EMC Status

Stretch 3 detailed baseline (Eurofins report dated February 2, 2024) plus Stretch 4 re-test requirements under FCC Part 15B and CISPR 32.

Why this page changed

The previous summary table was replaced with per-frequency emissions data from `EMC-STATUS.md`, including measured levels, limits, and explicit margin headroom values in dB.

Class A vs Class B limits are tracked explicitly because the margin targets differ materially.

Margin Status:Marginal (<3 dB)Tight (3-6 dB)OK (>6 dB)

Radiated field levels are reported in dBµV/m.

Stretch 3 Per-Frequency Emissions

Operational Mode (30 MHz - 1 GHz)

Worst margin: 1.934 dB @ 960 MHz

Stretch 3 operational mode radiated emissions with measured levels, limits, and margins
Frequency (MHz)	Level (dBµV/m)	Limit (dBµV/m)	Margin (dB)	Status	Notes
960	54.926	56.86	1.934	Marginal	Closest point to limit in operational mode
114.23	49.609	53.96	4.351	Tight	Part of 108-135 MHz cluster
112.06	48.689	53.96	5.271	Tight	Part of 108-135 MHz cluster
112.76	48.305	53.96	5.655	Tight	Part of 108-135 MHz cluster
135.26	48.579	53.96	5.381	Tight	Part of 108-135 MHz cluster
480	50.800	56.86	6.060	OK	USB-related harmonic, still within limit

Charging Mode (30 MHz - 1 GHz)

Worst margin: 2.827 dB @ 148.5 MHz

Stretch 3 charging mode radiated emissions with measured levels, limits, and margins
Frequency (MHz)	Level (dBµV/m)	Limit (dBµV/m)	Margin (dB)	Status	Notes
148.5	47.173	50.00	2.827	Marginal	Closest point to limit in charging mode
115.06 (H)	51.010	53.96	2.950	Marginal	Part of 108-135 MHz cluster
480 (H)	53.345	56.86	3.515	Tight	USB 2.0/Hub-related behavior
480 (V)	51.621	56.86	5.239	Tight	USB 2.0/Hub-related behavior
115.23 (V)	46.718	53.96	7.242	OK	Cluster-adjacent but comfortable
960 (H)	50.001	59.96	9.959	OK	Comfortable in charging mode

Marginal Emissions Highlights

960 MHz emission (operational)

1.934 dB

54.926 dBµV/m measured against a 56.86 dBµV/m limit.

Highest immediate pre-scan risk.

148.5 MHz emission (charging)

2.827 dB

47.173 dBµV/m measured against a 50 dBµV/m limit.

Likely sensitive to cable routing and charger setup.

108-135 MHz cluster

2.95 to 5.655 dB

Peaks at 112.06, 112.76, 114.23, 115.06(H), 115.23(V), and 135.26 MHz.

Cross-mode repeatability indicates a persistent source.

Stretch 4 Delta and Re-Test Requirement

Stretch 4 delta items that change EMC risk relative to Stretch 3
What changed	EMC impact	Risk
36V power system + new 36V/8A charger	Different conducted and radiated profile than Stretch 3 (12V + NOCO charger baseline no longer applies).	High
ESP32 WiFi/BT module	Adds intentional 2.4 GHz transmitter behavior and additional regulatory constraints.	High
Pimu V1 replaces Pimu V0	New PCB layout, power topology, and digital noise profile require fresh characterization.	High
3rd omni wheel motor/driver	Adds another PWM switching source and current transient path during motion tests.	Medium

Why full re-test is mandatory

1. Power architecture changed from 12V to 36V, with a different charger path.
2. Core electronics changed (Pimu V1), so prior emissions signatures are no longer representative.
3. Motion and switching profile changed with an added third omni motor channel.
4. ESP32 introduces intentional radiated behavior and additional compliance scope.

Immunity Outcomes

Stretch 3 immunity outcomes relevant to Stretch 4 planning
Test	Level	Criterion	Result	Notes
ESD (EN 61000-4-2)	±4kV contact, ±8kV air	B	Pass	Intermittent display/script freezes were self-recovering without reboot, meeting Criterion B.
Radiated Immunity (EN 61000-4-3)	3 V/m, 80-2700 MHz	A	Pass	No functional degradation observed in tested modes.

