ENGINEERING WORKUPrequested by Hank Written 2026-09-27 (Arizona time) · prices checked 2026-09-27

ComMarker B4 upgrade: motorized Z, fixed overhead camera, Raspberry Pi + Pico control

Machine: ComMarker B4 60 W JPT MOPA fiber laser. It has a JCZ/EZCAD-style galvo controller on USB, a 110 × 110 mm lens, a manual Z column with a crank, and dual red focus pointers. Today LightBurn 1.7.08 runs on an Ubuntu ThinkPad, and the laptop webcam streams to this page through MediaMTX.

1. Goals & constraints

• Motorized Z: a stepper on the Z column so focus height is set by numbers ("material is 3.2 mm thick" → head moves), repeatable to well under the depth of focus. Manual override stays possible.
• Built-in camera electronics: a camera fixed over the ~110 × 110 mm field for targeting, calibration and the live laserview stream. It replaces the laptop webcam.
• Off the laptop: camera and machine I/O move to a dedicated Raspberry Pi (Pi 5 preferred, Pi 4 acceptable).
• Use a Pico where it fits: real-time step generation, switches, interlock monitoring and relays, over USB serial to the Pi. You solder and can build simple boards, so the design uses through-hole or module parts on perfboard (or an Adafruit Pico terminal-block board if you'd rather skip soldering).
• Never auto-fire. Software may move Z, toggle the camera and switch the exhaust. Emission always needs a person at the machine (see §13).

2. Can a Raspberry Pi drive the galvo controller?

Short answer: not with LightBurn. With open-source software, yes, experimentally.

Only one program can own the galvo USB at a time. If you try MeerK40t on the Pi, move the USB cable (or use a manual USB 2.0 switch) and never have both connected.

3. Recommended architecture

Phases

1. Phase 1: Pi 5 + camera replaces the laptop webcam. Pico + Z drive + switches + E-stop/ARM chain go in. LightBurn stays on the ThinkPad, and laserview gets Hank-only Z controls.
2. Phase 2: Camera calibration (lens + homography) and a targeting overlay on laserview. Camera-based height check with the red pointers. Optional touch probe.
3. Phase 3 (optional): An x86 mini PC replaces the ThinkPad as LightBurn host, or you try MeerK40t/balor on the Pi for headless saved jobs. Keep LightBurn for design either way.

4. Motorized Z axis & auto-focus

Motor sizing (fill in with your measurements)

Required motor torque: T_motor = (F_crank × r_handle) / reduction × 2, which includes a 2× safety factor. Measure the pull force F with a luggage scale at the handle radius r while cranking up M4. Example: 15 N at 40 mm = 0.6 N·m, which is too much for a direct-drive NEMA17 (about 0.59 N·m holding and well under half that usable at speed). Use a 3:1 belt (0.4 N·m at the motor, still marginal) or a 5:1 planetary NEMA17 (17HS19-1684S-PG5, ~$29). If the crank turns easily (≤ 0.15 N·m), direct-drive a plain 17HS19-2004S1.

• Homing: an NC roller microswitch at the top of travel (Z home) and a second at the bottom as a hard limit. Home at startup and after any E-stop. Z coordinate = height of the lens bottom above the bed, calibrated once by jogging to perfect focus on a known surface.
• Focus model: Z_target = focus_distance(lens) + material_thickness + user_offset. focus_distance is the number ComMarker writes on the machine or manual (lens bottom to work surface) M5. Store one entry per lens (110 and 200 mm).
• Back-drive: check whether the head drifts down when you let go of the crank M7. If it does, keep the driver enabled at a reduced hold current (TMC2209 IHOLD). If it doesn't (trapezoidal screws are usually self-locking), the driver can be disabled at rest for silence.
• Manual override: the belt option keeps a knob on the crank. With direct drive, use a dual-shaft motor or turn the knob only when the driver is disabled (“Z free” button).

Auto-focus: three levels

1. Enter thickness (no hardware): type or pick the material thickness and the Pi moves Z. Covers 90 % of jobs.
2. Camera + red pointers (no extra hardware): the B4’s two red pointers cross at focus. The overhead camera finds both red dots (red-channel blob detection on the MJPEG snapshot), and their separation is proportional to the height error. Calibrate once by stepping Z through ±5 mm and fitting separation against ΔZ. Then “Auto-focus” means measure, move, and verify the dots coincide. Check whether the pointers can be switched on without firing M12.
3. Touch probe (optional): a pin probe (e.g. BIQU MicroProbe, $25.99) or a microswitch on a spring plunger beside the lens. Z moves down slowly until it triggers, then Z = trigger + offset. Probe with the laser disarmed, and retract before a job.

