MESAMESAMouse Trap Powered CarsMouse Trap Powered Cars

Basic Competition RulesBasic Competition RulesGreatest distance travelled Greatest distance travelled without leaving 6-foot wide trackwithout leaving 6-foot wide trackZero alteration of mousetrapZero alteration of mousetrap– do not take the spring apartdo not take the spring apart– do not drill holes in or paint the do not drill holes in or paint the

traptrapexcept screw attachment holesexcept screw attachment holes

– trap lock must be working and trap lock must be working and sprung with a pencil or similar sprung with a pencil or similar objectobject

Basic Car DesignBasic Car Design

Advanced Car Design

Physics of Mousetrap CarPhysics of Mousetrap CarFriction forcesFriction forces

DragDrag

AccelerationAcceleration

TorqueTorque

MomentumMomentum

FrictionFrictionRubbing forces on moving partsRubbing forces on moving partsEffect: slows car and prevents Effect: slows car and prevents maximum distancemaximum distanceCaused by:Caused by:– excess wheel to road contactexcess wheel to road contact– poor wheel alignmentpoor wheel alignment– various parts rubbing when in various parts rubbing when in

motionmotion

Wheel to road contactWheel to road contactSkinny wheels incur less Skinny wheels incur less friction than wide wheelsfriction than wide wheels

““total surface area” of all total surface area” of all wheelswheels

Skinny Wheels Skinny Wheels Skinny Wheels work best

Poor Wheel AlignmentPoor Wheel AlignmentAxles should be aligned Axles should be aligned perpendicular to car; if not, perpendicular to car; if not,

Cars veers to right of leftCars veers to right of left

Excess friction between front Excess friction between front and back axlesand back axles

Moving parts rubbingMoving parts rubbingAxles rubbing on car bodyAxles rubbing on car body

Axles rubbing on mounting Axles rubbing on mounting screws or holesscrews or holes

Lever arm against bodyLever arm against body

String against body or axleString against body or axle

Wheels against bodyWheels against body

DragDragAnything that slows or stops Anything that slows or stops the carthe car

Such as:Such as:

FrictionFriction

Parts hanging off carParts hanging off car

Wide lever arm or wheelsWide lever arm or wheels

AccelerationAccelerationGetting the car moving with trapGetting the car moving with trap

Strongest possible residual Strongest possible residual strength in mouse trapstrength in mouse trap

Optimum lever-arm to car length Optimum lever-arm to car length ratio (also consider trap position)ratio (also consider trap position)

Too long or short of lever arm Too long or short of lever arm reduces potential accelerationreduces potential acceleration

Friction reduces accelerationFriction reduces acceleration

TorqueTorque Getting power to the wheels: Getting power to the wheels: ability to get car movingability to get car moving Too much torque = Too much torque = less less distance (wheel spin)distance (wheel spin) Too little torque = car will not Too little torque = car will not

movemove Torque altered by changing Torque altered by changing power arm angle to axlepower arm angle to axle Firm string to axle attachment Firm string to axle attachment

MomentumMomentum Keeping the car moving after Keeping the car moving after

acceleration phaseacceleration phase

less friction = greater less friction = greater distancedistance

the heavier the car, the the heavier the car, the greater the momentumgreater the momentum

Long vs Short CarLong vs Short Car Long Cars:Long Cars:

less torqueless torque

less speedless speed

less less momentummomentum

much longer much longer acceleration acceleration periodperiod

Short Cars:Short Cars:

more torquemore torque

greater speedgreater speed

more more momentummomentum

shorter shorter acceleration acceleration periodperiod

Long Car

Short Car

Maximizing distanceMaximizing distance longest power arc longest power arc (arm length)(arm length)

ideal torque ideal torque

(mousetrap position)(mousetrap position)

largest wheel diameter largest wheel diameter (greatest distance per (greatest distance per wheel revolution)wheel revolution)

smallest axle diameter (most smallest axle diameter (most revolutions per inch of string)revolutions per inch of string)

2009

Long Arm

Large Wheel Diameter

Large Diameter wheels

Small Diameter Axles

Comes Down to Car withComes Down to Car with

trap not modified trap not modified

least amount of frictionleast amount of friction

maximizes design maximizes design acceleration capabilityacceleration capability

finds ideal torque for designfinds ideal torque for design

most possible momentummost possible momentum

stays on the trackstays on the track

Summary: Building TipsSummary: Building Tips

Large drive wheelsLarge drive wheels

Small drive axleSmall drive axle

Do not tie string to axleDo not tie string to axle

Axles perpendicular to carAxles perpendicular to car

Correct mouse trap relation Correct mouse trap relation to car lengthto car length

Connecting arm to trapConnecting arm to trap

Tip: Don’t tie string to axle

For More Info….

2002

Attaching axle to car

drrusshill@gmail.com

The End The End