Catapult Design Challenge – A Practical Engineering Analysis | 弹射器设计挑战

📚 Catapult Design Challenge – A Practical Engineering Analysis | 弹射器设计挑战 – 实战工程分析

Welcome to this case study walk‑through for Year 7 CCEA Engineering. We are going to follow the entire engineering process by exploring a classic hands‑on project: designing, building and testing a small catapult. This practical challenge will show you how engineers think, solve problems and improve their designs using real tests and data.

欢迎来到Year 7 CCEA工程学的案例实战演练。我们将通过一个经典的动手项目——设计、制作并测试一个小型弹射器——来完整经历工程流程。这个实践挑战会让你看到，工程师是如何思考、解决问题，并利用真实测试和数据来改进他们的设计的。

1. Introduction to the Challenge | 挑战介绍

The challenge brief: ‘Design and construct a working model of a catapult that can launch a 20‑gram projectile as far and as accurately as possible. Your catapult must be built using everyday materials such as lolly sticks, rubber bands, a plastic spoon and masking tape. You will need to record distance and consistency over ten trials, then propose and carry out one improvement.’

挑战任务书：“设计并制作一个能正常使用的弹射器模型，将20克重的抛射物发射得尽可能远且尽可能精准。弹射器必须使用日常材料，如冰棒棍、橡皮筋、塑料勺子和美纹胶带。你需要对十次试射的距离和一致性进行记录，然后提出并实施一项改进。”

This task mirrors what professional engineers do: they receive a design brief, work within constraints (materials, budget, time), and systematically test their creations. The catapult challenge introduces core ideas such as energy storage, trajectory and structural stability.

这项任务反映了专业工程师的工作：他们接到设计任务书，在约束条件下工作（材料、预算、时间），并系统地测试自己的作品。弹射器挑战引入了能量储存、弹道和结构稳定性等核心概念。

2. Understanding the Problem | 理解问题

Before picking up any materials, an engineer clarifies exactly what needs to be achieved. For our catapult, the key performance measures are range (how far the projectile travels) and accuracy (how close successive shots land to each other).

在拿起任何材料之前，工程师会先明确究竟需要达成什么。对我们的弹射器而言，关键性能指标是射程（抛射物飞多远）和精度（连续发射的落点有多靠近）。

We also need to think about constraints: we must use only the allowed materials; the catapult must be small enough to operate on a table; and we have just one lesson to build the initial version. These limits are similar to real‑world restrictions like weight, cost and safety regulations.

我们还需要考虑约束条件：只能使用给定的材料；弹射器必须小到可以在桌面上操作；而且我们只有一节课的时间来搭建最初版本。这些限制类似于现实世界中的重量、成本和安全法规等约束。

Finally, we ask: what scientific ideas will help? Energy transfer (elastic potential to kinetic), levers and the effect of launch angle are all relevant. Listing the important questions now saves time later.

最后，我们问：哪些科学原理能帮上忙？能量转换（弹性势能转化为动能）、杠杆原理以及抛射角度的影响都与此相关。现在就列出重要问题，可以为后面节省时间。

3. Research and Investigation | 研究与调查

Good design starts with research. We looked at historical catapults like the mangonel, which uses a torsion bundle of rope, and the Roman onager. We also examined simple rubber‑band powered launchers used in classroom models.

好的设计始于研究。我们研究了历史上的弹射器，比如使用扭绞绳束的投石机（mangonel）和罗马的野驴炮（onager）。我们还观察了课堂模型中使用的简易橡皮筋动力发射器。

From this research, we noted that three main types of small catapult are common: the tension catapult (stretching a band directly behind the projectile), the torsion catapult (twisting a band to spin an arm) and the trebuchet (using a counterweight and sling). However, a trebuchet is more complex and may not suit our materials.

