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Capstone Assessment Rubric
Academic Evaluation & Oral Defense Guide

Entropy Reducer Grading Rubric & Standards

Comprehensive 100-point assessment framework, week-by-week oral defense questions, and power/thermal budget verification for undergraduate-level mechatronics evaluation.

01 · Four-Pillar Mechatronics Rubric (100 Points)

The project is evaluated across the four core competencies of modern mechatronics systems engineering.

1. Mechanical & CAD Design

25 Points Maximum
  • Parametric Constraints: Fully constrained sketches in Fusion 360 (black lines, zero floating geometry).
  • DFAM Compliance: Pre-calibrated tolerances (+0.3mm holes, 45° overhang chamfers, no unnecessary supports).
  • Fastener Standards: M3 heat-set brass inserts with 6.5mm OD boss walls; D-shaft flat orientation.
  • Cam Kinematics: Correct 3.5mm lift profile over 25° for roller microswitch triggering.

2. Electrical & Hardware Hygiene

25 Points Maximum
  • Logic Level Safety: Strict isolation of 3.3V Pi logic from 5V/12V motor supplies.
  • Switch Debouncing: Hardware pull-ups and software debouncing on GPIO20/18.
  • Bus Integrity: SPI arbitration at 24MHz for ST7789; I2C address management (0x60 MotorKit, 0x39 AS7341).
  • Cable Management: 40-pin GPIO ribbon routing with strain relief and zero short-circuit hazard.

3. Firmware & State Machine

25 Points Maximum
  • Deterministic FSM: Explicit non-blocking states (Idle, Scan, Classify, Sort, Home).
  • 3-Phase Homing: Fast advance → Slow back-off → Datum offset (hysteresis elimination).
  • Tactile Event Loop: 7-button LCD menu navigation with Pillow framebuffer rendering.
  • Exception Handling: Graceful recovery on sensor disconnect or motor stall via motor_release.py.

4. Optics, ML & Telemetry

25 Points Maximum
  • Spectral Normalization: Vector sum-normalization eliminating specular glare and ambient shift.
  • Cosine Similarity: 8D centroid matching with >95% confidence on single-candy tests.
  • Run Telemetry: Batch logging with confusion matrix generation and throughput metrics (>35 Skittles/min).
  • Auto-Stop Heuristic: 3-consecutive empty pocket detection with automatic coil de-energization.

Interactive Grade Calculator

Adjust student scores across the four pillars to calculate total points and final academic classification.

Overall Result
95 / 100 (95.0%)
FIRST CLASS / DISTINCTION

02 · Milestone Oral Defense Question Bank

Use these targeted engineering questions during weekly check-ins to verify first-principles comprehension.

Why is a 3-phase homing algorithm necessary instead of stopping on the first limit switch contact?Week 5 · Steppers
Expected Answer: Mechanical snap-action switches have mechanical hysteresis (the release point is 0.2–0.5mm behind the trip point). Stopping immediately introduces 2–3° angular error depending on approach speed. Phase 2 slowly backs off until the spring resets, establishing a sub-degree datum.
Why does Euclidean distance fail for color classification when ambient room light changes, while Cosine Similarity succeeds?Week 8 · Classifier
Expected Answer: Euclidean distance $|\mathbf{x} - \mathbf{y}|$ measures magnitude difference. Brighter lighting scales all channels up, moving the point far away in 8D space. Cosine similarity $\frac{\mathbf{x}\cdot\mathbf{y}}{\|\mathbf{x}\|\|\mathbf{y}\|}$ measures angle between vectors, capturing relative color ratios regardless of absolute photon flux.
Why must we de-energize stepper motor coils when the machine is idle?Week 5 / 11 · Integration
Expected Answer: Stepper motors draw full rated current (holding torque) even when stationary, dissipating electrical power as heat through $I^2 R$ coil losses. Leaving coils energized continuously causes thermal creep, softening 3D-printed PLA motor mounts and draining power.
How does the rotary cam geometry prevent switch lever destruction during reverse motor moves?Week 3 / 6 · CAD
Expected Answer: The cam profile features a continuous tangential radius on both sides of the $+3.5\text{mm}$ lobe. A roller microswitch rides smoothly up and down the ramp in either rotation direction without catching or bending the lever arm.

