Fire Away Project

Our Project:

Proof Of Efficacy:

Proof Of Efficacy

In the directions no dimension could be longer than one meter. When we designed our project this was a hard thing to remember, but we got all the dimensions under one meter. Our design for our trebuchet was to have two sturdy planks drilled into the baseboard. Then we used a pvc pipe as the arm of our trebuchet. The arm also has weights in the shorter side. The axle of our trebuchet was hammered into the drilled pilot holes. We also drilled a hole in the pipe and then had the other side of the axle hammered in. At the end of both sides of our pvc pipe were nails. One side was to hook the rubber bands and the other to affect the angle of the projectile. At the back of the board is another nail, that is there for hooking the other side of rubber bands.

Modifications:

1. Projectile Mass: It was decided that the mass of the projectile should be about 7 grams for the best results. If the mass is more or less then you probably wouldn't get the furthest distance. When the mass is excessively larger and heavier it wouldn't go very far and it would be harder to transport using the trebuchet. If the mass is too tiny or lower in mass it will get affected by the wind. This would all affect the velocity of the projectile causing it to not go as far or as fast.
2. Length of String: It was also decided that the best length for the string should be pretty long (21.5 cm) to have the best distance. When the string is longer it causes the clayball to swing more. Therefore it creates more momentum and helps the clayball to travel further.
3. Arm Ratio: We added weight to one side of our pvc pipe to create a more even ratio between the effort side and the load side of the pipe. We added this weight so it is a 1 to 1.25 ratio between the two sides.
4. Shape of Projectile: The shape of projectile was decided to be a smooth sphere, with small volume and high density. This shape was decided because after testing this shape of projectile lead to the projectile gliding through the air better.
5. Lubrication: After testing, the best lubrication decided for the metal axle is saliva. The saliva helped the axle become more smooth for the pvc pipe to spin on it. The saliva contains 90 percent water and 10 percent mucus.
6. Number Of Rubber Bands: It was decided that the best number of rubber bands is 5 rubber bands. This amount of rubber bands was the perfect amount for the greatest distance. Too little rubber bands caused a greater height but not distance. Too many rubber bands caused very high height as well, but again not enough distance.
7. Rubber Band Placement: The placement of the rubber bands was decided best as 4 inches behind the legs of the trebuchet. This increased the tension of the bands and helped shoot the projectile the farthest.
8. Nail to improve Launch Angle: We placed the nail peeking out at the end of the load end of the pvc pipe. This nail helped direct the angle of the projectile when it was launched off of the arm. The nail helped shoot the projectile more forward and not as high in the air.
9. Calculations:

Answer: Explained

Mass of projectile=

Horizontal Distance= 27 meters

This is about 88.58 feet

Time in Air= 2.34 seconds

½ rising and ½ falling

Vertical Distance= 5.73 meters

This is about 18.79 feet

Horizontal Velocity= 11 meters per second

This is about 36 feet per second

Vertical Velocity= 11.46 meters per second

This is about 37.5 feet per second

Total Velocity= 11.95 meters per second

This is about about 39.20 feet per second

Angle of Release= 45 degrees

This is a vertical angle

Spring Constant= 116 newtons per meter

This is about 7.94 pounds per foot

Initial Spring Potential Energy= 12.4 J

This is about 9.14 foot-pound

Kinetic Energy of the ball= 0.95 J

This is about 0.700 foot-pound

Percent Energy Converted= 7%

Most energy is lost to moving the arm rather than the projectile.

Selling Points:

I would say some of the main selling points of our design are that our trebuchet was first built with this one idea of what we wanted it to look like. After we created that we then modified it. The modifications were done with data, research, and many trials. Our trebuchet was very consistent throughout the process. After all of the modifications our trebuchet was even more consistent, because we used the advice and data given to us by our classmates. We tried new rubber bands, new projectiles, etc. In the end we really stepped up our trebuchet and it is a very good trebuchet for what needs to get done.