Arm Fc Physical

arm-fc-physical

Arm a physical flight controller via MSP and download blackbox logs for analysis

When to Use This Skill

• Generate blackbox logs from physical FC for debugging
• Test firmware behavior without actual flight
• Capture sensor data for analysis
• Validate blackbox logging is working correctly

Quick Start

1. Configure FC (One-Time Setup)

# Check FC status
~/.claude/skills/flash-firmware-dfu/fc-cli.py status /dev/ttyACM0

# Configure MSP receiver and arming
cd claude/developer/scripts/testing/inav/sitl
python3 configure_fc_msp_rx.py --port /dev/ttyACM0

# Configure blackbox — pick ONE depending on how you want to trigger logging:
cd ../blackbox/config
python3 configure_fc_blackbox.py --port /dev/ttyACM0 --rate-denom 100          # logs only while armed
python3 configure_blackbox_arm_controlled.py --port /dev/ttyACM0 --rate-denom 100  # same, arm-gated variant
# OR set blackbox_arm_control=-1 (via CLI) to log continuously from boot — see
# "Logging Without Arming" below; skips configure_fc_msp_rx.py entirely.

# Calibrate accelerometer via INAV Configurator (if needed)

Directory note: these scripts live under claude/developer/scripts/testing/inav/ in subdirectories by function (sitl/, blackbox/config/, blackbox/analysis/, gps/injection/) — despite sitl/ in the path, several of those scripts (this one included) work against physical hardware too, not just SITL. Don't assume a script only applies to SITL from its directory name; check its own docstring.

2. Generate Blackbox Log

SAFETY: Remove propellers before arming!

cd claude/developer/scripts/testing/inav/sitl

# Arm for 30 seconds (default)
python3 continuous_msp_rc_sender.py /dev/ttyACM0

# Arm for custom duration
python3 continuous_msp_rc_sender.py /dev/ttyACM0 --duration 60

Avoid arm_fc_physical.py (claude/developer/scripts/testing/inav/sitl/arm_fc_physical.py) for this step — despite the name matching this skill, it arms via HITL mode, which bypasses the blackbox subsystem entirely (see Common Issues below). It's only useful for a quick "does MSP arming work at all" smoke test, never for generating a log.

Logging Without Arming

If you don't need a realistic arm-triggered log — e.g. bench-testing the SD/flash write path itself — set blackbox_arm_control = -1 via CLI (set blackbox_arm_control = -1 then save, in the same CLI session — see the note under Common Issues about settings reverting). This logs continuously from boot to power-off and sidesteps every arming prerequisite (accel cal, RX config, ANGLE/CAL flags). Pair it with claude/developer/scripts/testing/inav/gps/injection/gps_inject_no_arming.py if you want synthetic GPS data flowing into the log without attempting to arm.

3. Download Log

download_blackbox_from_fc.py only works for SPIFLASH (MSP_DATAFLASH_READ). For SDCARD, there's no MSP equivalent — reboot to USB mass-storage mode and copy the files off instead:

python3 .claude/skills/flash-firmware-dfu/fc-cli.py msc /dev/ttyACM0
sleep 3   # auto-mounts on Ubuntu
lsblk   # confirm which device is the card — don't assume /dev/sdb
cp /media/$USER/<label>/logs/LOG*.TXT ./
udisksctl unmount -b /dev/sdb1   # unmount before FC leaves MSC mode; use the confirmed device

4. Decode and Analyze

# Decode log to CSV
blackbox_decode test_log.TXT

# Creates: test_log.01.csv, test_log.01.gps.csv
# View data
head -50 test_log.01.csv

# Or classify the log as CLEAN/SUSPECT/CORRUPT (missing frames, mid-file zero
# blocks, truncation, torn header) instead of eyeballing the CSV:
python3 claude/developer/scripts/testing/inav/blackbox/analysis/check_blackbox_integrity.py test_log.TXT

Prerequisites

Hardware:

• Flight controller with USB connection
• FC appears as /dev/ttyACM0 (or similar)
• Propellers removed!

Software:

pip3 install pyserial
pip3 install git+https://github.com/xznhj8129/mspapi2

FC Configuration:

1. Accelerometer calibrated (via Configurator)
2. MSP receiver configured (rx_spi_protocol = MSP)
3. ARM mode on AUX1 (range 1700-2100)
4. Blackbox enabled (blackbox_device = SPIFLASH)

Common Issues

FC Won't Arm

Check arming flags:

~/.claude/skills/flash-firmware-dfu/fc-cli.py status /dev/ttyACM0

Common blockers:

• ACC - Calibrate accelerometer via Configurator
• CAL - Wait 5+ seconds after boot
• ANGLE - Level FC or disable small_angle check
• SETTINGFAIL - Fix RX settings with configure script

No Blackbox Data (0 bytes)

1. HITL mode was used - Use continuous_msp_rc_sender.py instead (never arm_fc_physical.py — see above)
2. FC not armed - Check arming flags
3. Blackbox not configured - Run configure_fc_blackbox.py
4. Flash full - Erase via Configurator
5. SD card has no filesystem - if blackbox_device = SDCARD, check status for Filesystem: Fatal - no FAT MBR partitions. The card is detected at the hardware level but won't accept writes until it's reformatted (single FAT32 partition) on a computer — INAV can't format it in place unless the target defines USE_USB_MSC (most don't; check target.h).