通过研究，我们注意到小型弹射器通常有三种主要类型：张力式（直接在抛射物后方拉伸橡皮筋）、扭力式（扭转皮筋带动抛射臂旋转）和投石机式（使用配重和投石索）。不过，投石机式比较复杂，可能不太适合我们的材料。

We also researched the best launch angle. Physics tells us that, neglecting air resistance, 45° gives the greatest range for a projectile released from ground level. But our catapult releases from a raised arm, so the optimum angle might be slightly less. This research will guide our design choices.

我们还研究了最佳发射角度。物理知识告诉我们，忽略空气阻力时，45°角能使从地面发射的抛射物射程最远。但我们的弹射器是从升高的臂上发射，所以最佳角度可能略小于45°。这项研究将指导我们的设计选择。

4. Generating Design Ideas | 产生设计想法

Every member of the team generated at least two rough sketches. Idea A was a simple tension catapult: a plastic spoon glued to a lolly stick pivot, with the rubber band stretched between the spoon handle and the base. Idea B used a torsion system: a rubber band twisted through a hole, winding up an arm made from two lolly sticks with the spoon at the end.

团队里每个成员都至少画了两张粗略草图。想法A是简单的张力弹射器：塑料勺子粘在一根冰棒棍支点上，橡皮筋在勺柄和底座之间拉伸。想法B采用扭力系统：橡皮筋穿过一个孔并扭绞，带动由两根冰棒棍组成的抛射臂，臂端装有勺子。

We drew each idea and labelled the main parts: base, pivot, throwing arm, energy storage element and projectile holder. Quick sketches help communicate ideas without wasting time on perfect drawings. The variety of ideas gave us more options to evaluate.

我们画出了每个想法并标注主要部件：底座、支点、抛射臂、储能元件和抛射物托架。快速草图有助于交流想法，而不会把时间浪费在完美的绘画上。多样的想法为我们提供了更多的评估选项。

5. Selecting the Final Design | 选择最终设计

We compared the two designs using a simple decision table. The criteria included expected range, ease of construction, consistency and how easily we could adjust the launch angle.

我们用一个简单的决策表来比较这两个设计。评判标准包括预期射程、搭建难易度、一致性以及调整发射角的难易程度。

Criterion	Tension Catapult (A)	Torsion Catapult (B)
Expected range	Medium (good elastic stretch)	High (greater energy storage in twist)
Ease of construction	Very easy – few parts	Moderate – needs a strong pivot
Consistency	Fair – band may slip	Good – arm returns to same stop
Adjustable angle	Difficult (fixed band)	Easier (change stop position)

After discussion, we chose Design B, the torsion catapult, because it stores more energy in the twisted band and offers better consistency. This is a trade‑off: a little harder to make, but better performance.

经过讨论，我们选择了设计B，即扭力弹射器，因为它能在扭绞的皮筋中储存更多能量，并且能提供更好的一致性。这是一种权衡：制作稍难，但性能更好。

6. Planning and Materials | 计划与材料

With the design chosen, we listed all materials and the exact quantities we needed: 10 lolly sticks, 3 rubber bands (different thicknesses), 1 plastic spoon, masking tape, a ruler and scissors. We also wrote a step‑by‑step plan.

选定设计后，我们列出了所有材料和所需的具体数量：10根冰棒棍、3条橡皮筋（不同厚度）、1个塑料勺子、美纹胶带、一把直尺和剪刀。我们还写了分步计划。

The plan showed the order of assembly: first build a strong triangular base with lolly sticks and tape, then create a pivot using a rubber band threaded through the base, attach two sticks as the throwing arm, secure the spoon at the top, and finally install a stop bar so the arm releases at the chosen angle.

计划显示了装配顺序：首先用冰棒棍和胶带搭建一个牢固的三角形底座，然后用一根穿过底座的橡皮筋制作枢轴，固定两根冰棒棍作为抛射臂，在顶端绑上勺子，最后安装一个止动杆，使抛射臂在选定的角度释放。

We also planned the testing procedure: mark a launch line on the floor, use a 20 g plasticine ball as the standard projectile, pull the arm back by the same amount each time (using a ruler to measure the pull‑back angle), and measure the distance from the launch point to the first bounce with a tape measure.

