The South Florida Industry Partners Education Mousetrap Car Design Seminar

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The South Florida Industry Partners
EducationMousetrap Car Design Seminar

• Presented by Glenn N. Cunningham, P.E.Senior
  AssociateHazen and Sawyer, P.C.

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Objectives of the Design Seminar
To define and explore concepts of the SECME
Mousetrap car enabling our students to

• Know the elements of the design required
• The Technical Report
• The Technical Drawing
• The Competition
• To exchange ideas in a common forum - industry,
  college, coordinators, parents and students

• Develop critical thinking skills, a solid science
  and math foundation with practical application
  and competitive excitement
• Design and build a mousetrap car that satisfies
  the rules
• Know the rules and scoring formulas

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What is a mousetrap car?

• Opportunity to learn elements of a good design
  while experiencing the thrill of competition
• Car with the body of a mousetrap propelled by the
  force of a spring
• Not a mice catcher
• Economical way to complete a design for a few
  dollars/unit
• Your ticket to Nationalsas a winner

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What are the components of a mousetrap car?

• Victor mousetrap
• Three or four wheels
• Gears (driver and follower gears)
• Bail and bail string
• Washers and plastic tubing ends
• Creativity and practice

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What does the mousetrap car look like?

• Mousetrap on wheels?
• NASA moon buggy?
• Anything your imagination wants it to look like
• Your creativity will make the difference

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An approved mousetrap car does not look like
these

• Mousetrap base cannot be altered in any way
• No batteries or external power is permitted
• The VICTOR plastic model mousetrap is not allowed
• Refer to the Survival Guide 2003-2004

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How does the mousetrap car work?

• The spring on the mousetrap car is tensioned
  (energized) by winding the bail-string unto the
  drive-shaft of the driver mechanism
• When released, the tensioned spring causes
  angular rotation on the drive-shaft, thus turning
  the rear wheels and producing linear motion on
  the mousetrap car

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What are gears?

• Toothed wheels simple machines
• Most common are spur gears (commonly used on
  mousetrap cars)
• Used to transfer force, increase or reduce linear
  distance traveled, increase or reduce speed, and
  change direction of rotary motion

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Why do we need gears? Consider a mousetrap car
without gears

• The energy stored in the spring is released into
  the wheels in an instant, producing a big bang,
  and spinning wheels trying to move the car at a
  high speed
• The result is usually a fast start and not much
  distance covered

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Why do we need gears? Consider a mousetrap car
with gears

• The energy stored in the spring is released in a
  steady controlled way
• The result is usually a constant speed and more
  distance covered

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How do gears work? - Consider a design using
two gears
The large gear is the driver gear and is mounted
on a drive-shaft
The small gear is the follower gear and is
mounted on the drive wheel axle
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How do gears work? - Consider a design using
two gears

• The driver gear is a 40 tooth spur gear and the
  follower gear is a 8 tooth spur gear
• The gear ratio is.408 or 51
• A gear ratio of 51 means that every-time the
  bail-string turns the drive-shaft, the gears
  produce five revolutions on the wheels
• Therefore, the car has the potential to travel
  five times the distance of a car designed
  without gears

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How does gear ratio relate to distance traveled?

• Consider same design using two gears
• Driver gear 40 tooth follower gear 8 tooth
• Total gear ratio 51
• Diameter of drive wheel 2.5-inch
• Linear distance traveled / revolution (2.5 x
  3.14) 7.85 inch/rev
• Converting, 7.85 inches X (2.54 cm/inch) 19.94
  cm/rev
• Target distance 25 meters 2500 cm
• Required drive axle rotation 2500 cm / (19.94
  cm/rev x 5) 25.0 rev

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Can we calculate how our mousetrap car is
likely to perform?

• Yes..We can calculate the expected performance
  of our car because
• We can design the length of our bail-string, gear
  ratio, wheel sizes, and calculate the expected
  distance traveled
• We know the length and weight of our car
• We can do the calculation !!

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What about the technical drawing and report?

• The Technical Drawing and Report are required as
  part of the submittal package without either
  the entry will be disqualified
• A good Technical Drawing and Report can earn 50
  points each (refer to Survival Guide 2003-2004)
• An entry could win the actual race, but lose the
  overall competition because of mediocre or poor
  performance in the Technical Drawing and Report
• Follow the rules in the Survival Guide
  2003-2004 - Every point earned may make the
  difference between first and second place

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What about the layout of the technical drawing?

• Sample layout

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Constructing a mousetrap car

• We are confident that everyone here can build a
  mousetrap car
• To demonstrate our confidence
• We are asking you , everyone, to build a
  mousetrap car
• . Starting NOW!!

