Agenda

• What is "Punkin Chunkin"?
• Chunker styles
• Safety
• Physics
• Get started!
• Q&A

Me

• Big maker nerd
  • LEGO Robo-Clippy, Bad AI In A Box, LED Lanyard
• Partner Solution Architect @ Microsoft (ex-Yahoo!, ex-Nortel)
• Trebuchet expert for Dude Perfect (S2.E6)
• Organizer of "SlingFest"
• Competed Punkin Chunkin

Address the Oliphaunt in the room

• Some people get siege weaponry information from social media

Vocabulary

From Wikipedia:

• Catapult - a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants
• Trebuchet - uses a rotating arm with a sling attached to the tip to launch a projectile
• A trebuchet is a type of catapult
  • e.g. All squares are rectangles, but not all rectangles are squares

Vocabulary

• Accuracy - ability to hit the intended target
• Precision - ability to hit same spot

History - Punkin Chunkin

• Annual event since 1985
• Organized by "World Championship Punkin Chunkin Association (WCPCA)"
• Cancelled and restarted multiple times due to injuries, legal and logistics issues
• 2023 was in Vinita, Oklahoma

History - Slingfest

• Annual event from 2011 - 2016 in DFW
• Last event had 1000+ attendees
• Local news coverage

Slingfest in Plano, TX

Air Cannon

If you ever built a potato gun or at least had the opportunity to shoot one, Air Cannons at the annual Punkin Chunkin are the big daddy of potato guns. Using compressed air, nothing flamable, these machines shoot pumpkins over 4,000 feet

University of Delaware video example

Centrifugal

These machines build up inertia in an circular motion and have ways to release the pumpkin at the optimal trajectory for an outstanding distance shot.

NOTE: Centrifugal force is a fictitious force and is actually an "inertial force".

Bad to the Bone video example

Torsion (e.g. Onager)

A Torsion machine is any device that uses twisted rope as its primary source of power. It relies on a rope that works by torsion or twisting. The rope stores mechanical energy when it is twisted. The amount of force it releases is proportional to the amount it is twisted.

Trebuchet - History

French for "overturn".

Earliest ones seen in China ~4th century BC (powered by men on ropes: traction trebuchet). Counterweight replaced people ~12th century.

Trebuchet

Modern trebuchets are powered by gravity, and use a counterweight attached to an arm to swing the ballistic attached to a sling around and release at an optimal angle.

Trebuchet video example

Fixed Counterweight Trebuchet

• Weight is attached directly to the arm
• Weight drops in an arc

Hinged Counterweight Trebuchet (traditional)

• Weight is atached to a pivot point on the arm
• This enabled a better "drop" of the weight
• Frame on wheels helps ensure more force is delivered to ballistic
• OG Hurler. All other designs are modern inventions

Floating Arm Trebuchet

Example - Slingfest
Example - Slingfest

Credit: LanceMakes @ Instructrables

MURLIN

Example - Slingfest
Example - Test shot

Walking Arm

A fun, simple, weekend project to toss tennis balls.

Human Powered

Machines can use any kind of stored energy that can be stored by a single person in two minutes.

Hamster wheel example

Colossal Thunder

• Built by Corey Winesburg + his welding students in OK
• Won Punkin Chunkin student division + Adult Trebuchet record holder (3377 feet, 2019)
• Split counterweight

Example
OK TV

Safety

• "Hourglass of Danger"
  • e.g. danger zones of a horse
• Invest in good firing mechanisms
  • e.g. snap shackles
• Treat loaded like loaded gun
• Pre-flight checks
• AVOID DRY FIRING (Like a bow and arrow)
• Check structrual integrity after each launch

Safety example

Pre-Flight Checks

Example:

• Safety on
• Ballistic loaded properly
• No twisted or obstructed rope
• Range is clear
• Nothing valuable in "cone of danger"

Physics

• Guinness world record: pneumatic cannon at 5,500+ feet
• Pie-ing a pumpkin (i.e. "pumpkin pie in the sky")

Pumpkins

• For large chunkers, structural integrity is important
  • e.g. Chunk Norris sorted 5000+ pumpkins and brought ~50
• Popular varities: La Estrella, Calabasa Verde, Fairytale
• WCPCA weight ranges rules:
  • Adult Classes: 8-10 lbs.
  • 11-17 Classes: 4-10 lbs.
  • 10 & Under Classes: 2-4 lbs.

Factors in building

• Release Angle
• Distance of axle to counterweight and sling
• Length of sling
• Materials used
• Rope will stretch
• Weather
• ...

How/where do I get started?

• Pick a design
  • Recommendation: Hinged counterweight (10 lbs)
• Start small
  • Recommendation: Baseball (5 oz) or Tennis ball (2 oz)
• Experiment + Learn
  • Recommendation: Outside (200 feet)
• Go bigger
  • Recommendation: Safety

Skills

• Basic woodworking
  • Measure, cut, join
• Knots
  • Knot 3D app
• Basic math
  • Find midpoints, calculate angles
• Project planning
  • Kanban board
• First Aid

Tools & Materials

• Saws (hand, circular, compound miter, table)
• Speed square
• Levels
• Clamps (SO MANY CLAMPS)
• Drills (standard, impact)
• Markers (carpenter pencils)
• Workbench (Simpson strong-tie)
• Marine tools (quick release snap shackle, marine rope)
• Digital angle finder
• Local Makerspace

Lumber

• Get started with Common boards (e.g. pine) from Home Depot / Lowes
  • Don't get treated wood (arsenic)
• Listed in depth and width (e.g. 1x3, 2x4, 1x8, etc.)
• Board is cut THEN planed (to make straight-ish)
  • e.g. 2x4 is NOT 2"x4". Actually about 1.5" x 3.5"
  • e.g. 1x4 is .75" x 3.5"
• Pilot holes are your friend

Pro Tips

Think in terms of a constructing a vessel and label pieces accordingly

• Foreward = where the ballistic is directed towards
• Stern / Aft = backside, opposite of foreward
• Port = When facing forward, on the left
• Starboard = When facing forward, on the right

Ready to build?

• Reddit - /r/trebuchet
• Reddit - /r/PunkinChunkers
• Facebook - Texas Trebuchet
• Your local makerspace
• 2024 Pumpkin Chunkin Events and Festivals
• Near Dallas? Nov 2nd in Lewisville! (Contact me)

FAQ

• How big should I make my arm/sling/counterweight/etc.?
  • Virtual Trebuchet
• How many people should I have on my team?
  • Two Pizza Team Rule
• Can my ballistic be too light?
  • Yup! Foam doesn't launch as nicely as tennis ball
• Can my ballistic be too heavy?
  • Depends on your objective...

Q&A

Slides available at:

https://lastcoolnameleft.github.io/how-to-punkin-chunkin/