Gao Guangyan Desmond Chan Ng Kia Boon Daniel Yip Raffles Institution

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NUS Physics Open House Projectile Competition
Gao GuangyanDesmond ChanNg Kia BoonDaniel
YipRaffles Institution

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Objectives

• To create a device propelling a projectile
• With a target range of 80 metres
• Furthest possible distance for the maximum
  points
• Device must be
• Accurate
• Consistent
• Method
• Consider options and conduct experiments
• Analyse and evaluate them

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Design Consideration

• Factors to Consider
• Distance (Enough power for a range of 80m)
• Projectile Size (Must consider projectile
  dimensions)
• Cost (Feasible to build financially)
• Portability (Not too bulky and easy to
  transport)
• Consistency (Consistently hit 80m accurately)
• Elegance (No unnecessary sophistication)

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Design Consideration

• Medieval Siege Weaponry k
• Trebuchet
• Able to propel projectile far if made correctly
• Not consistent due to nature of propulsion
  (sling)
• Onager
• Similar to Trebuchet / but uses torsion bundle
• Powerful yet small in size
• But not consistent

Small-scale onager model constructed to test for
feasibility
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Design Consideration

• Medieval Siege Weaponry k
• 3. Ballista
• Cross between a crossbow and an onager
• However, large model needed for 80m target
• 4. Crossbow
• Powerful crossbow required
• Projectile subjected to external influences
  (wind)

Small-scale crossbow model constructed to test
for feasibility
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Design Consideration

• Electro-Magnetic Acceleration
• Repulsion
• Several Options Thomsons Coil Gun, Railgun
  etc..
• Most common Railgun
• Requires
• Strong Rail system
• Extremely High Pulsed Current
• Pulse Capacitors
• Not suited for small scaling
• Very expensive
• Loud and Noisy operation

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Design Consideration

• Electro-Magnetic Acceleration
• Attraction
• Coil Gun Linear Asynchronous Motor
• Model Constructed Previously
• Powered by 729J at 450V
• Only 4.35 peak efficiency
• Relatively Expensive
• Projectile size too large
• Consistent and accurate
• But Large model required for 80m target too
  expensive to build

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Design Consideration

• Pressure Powered Propulsion
• Water Rocket
• Safe and relatively powerful device
• Difficult to hit our targeted 80m consistently
• Large body affected greatly by wind
• Operators might get wet
• Design commonly used
• Difficult to construct reliable watertight
  launcher

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Design Consideration

• Pressure Powered Propulsion
• Final Design Air Cannon
• Safe and relatively powerful device
• Similar to handgun or rifle, but pressures are
  lower
• Powered by compressed air (bicycle pump)
• Simple and elegant
• Original Design and completely self constructed
• Easy Operation and easy handling
• Comparatively Cheaper than other options
• Powerful, consistent, accurate.

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Accelerator Design
Pressure Powered Propulsion Final Design Air
Cannon
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Accelerator Design

• Construction Materials
• Final Design Air Cannon
• High Pressure Industry Class AW(VP) PVC pipes
  (rated 283psi)
• 1 Brass Ball Valve
• Bicycle Pumps
• Bicycle Tyre Valves
• Waterproof Plywoodboards for stand

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Accelerator Design

• Main Design
• Final Design Air Cannon
• 2 2 long 2 dia. Air tanks
• A 5 long 1 dia. Barrel
• Wooden base essential
• Gives accelerator stability and supports entire
  structure
• Projectile solid aluminium
• Less affected by wind due to mass

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Accelerator Design

• Operation
• Pumped using bicycle pumps
• Simple and easy to operate
• Device is muzzle loaded
• Flight Path
• Both Ballistic and Line of Sight paths possible
  due to power of the system.
• Low ballistic trajectory chosen
• Less affected by wind and other external
  influences

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Accelerator Design
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Physics Involved
Calculation of Output energy and projectile
velocity Air Tank Dimensions 2"dia 24" 2 
Barrel Dimensions 1"dia 12" 5  The barrel
cross section is therefore Pi r2
0.7854"2 Using Pi r2 h, we can calculate the
volume of the chambersAir Tank Volume
150.7964"3  gt  0.002472m3 Barrel Volume
47.12400"3  gt  0.00077225m3Total Volume
197.9204"3  gt  0.00324425m3
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Physics Involved
Calculation of Output energy and projectile
velocity We take the pressure to be 100psi,
projectile mass of 0.1kg The pressure changes
since air fills up the barrel which changes the
pressure. Since the volume of air does not
change, We can use the formula P1 V1 P2
V2 100 PSI Air Tank Volume P2 Total
VolumeTherefore, P2 76.19635 PSI, and there
is a pressure drop of 23.80365 PSI Knowing these
values, we can calculate the force acting on the
projectile throughout the barrel.
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Physics Involved
Calculation of Output energy and projectile
velocity The force acting on projectile
Pressure Area100 PSI (start of barrel), 100
0.7854"2 78.54lb 357N  76.19635 PSI (end of
barrel), 76.2 0.79"2 59.845lb 272N The
average force acting on the projectile in the
barrel is therefore (357285.6)/2 314.5N When
there is force and mass, there is acceleration.
And where there's a lot of force, there is a lot
of acceleration! Using the formula Fma,314.5
0.1 aa 3145ms-2
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Physics Involved
Calculation of Output energy and projectile
velocity And using the formula d ½ at2,1.524
metres ½ 3145 t2Therefore, t
0.0311313sTime taken for the projectile to
travel out of the barrel Hence, using these
values, Velocity Acceleration Time,
Thereforev 3145 0.0311313Velocity
97.90791ms-1  gt  352.4685km/h! And because K.E.
½mv2,Energy ½ 0.1 97.907912Energy
479.29Joules.
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Difficulties Limitations

• Lack of funding
• Could not construct more sophisticated device
• Lack of time
• Could not carry out more experiments
• Lack of testing grounds
• Difficult to test out projectile device (large
  area, at least 80m long required)

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Thank you.