我们还计划了测试程序：在地板上标记出发射线，用一个20克的橡皮泥球作为标准抛射物，每次将抛射臂拉到相同位置（用直尺测量拉回角度），并用卷尺测量从发射点到第一次弹跳落点的距离。

7. Building the Prototype | 构建原型

Following the plan, we assembled the catapult. We paid attention to making joints as tight as possible, because loose connections waste energy and reduce range. The tape was wrapped in multiple layers at key stress points.

我们按照计划组装了弹射器。我们特别注意将连接处做得尽可能紧密，因为松散的连接会浪费能量并缩短射程。在关键受力点缠绕了多层胶带。

One problem arose: the rubber band pivot twisted so much that the arm moved sideways during release. To fix this, we added two guide walls made from short lolly sticks either side of the arm. This was our first small design refinement—and it happened during construction, just like in real engineering.

出现了一个问题：橡皮筋枢轴扭绞得太厉害，导致释放时抛射臂向侧边偏移。为了解决这个问题，我们在抛射臂两侧各增加了一堵由短冰棒棍制成的导向壁。这是我们第一次小小的设计改良——而且就发生在制作过程中，就像真实的工程项目那样。

Throughout the build, we kept a note of any changes from the original plan, so we could refer back later when evaluating the project.

在整个制作过程中，我们记录下了所有与原计划不同的更改，以便稍后在评估项目时可以回顾参考。

8. Testing and Data Collection | 测试与数据收集

Testing was organised carefully. Each team member had a role: one person operated the catapult, one measured the pull‑back angle to 90°, one marked the landing point and one recorded the data. We carried out ten trials.

测试被精心组织。每名团队成员各司其职：一人操作弹射器，一人将拉回角度测量为90°，一人标记落点，一人记录数据。我们进行了十次试射。

We recorded the distance in centimetres for each shot. The results were: 245, 251, 238, 242, 255, 247, 235, 260, 244, 239 cm. Immediately we noticed that one shot (260 cm) was unusually long, and one (235 cm) was a little short.

我们以厘米为单位记录了每次射程。结果是：245、251、238、242、255、247、235、260、244、239厘米。我们立刻注意到一次试射（260厘米）特别远，一次（235厘米）稍短。

We calculated the mean (average) distance: add all values and divide by 10. The sum is 2456 cm, so the mean is 245.6 cm. We also noted the range of results: from 235 cm to 260 cm, a spread of 25 cm. This tells us about consistency.

我们计算了平均射程：所有数值相加再除以10。总和是2456厘米，因此平均值为245.6厘米。我们也注意到了结果范围：从235厘米到260厘米，跨度为25厘米。这告诉我们有关一致性的信息。

9. Analysing Results | 结果分析

With data in hand, we looked for patterns. The mean range of 245.6 cm met our initial target of 2.4 m, so the basic design was successful. However, the spread of 25 cm suggested the catapult was not perfectly consistent.

手里拿着数据，我们开始寻找规律。245.6厘米的平均射程达到了我们最初2.4米的目标，所以基本设计是成功的。然而，25厘米的散布范围表明弹射器的表现并非完全一致。

We suspect two reasons for the variation: the rubber band may have been twisted by slightly different amounts each time, and the masking tape joints may have loosened during the set of trials. An engineer always asks ‘what could have caused the variation?’

我们推测造成波动的原因有两个：橡皮筋每次试射的扭绞量可能略有不同，而且在试射过程中美纹胶带的连接处可能松动了。工程师总是会问：“造成波动的原因可能是什么？”

We also plotted a simple bar chart of distance versus trial number. This visual helped us see that distances decreased slightly in trials 3, 6 and 10, which correlated with times we had not waited long enough for the rubber band to cool down (it warmed up after stretching). Recording observations alongside numbers is vital.

我们还绘制了一张简单的射程与试射序号的条形图。这张图帮助我们看出，在第3、第6和第10次试射中距离略有下降，这和我们没有足够时间让橡皮筋冷却下来（拉伸后变热）的情况吻合。在记录数据的同时记下观察情况至关重要。

10. Evaluation and Improvements | 评估与改进

Evaluating honestly is what turns a model‑making activity into a real engineering lesson. We asked three main questions: what worked well, what went wrong, and what could be better?