Settings Silently Not Taking Effect

Two real gotchas hit during hardware testing:

• configure_fc_blackbox.py (and other scripts using MSP2_COMMON_SET_SETTING) print "✓" without confirming the write actually landed. Always verify with fc-cli.py "get <setting>" after running one of these scripts — don't trust the script's own success message.
• Changes made via separate fc-cli.py invocations can revert. Each invocation opens and closes its own serial connection; an unsaved set from one invocation can be lost before a later invocation's save commits it. Combine set and save in a single invocation instead: fc-cli.py $'set some_setting = 1\nsave' /dev/ttyACM0.
• blackbox_rate_denom may get silently overridden at boot. INAV enforces a hard 1kHz cap on blackbox logging rate regardless of what you set (fc_init.c, blackboxLooptime check) — "run faster than 1kHz can cause UAV to drop dead when digital ESC protocol is used." On a board with a fast PID loop (e.g. ~2kHz), rate_denom=1 gets silently raised to whatever the fastest allowed value is (e.g. 2). Check the actual value with fc-cli.py "get blackbox_rate_denom" after reboot rather than assuming what you set stuck.
• Two clients can't share the serial port. If INAV Configurator (or any other tool) is already connected to the FC, MSP requests from your script will time out with no useful error. Check ps aux | grep -i configurator and disconnect it first.
• CLI mode blocks MSP indefinitely, with no timeout. If a tool enters CLI mode (####) and closes the connection without sending exit, the FC stays latched in CLI — any MSP arming script run afterward gets silently ignored (visible as the CLI arming-disabled flag). Fixed in fc-cli.py (now sends exit before closing); still, prefer MSP over CLI for routine checks when possible.
• blackbox_arm_control = -1 on SDCARD races SD-card mount at boot — blackboxStart() can fire before AFATFS finishes mounting, and gives up permanently for that boot. Use arm-triggered logging (= 0, the default) instead.
• A freshly-reformatted SD card can be slow to accept its first log — AFATFS reserves free space (FREESPAC.E) before the logs dir exists; give it a few minutes if the first log never appears.

Serial Port Permission Denied

sudo usermod -a -G dialout $USER
# Log out and back in

Key Scripts

Scripts live under claude/developer/scripts/testing/inav/ in subdirectories — see the directory note in step 1 above; not everything under sitl/ is SITL-only.

• sitl/continuous_msp_rc_sender.py - Arm FC and send RC frames (physical FC; despite the dir name, does NOT use HITL)
• sitl/arm_fc_physical.py - Quick MSP-arm smoke test via HITL — do NOT use for blackbox logging (HITL bypasses it)
• sitl/configure_fc_msp_rx.py - Configure MSP receiver and ARM mode (formerly referenced here as configure_fc_for_msp_arming.py, which no longer exists)
• blackbox/config/configure_fc_blackbox.py - Configure blackbox settings (arm-gated logging)
• blackbox/config/configure_blackbox_arm_controlled.py - Same purpose, arm-gated variant
• blackbox/config/download_blackbox_from_fc.py - Download log via MSP
• blackbox/analysis/check_blackbox_integrity.py - Classify a downloaded log as CLEAN/SUSPECT/CORRUPT (missing frames, mid-file zero blocks, truncation, torn header); supports --dir/--compare for before/after A-B testing
• gps/injection/gps_inject_no_arming.py - Inject synthetic GPS data without arming; pairs with blackbox_arm_control = -1 for log-from-boot testing

Technical Details

RC Frame Rate: 50 Hz (matches CRSF standard) Download Speed: 2.5 KB/s (20s for 50KB log) MSP Commands Used:

• MSP_SET_RAW_RC (200) - Send RC channels
• MSP_DATAFLASH_SUMMARY (70) - Query flash status
• MSP_DATAFLASH_READ (71) - Download data

RC Channel Mapping (AETR):

• Channel 3: Throttle (1000=low, 1600=mid)
• Channel 5: AUX1 ARM (1000=disarm, 1800=arm)

See Also

• Detailed Guide: .claude/skills/arm-fc-physical/REFERENCE.md
• Flash Firmware: /flash-firmware-dfu
• Build Firmware: /build-inav-target
• Arm SITL: /sitl-arm
• MSP Protocol: /msp-protocol