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Building a mousetrap car materials required

• Mousetrap (wood victor)
• Balsa wood strips (1/4-inch sq.)
• Wood glue (super glue)
• Wood dowels (1/8-inch dia.)
• Leggo gears (40 tooth and 8 tooth)
• Wheels (2-inch and 1-inch dia.)
• Washers (type No 6)
• Tubing (1/8-inch inner dia.)
• Grease

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Building a mousetrap car tools required

• Tool box
• Hammer
• Small hand-saws
• Rulers
• Scissors
• Exacto knives (utility knives)
• Screw-drivers (flathead and phillips)
• Drill and drill-bits
• Drummels
• Pliers (needle-nose and standard)

• Soldering iron and solder
• Hot glue gun and glue sticks
• Tape measure
• Misc. attachments

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Building a mousetrap car a basic design

• A basic design, using gears, is presented to
  provide hands-on instructions on building a
  mouse-trap car.
• A basic design, not using gears, can also be
  completed by deleting Step No 5, Fourth Mark,
  and also noting that the Third Mark would
  become the location of the driver wheel axle

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Building a mousetrap car preparing the
mousetrap

• Hold mousetrap firmly on hard surface
• Remove all accessories not required(bait-hook,
  locking lever and fasteners)
• Use needle-nose pliers to open gap onloop at end
  of bail arm. Straighten bail carefully (bail
  will break at weakened 90-degreebends)

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Building a mousetrap car prepare wood-frames
axles, gears

• Cut 3 pieces for axles from the 1/8-inch
  dowel(two 9 cm long and one 10 cm long)
• Cut 4 pieces for car frames from the 1/4-inch
  balsa(four 21 cm long)
• Glue 2 pieces for the car frame together. Repeat
  this for the other 2 pieces, to form two
  1/2-inch x 1/4-inch pieces
• Label each car frames as shown T Top, B
  Bottom (on the 1/4-inch faces) and I Inside,
  O Outside (on the 1/2-inch faces)

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Building a mousetrap car mark wood-frames
axles, gears

• Holding one side of the car frame, (with O -
  Outside marking facing up),insert 4 markings in
  the following places
• First mark 1 cm from end of car frame Use an
  axle to make an impression into the frame, 2 mm
  below the center-line of the frame. (This is
  the location of the front wheel axle)
• Second mark 12 cm from same end of car frame
  (This is the location of the rear-end of
  mousetrap) Note that the red V is located at
  the rear-end of mouse-trap

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Building a mousetrap car mark wood-frames
axles, gears

• Continued..
• Third mark 15 cm from same end of car frame Use
  an axle to make an impression into the frame,
  2 mm above the center-line of the frame. (This
  is the location of the driver gear axle)
• Fourth mark To complete this, place the large
  gear over the 15 cm mark. With the large gear
  held in place, engage the small gear. Use an
  axle to make an impression into the frame, 2 mm
  below the center- line of the frame. (This is the
  location of the follower gear mounted on the
  rear wheel axle)

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Building a mousetrap car tape wood-frames
together

• Tape both frame pieces together, (making sure
  that the tape does not cover any of the
  impressions marked in No. 5)
• Both frames should be lined up with the
  markings,T - are together, B - are together, I -
  are inside, and O - are outside.

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Building a mousetrap car Putting the pieces
together

• Drill holes at centers of the three impressions
  (front wheel axle, driver gear axle and follower
  gear drive wheel axle), marked in No 5. Before
  removing tape, examine to make sure that holes
  are properly aligned
• Glue inside of first frame (glue on inside) to
  side of mousetrap
• Install gears, axles and second frame (hand-held
  in place) to verify proper alignment. (Note that
  axles should be at right angles to frames)
• Glue inside of second frame (glue on inside) to
  other side of mousetrap

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Building a mousetrap car Putting the pieces
together

• Align gears, test gear rotation and glue center
  of gear to axle. (Carefully apply 1 drop of glue
  only)
• Complete installation of wheels, washers and
  tubing ends. Test wheel rotation.
• Attach bail-string to bail and bail-string
  attachment to the driver axle. First,
  attach bail-string to closed loop at end of bail
  and cut bail-string to proper length, depending
  on the option selected for bail-string attachment
  to the driver axle Option 1 String
  over-lapping rap method. Holding end of string,
  wrap string around the driver axle,(by rotating
  the driver axle by hand), making sure that the
  succeeding wraps overlap the previous
  onesOption 2 - Loop and fixed attachment
  method. Form loop at end of string. Glue ¼-inch
  long dowel attachment to driver gear axle. Place
  string-loop over fixed dowel attachment and wrap
  string around axle,(by rotating the driver axle
  by hand)

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Building a mousetrap car Putting the pieces
together

• Check and verify proper alignment of components
• Test mousetrap car and make adjustments as
  necessary
• Great job!!!

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The finished product
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Store materials and tools in a safe area upon
completion
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The South Florida Industry Partners
EducationMousetrap Car Design Seminar

• CONGRATULATIONS and THANK YOU.
• You are absolutely the very best.

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Lets make it happen We support S.E.C.M.E.