With Daniel Ford and Maddie Cinelli
Our task was simple: build a launching device to make a projectile go as far as possible. Our trebuchet might not look like much, but it packs a punch. We spent 2 days building it and another 2 days modifying it and calculating technical specifications so we did not have a whole lot of time. Nonetheless I think my group and I did very well with this project and I am proud of our creation.
Trebuchet Proof Of Efficacy
Design Description
Base: 13.5x56x4cm
Tallest Point: 31.5 cm
Arm: 35.5x4x2cm
Legs: 28x4x2cm 9.5 cm apart
Axle: .75 cm thick
Front of Base to Leg: 25 cm
Back of Base To Leg: 28 cm
Axle to Firing side of the Arm: 22 cm
Axle to End of Arm With 5 Rubber Bands Attached: 11 cm
Launching Nail to Firing End of Arm: 37 cm
Axle to Rubber Bands on Arm: 12 cm
Axle to Firing end of Arm: 22 cm
We decided to use a firing rubber band attached to a different nail to shoot our trebuchet so we wouldn’t have to manually pull the arm back and let go. This allows for a more consistent firing distance.
Modifications
CLEAR Paragraph
The ideal string length attached to a 11.7 gram clay ball to make a projectile launch the farthest out of a trebuchet is 30 centimeters total, but when it is attached to the ball, it is folded in half so the distance from the nail on the trebuchet to the ball is 15 centimeters. We conducted an experiment where we modified the length of the string. The shortest length we used was 20 centimeters and the longest was 40 centimeters. The average distance the projectile traveled when the length of the string was 20 centimeters was 1.25 meters. The average distance the projectile travelled when the length of the string was 40 centimeters was 2.25 meters. With the length of the string being 30 centimeters, however, the average distance the projectile traveled was 3.75 meters. The longer the string is the greater distance the projectile travels in the same amount of time. This makes the projectile have a greater velocity. However, if the string is too long, when it is launched, the projectile drags along the ground, causing friction to slow it down. We found that a string length of 30 centimeters was the perfect middle-ground.
Technical Specifications
Time In The Air: 3.2 seconds
Horizontal Distance: 31 meters or 102 feet
Vertical Distance: 12.5 meters or 41 feet
Horizontal Velocity: 9.7 meters/sec or 22 mph
Vertical Velocity: 15.68 meters/sec or 35 mph
Total Velocity: 18.5 meters/sec or 41 mph
Spring Constant: 490 Newtons/meters (98 N/m per rubber band)
Potential Energy Of The Spring: 7.9 joules
Kinetic Energy Of The Projectile: 1.2 joules
Percentage Of Conversion Of Kinetic Energy To Potential Energy: 15%
Angle Of Release: 55 degrees
Advantages/Selling Points
Concepts
Time in Air: This represents the time the projectile was in the air after it was launched.
Horizontal Distance: This represents the distance lengthwise the projectile was launched.
Vertical Distance: This represents the maximum height of the projectile on its path of trajectory.
Horizontal Velocity: This is the velocity of the projectile horizontally or parallel to the ground.
Vertical Velocity: This is the velocity of the projectile going vertically.
Total Velocity: This is the final velocity that takes into account both vertical and horizontal velocities.
Spring Constant: This measures the strength of the spring of the machine. In our case this is the strength of the rubber bands.
Potential Energy of the Spring: This is the potential energy the spring has before launch.
Kinetic Energy of Projectile: This is the energy in motion the projectile has when launched.
Energy Conversion Percentage: This is the percent of potential energy transferred to kinetic.
Angle of Release: This is the angle at which the projectile left the trebuchet.
Base: 13.5x56x4cm
Tallest Point: 31.5 cm
Arm: 35.5x4x2cm
Legs: 28x4x2cm 9.5 cm apart
Axle: .75 cm thick
Front of Base to Leg: 25 cm
Back of Base To Leg: 28 cm
Axle to Firing side of the Arm: 22 cm
Axle to End of Arm With 5 Rubber Bands Attached: 11 cm
Launching Nail to Firing End of Arm: 37 cm
Axle to Rubber Bands on Arm: 12 cm
Axle to Firing end of Arm: 22 cm
We decided to use a firing rubber band attached to a different nail to shoot our trebuchet so we wouldn’t have to manually pull the arm back and let go. This allows for a more consistent firing distance.
