- Difficulty
- Intermediate
- Build time
- 65-100 min
- Estimated cost
- $0-$8
- Age range
- 10-18
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The device retrieves a 100-gram model supply bag from 1 metre away and places it in a target box within two minutes.
Learning goals
- Identify how hand motion outside a marked boundary produces controlled pickup and placement of a payload.
- Construct and explain a remote pull, push, or linkage motion-to-object transport system.
- Measure how end-tool geometry changes performance.
- Diagnose losses caused by tool flex and grip slip.
Before you build
Materials, tools, and safety
Reuse-material cost: $0-$3 with reused materials. Supervision: Adult help recommended for sharp or heated tools.
Tools
- Ruler
- Pencil
- Scissors
- Timer or phone stopwatch
Low-cost swaps
- Use reclaimed paper and packaging while keeping material limits equal for every team.
- Replace metal test weights with labeled bags of coins or washers.
- Use cardboard strips, drinking straws, and a paper-cup scoop rather than commercial gripper parts.
Project-specific safety
- Keep load and drop tests below shoulder height and away from faces.
- Clear the test zone before releasing moving objects or suspended loads.
- Use only lightweight model payloads on the floor, keep the device below shoulder height, and prohibit swinging or throwing.
Orient the build
Place the build so hand motion outside a marked boundary is on your left and controlled pickup and placement of a payload is on your right. Call the side facing you the front, the far side the back, the tabletop the bottom, and the opposite face the top.
Build it
Step-by-step instructions
Step 1
Define the scenario
Tape a boundary 1 metre from the payload and place the target beside the operator.
Set a two-minute limit.
Step 2
Choose a pickup method
Sketch a hook, scoop, clamp, or loop and explain why it matches the bag.
Identify one likely failure.
Step 3
Build the reach beam
Join members with long overlaps and add depth using a triangular or box section.
Keep mass low at the far end.
Builder checkpoint: After build the reach beam, the first subassembly should stay aligned when handled gently.
Step 4
Create the end tool
Attach the chosen pickup geometry and test it by hand first.
Round all edges touching the bag.
Watch for: If this stage binds or drifts, inspect operator misalignment before adding more parts.
Step 5
Add remote control
Route string or a linkage to the operator handle.
Provide a return spring when the tool must reopen.
Step 6
Run a no-load reach test
Move the tip through the full path without crossing the boundary.
Reinforce visible bending.
Builder checkpoint: After run a no-load reach test, operate the build slowly and confirm that controlled pickup and placement of a payload begins without binding.
Step 7
Practice one retrieval
Pick up the bag, clear the zone, and lower it into the box.
Do not drag it across the boundary.
Step 8
Complete three scored runs
Record time, boundary contacts, drops, and successful delivery.
Change one feature between rounds.
Builder checkpoint: At the final checkpoint, The device retrieves a 100-gram model supply bag from 1 metre away and places it in a target box within two minutes.
See the engineering
Why it works
- Input
- hand motion outside a marked boundary
- Output
- controlled pickup and placement of a payload
- Motion
- remote pull, push, or linkage motion-to-object transport
- Energy losses
- tool flex, grip slip, joint backlash, operator misalignment
Why this works
Constraint-based mechanism design
A rescue tool must transmit hand motion across distance while supporting the payload. Long reach increases bending and reduces control, so stiffness and grip geometry must be balanced.
Look for: Watch the far end while a teammate moves the handle 5 cm; compare intended and actual tip motion.
Where the energy goes
Efficiency and losses
The ideal model leaves out tool flex, grip slip, joint backlash, operator misalignment. These effects turn some input energy into heat, sound, vibration, or unwanted motion, so measured performance will be lower than an ideal calculation.
Look for: Run the build slowly and locate the first place where tool flex becomes visible or audible.
Math bite
Calculate payload moment
Formula: moment = payload force × horizontal reach
- Payload force = 1.0 N
- Reach = 1.0 m
Substitute: moment = 1.0 × 1.0 = 1.0 N·m
Result: The handle and beam resist about one newton-metre from the payload alone.
The device's own mass adds more bending moment.
The payload may not stay exactly horizontal.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Operate the end tool by hand before attaching the long reach beam.
Success looks like: The device retrieves 100 grams from 1 metre and places it in the target within two minutes.
Measure: Time, drops, boundary touches, tip deflection, and grip success.
Change: end-tool geometry
Keep constant: reach, payload, boundary, operator position, target, and time limit
- hook
- scoop
- clamp or loop
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The beam bends too far | Section is shallow or tip is heavy | Hold the payload 5 cm above the floor | Deepen the beam and lighten the tool |
| The bag slips | Contact shape or normal force is poor | Lift only 2 cm and pause | Widen contact or add nonslip paper |
| Control reverses unexpectedly | String routing crosses or linkage flips | Move the handle slowly unloaded | Separate guides and add hard stops |
| The target is missed | Tip motion is too sensitive | Move the handle 1 cm and measure tip travel | Shorten lever arm or add a larger handle |
Choose your tradeoff
Stiffen the long beam without making the far end heavy. A firm grip prevents drops, but excessive force can make release into the target difficult.
Keep experimenting
Try another version
Fifty-gram payload
Use a wide scoop from 60 cm away.
Two-object rescue
Retrieve two shapes with one tool.
Operator feedback
Add a mechanical indicator that shows grip closure.
Build together
Classroom and access options
Classroom version
Teams can compare end-tool geometry while keeping reach, payload, boundary, operator position, target, and time limit. Assign builder, tester, recorder, and explainer roles; have each team predict the result before collecting three trials.
Access adaptations
- Assign varied roles such as designer, builder, tester, recorder, and presenter.
- Provide pre-measured materials and a visual checklist when helpful.
- Offer hook, scoop, and gripper strategies plus roles for operator, spotter, designer, and recorder.
Reflect on the design
- How did end-tool geometry change the measured result?
- Where did tool flex affect the build most strongly?
- What evidence shows that constraint-based mechanism design explains the motion?
- Which change would improve controlled pickup and placement of a payload without creating a new problem?
Glossary
- Constraint-based mechanism design
- A rescue tool must transmit hand motion across distance while supporting the payload.
- Input
- The action or energy supplied to a system; here it is hand motion outside a marked boundary.
- Output
- The useful response produced by a system; here it is controlled pickup and placement of a payload.
- Efficiency
- The fraction of input energy that becomes useful output instead of friction, sound, heat, or unwanted motion.
Build your dreams
One build can start the next.
Share what you learned, change one variable, and help another builder understand what worked.
Explore more guidesSources and build notes
A common classroom engineering challenge implemented with original constraints, diagrams, and measurement guidance.
- Classroom challenge basis: A controlled-variable engineering activity with original constraints, scoring ideas, and measurement guidance.
Written and edited by BrickLabClips. Published 2026-07-22; updated 2026-07-22.