Sample Subway — Nuclear Pressure Tube Sampling System

01 // SYSTEM OVERVIEW & SPECIFICATIONS

// PROJECT SCOPE & CLIENT VISION

Electromechanical remote sampling tool engineered for Canadian Nuclear Laboratories (CNL) to collect [ 30–80 mg ] metal samples from 4-inch ID, 15-foot nuclear pressure tubes for hydrogen embrittlement destructive testing. The lead engineer from Canadian Nuclear Laboratories emphasized a strong interest in seeing unique, innovative, and fully developed solutions rather than standard off-the-shelf concepts.

// DESIGN CONSTRAINTS & BOUNDARIES

Strict $100 CAD total project budget, complete setup and handling by a single operator with zero radiation exposure, dual-orientation travel (horizontal/vertical), 100% failsafe retrievability, self-contained onboard power, and cycle completion within a 10-minute operational window.

Sample Subway CAD Render — CAD rendering of the complete Sample Subway electromechanical assembly.

// SYSTEM ARCHITECTURE BREAKDOWN

Processing & Logic

ESP32-WROOM-C3 Microcontroller (C++ / Arduino IDE Firmware)

Movement & Recovery

Dual 12V N20 200 RPM Gearmotors (Drive Motors) + Custom Winch Spool & Paracord Tether (Vertical Recovery)

Actuation & Scraping

JGB37-520 12V 7RPM High-Torque Gearmotor + BTS7960 43A High-Power H-Bridge Driver + MGEHR1212 Lathe Tooling

Sensor & ADC Circuitry

100g Strain-Gauge Load Cell + HX711 24-bit Differential ADC Module

Power System & Regulators

Custom 3S1P Li-Ion Battery Pack (3x Molicel 21700 P42A Cells, 11.1V Nominal, 4500mAh) + 3S 40A BMS Board + LM2596 Buck Regulator (5V/3.3V Logic)

Communications

ESP32 Bluetooth + WiFi Telemetry + Mobile Operator UI/UX Tablet Application

02 // ENGINEERING METHODOLOGY & TARGET SPECIFICATIONS

USER REQUIREMENTS

Needs Analysis & Prioritization

Transformed CNL client statements into prioritized engineering design criteria:

Safety & Exposure Limitation: Self-sealing sample containment & zero direct radioactive contact.
Single-Operator Handling: Fully deployable, operable, and retrievable by 1 technician without secondary assistance.
Budgetary Ceiling ($100): Total prototype procurement and BOM strictly capped under [ $100 CAD ].
Unique & Fully Developed Solution: Novel electromechanical architecture fulfilling CNL lead engineer's mandate for distinctive solutions.
Complete Removability: Winch tether emergency recovery failsafe for 100% retrieval guarantee.
Payload Precision: Target sample extraction of [ 30–80 mg ].
Data Feedback: Prototype mass verification via onboard ESP32 Bluetooth + WiFi to avoid umbilical cable complexity.
Modularity & Envelope: Length < 4 ft, diameter < 4 in.
Self-Contained Power: Onboard high-current Li-ion battery pack.
Operational Speed: Cycle completion within < 10 minutes.

DESIGN ENVELOPE & BOUNDARIES

Functional Limits & Constraints

Target engineering performance envelope, cost ceiling, and boundary constraints:

Functional Requirements

Single-Operator Usability: Solo deployment, guidance, and recovery
Mass Collection: [ 30–80 mg ] (verified via scale feedback)
Complete Removability: 100% retrieval guarantee with tether backup
Enclosed Sample: Self-sealing spring-loaded lid
Distance Traveled: [ 15 ft ] inside pressure tube
Cycle Time: [ < 10 min ] total deployment

Physical & Budgetary Constraints

Total Project Budget: [ $100 CAD ] strict financial limit
Operator Footprint: [ 1 Operator ] single-person handling
Outer Diameter: [ < 4.0 in ] envelope
Total Tool Length: [ < 4.0 ft ]
Total Tool Mass: [ < 5.0 kg ] man-portable
Operator Contact: Zero manual touch on radiation tooling

CONCEPT COMPARISON

Trade-off Analysis & Architecture Selection

Evaluated 4 global concepts (Sample Subway, Pipe Worm, Pneumatically Deployable Tool, and Flywheel Flinger) against weighted client criteria, target engineering specifications, and manufacturing feasibility.