5. Overhead camera

• Camera: Raspberry Pi Camera Module 3 standard (IMX708, 12 MP, autofocus, 66° × 41°, $29.25). The standard lens has less distortion than the 120° Wide ($38.50). Pick the Wide only if the camera has to sit very close. Avoid NoIR versions: the IR-cut filter helps with the 1064 nm beam's glare.
• Mounting: fix it to the base on a 2020 extrusion post, not to the head. Put it beside the head, outside the beam cone, tilted about 20–30° toward the field center (see mechanical.svg). Because it doesn't move with Z, one calibration holds, and the Pi reprojects for the known material height. Put a cheap sacrificial window (thin glass or polycarbonate) in front of the lens to keep fume deposits off.
• Coverage: at ~220 mm slant distance the standard lens sees ~290 × 165 mm, so the 110 mm field fits the short axis with margin. That's ~0.06 mm/px on full-resolution stills and ~0.22 mm/px on the 720p stream.
• Focus lock: set autofocus once, then lock it (rpiCameraAfMode: manual, rpiCameraLensPosition) so the calibration doesn't drift.
• Lighting: a small diffuse white LED strip on the post gives consistent exposure. Fix the exposure and white balance after setup.
• Calibration: (1) lens calibration with a printed checkerboard (OpenCV calibrateCamera), (2) alignment: the laser marks a 3 × 3 grid of crosses on anodized aluminum or card, the Pi detects them and fits a homography from image to galvo coordinates, (3) apply a height correction from the known material thickness. LightBurn 2.1+ (Windows/macOS) can instead use the Pi’s network stream directly through its new camera system. On Linux 1.7.08 that isn't available, so targeting happens on laserview plus red-dot framing.
• Cable: Pi 5 uses 22-pin FFC. A 500 mm 22→15-pin cable costs $2.50. Route it away from the galvo and laser-source power leads. If the Pi has to sit more than ~0.5–1 m away, use a USB UVC camera instead (MediaMTX “generic webcam” path).

6. Wiring diagram & schematic

Pico pin map

Grounding: PSU −V, TMC2209 GND and Pico GND are common (through the driver board). Earth the PSU case and the B4 chassis. Use shielded 4-core motor cable with the shield grounded at the driver end only. Put a 100 µF/50 V electrolytic at the driver’s VM pin. Never unplug the motor while the driver is powered.

7. Pico firmware outline

Recommended: Arduino-Pico core (earlephilhower) + TMCStepper (UART config) + AccelStepper or a PIO step generator. These are mature libraries and keep the code small. Alternative: flash Klipper on the Pico and run Klipper + Moonraker on the Pi (manual_stepper, endstops, output_pin, TMC2209 UART are all built in). That's well-proven stepping with almost no firmware to write, but it's more stack than a single Z axis needs.

// laser-io Pico firmware (outline)
setup():
  pinMode(EN_N, OUTPUT); digitalWrite(EN_N, HIGH);   // driver OFF first
  inputs with pull-ups; 5 ms debounce
  Serial (USB CDC) 115200; Serial2 (UART1 GP8/GP9) 115200 → TMCStepper
  tmc.begin(); tmc.rms_current(CFG.run_ma); tmc.microsteps(16);
  tmc.en_spreadCycle(false); tmc.pwm_autoscale(true); tmc.ihold(CFG.hold_pct)
  watchdog_enable(500 ms)
  state = UNHOMED

loop():                           // never blocks
  watchdog_update()
  read_inputs()                   // HOME ZMIN PROBE ESTOP DOOR ARM, V24
  if ESTOP or V24 < 20 V:  stop_now(); EN_N=HIGH; state=ESTOP   // latched until E-stop released AND host sends RESET
  if moving and (ZMIN or (HOME and dir==up)): stop_now(); fault("limit")
  if moving and host_heartbeat_age > 2 s:  stop_now(); fault("host lost")
  stepper.run()                   // accel ramps
  handle_serial_line()
  every 200 ms: emit STATUS if changed