Modifications
- Spacers: We added spacers on the axle the arm was on between the legs and the arm to minimize the unwanted wobble of the arm both as it fires and before.
- 10 Gram Projectile: We made our projectile 10 grams to make it easier for it to go farther. Less mass equals greater distance when the same force is applied to it.
- 60 Degree Release Nail: We modified our release nail to be slanted 60 degrees in the direction we were firing to make it easier to for the string to slide off the nail ultimately causing it to go farther.
- Thicker Rubber Bands: Instead of using the thin long rubber bands we switched to using the thicker rubber bands because they are stronger and have a greater spring constant.
- 15 Centimeter String From Ball to Nail: We used a 15 centimeter string because we wanted it to be long to maximize the distance traveled in the same amount of time as it is being fired to increase distance. However, if the string is too long, it would drag across the ground and create friction.
- Stable Legs: We made our legs more stable by attaching them to the base with more screws. This reduced the wobble of the legs which straightened out the axle. This made the swing of the arm smoother with increased the distance.
- 2 to 1 Arm Length Ratio: We made our arm ratio 2 to 1. The side of the arm that had the rubber bands attached to it was half as long as the side with the projectile. This increases the distance the side with the projectile goes as it is being launched over the same amount of time as the smaller side is being pulled down, so the projectile travels farther.
- 5 Rubber Bands: We used 5 rubber bands instead of one to multiply the spring constant by 5, which increased the speed of launch and, as a result, the distance.
CLEAR Paragraph
The ideal string length attached to a 11.7 gram clay ball to make a projectile launch the farthest out of a trebuchet is 30 centimeters total, but when it is attached to the ball, it is folded in half so the distance from the nail on the trebuchet to the ball is 15 centimeters. We conducted an experiment where we modified the length of the string. The shortest length we used was 20 centimeters and the longest was 40 centimeters. The average distance the projectile traveled when the length of the string was 20 centimeters was 1.25 meters. The average distance the projectile travelled when the length of the string was 40 centimeters was 2.25 meters. With the length of the string being 30 centimeters, however, the average distance the projectile traveled was 3.75 meters. The longer the string is the greater distance the projectile travels in the same amount of time. This makes the projectile have a greater velocity. However, if the string is too long, when it is launched, the projectile drags along the ground, causing friction to slow it down. We found that a string length of 30 centimeters was the perfect middle-ground.
Technical Specifications
Time In The Air: 3.2 seconds
Horizontal Distance: 31 meters or 102 feet
Vertical Distance: 12.5 meters or 41 feet
Horizontal Velocity: 9.7 meters/sec or 22 mph
Vertical Velocity: 15.68 meters/sec or 35 mph
Total Velocity: 18.5 meters/sec or 41 mph
Spring Constant: 490 Newtons/meters (98 N/m per rubber band)
Potential Energy Of The Spring: 7.9 joules
Kinetic Energy Of The Projectile: 1.2 joules
Percentage Of Conversion Of Kinetic Energy To Potential Energy: 15%
Angle Of Release: 55 degrees
Advantages/Selling Points
- Small, and easily portable.
- No need to pull back to fire, all you need to do is pull the firing rubber band off the nail.
- Launches the 10 gram projectile a consistently large distance.
- Stable legs that support the axle and arm which minimizes the wobble of the arm when firing.
Concepts
Time in Air: This represents the time the projectile was in the air after it was launched.
Horizontal Distance: This represents the distance lengthwise the projectile was launched.
Vertical Distance: This represents the maximum height of the projectile on its path of trajectory.
Horizontal Velocity: This is the velocity of the projectile horizontally or parallel to the ground.
Vertical Velocity: This is the velocity of the projectile going vertically.
Total Velocity: This is the final velocity that takes into account both vertical and horizontal velocities.
Spring Constant: This measures the strength of the spring of the machine. In our case this is the strength of the rubber bands.
Potential Energy of the Spring: This is the potential energy the spring has before launch.
Kinetic Energy of Projectile: This is the energy in motion the projectile has when launched.
Energy Conversion Percentage: This is the percent of potential energy transferred to kinetic.
Angle of Release: This is the angle at which the projectile left the trebuchet.