fpv-spider

This is just dumped from Grok and has not been verified.

Outdoor confined-space survey / recon crawler. Possible SAR support later. Pilot it from a standard FPV-drone ELRS radio with FPV goggles. Not a certified rescue device. A human team still owns any rescue.

Use a hexapod when you need discrete footholds, stepping over debris, a narrow/tall profile, static stability with one jammed leg, or body-pose peeking around a corner with feet planted.

Do not use this platform if target gaps are under ~150–180 mm. Build a tracked or snake chassis instead.

Professional confined-space work usually uses tethered tracked inspection robots or caged drones. This is a recon tool that can go where wheels smear or get stuck.

An FPV drone maps sticks almost 1:1 to motors. A hexapod cannot. Eighteen servos must stay coordinated (tripod gait, IK, body pose). The ELRS receiver sends high-level commands. A gait computer sits in the middle.

ELRS radio (existing handset)
        |
   ELRS RX  -- CRSF serial -->  ESP32 gait computer
                                      |
                                 2x PCA9685
                                      |
                                 18x MG92B
                                      +
              analog FPV cam + VTX + lights + optional DVR
                                      +
                         2S pack + dual BEC + recovery tether

PWM-only receivers (ER6/ER8) are wrong as the only brain. They cannot run a gait. Use CRSF into an MCU.

Keep video independent of control, same as a drone.

Circular body so there is no long axis to snag. Micro servos so stance stays near 350 mm. FPV mast and tether hook printed in.

Leg geometry in the generator (mm):

MG92B torque is only ~3.5 kg·cm at 6 V. That is the size/torque compromise that keeps a 35 cm stance. Payload is FPV + small VTX + 2S + lights. A full thermal module is v1.5, not v1. Do not hang a Jetson on this frame.

Standard-size 20 kg servos blow the diameter past ~420 mm. Wrong for a void crawler.

• voidcrawler_vc35/stl/ printable parts plus non-printable _preview_assembly.stl
• voidcrawler_vc35/src/generate_frame.py regenerate STLs
• voidcrawler_vc35/docs/vc35_top_view.png dimension sketch
• voidcrawler_vc35/VC35_BOM_and_build.xlsx live cart / print list / wiring / radio map
• voidcrawler_vc35.zip whole pack

STLs are v0.1 block geometry. Dimensionally aimed at an MG92B pocket. Servo brands vary by a few tenths of a millimetre. File the first pocket before printing the other five of each leg part.

Regenerate after changing lengths:

python3 src/generate_frame.py

Edit COXA_LEN, FEMUR_LEN, TIBIA_LEN, BODY_R at the top of the generator.

Printer notes:

• Nozzle 0.4 mm.
• Bed: PETG 75–85 °C, ASA 90–100 °C, TPU 40–50 °C.
• Dry filament.
• Orient legs so layer lines run along the beam, not across servo ears.
• PLA is acceptable only for a first fit-check of body_top / tray — not for outdoor legs.
• Body design intent: one sealed-ish electronics tub, servos outside, belly clearance, service hatch, TPU replaceable feet, ELRS antenna high and clear of the 5.8 antenna, printed rear tow hook.

Planning total ~$414 at the 2026 street estimates in the workbook. Yellow price cells are meant to be overwritten. Status dropdown: Buy / Have / Skip / Ordered.

Two power domains. Never share one weak 5 V BEC across servos, RX, and VTX.

2S pack → switch → XT30
              ├─ XL4015 @ 6.0 V → PCA9685 V+   (servos only)
              └─ Mini buck @ 5.0 V → ESP32, ELRS RX, camera, VTX

ELRS TX → ESP32 RX
ELRS RX → ESP32 TX
ESP32 SDA/SCL → both PCA9685 (0x40 and 0x41)

Brownout is the number-one killer of first hexapods. Eighteen MG92B servos can spike well past 10 A. If the ESP32 resets when the robot stands, the 6 V BEC is too weak or the pack cannot deliver stall current. First stand-up on a current-limited bench supply, not a LiPo.

Label legs L1–L3 / R1–R3 clockwise from the camera.

Mode 2 assumed. Packet rate 50 Hz or 100 Hz Full. Switch mode 8ch or 16ch/2. Walking does not need 500 Hz. Unique bind phrase. 900 MHz preferred for interior / timber; 2.4 GHz is fine in open fields if that is all the radio has.

Failsafe: sit or freeze joints, lights stay on, VTX stays on. Never hold-last walk command. You still need the picture to recover the robot.

Send pack voltage telemetry back to the radio.

Do not write a gait engine from scratch.

1. Stand the robot with any ESP32 hexapod sketch that already talks to two PCA9685 boards. RookiDroid-style UDP firmware is a reasonable donor. rasheeddo/hexapod_dev_esp32 already speaks SBUS from a radio — closest existing architecture.
2. Replace the UDP/SBUS parser with CRSF using AlfredoCRSF or CRSFforArduino.
3. Map CH1–CH4 to body X/Y/yaw/speed. CH5 is ARM. Failsafe sits.
4. Later: body pitch/roll from the left stick while feet are planted (the rubble peek move).

