Catapult Project Part 2.doc - StickySituation - home

By Danny Henderson,2014-11-11 02:48
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Catapult Project Part 2.doc - StickySituation - home

    Best Potential Solution(s):

    ; Type of wood material we could possibly use: Cherry, Oak, Pine, Birch

    - Cherry wood splinters easily and it’s not that strong

    - Oak wood can be a little pricey

    - Pine wood is strong, and durable.

    - Birch wood splits easily, and it is not the strongest wood.

; Type of springs we could possibly use: spring, bungee cord

    - The spring may break easily, and once on the catapult it is hard to remove.

    - A bungee cord is preferred because it can be taken off.

    ; Type of catapult arm we could possibly use: long, medium, short

    - A long arm will be harder to control and it would use more wood.

    - A medium arm is preferred because is easy to control and will throw the tennis ball

    the perfect distance.

    - A short arm will be harder to control

; Type of catapult we could possibly use: trebuchet, onager

    - A trebuchet requires more strength and power to pull back. It is also very complicated,

    and contains more moving parts.

    - An onager catapult is less complex, and doesn’t have that many moving parts.

    ; Type of catapult base we could possibly use: hallow base, full base

    - Hallow base cost less, and uses less effort to make.

    - Full base uses more material and is a little harder to make.

    ; Don’t forget this is still possible solutions, so it does not necessarily

    mean we will use it, but it would make the best solution if we did.

    NOTE: Best possible solution is highlighted

    Page 24

Select an Approach:

Design Matrix:

    M or O Criteria Avani’s Brian’s Kyle’s Nicole’s Hybrid

    Design Design Design Design Design M Can throw from a 2 2 2 3 5

    distance of 4 feet.

    M Throw tennis ball at 3 3 4 4 5

    least 30 feet

    M The frame of the 4 4 4 4 5

    catapult is made of


    M Trajectory angle is 0 0 0 5 5

    drawn on the arm

    M That catapult is not 5 5 5 5 5

    taller than 24”

    M Catapult base is a 5 5 5 5 5

    max of 24 by 24


    M User safety 4 4 4 4 5 M Durability 3 3 3 3 5 O Appeal 5 5 5 5 5 O Cost 4 4 4 4 5 O Difficulty of 4 3 4 3 5

    building the


    M Dimensioned 4 4 3 4 5 O Neatness 5 1 1 4 5 M Drawn with straight 5 1 1 5 5


    TOTAL 53 44 45 58 70

    Page 25


    5- Fits the criteria the best ( This rating is the best there can be)

    4- Fits the criteria better than average standards 3- Fits the criteria okay (This rating may include meet the criteria, but not to the extent

    where it’s considered really good)

    2- Criteria falls below standards

    1- Does not fit the criteria at all

The ranking for possible solutions:

    1) Hybrid Solution- 70

    icole’s Solution- 582) N

    3) Avani’s Solution- 53

    4) Kyle’s Solution- 45

    5) Brian’s Solution- 44

    Page 26

Process Took to Choose Solution:

    We wanted to know why the other solutions couldn’t get a high score like the hybrid solution. So we looked further into the next highest ranking which was Nicole’s. We

    came to learn that her sketch was very well drawn and contained my positive aspects, but her sketch was hard to follow. Next we looked at Avani’s design. Avani’s sketch was

    also good with dimensions, but the arm had no angle. Then we looked at Kyle’s design.

    His sketch had no angle and was sloppy with no straight lines. Last, we looked at Brian’s

    design. Brian’s sketch followed the same tendency of no trajectory angle, and efficiency in drawing the sketch.

What solution we choose:

    1) Hybrid

The Following Solution Will Be:

    - Pine wood is strong, and durable.

- Bungee Cord it can be taken off.

    - Medium Sized Arm easy to control and will throw the tennis ball the

    perfect distance.

- Onager less complex, and doesn’t have that many moving parts.

- Hollow Base cost less, and uses less effort to make.

Why We Choose What We Did:

    We chose the hybrid solution because it had the highest score, and contained all the constraints. This solution contained a fully drawn catapult with correct dimensions, and a correct trajectory angle. According to the design matrix it was the best when it came to mandatory and even optional solutions. For example, optional solutions like appearance, and cost got the highest ranking possible. All, in all we think this sketch will provide us with the dimensions and constraints we need to successfully pass this project.

    Page 27

Develop a Design Proposal

Detail CAD Drawings:

Page 28

    Develop a Design Proposal

    Bill of Materials:



    Base Provides support for 5 Home Depot $3.25 $16.25

    catapult and allows it

    to be set down

    Frame Where the arm 2 Home Depot $2.50 $5.00

    revolver will be set

    Metal Hold back the arm 1 Home Depot $7.90 $7.90 Rod from firing at the

    wrong angle

    Cross Bar Provides support 1 Home Depot $5.30 $5.30

    between arm stands

    Arm Holds tennis ball and 1 Home Depot $5.60 $5.60

    throws it

    PBC Holds the pole to 3 Home Depot $7.50 $23.50 piping take the arm back

    Peg Stops the catapult 1 Home Depot $1.10 $1.10

    from firing

    Bungee Makes arm jerk 2 Home Free Free Cords forward

    String To rewind the arm 10 ft Home Free Free Eye hooks Holds bungee cords 5 Home Free Free

    in place

    Box of Holds pieces 1 Box of Home Free Free Screws together Screws

     Total Cost-


    Page 29

    Build Process

    The Base of the Catapult:

    ; Measure a piece of wood that is 16 inches long and cut it. The piece of wood

    should have the dimensions 1.5 by 3.5 by 16 inches.