commands (one line in → one JSON line out):
  HELLO                    → {"ok":true,"fw":"lz-1.0","steps_mm":1600}
  STATUS                   → {"z":42.315,"homed":true,"moving":false,"estop":false,
                              "door":true,"armed":false,"probe":false,"lim":[0,0],"v24":24.1,"fault":null}
  HOME                     → up at low speed to HOME, back off 1 mm, re-approach slowly, z := Z_TOP
  MOVE <z_mm> [mm_s]       → absolute; refused unless homed, not ESTOP, inside soft limits;
                              final approach always from above (backlash), then report
  JOG <dz_mm>              → relative, max 10 mm per command
  PROBE [max_mm]           → slow down until PROBE, report z, back off 2 mm
  STOP                     → controlled decel
  FREE / HOLD              → disable / enable driver (manual crank)
  RELAY exh|valve 0|1      → outputs (exhaust stays controllable during E-stop)
  CFG key=value …          → run_ma, hold_pct, steps_mm, soft_min, soft_max, z_top (saved to flash)
  PING                     → heartbeat (host sends every 500 ms while a move is active)
  RESET                    → clear latched fault (only if ESTOP released)

never:  anything that touches laser emission. The Pico reports ARM/ESTOP/DOOR only.

udev (on the Pi) gives it a stable name: SUBSYSTEM=="tty", ATTRS{idVendor}=="2e8a", ATTRS{serial}=="<your-pico-serial>", SYMLINK+="laser-pico".

8. Pi software stack & laserview integration

Camera: MediaMTX with rpiCamera

# /etc/mediamtx/mediamtx.yml (Pi) — excerpt; MediaMTX arm64 release (v1.21.x at time of writing)
rtspAddress: 127.0.0.1:8554        # local only; the tunnel carries the stream
hls: no
webrtc: no
paths:
  cam:
    source: rpiCamera
    rpiCameraWidth: 1280
    rpiCameraHeight: 720
    rpiCameraFPS: 15
    rpiCameraBitrate: 2500000
    rpiCameraAfMode: manual          # lock focus after setup
    rpiCameraLensPosition: 4.5       # dioptres — set from your setup (measure)
    # publish to the laserview server over the tunnel (same as the laptop does today)
    runOnAvailable: ffmpeg -rtsp_transport tcp -i rtsp://127.0.0.1:8554/cam -c copy -f rtsp rtsp://…publisher…@127.0.0.1:<tunnel-port>/laser
    runOnAvailableRestart: yes
  snap:
    source: rpiCamera
    rpiCameraSecondary: true         # MJPEG by default for secondary streams
    rpiCameraWidth: 1536
    rpiCameraHeight: 864
    rpiCameraFPS: 5
    rpiCameraMJPEGQuality: 85

(Older MediaMTX releases call the hook runOnReady. The publisher credential stays in the Pi's env file and never goes into the page or a repo.) Nothing changes on the laserview server: the Pi simply takes over as the publisher of the laser path. The existing on/off toggle keeps working, with the Pi's agent starting and stopping the camera path instead of the laptop's.

laser-io API (FastAPI on the Pi, loopback + LAN only)

• systemd units on the Pi: mediamtx.service, laser-io.service (User=laserio, in the dialout and video groups), laserview-agent.service, laserview-tunnel.service (autossh, outbound only). Add Restart=always and a hardware watchdog (dtparam=watchdog=on).
• How laserview calls it: browser → laserview API (the existing Hank-only gate: same-origin check + account check) → reverse tunnel → Pi laser-io. The public page never talks to the Pi, and anonymous users only see the stream. New Hank-only buttons: Home Z, Jog ±0.1/1/10 mm, Material thickness → Focus, Auto-focus, Z free, Exhaust, and a status strip (Z, homed, E-stop, door, ARMED).
• “Job active” interlock for Z: the laserview run feature already knows when it started a job. laser-io refuses Z moves while a run is active. As a hardware backstop, check whether the galvo board has a free output you can set during marking and wire it into a spare Pico input (optional, M14).
• Phase 3 option: install MeerK40t (Pi64 build or pip install meerk40t) plus a udev rule for 9588:9899. It can then run saved jobs headless from its console, with the same ARM rules.