// TABLE 01: CONCEPT SUBSYSTEM ARCHITECTURE

Concept	Movement	Sampling Tool	Containment	Emergency Failsafe	Evaluation & Trade-offs
Sample Subway SELECTED	Modular Drive Wheels (Dual 12V N20 Motors)	Lathe Tool Bit Scraping Profile	Spring-Loaded Sliding Lid / Retention Lip	Paracord Tether & Winch Spool	Superior traction in dual orientations; predictable cutting depth without stalling; failsafe mechanical tether ensures 100% recovery.
The Pipe Worm	Pneumatic Inchworm (Inflatable Caps + Actuator)	Abrasive Rotary Sanding Pad	Suction Vacuum Chamber	Negative Pressure Vacuum Pull	Slow multi-step peristaltic movement; abrasive sanding dust created high residue contamination risks in tube.
Pneumatic Tool	Telescoping Inflatable Segmented Tube	Articulated Arm / Multi-Tool Head	Pneumatic Clamshell Vessel	Deflate & Reverse Tension Pull	Compact storage, but managing external high-pressure pneumatic lines added operational complexity and puncture risk.
Flywheel Flinger	High-Speed Dual Flywheel Launcher	Dynamic Flap Friction Scraper	Spring-Loaded Flap Closure	Tensioned Recovery Line & Spool	High initial velocity, but uncontrolled ballistic impacts risked tube wall damage and loss of sample capture.

// TABLE 02: CONCEPT EVALUATION & FEASIBILITY WEIGHTING

Scoring Scale: 1 = Poor / High Risk · 2 = Moderate / Acceptable · 3 = Superior / Optimal

Evaluation Criteria	Sample Subway (C1)	The Pipe Worm (C2)	Pneumatic Tool (C3)	Flywheel Flinger (C4)
Radiation Containment & Operator Safety	3	1	3	1
100% Removability & Emergency Tether	2	1	3	1
Modular & Lightweight Packaging	2	2	3	2
Novelty & Creative Solution	1	3	3	3
Operational Speed & Cycle Time	3	1	3	3
Packaging & 4.05" Pipe Bore Clearance	2	1	3	3
Mechanical Complexity & Execution	3	2	1	2
Raw Concept Score (out of 21)	16 / 21	11 / 21	19 / 21	15 / 21
Overall Feasibility Weighting Factor	1.00x	0.65x	0.60x	0.75x
Final Feasibility-Adjusted Score	16.0 SELECTED	7.2	11.4 HIGH RISK	11.3

// Selection Justification & Feasibility Trade-offs: In the initial unweighted concept evaluation, the Pneumatically Deployable Tool (Concept 3) scored the highest raw score (19 / 21) due to its high architectural novelty, compact storage, and rapid theoretical inflation. However, due to its low rating for manufacturing feasibility (requiring custom airtight segmented bladders, multi-port pneumatic valves, and complex micro-rotary joints), the team could not envision fabricating and delivering this design within the strict $100 CAD budget ceiling and semester deadline. Applying an overall feasibility weight factor to account for timeline and budgetary constraints, the Sample Subway (Concept 1) emerged as the winning design with an adjusted score of 16.0. It achieved a 1.00x feasibility rating, reliable traction in dual orientations, a foolproof mechanical tether failsafe, and predictable lathe-bit cutting geometry, allowing the group to successfully build, test, and validate a physical prototype under budget ($96.19 actual BOM).

03 // SAMPLE SUBWAY SUBSYSTEM BREAKDOWN

SUBSYSTEM 01 // SAMPLING & SCRAPING TOOLING

Lathe Tool Bit & Scraping Profile

Integrates a high-torque JGB37-520 12V 7 RPM DC gearmotor driving an industrial MGEHR1212 lathe tool bit through a high-power BTS7960 H-bridge driver. We performed geometric cross-sectional modeling in OnShape of the 4.05-inch pipe wall and crawler chassis radius to calculate the cutting trajectory. By optimizing motor placement and cutting radius, the tool extracts an estimated target mass of [ 65 mg ] (within the client's [ 30–80 mg ] spec window) without cutting too deep, preventing motor stalls or excessive tube wall damage.