诚实进行评估，是把模型制作活动变为真正的工程学课程的关键。我们提出了三个主要问题：什么做得好？哪里出了问题？还能怎么改进？

Strengths: the torsion design was easy to tweak, the triangular base provided good stability, and using a ruler to set the pull‑back angle improved repeatability. Weaknesses: the spoon had a sharp edge that sometimes cut the rubber band, and the tape stretched slightly, altering the geometry.

优点：扭力设计容易调整，三角形底座提供了良好的稳定性，使用直尺来设定拉回角度提高了重复性。缺点：勺子有一个锋利的边缘，有时会割伤橡皮筋；胶带略微拉伸，改变了整体几何结构。

As a result, we proposed two improvements. First, replace the plastic spoon with a small bottle cap that has smooth edges. Second, reinforce the pivot with a second rubber band alongside the original one, to give a more balanced twist. We tested the new design with another ten shots and found the average range increased to 258.2 cm and the spread reduced to 14 cm. The improvement worked.

于是，我们提出了两项改进。第一，用一个边缘光滑的小瓶盖代替塑料勺子。第二，在原来的橡皮筋旁边增加一根橡皮筋来加固枢轴，以提供更均衡的扭绞力。我们用新设计又进行了十次试射，发现平均射程提高到258.2厘米，散布范围缩小到14厘米。改进起作用了。

11. Presentation and Communication | 展示与沟通

Engineers must communicate their findings clearly. We prepared a short report that included the original brief, our design sketches, the decision table, a photo of the prototype, the data table, the bar chart and a paragraph explaining our improvement.

工程师必须清晰地交流自己的发现。我们准备了一份简短报告，内容包括原始任务书、设计草图、决策表、原型照片、数据表、条形图以及一段说明我们改进措施的段落。

We also gave a two‑minute live demonstration to the class. During it, we explained the role of elastic potential energy: U = ½ k θ², where k is the spring constant of the twisted band and θ is the twist angle in radians. While the full equation is advanced, we explained that storing more twist gives the projectile more kinetic energy.

我们还向全班进行了两分钟的现场演示。在演示中，我们解释了弹性势能的作用：U = ½ k θ²，其中k是扭绞皮筋的弹性常数，θ是以弧度表示的扭绞角度。虽然这个公式比较高级，但我们说明了，储存更多的扭绞能量会赋予抛射物更多的动能。

We also discussed trajectory: the ball follows a parabolic path. The optimum angle for our raised release point was around 40°, which we estimated by gradually tilting the stop bar and measuring ranges. Communicating the science behind the results impressed our audience.

我们还讨论了弹道：小球沿抛物线路径飞行。我们通过逐步倾斜止动杆并测量射程，估算出我们这个高位释放点的最佳角度大约在40°左右。清楚地表达出结果背后的科学原理，给听众留下了深刻印象。

12. Conclusion | 结论

The catapult case study taught us far more than just how to fling a ball. We followed a structured engineering approach: define, research, design, build, test, analyse and improve. Each step mirrored the work of professionals.

这个弹射器案例教给我们的，远不止是如何把一个球弹出去。我们遵循了一套有条理的工程方法：定义、研究、设计、制作、测试、分析、改进。每一步都反映着专业工程师的工作。

Most importantly, we learned that failure and imperfection are part of the process. The first prototype was not perfect, but by measuring its performance, identifying weaknesses and making evidence‑based changes, we created a better product. That is what real engineering is all about.

最重要的是，我们懂得了失败和不完美本身就是流程的一部分。第一个原型并不完美，但通过测量其性能、找出弱点并进行基于证据的更改，我们创造出了更好的产品。这正是真实工程的全部意义所在。

Published by TutorHao | Engineering Revision Series | aleveler.com

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Catapult Design Challenge – A Practical Engineering Analysis | 弹射器设计挑战 – 实战工程分析