Fire Away!

Our Trebuchet: 

Our design consists of 2 legs (40 cm by 13.cm) and an arm (58.5 cm by 4 cm) with a bolt attached on either side, one to pull down to launch and the other to attach rubber bands, we also have a metal axle to hold the arm in place with washers to keep the arm secure, also on our arm we have a nail to hold our projectile when being launched. On our base (86 cm by 33 cm) we also have another bolt connected to it, which holds the rubber bands in place. But the overall dimensions of our trebuchet is 86 by 33 by 66 cm.

Main selling points:

Power: The main things about our Trebuchet are the amount of rubber bands we use to maximize power and hopefully distance.

Pull back: We used a bolt attached to our arm to pull down the arm,which is a crucial part of our trebuchet because without it, it would be almost impossible to pull down, considering the force of the rubber bands.

Strudyness: since our legs and arms are rather thick and dense our strength of the wood is very good as well, which minimizes breaks and cracks.

8 Modifications:

Amount of Rubber Bands:

At the start we used a good amount of rubber band, but then we learned more rubber bands mean more power so we started to pack more and more on our trebuchet.

Size of Arm:

At the start our arm wasn't very good, it was bulky and rather heavy, so we got a new one that is way thinner and lighter weight, which is easy for the rubber bands to “fling” resulting in more distance.

Size of String:

At the start we just used a decent size clay ball, but towards the end we notice everyone is using strings attached to their projectile so we did the same, and since we now know the 3 inches it the best size for the string that's just what we did.

Size of projectile:

At the start we used any piece of clay we could find, but after the research we now know that the weight of the projectile matters greatly on how far it launches, so we used a projectile of about 5 grams. 

Decreased friction:

To decrease friction and to hopefully increase distance we widened the hole for our axle because with less friction means less energy consumed due to heat and possible further distance.

Axle height:

When we replaced the legs we also had to make a new hole for the axle, so we decided to make it higher up so the projectile will start higher which would lead to the projectile taking longer to fall, resulting in more distance.

Placement of Projectile:

At the start we use a cup to launch our projectile, but the cup would always release the projectile late or at a weird angle resulting in an unconstant distance every time, so we decide to use a string and place it at the very end of our arm, and from the placement of the projectile it lead it to launch further.

Load to effort ratio of arm:

This is the hole where the axle goes through on the arm, and from our research we know that a hole in the middle for the axle would maximize our distance since the weight is equal on both sides. 

Calculations:

Mass of projectile: 0.016kg - this is the weight of the projectile that's being launched.

Horizontal distance: 21m - this is how far the projectile went. 

Time in air: 1.7s - this is how long the projectile was in the air

Vertical distance: d = ½(9.8) (0.66)^2  = 2.1344 = 2.13m/s - this is how far it falls

Horizontal velocity: v = 21/1.7 = 12.4m/s - how fast its moving horizontally 

Vertical velocity: v = (9.8)(0.66) = 6.468m/s - how fast it's moving vertically. 

Total Velocity: (12.4^2 + 6.468^2 = 14m/s) - In all how fast it was moving.

Release angle: tan θ = 6.468/12.35 = 27 ° - The angle in which the projectile is launched 

Spring constant: k = 30/0.035 = 857n/m - this is how quickly it increases force 

Initial Spring Potential Energy: PE = ½(857)(0.41)^2 = 81.61J - this is energy of the ball right before its fired.

Kinetic energy of the ball: KE = ½ 0.016 x 14^2 =  1.568J - this is energy when the projectile is launched.

Percent energy converted: 1.568/81.6 = 2% - this is the amount of energy converted when launched. 

My Poster:

Reflection:

Overall the projects had its ups and downs, but I still think everything worked itself out. One thing I did well was being consistent and use my time efficiently and sufficiently and completing the proof of efficiently document on time. Another thing, I did well on was trying lead my group anytime I could to get the project done.

However, there were also a few things that didn't go as smoothly. One thing we could improve for our design is how the rubber band always either break or fly off our machine after every launch. Another thing that wasn't ideal was the thickness and length of our base, first off it made it hard to transport and plus it was difficult to get a nail to stay.