SUBSYSTEM 02 // SAMPLE CONTAINMENT

Spring-Loaded Self-Sealing Vessel

Custom 3D-printed containment container featuring an automated spring-loaded sliding lid. Upon insertion into the Subway's tool head, a mechanical retention lip catches the container's edge to hold the sliding door open directly beneath the cutting bit during active scraping; upon removal, dual internal compression springs automatically force the lid shut, securely isolating the sample so the operator is shielded from radioactive exposure.

SUBSYSTEM 03 // LOCOMOTION & TRACTION

Bi-Directional Drive & Friction Interface

Driven by dual 12V N20 200 RPM micro-metal gearmotors powering modular drive wheel assemblies. Tested multiple wheel surface interfaces—progressing from raw 608 steel bearings (high slip) to 3D-printed TPU sleeves, and finally compressible rubber traction bands to maintain necessary normal wall force and prevent chassis rotation under scraping counter-torque across both horizontal and vertical pipe runs.

SUBSYSTEM 04 // EMERGENCY FAILSAFE & RECOVERY

High-Tensile Tether & Winch Recovery

Independent mechanical recovery failsafe featuring a 550 Paracord tether line anchored to a reinforced structural chassis tow-eyelet and spooled onto a manual/motorized retrieval winch. Guarantees 100% physical retrieval of the crawler and contained sample in the event of battery exhaustion, motor stall, or signal loss inside the 15-foot pressure tube.

// DESIGN CONCEPTS & CAD SCHEMATICS

04 // PROJECT EXECUTION & PROTOTYPING TEST PLAN

Structured engineering development framework tracking progressive milestone tasks, risk mitigation, and staged subsystem prototyping plans from initial concept validation through final client delivery for Canadian Nuclear Laboratories.

// 01. PROJECT SCHEDULE & MILESTONE TASK PLAN

Phased development plan executed across the 13-week engineering lifecycle, tracking critical deliverables, software modeling, and hardware fabrication tasks managed via Trello and Gantt scheduling:

Phase / Milestone	Timeline	Key Objectives & Engineering Deliverables	Tooling & Platform	Status
Phase 01: Needs & Requirements	Weeks 1–3	Client interviews, interpreted needs hierarchy, target specification definitions (30–80 mg payload window, <$100 budget ceiling), and technical benchmarking.	Google Docs, Sheets	DONE
Phase 02: Conceptual Ideation	Weeks 4–6	Developed 4 global architectures across 4 subsystems (Movement, Sampling, Containment, Failsafe); evaluated trade-offs via quantitative decision matrix and feasibility weighting.	OnShape, Miro	DONE
Phase 03: CAD & Schematic Design	Weeks 7–8	Parametric 3D chassis modeling, lathe bit cross-sectional geometric scraping analysis, circuit schematic capture, and dual-voltage power tree routing.	OnShape, KiCad	DONE
Phase 04: Progressive Subsystem Builds	Weeks 9–11	Iterative fabrication of 5 focused Lo-Fi/Hi-Fi prototypes: load cell flexure & DSP filtering, lathe bit cutting armature, spring-loaded containment, and drive locomotion.	Bambu A1, Arduino IDE	DONE
Phase 05: Integration & Validation	Weeks 12–13	Comprehensive electromechanical integration, 15 ft pipe run testing, Bluetooth telemetry data logging, Figma tablet operator UI, and final CNL client design day presentation.	Keyshot, Figma, Serial API	DONE

// 02. STAGED PROTOTYPE TEST PLAN & STOPPING CRITERIA

Iterative test matrix guiding subsystem validation, quantitative metrics, and stopping criteria across 5 staged prototypes:

Prototype Stage	Target Subsystem	Fidelity & Scope	Evaluation Metrics & Stopping Criteria	Test Results & Key Design Iterations
Prototype I	Instrumentation & Measurement	Focused Hi-Fi 100g Load Cell + HX711 ADC	Stable mass detection with ±1 mg resolution; noise floor <10 mg over 5 consecutive test runs.	Raw noise (±100 mg) was stabilized down to ±9.5 mg via recursive moving average and dynamic zero-tracking creep compensation.
Prototype II	Sampling & Tooling	Focused Hi-Fi JGB37 Motor + MGEHR1212 Lathe Bit	Successful material extraction yielding 30–80 mg shavings without stalling motor or binding in tube.	Validated OnShape geometric cutting arc. Scraping rotation extracted ~65 mg target yield while maintaining safe motor current limits.
Prototype III	Sample Containment	Focused Hi-Fi Spring-Loaded Sliding Vessel	Zero manual touch on radiation payload; 100% automated lid closure upon chassis extraction over 5 cycles.	Eliminated magnetic latching due to ADC interference; engineered 3-spring dual rail mechanism for positive mechanical closure.
Prototype IV	Locomotion & Traction	Focused Lo-Fi Dual N20 Motors + Wheel Mounts	Traverse 15 ft pipe in <2 min; maintain traction under scraping counter-torque across horizontal/vertical runs.	Tested progression: 608 steel bearings (slipped) ➔ TPU printed sleeves (insufficient grip) ➔ high-friction compressible rubber tires (passed).
Prototype V	Comprehensive System & UX	Comprehensive System Chassis + Electronics + Figma UI	Full mission cycle <10 min; live Bluetooth wireless telemetry; successful tether recovery failsafe.	Integrated complete electromechanical package under $100 budget ($96.19 actual); verified live mass telemetry and operator workflow.

// 03. PROTOTYPING EQUIPMENT & SOFTWARE STACK

HARDWARE TOOLCHAIN

Fabrication & Assembly Equipment

Bambu Lab A1 3D Printer: Additive rapid prototyping of PETG/PLA chassis, wheel mounts, and containment slider.
Soldering & Fume Station: High-current wiring harness, BTS7960 motor driver, and ESP32 power rails.
Spot Welder & Heat Gun: Custom 3S1P Molicel 21700 cell pack spot-welding and insulated conduit heat shrinking.
Digital Multimeter: Voltage drop profiling, load-cell excitation calibration, and current draw analysis.

SOFTWARE TOOLCHAIN

CAD, Firmware & UI Platforms

Onshape (Parametric CAD): 3D geometry modeling, chassis assembly fit, and cross-sectional cutting arc simulation.
KiCad (Electronic EDA): Power delivery tree schematic capture, buck converter routing, and noise rejection layout.
Arduino IDE (Embedded C++): Real-time ESP32 firmware, moving-average DSP filtering, and Bluetooth telemetry streaming.
Figma & Keyshot: Interactive mobile operator UI/UX wireframing and high-fidelity photorealistic CAD rendering.

05 // HARDWARE & SENSOR CIRCUITRY

VOLTAGE REGULATION

Dual-Voltage Power Tree

Unregulated 12V bus powering the BTS7960 and N20 motor drivers. Stepped down via LM2596 buck converter to 5V VIN for the ESP32, which supplies 3.3V logic rails.

[ 3S1P Li-Ion Pack: 11.1V / 4500mAh ]

├── Unregulated 12V Bus ➔ BTS7960 & N20 Motors

└── LM2596 Buck Regulator ➔ 5V VIN ➔ ESP32 ➔ 3.3V Logic Rails

ANALOG INSTRUMENTATION

Strain-Gauge Flexure & 24-Bit ADC

Wheatstone bridge load cell interfaced with the HX711 24-bit ADC. Implemented twisted-pair wiring to reduce electrical noise from adjacent DC motors inside the chassis.

[ 100g Strain Gauge Wheatstone Bridge ]

└── Twisted-Pair Differential Wiring (Noise Rejection)

└── HX711 24-bit ADC Module ➔ ESP32 GPIO

06 // EMBEDDED C++ FIRMWARE & COMMUNICATION STRATEGY

Custom C++ firmware and Python ground station toolchain developed for load cell acquisition, BTS7960 high-current scraping actuation, dual N20 locomotion, digital filtering, and Bluetooth telemetry data logging. Bluetooth communication was an internal engineering decision adopted to eliminate the cost, weight, and failure modes of wired slip rings or umbilical cables. Because the low-cost ESP32 development board featured integrated Bluetooth hardware, it drastically reduced project spending while allowing the team to concentrate resources on the primary mechanical scraping, traction, and containment subsystems.