Donor projects worth reading, not cloning blindly:

• RookiDroid Hexapod / Mochi — ESP32, printable, gait LUTs, web cal. Mochi settled on MG92B after 21g servos jittered.
• rasheeddo hexapod_devesp32 — SBUS radio + IK on ESP32 + dual PCA9685.
• ggldnl Hexapod — Servo2040 + real IK. Heavier first week.
• AlfredoCRSF / CRSFforArduino — ELRS channel + telemetry libraries.

Must have on v1:

• Analog FPV camera with a starlight sensor (Ratel 2 / T-Rex class) for dusk and interiors.
• 25–200 mW 5.8 GHz VTX, adjustable from the radio if possible.
• Onboard DVR or cheap HD action camera pointing the same way. FPV is for driving. Survey work needs a file.
• 2–5 W white flood, switched. Confined spaces are dark.
• Pack voltage, current, IMU so the body can level on a slope.
• Camera at the front, 15–30° down, so you see the ground you are about to step on. Foam-mount it. Gait vibration is real.

Add on v1.5 after it walks outside:

• One-axis tilt, maybe pan.
• 850 nm IR illuminator + IR-sensitive analog cam.
• Cheap thermal (Lepton class) as a second view, not the pilot view.
• Lav or contact mic if you care about voices through debris.
• GPS only for outdoor survey breadcrumbs. Ignore GPS indoors.

Leave for v2:

• Depth camera / LiDAR mapping
• Companion computer
• Gas sensors (CO, O2, LEL) only if actually supporting a fire/rescue team who know how to interpret them
• Autonomy

Analog FPV is the right pilot link in clutter: it snows before it dies. Digital stays pretty until it freezes. Caddx Gazer / Infra-style analog cameras exist if you want zoom or IR later.

2.4/900 MHz ELRS and 5.8 GHz video coexist if antennas are separated and the VTX is not sitting on the RX.

• [ ] Print body + one coxa/femur/tibia/foot and test-fit a servo. Pass: servo seats without cracking plastic.
• [ ] Print remaining structural set in PETG/ASA + TPU feet. Pass: all 6 legs identical.
• [ ] Servos center every servo with a tester at 1500 µs before installing horns. Pass: horn spline at mid-travel.
• [ ] Legs assemble 6 legs loosely; label L1–L3 / R1–R3 clockwise from camera. Pass: each joint moves 90°+ without bind.
• [ ] Power set 6.0 V and 5.0 V bucks on the bench. Never guess. Pass: DMM confirms voltages.
• [ ] Brain wire ESP32 + both PCA9685 + ELRS RX on the tray. No servos yet. Pass: RX binds, serial monitor sees CRSF.
• [ ] Body install tray, pack, switch, VTX (antenna ON), camera. Pass: no metal shorting the buck modules.
• [ ] Integrate mount 6 legs. Power via current-limited supply first time. Pass: sits / stands without brownout.
• [ ] Radio load EdgeTX model map. Pass: ARM switch sits the robot.
• [ ] Field fit tether before any void. Walk gravel, then a pallet tunnel. Pass: failsafe sits, picture stays up.

Week 1–2

print, assemble, calibrate, walk on carpet.

Week 3

gravel, roots, wet grass. Tune step height and body height from the radio.

Week 4

night walk with lights + analog FPV. Practice sitting on failsafe and pulling the tether.

Week 5

constructed yard void (pallets, pipe, furniture) before any real structure.

Practice body-pose mode: freeze the feet, pitch/yaw the body and camera around a corner. That is the move that makes hexapods useful in rubble.

First milestone that actually matters:

1. Robot stands and sits from AUX1.
2. Forward / turn from the right stick, speed from throttle.
3. Failsafe sits.
4. Analog FPV picture while it walks across a room.

• Always tether in a void. 3–5 mm line from the rear hook to a person outside. Radio multipath and battery sag will otherwise strand it.
• Optional later umbilical: power + analog video up the same line.
• Lights on before you lose the analog picture.
• If the picture snows, turn around. Do not "just a little further."
• Low-voltage telemetry on the radio. Sit, then reel.
• Failsafe sits, lights stay on, VTX stays up.
• Do not present this as a life-safety appliance. No onboard "find the victim" autonomy on v1.

• Do not drive 18 servos directly from an ER8 PWM receiver.
• Do not start with 9g plastic-gear servos.
• Do not share one weak 5 V BEC between servos, RX, and VTX.
• Do not write a gait engine from scratch if an existing ESP32 hexapod already walks.
• Do not start with LiDAR and a Jetson.
• Do not use PLA on outdoor legs.
• Do not invent a new chassis until one donor gait stands on the bench.
• Do not skip centering servos before horns.
• Do not power a VTX without an antenna.

Yard/trail surveyor class is ~45 cm, 2–3.5 kg, 25–35 kg·cm servos, ~1 kg payload, HexArth-sized. Rejected for the void crawler because it will not fit the holes. Keep that as a second robot if outdoor payload outgrows MG92B.

Waveshare HexArth reference (too big here): 344 × 429 × 155 mm standing, 2.1 kg, 1 kg payload, 30 kg·cm bus servos, ESP32 + optional Pi.

• Firmware: CRSF → gait on this channel map.
• v0.2 parts after measuring the actual servo batch (pocket slop, horn height, cable exits).
• 900 vs 2.4 on the handset you actually own.
• Whether throttle is walk speed or body height.
• Whether to donor RookiDroid firmware or rasheeddo IK.

• Hexapod Spider Robot with Servo & Arduino