9. Mechanical notes

• Option A (direct drive): remove the handwheel. A flexible beam or jaw coupler (5 mm motor side, crank-shaft Ø on the other side) connects to a NEMA17 on a four-standoff or 3D-printed bracket bolted to the column’s top cap. It's the cheapest and has no belt backlash, but it needs coaxial alignment. The coupler forgives only small misalignment.
• Option B (GT2 belt, recommended if torque is high): a 20T pulley on the motor, 40T or 60T on the crank shaft (bore = crank Ø, set screws on the flat), and a closed-loop 6 mm GT2 belt. The motor sits on a slotted L-bracket clamped to the column; the slots set belt tension. You keep a small knob on top for manual turning, and get 2–3× more torque and resolution.
• Bracket material: PETG or ASA printed brackets are fine for a NEMA17 at these loads. Use aluminum plate if the column gets warm or you want it permanent. Don’t drill the column without checking what’s inside (lead screw, wiring for an electric-lift variant).
• Limit switches: roller-lever microswitches on small printed brackets, triggered by the carriage at the top and bottom of travel. Make them adjustable (slotted holes).
• Camera mount: a 2020 post bolted to the base plate (use existing holes or add a clamp plate). Add a short arm, then a printed tilt mount with an M2 or M2.5 hole pattern for Camera Module 3. It must be rigid: any knock means redoing the alignment.
• Electronics box: Pi + Pico board + TMC2209 + PSU in a ventilated enclosure away from the beam, with the E-stop and ARM key on the front where you can reach them from the operator position.

10. Measurements Hank must take

11. Bill of materials

12. Price list (real prices, cited)

All prices are USD, listed on the vendor's own product page and checked 2026-09-27. Prices exclude tax and shipping. Stock was “in stock” on the product page unless noted. Rows marked ESTIMATE are my estimates, not quotes. Prices move: Raspberry Pi boards and mini PCs are noticeably more expensive in 2026 than at launch.

Arithmetic: $317.78 + $85–175 = $402.78–$492.78. Adding $19.24 + $11.00 + $12–23 + $25.99 + $249.99 gives $720.99–$821.99.

13. Safety

14. Build & test plan

1. Take M1–M14. Choose Option A or B and direct-drive vs geared. Order parts.
2. Bench-build the Pico board. Flash the firmware. With the motor on the bench, test UART config, current, direction and microsteps, and confirm the driver stays disabled at boot.
3. Build the safety box (E-stop, ARM key, door jumper). Verify with a meter that pressing E-stop removes 24 V and B4 mains, that the key gates only the B4, and that the Pico sees each contact.
4. Set up the Pi: OS, MediaMTX with the camera, then laser-io. Test /status, home, and moves from the Pi shell.
5. Mount the motor and limit switches on the column. Home repeatedly and measure repeatability with a dial indicator (target ≤ 0.02 mm). Calibrate Z_TOP and focus per lens with a focus-ladder test.
6. Mount the camera. Lock focus. Do lens calibration and homography, then add the red-dot auto-focus calibration.
7. Switch laserview's publisher from the laptop to the Pi. Add the Hank-only Z panel to laserview.
8. Optional: set up the mini PC as LightBurn host, and/or run a MeerK40t trial with the galvo USB moved to the Pi (one host at a time).

15. Sources (checked 2026-09-27)

• LightBurn docs, Installing LightBurn: 1.7 is the last Linux-compatible version; OS compatibility table; Windows-on-ARM USB driver limitation.
• LightBurn forum, LightBurn on Pi4 (LightBurn Linux dev: no ARM build due to library dependencies) and Install LightBurn on Raspberry (unsupported; emulation only).
• LightBurn docs, Cameras: 2.1 introduced the new camera system, including IP (network) cameras.
• MeerK40t release 0.9.8100 (Pi64 build), Balor operation help (MOPA pulse width 1–250 ns), balor-meerk40t (USB 9588:9899), Bryce Schroeder’s Balor notes.
• MediaMTX docs, Raspberry Pi Cameras and the reference config (rpiCameraCodec: auto → softwareH264 when there's no hardware encoder; secondary MJPEG stream; runOnAvailable).
• ComMarker B4 product page (electric lifting on some builds, dual red locators, 110/200 mm lenses) and B4 user manual (focus distance written per machine).
• Vendor product pages for every price in §12 (PiShop.us, Adafruit, biqu.equipment, StepperOnline, TRC Electronics, Newegg, RS Americas, UltiMachine, GMKtec, Beelink).

Engineering workup for Hank · laserview.hankelsner.tech/workup/index.html · 2026-09-27. Diagrams: architecture.svg · wiring.svg · schematic.svg · mechanical.svg. Treat values marked “measure” or ESTIMATE as unconfirmed until checked on the machine or quoted.