4.6 Connect Spindles

• The section name is the type. Each spindle is a separate block at zero indent in the YAML — there is no spindles: group around them. Sections A–H below give a working block for each.
• G-code has no laser or VFD commands, so FluidNC treats every one of these as a spindle: M3 / M4 run it, M5 stops it, S sets the level.
• M4 is only accepted when the section has a direction, forward or reverse pin. Without one, only M3 and M5 mean anything.

The PWM 5V header — GPIO.45 (PWM), GPIO.46 (Laser), GND — with indicators LED44 and LED45.

• GPIO.45 → driver PWM / speed input, GND → driver signal ground.
• 5 kHz PWM. Check with a multimeter first: S10000 ≈ 5 V, S5000 ≈ 2.5 V, M5 = 0 V.

pwm:
  pwm_hz: 5000
  output_pin: gpio.45
  enable_pin: NO_PIN
  disable_with_s0: false
  s0_with_disable: true
  tool_num: 0
  speed_map: 0=0.000% 10000=100.000%
  off_on_alarm: false

Figure B1 — a laser module has three leads. PWM/TTL+ and GND go to the PWM 5V header; 12V+/VCC comes from the module's own supply and never touches the controller — but that supply's negative must sit on the same ground as the controller, or the TTL signal has no return path. The test YAML puts the laser on GPIO.46 — GPIO.45 serves equally well as long as the YAML names the pin you actually wired. Click the image to view it full size.

• GPIO.46 → laser module TTL / PWM input, GND → its signal ground (same header as above).
• Scale is 0–255, not 0–10000 — full power is S255.
• The laser only fires while moving. Set power with M3 S255, then send a move such as G1 F1000.

• A laser fires only in G1, G2 and G3 moves — never during G0, jogging or homing. If you need output in those modes, use a pwm section instead of Laser.
• Keep off_on_alarm: true so a triggered alarm cannot leave the laser burning.
• The last entry of speed_map is the maximum S your CAM software should emit — 255 here.

Laser:
  pwm_hz: 5000
  output_pin: gpio.46
  enable_pin: NO_PIN
  disable_with_s0: false
  s0_with_disable: true
  tool_num: 1
  speed_map: 0=0.000% 255=100.000%
  off_on_alarm: true

The 0–10V terminal — GPIO.8 (out2/Rev), GPIO.7 (out1/Fwd), out Common, GPIO.6 (0–10V), GND — with LED4 (M4 Rev), LED5 (M3 Fwd), LED6, and the 10 V adjustment trimmer (item ③).

Figure C1 — the basic connection: three digital wires (X1, X2, COM) and two analog wires (VI, GND). X3 stays empty here — see C2 if your drive needs it. Terminal names and the pushbutton station differ between brands; this drive is one example. Click the image to view it full size.

• out Common is not a ground. GPIO.7 with out Common, and GPIO.8 with out Common, are the two ends of an optocoupler — think of each pair as a switch. Its common end belongs on the drive's digital common (COM / DCM). The separate GND pin on the same terminal block is the return for the 0–10 V signal only, and the two are wired to different places on the drive.
• The two channels share one common — they are a pair of switches with a common pole, not two independent floating contacts, so both must return to the same drive terminal.
• The optocoupler output passes no voltage of its own to the drive; it only completes the drive's own input circuit. It does conduct in one direction only — see C2 if your drive uses source-type (PNP) inputs.
• Set the drive to take its run command from the terminals and its speed reference from the analog input, not from the keypad. Parameter numbers differ by brand — look them up in the drive's own manual.
• The 0–10 V output is factory-calibrated to 10 V — only touch the trimmer if your drive needs a different full scale, and watch a multimeter while you do.
• What the G-code does: M3 S12000 closes Fwd and sets the analog voltage; M4 releases Fwd and closes Rev; M5 releases both contacts and, with s0_with_disable: true, drops the analog output to the S0 value at the same time.

10V:
  forward_pin: gpio.7          # out1/Fwd - X1
  reverse_pin: gpio.8          # out2/Rev - X2
  output_pin: gpio.6           # 0-10V - VI, GND - analog common
  enable_pin: NO_PIN           # no enable contact in Figure C1
  direction_pin: NO_PIN
  pwm_hz: 5000
  disable_with_s0: false
  s0_with_disable: true
  spinup_ms: 0
  spindown_ms: 0
  tool_num: 2
  speed_map: 0=0.000% 1000=0.000% 24000=100.000%
  off_on_alarm: false

• The drive is set for three-wire control, where the STOP input must be held closed before it will start at all.
• A multi-function input is assigned to run-enable or external stop and has to be closed.
• The drive's digital inputs are source (PNP) type. An optocoupler output conducts in one direction only; a relay contact has no polarity and works either way.
• You need contacts with independent commons — the two optocoupler channels share one.

