Grade 5 · 3D Printing · Lesson 03

Build a Community Connector

Engineer a model bridge that balances strength, cost, and material use.

Time3 × 60 minutes + adult printingTeamsTeams of 3–4EquipmentBambu P1S fleet

Project inspiration · 3 images

See, build, and test

Use these images to understand the kind of making, details, and testing involved. They are inspiration—not designs students must copy.

Community connector bridge project overview
01Project overview
Low side angle showing the bridge trusses and span
02Side structure
Bridge, load cup, ruler and data sheet seen from above
03Top view

Student directions · Grade 5

What will you make and do?

You will build a model bridge that connects two places across a classroom gap. It needs a usable deck and must carry the teacher’s test load without support underneath.

Teacher overview: Students will plan the specific object described below, make and test a first version, then use their results to improve it. Read one step together, demonstrate the unfamiliar action, and let students complete that step before moving on.

  1. 1Plan your project

    Measure the gap and read the load target. Sketch two ways to support the deck; mark where each bridge rests on the banks.

  2. 2Make the first parts

    Build a low-tech bridge model from approved beams, folded paper or cardboard. Join the supports firmly and keep the space underneath clear.

  3. 3Put it together

    Add a level deck and a path wide enough for the model user or vehicle. If using fabricated parts, test their cardboard versions before adult fabrication.

  4. 4Test it fairly

    Place the bridge on the same marked banks. Add the same small weights in the same order and location; record load and visible bending. Keep hands and feet out of the drop area.

  5. 5Improve one part

    Strengthen one weak joint or change one support shape. Retest with the identical gap and loading sequence.

  6. 6Show and turn in

    Demonstrate the bridge with the approved load. Submit labeled plans and a load table showing what changed and what the evidence supports.

How will you know it works?

  • Spans the full gap without support below
  • Carries the target load
  • Includes a usable deck
  • Remains stable during testing

Before you move on

Explain which measurement, input or design choice you are testing. Predict the result and record what stays the same so your comparison is fair.

Machine cutting, printer setup and electrical power-on require adult approval. A basic-materials model is a valid way to demonstrate the design when equipment is unavailable.

Keep your plan, test notes and before-and-after evidence with the printable design brief below. Use the detailed teacher plan and any coding guide for tool instructions. These steps continue across the lesson’s meetings, not all in one sitting.

For teachers

Engineering standards

This shows how the lesson connects to the national NGSS engineering standards and what student work you can collect.

Assessed

3-5-ETS1-1

Teams translate a community scenario into measurable span, load, cost, and material requirements.

What students show: Design brief with prioritized criteria and quantified constraints.
Assessed

3-5-ETS1-2

Teams score three bridge concepts with a weighted decision matrix.

What students show: Completed matrix and evidence-based selection statement.
Assessed

3-5-ETS1-3

Teams use identical supports and incremental loads, locate failure points, and revise the structure.

What students show: Load data, failure map, revised model, and efficiency calculation.

Materials

  • Craft sticks or index-card strips
  • Masking tape or glue dots
  • Two equal support blocks
  • Washers or identical masses and a hanging cup
  • Digital scale and rulers
  • Graph paper
  • Computer with 3D-design software
  • PLA filament; target 20–35 g per team

Teacher preparation

  1. Choose a scenario such as connecting two neighborhoods across a creek while preserving space below.
  2. Set a 20 cm prototype span and a target load appropriate to available masses.
  3. Prepare a stable testing zone and eye protection according to school procedures.
  4. Create file rule: G5_Team##_Connector_v1.
  5. Plan printer queue by estimated duration and combine compatible models on build plates.

Step by step

How to teach it

Day 1 · 0–20

Define the challenge

  1. Read the community scenario and identify users.
  2. Set measurable criteria: clear span, target load, usable deck, and stability.
  3. Set constraints: material quantity, maximum mass, footprint, and production time.
Day 1 · 20–60

Develop and decide

  1. Sketch beam, arch, and truss-inspired concepts.
  2. Weight criteria from 1–3 based on importance.
  3. Score each concept, calculate totals, and select or combine features with justification.
Day 2 · 0–35

Prototype and test

  1. Build the selected concept to the set span.
  2. Add identical load increments at the same location and rate.
  3. Run at least two trials or explain why the first test caused permanent failure.
  4. Record maximum supported load and mark the first failure point.
Day 2 · 35–60

Analyze and revise

  1. Calculate efficiency: maximum load divided by bridge mass.
  2. Graph or table team results.
  3. Revise one structural feature based on failure evidence and peer critique.
Day 3

Model, print, and defend

  1. Create a scaled digital model that meets the print constraints.
  2. Run teacher checks for span, thickness, orientation, material use, and print time.
  3. Adult prints approved models.
  4. Teams test or inspect final models and present the tradeoff they chose to prioritize.

Assessment

  • Brief includes measurable criteria and constraints tied to the scenario.
  • Decision matrix compares three concepts and supports the final choice.
  • Test uses consistent supports, load location, and increments.
  • Revision targets the recorded failure point.
  • Final explanation uses data and acknowledges a tradeoff.

Supports & extensions

  • Provide a partially completed decision matrix.
  • Use color-coded structural members and a physical joint demonstration.
  • Allow calculator use and shared data-recording roles.
  • Offer prebuilt test rigs and measured material bundles.
  • Extension: minimize projected print mass while maintaining a required safety factor.

Safety & responsible use

  • Keep faces and hands away from loaded structures and falling masses.
  • Use a defined test zone and stable supports.
  • Students do not touch hot or moving printer components.
  • An adult handles slicing approval, printing, part removal, and sharp tools.

No-machine alternative

Build the final bridge with cardboard strips, craft sticks, paper tubes, or reusable construction pieces. Use the same span, load test, efficiency measure, and revision requirement.

Printable student design brief

The challenge

Design a model bridge that connects a community across a 20 cm gap while using materials efficiently.

Success criteria

  • Spans the full gap without support below
  • Carries the target load
  • Includes a usable deck
  • Remains stable during testing

Constraints

  • Uses only the provided material budget
  • Stays within the maximum mass
  • Fits the fabrication envelope
  • Uses identical test conditions

Engineer’s notes

The most important criterion is… because…
Our matrix showed…
Our maximum load was…
The first failure point was…
Our load-to-mass efficiency is…
We revised… because the data…
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