Ranked Risk Assessment

Top EMC risks ranked by failure likelihood and impact
Rank	Risk	Why it matters	Mitigation	Severity
#1	960 MHz operational peak is only 1.934 dB below limit	Single small layout/cabling change could push this over the limit.	Targeted pre-scan around 960 MHz with cable and grounding variants before lab booking.	High
#2	148.5 MHz charging peak is only 2.827 dB below limit	Charging setup sensitivity increases failure probability during formal testing.	Validate charger cable/ferrite/common-mode choke options in pre-scan.	High
#3	108-135 MHz cluster appears in both modes	Repeated emissions across multiple nearby frequencies suggest a structural source.	Investigate USB hub/clock harmonics and run targeted shielding/routing experiments.	High
#4	Stretch 4 power architecture changed (36V battery + new charger)	Stretch 3 conducted margins cannot be reused due to different supply chain path.	Treat all conducted tests as net-new and run full pre-compliance sweep.	High
#5	ESP32 WiFi/BT adds intentional radiator compliance exposure	2.4 GHz emissions and approval path are materially different from Stretch 3 baseline.	Confirm modular approval/FCC Part 15B strategy before final compliance campaign.	High
#6	Pimu V1 and added 3rd omni motor alter total system noise	Board and motor topology changes can shift both low-band and harmonics behavior.	Run full-system motion profiles in pre-scan and compare against baseline peaks.	Medium

Stretch 4 EMC Checklist (Updated)

0 / 37 complete based on the latest EMC-STATUS.md pre-scan plan.

Pre-Lab Hardware Preparation

14 items

#1Confirm Stretch 4 prototype is fully assembled with production-intent cabling.

#2Verify all PCBs are final revision (Pimu V1 Calder, stepper boards, Wacc).

#3Flash latest firmware on Pimu, steppers, Wacc, and ESP32.

Track exact firmware versions for test report traceability.

#4Verify USB hub is V1 (ESD-fixed) and all hello-* devices enumerate correctly.

#5Confirm 36V 8A charger is the production-intent unit.

#6Prepare common-mode choke for charger cable.

#7Prepare custom charger cable with ferrite beads as fallback mitigation.

#8Prepare filtered HDMI cable (or ferrite snap-on).

#9Document all cable lengths to match customer-shipping configuration.

#10Label all EUT ports with reference IDs matching report tables.

#11Prepare support equipment list: monitor, keyboard/mouse, USB drives, Ethernet, optional servos.

#12Verify WiFi connectivity and continuous external ping.

#13Verify ESP32 stays connected to Firebase and sends telemetry continuously.

#14Verify NUC maintains stable SSH over Ethernet.

Software and Script Preparation

4 items

#15Write `S4_emc_test.py` with charging/operational mode flags.

#16Run script for at least 30 minutes on bench without crashes.

#17Add auto-restart/watchdog behavior so test script does not exit.

#18Document pass/fail criteria in Eurofins-compatible format.

Documentation Preparation

7 items

#19Update equipment configuration table (model, serial, revision).

#20Update ports/cabling table with cable type, length, and shielding state.

#21Prepare block diagrams for Developer/Debug and Autonomy modes.

#22Write EUT description and intended-use statement.

#23Define performance criteria A/B/C for each test mode.

#24Specify highest internal clock frequency used in filing.

#25Document firmware and software versions used during testing.

Day-Before Lab Checklist

6 items

#26Run full cold-boot flow from power-on to script running in under 5 minutes.

#27Run script for 1 hour in charging mode and 1 hour in operational mode.

#28Verify base is suspended so wheels can rotate freely for motor tests.

#29Pack spare charger, spare cables, and spare USB drives.

#30Pack JTAG flasher (Atmel ICE) for emergency firmware recovery.

#31Bring laptop with SSH and firmware reflash capability.

At-Lab Execution Checklist

6 items

#32Set up EUT on insulating material (<=150 mm) per procedure.

#33Route all cables exactly as expected in real deployment.

#34Start script and confirm continuous operation before scans begin.

#35Capture setup photos from front/rear/left/right/top views.

#36Log all anomalies with timestamps during testing.

#37If any pre-scan emission is within 3 dB of limit, record antenna position and frequency for mitigation.