Figure C2 — three relay contacts do forward, reverse and start/stop. The 0–10 V pair is wired exactly as in C1; only the digital side changes. The relay board is a PiBot IsoSwitch V4, driven from I2SO.23 / I2SO.21 / I2SO.20 plus GND. Click the image to view it full size.

• The three COM terminals are separate. The board does not join them internally — the drawing bridges them with a short external link so all three contacts return to the drive's COM.
• Each channel is a NC / COM / NO changeover contact. These connections use COM–NO, so a de-energised board leaves the drive stopped.
• The IsoSwitch V4 runs from its own 4.5–40 V DC supply (24 V by default), takes 5 V or 3.3 V logic on S1 / S2 / S3, and its INPUT GND must be tied to the V5.88 GND. Trigger jumpers JP4→S1, JP5→S2, JP6→S3 — full detail in 4.3 Connect External Relay and the IsoSwitch V4 reference.
• I2SO.23 / I2SO.21 / I2SO.20 are the C-axis EN/STP/DIR signals in the test YAML — use them only when that axis is unused. Any spare output works; the pin names live in your YAML, not in the hardware.
• You can mix the two drawings. Keep Fwd and Rev on the optocouplers as in C1 and spend a single relay on the enable contact — then forward_pin: gpio.7, reverse_pin: gpio.8, enable_pin: I2SO.23.

10V:
  forward_pin: I2SO.20         # K3 - X1 (FWD)
  reverse_pin: I2SO.21         # K2 - X2 (REV)
  enable_pin: I2SO.23          # K1 - X3 (STOP / enable)
  output_pin: gpio.6           # 0-10V - VI, GND - analog common
  direction_pin: NO_PIN
  pwm_hz: 5000
  disable_with_s0: false
  s0_with_disable: true
  spinup_ms: 0
  spindown_ms: 0
  tool_num: 2
  speed_map: 0=0.000% 1000=0.000% 24000=100.000%
  off_on_alarm: false

• FluidNC drives levels, never pulses. A contact closes on M3 / M4 and opens on M5 — which is exactly what two-wire control expects, so start there if your drive offers it.
• Three-wire needs the enable contact. Releasing the start input does not stop a latched drive; only opening its STOP input does, and that is the contact enable_pin holds.

• A → VFD A, B → VFD B. Two wires only. If it does not communicate, swap A and B.
• The RS485 interface is galvanically isolated. Internally it is UART1 — TX GPIO.12, RX GPIO.11.
• Match baud and format at both ends, and set the VFD's modbus_id to match.

uart1:
  txd_pin: gpio.12
  rxd_pin: gpio.11
  rts_pin: NO_PIN
  baud: 9600
  mode: 8N1

ModbusVFD:
  uart_num: 1
  modbus_id: 1
  poll_ms: 250
  retries: 5
  spinup_ms: 6000
  spindown_ms: 6000
  tool_num: 3
  speed_map: 0=0.00% 24000=100.00%
  off_on_alarm: false

No VFD on the bench? A USB-to-RS485 adapter plus the PiBot VFD simulator proves the RS485 side works first.

• For a router or motor with no speed input at all. Any S value above 0 turns the output fully on; M5 turns it off.
• Never drive a relay with a PWM signal — the coil chatters and the contacts fail. That is exactly what this type avoids.
• Two ways to wire it on the V5.88:
  • MOSFET channel GPIO.4 or GPIO.5 — 500 mA each with an on-board flyback diode, enough for a DC relay coil or contactor coil of that size. They are M7 / M8 coolant in the test YAML, so free the one you take.
  • A relay module such as the PiBot IsoSwitch V4, fed from a spare 5 V, I2SO or Extra-GPIO output — see 4.3 Connect External Relay.
• Mains switching stays on the contact side, in a rated enclosure, with the contact chosen so that a power loss leaves the spindle off.
• Give spinup_ms a real value — a router started this way needs seconds to reach speed, and FluidNC will hold the next move for that long.