MODULE 01 // DSP FILTER

100-Sample Moving Average Filter

Reduces raw load cell fluctuation from [ ±100 mg ] down to an acceptable noise floor of [ ±9.5 mg ] for accurate sample mass determination.

float applyMovingAverage(float sample) {
  sum -= samples[index];
  samples[index] = sample;
  sum += sample;
  index = (index + 1) % 100;
  return sum / 100.0f; // ±9.5mg noise
}

MODULE 02 // CALIBRATION

Dynamic Creep Drift Auto-Tare

Monitors 30-second thermal and physical sensor drift. If variance stays below [ 10 mg ], the routine auto-tares the scale to eliminate baseline creep.

long correctCreep(long weight_mg) {
  unsigned long curr = millis();
  if (curr - lastCreep >= 30000) {
    float offset = weight_mg - prevWt;
    if (abs(offset) < 10.0f) {
      scale.tare(); // Auto-tare drift
      prevWt = 0; return 0;
    }
    prevWt = weight_mg; lastCreep = curr;
  }
  return weight_mg;
}

MODULE 03 // MOTOR ACTUATION

BTS7960 PWM Scraping Control

Drives the JGB37-520 12V high-torque motor with controlled PWM duty cycles (50% forward cutting, 75% clearing reverse) to prevent high-current BMS cutoffs.

void executeScrapingCycle() {
  digitalWrite(REN, HIGH); digitalWrite(LEN, HIGH);
  analogWrite(RPWM, 127); // 50% cutting torque
  analogWrite(LPWM, 0);
  delay(3000);            // 3-second cutting arc
  analogWrite(RPWM, 0);   // Spindle halt
  delay(1000);
  analogWrite(LPWM, 191); // 75% reverse clear
  delay(3000);
  analogWrite(LPWM, 0);
}

MODULE 04 // LOCOMOTION

Dual N20 Directional Drive

Controls dual 12V 200 RPM drive motors through timed directional pulses and PWM enable staging for navigating 15-foot horizontal pipe sections.

void traversePipe(int direction, int durationMs) {
  analogWrite(ENA, 255); // 100% drive duty
  if (direction == 1) {  // Forward locomotion
    digitalWrite(IN1, HIGH); digitalWrite(IN2, LOW);
  } else {               // Reverse locomotion
    digitalWrite(IN1, LOW);  digitalWrite(IN2, HIGH);
  }
  delay(durationMs);
  digitalWrite(IN1, LOW);  digitalWrite(IN2, LOW);
}

MODULE 05 // TELEMETRY

Secure Bluetooth Serial (RFCOMM)

Streams paired 9600-baud CSV packets (Timestamp, Raw Mass, Filtered Mass) to ground monitoring devices without requiring wired umbilical slip rings.

void setupTelemetry() {
  SerialBT.begin("ESP32_BT_Logger", true);
  SerialBT.setPin("1234"); // Secure PIN pair
  SerialBT.println("START");
}

void broadcastSample(unsigned long t, long mg) {
  SerialBT.printf("DATA,%lu,%ld\n", t, mg);
  Serial.printf("%lu,%ld\n", t, mg);
}

MODULE 06 // GROUND STATION

Python Real-Time CSV Data Logger

Ground monitoring script featuring automated COM-port reconnection, safe UTF-8 byte stream decoding, and continuous append logging to scale_data.csv.

import serial, time

ser = serial.Serial("COM9", 9600, timeout=5)
with open("scale_data.csv", "w") as f:
    f.write("Time(ms),Weight(mg)\n")
    while True:
        line = ser.readline().decode("utf-8", errors="ignore").strip()
        if line.startswith("DATA,"):
            data = line.replace("DATA,", "")
            f.write(data + "\n")
            print(f"Logged: {data}")

07 // UI/UX & SYSTEM INTEGRATION

Mobile Operator Interface

Mobile app interface enabling safe remote operation outside vault radiation zones.

Interface Features

[✓]

Technician Authentication: Secure role-based login protocol for operators.

[✓]

Fuel Channel Grid Selection: Spatial reactor core fuel tube channel map.

