# SLOP4408 — Week 4: Understand the Mechanism

Campus / printable lab pack · Semester 1, 2027

## The task

A carriage does not behave as required. Identify the failed dependency, choose a test that distinguishes it from an alternative and verify the repaired motion.

In-person teaching is preferred. The paper route is a complete conceptual activity when apparatus is unavailable; online students use the equivalent controls and keep the same learning record.

After recording the diagnosis and verifying the required motion, **engage the tested cradle drive**: operate the low-force model or move its labelled cradle token to the receiving platform according to the verified output. Have a partner record **Cradle reached its platform** after checking the output and support condition. A solo learner records this as a self-check; a token move is simulated evidence.

## Learning outcomes

- Predict gear direction and movement from the published relation.
- Use inspections to distinguish causes before changing apparatus.
- Verify a targeted repair against the whole required motion and changed target.

## Equipment

Printed gear discs labelled 12, 24 and 36; card cam and follower; cardboard carriage; paper fasteners; a removable interlock tab. Use an animation or facilitator model if fabrication is unavailable.

## Facilitator setup

Prepare the configurations from the facilitator cards below. Keep their readings separate from the student task, revealing the requested inspection after the student predicts its value. Use paper gear cards when a working model is unavailable.

## Complete supplied rules

**ME-01** gives the mechanism rules and inspection options. **ME-02** gives the target and initial inspection cards for each phase.

- A 12-tooth driver externally meshes with a selectable 12-, 24- or 36-tooth follower. Output turns = 12 ÷ follower teeth × input turns; direction is opposite.
- Motion requires a released interlock, attached return spring and specified cam angle. An engaged interlock blocks cam adjustment.
- Practice: four input turns must produce two outputs; cam datum 180 degrees.
- Skill check: four input turns must produce four outputs; datum 180 degrees.
- Transfer: six input turns must produce two outputs; datum 90 degrees.
- Choose inspections of brake/interlock, return spring, cam datum or gear teeth. Record evidence and a diagnosis **before** using adjustment controls.
- One initial fault exists in each phase. Its identity is not supplied in the task; compare the revealed conditions with the rules.
- After a targeted correction, verify movement, direction and the required return. This is an educational mechanism, not a commercial lock.

## Two-hour schedule

These are the teaching session's time blocks, not six compulsory game objectives. Adjust timing as needed; reasoning matters more than speed.

| Time | Activity |
| --- | --- |
| 0–10 minutes | Draw the input-to-output chain and list two explanations for a stalled carriage. |
| 10–30 minutes | Use the alternate example to predict an informative inspection. |
| 30–60 minutes | Inspect the first mechanism, record a diagnosis, then repair and test. |
| 60–80 minutes | Diagnose the second initial fault independently; preserve evidence before changing controls. |
| 80–105 minutes | Meet changed motion/cam requirements and distinguish target changes from component faults. |
| 105–120 minutes | Compare diagnostic traces and retain a rejected explanation with evidence against it. |

## Worked example · a different scenario

The separate conservatory lift has an 18-tooth driver and needs three output turns from five input turns. A 30-tooth follower satisfies 18 ÷ 30 × 5 = 3, in the opposite direction. The correct ratio still cannot move a blocked mechanism: the demonstrator releases the interlock, sets the cam to 270 degrees and attaches the spring before testing. A later requirement of two output turns from four input turns needs a 36-tooth follower. The valid readiness conditions remain, while the ratio is recalculated. Before blaming the gear ratio for a stall, the demonstrator inspects the interlock. That inspection distinguishes a blocked mechanism from an incorrect movement ratio; the recorded test precedes the adjustment.

[Watch this separate example and inspect its finished record](/demonstrations/lab-04/).

The example explains a method. Its completed decisions are not the assigned task. Use the materials above for your own choices.

## Practice

Predict two candidate causes and request an inspection before changing the first configuration. Record the diagnosis and test a repair.

## Skill check

Diagnose the second initial configuration, preserving inspection evidence before selecting an adjustment.

## Transfer challenge

Meet the changed target after identifying the new initial fault; distinguish required target change from repairing a fault.

## Student record

**Named output: mechanism-diagnosis.**

Keep candidate faults, the selected inspection and its prediction, observed evidence, diagnosis before repair, change made and verified final movement. Name one condition retained.

Record your name/role, phase and scenario, prediction before action, evidence requested, result, decision, alternative and remaining uncertainty. Include assistance, format used and any physical-model limitation. Keep a failed attempt that explains a revision.

After recording the diagnosis and verifying the required motion, **engage the tested cradle drive**: operate the low-force model or move its labelled cradle token to the receiving platform according to the verified output. Have a partner record **Cradle reached its platform** after checking the output and support condition. A solo learner records this as a self-check; a token move is simulated evidence.

## Explanation — reveal after an attempt

The diagnosis must precede adjustment. Compare the original inspection with the model's requirements; verify actual output after the targeted correction. A working final arrangement without evidence of the initial condition does not establish which fault caused the failure.

A facilitator judges the reasoning. The record's existence and the model's successful result do not by themselves establish learning.

## Facilitator evidence cards · reveal on request

Prepare each configuration without labelling its fault for the student. Reveal only the requested inspection:

| Phase | Interlock/brake | Return spring | Cam datum | Driver/follower |
| --- | --- | --- | --- | --- |
| Practice | Engaged | Attached | 180° | 12/24 teeth |
| Skill check | Released | Attached | 180° | 12/24 teeth |
| Transfer | Released | Absent | 90° | 12/36 teeth |

The student compares readings with the target before recording a diagnosis. Practice's brake prevents movement; check's current ratio misses the four-output target; transfer's return connection is missing. After the student proposes a correction, compute movement from the published relation and reveal it. Do not automatically adjust unrelated components. Keep theory separate from fabrication imperfections.

The full pack remains available for accessible and solo study. Label assistance if you inspected all cards before choosing a test. No hidden rules or secret grading are involved.

## Reflection and later use

Which observation would have disproved your first diagnosis?

A1 combines mechanism diagnosis with observation and spatial modelling. Physical recovery and stabilisation can need a support mechanism; digital recovery need not repeat an unrelated cradle exercise.

## Evidence and limitations

Save **mechanism-diagnosis** with your explanation. Physical activities are proposed teaching designs, not hardware-tested equipment. Distinguish model-card results from actual measurements. Neither browser success nor paper completion establishes physical dexterity or classroom enjoyment. A dated station record is sufficient; a duplicate browser run is not required.

## Printable model sheet

[Printable connector and mechanism sheet](./spatial-mechanism-sheet.svg). Print at 100% on A4 and check the labelled 50 mm line. These are conceptual paper aids, not physically validated apparatus.