPerformance Rules Refer to Mousetrap Car Refer to Mousetrap Car

Construction and Construction and Operation RulesOperation Rules

BailBail• dondon’’t cut or remove or t cut or remove or

add to itadd to it• OK to straightenOK to straighten

TerminologyTerminology

Potential to kinetic Potential to kinetic energy transferenergy transfer

TorqueTorque AccelerationAcceleration SpeedSpeed MomentumMomentum FrictionFriction

DesiredDesired OutcomesOutcomes

A small car that travels 2500 cm A small car that travels 2500 cm quickly and doesnquickly and doesn’’t weigh mucht weigh much

A gradual transfer of energy that has A gradual transfer of energy that has just enough torque to establish just enough torque to establish motionmotion

A sustained transfer of energy that A sustained transfer of energy that delivers sufficient momentum to delivers sufficient momentum to cover the distancecover the distance

Wheel DesignWheel Design

Wheel diameterWheel diameter

Wheel DesignWheel Design

Wheel ConstructionWheel Construction

Rubber bands around wheels for tractionRubber bands around wheels for traction

Axle DesignAxle Design Axle diameter and mechanical advantageAxle diameter and mechanical advantage

Simple ratio of diameters Simple ratio of diameters For distance cars use the smallest axle For distance cars use the smallest axle

that provides sufficient mechanical that provides sufficient mechanical advantage to drive a large wheeladvantage to drive a large wheel

Glue at least one drive wheel to axle Glue at least one drive wheel to axle

Two Step AxleTwo Step Axle At start, use the thick part of the axle for At start, use the thick part of the axle for

increased torqueincreased torque Once rolling, use the thin part of the axle Once rolling, use the thin part of the axle

for more distance for more distance

Wheel and Axle DesignWheel and Axle Design Minimize friction lossMinimize friction loss

Lubrication – silicone or graphite Lubrication – silicone or graphite powder – WD-40 not recommendedpowder – WD-40 not recommended

Construction TechniquesConstruction Techniques Releasing the drive string from an axle to allow Releasing the drive string from an axle to allow

coastingcoasting

Being able to disconnect drive strings on either Being able to disconnect drive strings on either end might make it easier to wind a car with a end might make it easier to wind a car with a more complex pulley or gear drivemore complex pulley or gear drive

Construction TechniquesConstruction Techniques Creating an axle hook on a solid shaftCreating an axle hook on a solid shaft

Construction TechniquesConstruction Techniques

Simple, easy to Simple, easy to tie knotstie knots• SurgeonSurgeon’’s Loop – s Loop –

useful for useful for making a loop at making a loop at the end of a the end of a stringstring

Another Axle HookAnother Axle Hook

• Plastic wire tiePlastic wire tie

Prepping the TrapPrepping the Trap

• Parts of the trap that are OK to removeParts of the trap that are OK to remove

• DonDon’’t cut the bail!t cut the bail!

Super Glue – Gel ControlSuper Glue – Gel Control

• Safety first! (immediate clean up with Safety first! (immediate clean up with soap and water, goof-off, nail polish soap and water, goof-off, nail polish remover)remover)

• Gel Control formula isnGel Control formula isn’’t runny – a little t runny – a little goes a long way (and dries faster)goes a long way (and dries faster)

Making the FrameMaking the Frame

• Align the axle holesAlign the axle holes

• Not the ends of the side railsNot the ends of the side rails

PrototypingPrototyping

What problems were encountered?What problems were encountered? What solutions were effective?What solutions were effective? What can be done for further What can be done for further

improvement?improvement?

Maximizing Axle Maximizing Axle RotationsRotations

Options to control torque, acceleration, Options to control torque, acceleration, speed, and number of rotationsspeed, and number of rotations• LeversLevers• PulleysPulleys• GearsGears

Use of LeversUse of Levers

• Length of lever vs. torqueLength of lever vs. torque

Use of LeversUse of Levers

• Position of lever arm for max torque at Position of lever arm for max torque at startupstartup

Use of LeversUse of Levers• Torque (and acceleration) due to use of a leverTorque (and acceleration) due to use of a lever

• A simple demonstration of levers and torqueA simple demonstration of levers and torque

Use of LeversUse of Levers

• A good distance carA good distance car

Cars with LeversCars with Levers

Cars with LeversCars with Levers

Cars with LeversCars with Levers

Car with PulleysCar with Pulleys

Car with PulleysCar with Pulleys

• A simple pulley demonstration…A simple pulley demonstration…

Use of GearsUse of Gears• Why are gears generally used?Why are gears generally used?

Transmit torque from one shaft to anotherTransmit torque from one shaft to another Increase or decrease the speed of rotationIncrease or decrease the speed of rotation Reverse the direction of rotationReverse the direction of rotation

• Why are gears useful in this applicationWhy are gears useful in this application SmallSmall LightweightLightweight Significant multiplications possibleSignificant multiplications possible Enables unmodified mousetrap bailEnables unmodified mousetrap bail

GearsGears GearsGears

A simple gear demonstration…A simple gear demonstration… gear-animation[1].swf

Gear TrainsGear Trains

Compound gear trains using double Compound gear trains using double spur gearsspur gears

A simple gear train demonstration…A simple gear train demonstration… geartrain-animation[1].swf

Cars with GearsCars with Gears

Cars with GearsCars with Gears

Cars with GearsCars with Gears

Cars with GearsCars with Gears

Cars with GearsCars with Gears

DiscussDiscuss limitationslimitations

What are the limitations with the use of a What are the limitations with the use of a lever?lever?

What are the limitations with the use of What are the limitations with the use of pulleys?pulleys?

What are the limitations with the use of What are the limitations with the use of gears?gears?

OptimizationOptimization Use rubber bands on the wheel surface for Use rubber bands on the wheel surface for

traction?traction? Reduce size and weight?Reduce size and weight? Use axle bushings to reduce friction?Use axle bushings to reduce friction? Use guides/bushings for string alignment?Use guides/bushings for string alignment? Maintain alignment of axles and wheels? Maintain alignment of axles and wheels? Maintain alignment of shafts/pulleys/gears? Maintain alignment of shafts/pulleys/gears? Use the space between the wheels?Use the space between the wheels? Use the space above and below the trap? Use the space above and below the trap? Figure out a faster way to wind it up?Figure out a faster way to wind it up? Lube the axles with powdered graphite?Lube the axles with powdered graphite?

Drawing GuidelinesDrawing Guidelines

Views – Front, Top, Side (RH rule)Views – Front, Top, Side (RH rule) ScaleScale Hidden linesHidden lines Center linesCenter lines Dimension linesDimension lines Identify componentsIdentify components Title BlockTitle Block Engineering paper = VellumEngineering paper = Vellum

Most importantMost important

Have Fun!Have Fun!