Relay:
  output_pin: gpio.4           # MOSFET channel, or any spare output driving a relay module
  enable_pin: NO_PIN
  direction_pin: NO_PIN
  disable_with_s0: false
  s0_with_disable: true
  spinup_ms: 3000              # let the spindle reach speed before cutting
  spindown_ms: 3000
  tool_num: 4
  off_on_alarm: true

• For a brushless motor driven through an ESC (the drone/RC kind, used as a light high-speed spindle), or for a hobby servo such as a pen lift.
• The signal is RC-style: a pulse of roughly 1–2 ms inside a 20 ms period, so pwm_hz: 50. min_pulse_us and max_pulse_us come from your ESC's own documentation, and speed_map is then a plain percentage of that span — no duty-cycle arithmetic.
• It needs a raw PWM pin: GPIO.45 or GPIO.46 on the 5 V header. Do not use the 0–10 V terminal — that output is a filtered analog voltage, not a pulse train.
• Three wires: signal, ground and power. The signal goes to GPIO.45 or GPIO.46, the ground to that header's GND, and the power to a 5 V source — the board's +5V pin for a small servo, or its own supply for an ESC and motor.
• An ESC that expects an arming sequence at power-up can be walked through it from G-code — M3 S0 for minimum throttle, M3 S1000 for full, M3 S500 for mid.
• The same section drives a pen-lift servo: M3 S1000 down, M5 up. FluidNC also has an RC servo axis feature if you want it on an axis instead.

Figure F1 — the wiring path for a 5 V hobby servo: signal (white) to a PWM pin on the PWM 5V header, black to that header's GND, and red to the +5V pin on the RS485 terminal block. The servo in the photograph is there to show the three leads, not as a recommended size — see the note below. Click the image to view it full size.

BESC:
  output_pin: gpio.45          # raw PWM pin - not the 0-10V terminal
  pwm_hz: 50                   # 20 ms period
  min_pulse_us: 1000           # ESC "off" pulse - check its datasheet
  max_pulse_us: 2000           # ESC full-power pulse
  tool_num: 5
  speed_map: 0=0% 1000=100%

• Like a PWM spindle, but with one PWM output per direction. While one is toggling the other is held low, and M5 turns both off.
• GPIO.45 and GPIO.46 are the two buffered 5 V PWM outputs — the natural pair for output_cw_pin and output_ccw_pin. They drive the inputs of an H-bridge module, which needs its own supply.
• The MOSFET channels cannot do this. They are low-side switches: they can turn a DC load on and off, but they cannot reverse it.
• There is no direction_pin in this section — the two output pins carry the direction.

HBridge:
  pwm_hz: 5000
  output_cw_pin: gpio.45
  output_ccw_pin: gpio.46
  enable_pin: NO_PIN
  disable_with_s0: false
  spinup_ms: 1000
  spindown_ms: 1000
  tool_num: 6
  speed_map: 0=0.000% 10000=100.000%
  off_on_alarm: false

• This section has no speed output. enable_pin fires the torch, and arc_ok_pin is an input that confirms the arc transferred.
• If arc_ok_pin goes inactive while cutting, motion is aborted with an alarm. arc_wait_ms is how long FluidNC waits for the confirmation before giving up.
• On the V5.88: fire the torch through a relay contact (E), and take arc OK into one of the ten optocoupler-isolated inputs you are not using for limits. Add :low if the signal is active-low.
• Plasma is a development feature in FluidNC — read its own plasma page for the hardware notes before wiring a torch.

Plasma:
  enable_pin: I2SO.23          # torch start, through a relay contact
  arc_ok_pin: gpio.36:low      # a free optocoupler input
  arc_wait_ms: 1000
  tool_num: 7
  off_on_alarm: true

• Define as many as your hardware supports. Each is its own section and they act independently — a machine can carry a router, a laser and a VFD at once.
• Every spindle needs its own pins. The config parser rejects a pin used twice, and FluidNC has to be able to control each spindle separately during tool changes and alarms.
• Tool numbers decide which spindle is active. tool_num is the first tool of that spindle's range, and the range runs until the next spindle's tool_num. One of them must be 0 so every tool number is valid. Break the rule and FluidNC warns, then hands out temporary ranges of 100 in config-file order.
• Keep T and M6 on the same line, the way the bench pages write M6 T2. A T on its own only sets the next tool; the change happens on M6. Send $G to read back the current tool and modal state.
• Send M5 before switching, so the previous output is left at zero. When M6 selects a tool inside the current spindle's own range, the S value is reset to 0.
• Use shielded cable for the analog and RS485 runs, and keep them away from motor and limit-switch wiring. A VFD is the noisiest device on the machine.