[✓]

Dual-Orientation Switching: Instant switching between horizontal and vertical profiles.

[✓]

Target Mass Configuration: Configurable setpoint ([ 65 mg ] target within [ 30–80 mg ] spec).

[✓]

Live 4-Stage Lifecycle Tracking: Stage state machine (Deployment ➔ Sampling ➔ Contained ➔ Retracted).

[✓]

Automated CSV Data Logging: Automatic CSV export for lab testing records.

// STAGE TRACKING LIFECYCLE01Deployment: Drive motors / winch navigate tool to target pressure tube zone.
02Sampling: JGB37-520 actuates lathe bit; HX711 measures mass accumulation.
03Contained: Container disengages retention lip; internal compression springs automatically seal [ 65 mg ] radioactive sample vessel.
04Retracted: Winch/tether extracts tool back to channel access breach safely.

08 // POST-MORTEM & FUTURE ROADMAP

01

Root Cause Failure Analysis

High scraping torque during pipe engagement induced motor stalls. Peak stall current spikes exceeded the 3S BMS threshold, tripping overcurrent protection and cutting system power.

02

Custom PCB Design Roadmap

Transitioning from discrete breakout modules and point-to-point breadboard wiring to a unified 2-layer custom PCB with dedicated power planes and high-current traces.

03

Mechanical Safety Integration

Engineering a calibrated shear notch on the lathe bit holder. Under binding torque, the bit holder snaps safely, preventing motor stall current spikes and ensuring smooth recovery via winch failsafe.

09 // COMPLETE BILL OF MATERIALS & HARDWARE STANDARDIZATION

Full prototype component bill of materials breakdown totaling CAD $96.19. We developed this structured naming scheme (e.g., PD for Power Delivery, CL for Control Logic, SC for Structural Components) so the multidisciplinary group could more easily compartmentalize the workload. This allowed team members to clearly describe and reference the specific subsystem they were working on without confusing others with changing model numbers, manufacturer brand names, or vendor codes.

To streamline assembly and rapid prototyping, we actively standardized components wherever possible, utilizing M3 and M4 nuts and bolts exclusively alongside heat-set brass threaded inserts. Through strategic vendor selection and precise sizing, we were able to deliver a fully functional, fully integrated prototype for $96.19—staying under the client's $100 CAD project budget with materials to spare.

Item Code	Part Description	Vendor	Qty	Cost (CAD)
// POWER DELIVERY
PD01	22 AWG Hookup Wire	Amazon	1	$0.80
PD02	XT60 Battery Connectors	AliExpress	1	$1.60
PD03	16 AWG Power Wire	Amazon	1	$0.80
PD04	Molicel 21700 P42A Li-Ion Cells	18650 Battery	3	$15.00
PD05	3S 40A BMS Board	AliExpress	1	$2.94
PD07	LM2596 DC-DC Buck Converter	AliExpress	1	$0.45
// CONTROL LOGIC
CL01	ESP32-WROOM-C3 Board	Elegoo	1	$9.99
CL02	BTS7960 43A Motor Driver	AliExpress	1	$7.41
CL03	HX711 24-Bit ADC Module	AliExpress	1	$1.80
// MEASUREMENT
M01	100g Micro Load Cell	AliExpress	1	$4.93
// STRUCTURAL
SC01	PETG / PLA Filament (~0.7kg)	Bambu Lab	1	$16.99
SC02	M3 Brass Threaded Inserts	AliExpress	1	$0.80
SC03	M3/M4 Fasteners Assortment	AliExpress	24	$1.00
// TOOLING
ST01	MGEHR1212 Lathe Bit & Holder	AliExpress	1	$3.25
ST02	JGB37-520 12V 7RPM Motor	AliExpress	1	$11.28
// MOVEMENT
MV01	608ZZ Ball Bearings	AliExpress	8	$4.69
MV02	N20 12V 200RPM Drive Motors	AliExpress	2	$10.78
MV03	High-Friction Rubber Bands	Amazon	8	$1.68
TOTAL COST:				$96.19

10 // TECHNICAL HARDWARE GALLERY

High-resolution CAD renderings, strain-gauge test setups, and battery pack integration. Click any image to launch the uncropped lightbox modal preview.