03 · Electrical Power & Thermal Dissipation Budget

System power rail verification under continuous peak sorting load.

Subsystem Operating Voltage Peak Current (mA) Power (Watts) Thermal Dissipation Mechanism
Raspberry Pi Zero 2 W (SoC active) 5.0 V 450 mA 2.25 W Passive PCB ground plane heatsinking
ST7789 1.3″ TFT Bonnet (Backlight ON) 3.3 V (via Pi LDO) 65 mA 0.21 W Backlight LED radiation
AS7341 Spectral Sensor + White LED 3.3 V (via Pi LDO) 35 mA 0.12 W Opto-chamber illumination dissipation
WS2812B NeoPixel Ring (5 LEDs full white) 5.0 V 300 mA 1.50 W Aluminium heat sink / PCB copper pad
NEMA-17 Stepper #1 (Inspector Wheel) 12.0 V (Motor HAT) 800 mA 9.60 W Motor stator case ($I^2 R$ coil losses)
NEMA-17 Stepper #2 (Sorting Slide) 12.0 V (Motor HAT) 800 mA 9.60 W Motor stator case ($I^2 R$ coil losses)
TOTAL SYSTEM PEAK LOAD 5V Rail / 12V Rail 750 mA (5V) / 1.6A (12V) 23.28 W Requires 5V/2.5A USB-C PSU + 12V/2A DC Barrel Jack

04 · Student Logbook Milestone Sign-Off

Formal weekly milestone tracking for instructor sign-off.

Week Milestone Deliverable Target Metric Status Sign-off Date
W0–W2 Headless Pi SSH + Breadboard Switches & LEDs Remote VS Code link & debounced GPIO read Complete ____ / ____ / 2026
W3–W4 Parametric CAD & 3D Print Fits M3 brass inserts flush; D-shaft press-fit tight Complete ____ / ____ / 2026
W5–W6 3-Phase Dual-Axis Homing & Cam Assembly <1.0° datum repeatability after 10 homing cycles Complete ____ / ____ / 2026
W7–W8 8-Channel AS7341 Classifier & Cosine Metric >95% single-candy classification accuracy Complete ____ / ____ / 2026
W9–W10 Sorting Chute & Rotary Feeder Assembly Zero jams across 10 continuous feeds Complete ____ / ____ / 2026
W11–W12 Full System Integration & Live Retrospective Full bag sort trial >35 Skittles/min + Confusion Matrix Complete ____ / ____ / 2026

05 · Engineering Failure & Redesign Log

The mark of a true engineer is how problems are diagnosed, documented, and solved. Log all mechanical jams, electrical glitches, and software bugs here.

Date Subsystem Observed Failure & Root Cause Analysis Engineering Redesign / Corrective Action Verified
Wk 5 (Example) Inspector Wheel Wheel missed datum by 2.5° after fast homing. Root cause: microswitch mechanical spring hysteresis. Implemented Phase 2 slow reverse step-back in home_wheel() to release switch contacts. PASS (<0.5°)
Wk 7 (Example) Colour Sensor Purple and red Skittles confused under bright sunlight. Root cause: ambient glare shifted raw ADC counts. Enforced 8-channel vector sum-normalization + Cosine distance metric in skittles_classifier.py. PASS (98.2%)
____ / ____ Feeder / Hopper _________________________________________________________ _________________________________________________________ [   ] PASS
____ / ____ Sorting Chute _________________________________________________________ _________________________________________________________ [   ] PASS
____ / ____ Firmware / FSM _________________________________________________________ _________________________________________________________ [   ] PASS

06 · Capstone Certificate of Completion

Formal certificate to be signed upon successful completion of the Week 12 live batch sort demonstration and oral defense.

Certificate of Mechatronic Excellence

Entropy Reducer Capstone Project

This certifies that the engineering candidate has successfully designed, fabricated, wired, programmed, and demonstrated the full autonomous

Elliot

Having demonstrated mastery across Parametric CAD in Fusion 360, Additive Manufacturing Tolerances, I2C/SPI Sensor & Stepper Firmware, 8-Channel Spectral Cosine Classification, and Finite State Machine Integration.

Olivier Dehon
Lead Instructor
DISTINCTION
Verified Capstone
____ / ____ / 2026
Completion Date