    ; Repeat the step above 5 times.

    ; Using a screw, screw the base together using the four 16 inch pieces (the other

    piece will be a brace on the frame). When it is assembled, it should be 19 inches

    wide and 16 inches long.

    ; Put 2 eye hooks in the back of the base, one at 7.5 inches from the end, and one

    8.5 inches away. Both should be 1.75 inches off the ground.

    The Frame of the Catapult:

    ; Measure a piece of wood that is 20 inches long and cut it. The piece of wood

    should have the dimensions 1.5 by 3.5 by 20 inches.

    ; Mark a dot that is 6 inches above the bottom of the plank. Cut a hole through the

    dot so it makes a circle. The diameter of the hole should be 1.25 inches.

    stnd; Do the 1 and 2 step two times.

    ; Measure a piece of wood that is 14 inches long and cut it. The piece of wood

    should have the dimensions 1.5 by 3.5 by 14. This piece is the Cross Bar. ; Assemble the Frame by screwing the cross bar to the sides of the top of the frame

    height (refer to CAD drawings if help is needed).

    ; Screw the frame into the front of the catapult, 1.5 inches away from the front

    piece of wood.

    Attaching base and frame

    ; Line up frame 1.5 inches away from the front of the catapult.

    ; Mark a spot 2.75 inches away from the catapult. This should be in the middle of

    the board.

    ; Counter bore a hole .3 inches wide 1 inch deep.

    ; Use a 3/16 drill bit to drill a pilot hole 2 ? inches up into the wood ; Take the Screw and screw in, until secured firmly

    ; Repeat once more for the same side, then do twice on the other side

    The Arm and Arm Revolver:

    ; Measure a piece of PBC pipe that is 1.5 inch in diameter and 7.5 inches and cut it

    on the compound miter saw.

    ; Do this twice

    ; Plug both ends of the PBC pipe into a t section of PBC at either end of the top of

    the ‘t’

    ; Cut a 35 inch section of a wooden dowel that is 1.5 inches in diameter

; Put one end into the bottom stem of the ‘t’; glue this in with gorilla glue.

    ; Let glue set

    ; Let dowel rod fall and mark the spot where the middle of the 2 eye hooks are. ; Drill an eye hook on the mark

    ; To put in the holder of the tennis ball, drill a hole in the middle of a can with a

    3/16 inch drill bit.

    ; Using the hole as a guide drill through the hole of the can into the dowel, ? of the

    way through.

    ; Screw a screw in, using a Phillips head drill bit.

    Angle Gauge

    ; Start by placing a piece of wood next to the catapult this wood should hit the back

    of the base and the top of the frame

    ; Trace the edges of the frame and base onto the piece of wood.

    ; Cut along the lines with the compound miter saw

    ; Do steps above once more

    ; Put the arm at 75 degree angle and mark a spot .25 inches in front of it. ; Do this for the angles 60, 45, 30 and 15.

    ; Using a ? in drill bit, drill a pilot hole on every mark

    ; Unclamp and drill a .5 inch hole through each of the .25 inch pilot holes ; Clamp the two pieces of wood together

    ; Using a pencil, put a mark on the other piece of wood by putting a pencil through

    the ? inch holes on the wood

    ; Using a ? in drill bit, drill a pilot hole on every mark

    ; Unclamp and drill a .5 inch hole through each of the .25 inch pilot holes ; Attach the angle guide with the side with the higher angle cut on the frame,

    parallel to the right side of the catapult

    ; Drill a 3/16 inch pilot hole 1 inch away from the top of the angle guide, drilling

    on an angle

    ; Put a screw into the hole using a 3/16 inch drill bit

    ; Do the same for the bottom of the angle guide getting attached to the base of the


    ; Do the 4 steps above only having the angle guide on the left side of the catapult

Attach Bungee Cords:

    ; Using metal clips, attach two of them to the cross bar. They should be 5 inches

    from the side of the Cross Bar.

    ; Attach two more to the top of the catapult arm, using hooks with screws on the

    bottom to attach

    ; Put the Bungee cord hooks around the metal clips.

    Page 31

Test Plan:

For Trial 1,2,3,4, and 5 Use This Template:

    Straight Distance Right/Left Angle Safety Can Be Let Go

    Catapult Angle Traveled from Norm From 4 Ft.








For Ways to Correct/Modify Launch Template:

Catapult Ways to Correct/Modify Launch








    Page 32

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