MASTER ROSHI TOLD GOKU & FRIENDS THAT THEY WILL NOT APPRECIATE THEIR POWERS WITHOUT REALIZING THE STRUGGLES OF THE PAST WHEN PEOPLE HAD TO USE CATAPULTS TO INFLICT MAJOR DAMAGE ON THEIR FOES. THEIR TASK IN THE DOJO: TO MAKE A FUNCTIONAL CATAPULT!
intro:
The purpose of this project is to reinforce the topics covered in class. A catapult covers kinematics, forces, dynamics and an assortment of other topics. There are many different types of catapults, each having their pros and cons. The three main catapult types are: A Trebuchet, an Onager and a Mangonel
A TREBUCHET:
AN ONAGER:
An onager utilizes a completely different way of launching the payload. An onager launches the payload through the use of a rope (torsion). Its shooting arm has where the payload in placed on a sling/cup. There is another rod near one end of the onager, with rope holding the shooting arm. When the latch is pulled, the torsion powered rope launches the payload.
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A MANGONEL:
A mangonel is similar to an onager though it does offer some differences. It still a launches a payload through the use of a torsion powered rope near the base of the fulcrum. The telling difference is that a mangonel has a winding motion, where the user winds the fulcrum down to a certain point. The user can then let the latch go and the payload would shoot according to the force exerted of that point.
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After much debate, our group decided to build a modified onager. There is no extra rod however, it offers the same torque as an onager or a mangonel. It is very convenient and offers minimal weakness and the construction process is a a more straight forward. We also agreed that this kind of onager would make for a more pleasant final look as it offers simplicity but effectiveness.
possible questions:
1. Does changing the mechanism holding the payload change the displacement? (Sling/Bucket/Cup)
2. Does changing the angle of launch make a big difference on displacement?
3. Will the velocity of the payload launched affect the components?
4. What is the max range when launched with maximum torque on the rope?
5. Will the torsion of the rope weaken as multiple launches are incurred?
2. Does changing the angle of launch make a big difference on displacement?
3. Will the velocity of the payload launched affect the components?
4. What is the max range when launched with maximum torque on the rope?
5. Will the torsion of the rope weaken as multiple launches are incurred?
MATERIALS & cOSTS:
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sCHEMATICS:
This is the proposal of the torsion powered onager, split into three different views. Shown are the three different views of the proposal. There is the top view, the back view as well as the side view of the catapult
CATAPULT BUILDING
Day one
The required materials were acquired and we had began constructing our catapult. The first day of building concluded with a finished frame and base. We spent a lot of time verifying an adequate height, length and width for maximum effectiveness when launching. The frame was also not completely stable and required some tweaking for the next building day.
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Day two
The second day consisted of tweaking the base and frame so that it would be more sturdy. We also tied the nylon rope around the two sides and the wood roughly to get an idea of how our torsion device would function. We spent most of the time determining what we would use as a fulcrum. A piece of lumber used as the fulcrum was too heavy. After some debating we decided to use a hockey as it offers flex and is lightweight.
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Day Three
On the third day, we completed our torsion device and tested tennis ball holders. Upon the first test, the hockey stick rose up and hit the frame at a rapid speed generating a very loud noise. We were impressed by the amount of force. The next few hours were spent determining whether to use a sling or a cup. We wanted to be confident we had a working catapult that could consistently launch the payload at least 18-20 m so that there would 3 different ranges/2 different heights. After many vigorous testing sessions we decided to use a sling as its displacement when shot is much farther.
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Day four
On day 4, we realized that as sturdy as our catapult was, it getting beat up from rigorous testing. We immediately added temporary support frames for the duration of our testing. A problem that occurred on day 3 was that the ball would get stuck in the sling. To rectify this problem, we created a new sling which, consistently fired tennis balls 15-20 metres. The rest of the day was spent analyzing the catapult and seeing what could be improved to fire a greater distance. For the next building day we planned on experiment with different slings and retying our torsion device more efficiently.
Day Five
Due to the extension, we decided we didn't have to settle for less. We took all of things we learnt from the errors of our first catapult and began building a new one. With our increased confidence in our wood working skills, we rapidly finished the base mostly reusing most of the materials from the first catapult. This time, we used a smaller width so we could get more out of nylon rope and make a more efficient torsion device.
DAY SIX
On the sixth day, we added support frames to our second catapult were added, although due to some issues with our drill and a double the amount of wood required to drill through, it was difficult to drill holes into the frame for the torsion device. After obtaining a more powerful drill, the holes were finally completed and we began the torsion bundle. We quickly tied the rope and found that this catapult was worse than our old one in terms of power. After lots of trial and error with no results, we called it a day and decided to try again the next day.
DAYS Seven-NINE
The next three working days consisted of retying the catapult rope multiple times in order to get better torque. After multiple hours of work with no results, we finally realized that the reason the catapult was weak was because the handles weren't turned enough. Some screws were causing friction and limiting our torque. We removed the screws, and taped the wood there instead. Within the next 30 minutes after retying our torsion bundle, we had an EXTREMELY high amount of torque. Over the next 2 hours of testing, part of the frame broke near the holes for the torsion bundle. The force of the rope caused the screws to horizontally rip out of the the whole block of wood.
DAY TEN
We made rapid progress on tenth day, we quickly repaired the broken catapult, retied our torsion bundle, and added screws everywhere to make it more stable. We also tested multiple alternative slings but realized that our previous sling was best. We also experimented with the length of the sling to optimize distance. While testing, we achieved consistent 30 metre shots. The highest one was 33 metres. Although the placement of the sling was a big factor as if it was not placed right, the ball would get stuck in the sling or go too high.
DAY ELEVEN
On this day, we were satisfied with the distance the catapult fired, however there was no launch mechanism and the catapult was not elevated such that its handles could turn without placing blocks of wood beneath it. We also found that the catapult's impact protection was weak. The stick was taking a major beating from all of the firing. We started by elevating the catapult by putting blocks on the front. After that, a block of sponges were taped on the point of impact on the catapult frame. The next two hours were spent devising a plan for the launch mechanism. We wanted to create a system where we could pull rods from different heights to initiate launches however, we were lacking materials to execute that idea. Instead, we created a holder for the stick at it's lowest point and attached a rope to the stick. Upon pulling the rope, the stick would come out of the holder launching the tennis balls into the air. The launch mechanism worked well however the furthest shot fired during testing was 31.3 metres, a bit less than the 33 metres of the previous testing day.
End Result
Although the catapult fired the furthest in the two classes, it took an extremely long amount of time to build due to lots of trial and error. Multiple errors occur and the amount of things which need to be accounted for to maximize the shooting range is very high. Things such as the width of the frame being too wide to use the rope efficiently, and the friction between screws and handles limiting the torque were things that we had never even thought about. The majority of our time was trying to find solutions to the problems caused as a result of these issues and when that failed, the rest of the time was dedicated to looking for the root of the problem.
Overall, despite being a complete struggle, it was a great experience which improved our wood-working skills and our knowledge of launching projectiles with catapults which could become useful in life during future physics projects in high school and beyond.
Overall, despite being a complete struggle, it was a great experience which improved our wood-working skills and our knowledge of launching projectiles with catapults which could become useful in life during future physics projects in high school and beyond.