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VFD Spindle Setup

grblHAL supports controlling VFD (Variable Frequency Drive) spindles directly via Modbus (RS485). This allows for precise RPM control, direction switching, and real-time status feedback (voltage, current, actual RPM) without using a simple 0-10V analog signal.

Supported VFDs​

The following VFDs are supported by the plugins/spindle/vfd modules:

  • Huanyang (SL series and others using the common protocol)
  • H-100 (Common cheap VFDs)
  • GS20
  • YL-620
  • Nowforever
  • ModVFD (Generic configurable driver)

1. Wiring (RS485)​

To connect a VFD, you nominally need an RS485 module connected to your microcontroller's UART pins.

RS485 ModuleVFD Terminal
A+RS+ / A+ / 485+
B-RS- / B- / 485-
GNDGND / COM
Wiring Best Practices
  • Use twisted pair cable for A and B.
  • Use shielded cable, grounding the shield at the controller side only.
  • RS485 is sensitive to noise; keep it away from the main spindle power cables.
  • If communication fails, try swapping A and B lines (labeling varies by manufacturer).

2. Firmware Compilation​

VFD support is enabled by defining the spindle type for a specific spindle slot (0-3). Use the following IDs:

IDVFD Type
1Huanyang (SL Series)
3GS20
4YL-620A
5ModVFD (Generic Configurable)
6H-100

Example Configuration​

In your map file or CMake configuration (e.g., my_machine.h), assign the ID to a spindle enable slot:

// Example: Spindle 0 is PWM, Spindle 1 is Huanyang
#define SPINDLE0_ENABLE 11  // PWM Spindle
#define SPINDLE1_ENABLE 1   // Huanyang VFD
#define SPINDLE_OFFSET  1   // Enable Offset Plugin

3. grblHAL Configuration​

Once flashed, you must tell grblHAL which spindle is the VFD and how to talk to it.

Step A: Configure Modbus Communication​

Before binding a spindle, ensure grblHAL talks the same language as your VFD.

SettingDescriptionCommon ValueNotes
$374Baud Rate19200 (Index 1)Most VFDs default to 19200. Check manual (e.g., PD164/F164).
$375Timeout (ms)50 - 200Increase if you get sporadic communication errors.
$681Serial Format0 (8N1)1=8E1, 2=8O1. (Default: 0/8N1).

Step B: Bind the Spindle​

Use the following settings to map the VFD to a Spindle ID.

  • $395: Selects the Primary Spindle type.
  • $511: Selects Spindle 1 (Secondary).
  • $512: Selects Spindle 2 (Tertiary).

Use $SPINDLES to verify which ID corresponds to your VFD.

Step C: Set Modbus Address​

The VFD must have a Modbus address set in its own front panel parameters (usually PD002 or similar). grblHAL needs to match this.

SettingDescriptionDefault
$476Address for Spindle 01
$477Address for Spindle 12
$478Address for Spindle 23

Step D: Generic ModVFD Configuration​

If you are using the ModVFD driver (ID 5) for a VFD that doesn't have a native driver, you must map the grblHAL settings to your VFD's Modbus registers. Consult your VFD manual's "Communication" or "Modbus" section.

SettingDescriptionDefaultNotes
$462Control Register8192 (0x2000)The register address to write Run/Stop commands to.
$463Set Frequency Register8193 (0x2001)The register to write the target frequency/RPM to.
$464Get Frequency Register8451 (0x2103)The register to read the actual current frequency/RPM from.
$465Command: Run CW18 (0x12)The value to write to $462 to start Forward motion.
$466Command: Run CCW34 (0x22)The value to write to $462 to start Reverse motion.
$467Command: Stop1 (0x01)The value to write to $462 to Stop.
$468RPM Prog Multiplier50Used to scale RPM to VFD units.
$469RPM Prog Divider60Value = (RPM * Mutliplier) / Divider
$470RPM Read Multiplier60Used to scale VFD units back to RPM.
$471RPM Read Divider100RPM = (Value * Multiplier) / Divider

4. VFD-Specific Settings (Examples)​

Different VFDs require different handling. Identify yours below.

1. Huanyang (SL Series)​

  • Driver ID: 1
  • VFD Panel Settings:
    • PD001 = 2 (Source of Run Commands: Comm Port)
    • PD002 = 2 (Source of Operating Frequency: Comm Port)
    • PD163 = 1 (Comm Address, matches $476)
    • PD164 = 2 (Baud Rate: 19200 - Common Default)
    • PD165 = 3 (Data Format: 8N1 RTU)

2. H-100 VFD​

  • Driver ID: 6
  • VFD Panel Settings:
    • F001 = 2 (Control Mode: Comm)
    • F002 = 2 (Frequency Mode: Comm)
    • F163 = 1 (Slave Address)
    • F164 = 2 (19200 Baud - Common Default)
    • F165 = 3 (Data Format: 8N1)

3. PwnCNC VFD​

  • Driver ID: 5 (ModVFD)
  • grblHAL Manual Register Mapping:
    • $395 = (Select ModVFD ID)
    • $462 = 40960
    • $463 = 40961
    • $464 = 36864
    • $465 = 1 (CW)
    • $466 = 2 (CCW)
    • $467 = 6 (Stop)
    • $468 = 25
  • VFD Panel Settings (Auto Mode):
    • P0.0.03 = 2
    • P0.0.04 = 9
    • P4.1.00 = 04
    • P4.1.01 = 4

4. GS20 / YL-620A​

  • Driver ID: 3 (GS20) or 4 (YL-620A)
  • Settings: $461: RPM to Hz ratio. (Default: 60).

5. Spindle Offsets (Laser/Dual Tool)​

If using the VFD as a primary spindle and a laser as secondary, you can configure physical offsets if the spindle_laser_offset plugin is enabled.

  • $770: Laser X Offset (mm).
  • $771: Laser Y Offset (mm).
  • $772: Offset Options (Update G92 vs. Keep Position).

Troubleshooting​

"Error: Spindle not responding"​

  1. Check Baud Rate: standard grblHAL VFD plugins usually default to 9600 or 19200. Check the source (init function) or your VFD manual.
  2. Swap lines: A/B signaling is often mislabeled. Swap them and retry.
  3. Ground: Ensure common ground between VFD control board and CNC controller.

Spindle Runs Backward​

  • Swap any two of the three uvw phase wires connecting the VFD to the motor. Do not swap input power wires.

Alarm 14: Spindle at Speed Timeout​

This alarm triggers if the spindle takes too long to reach the target RPM.

  • Increase Timeout: Check your Spindle at Speed Timeout setting (often $339). VFDs ramp up slowly; increase this value.
  • Increase On Delay: Increase $394 (Spindle On Delay) if not using at-speed feedback.
  • Check Feedback: If using "at-speed" feedback (e.g., encoder or VFD register), ensure the signal is valid.

Error 19: Modbus Exception​

The VFD received a command it rejected, or communication failed entirely.

  • VFD Not Ready: The VFD may still be booting up or not powered on.
  • Modbus Disconnected: Check for broken wires or loose terminals on the RS485 wiring.
  • Wiring Noise: Electrical noise can corrupt packets. Use shielded twisted pair cable.
  • Check Baud Rate: Verify $374 matches the VFD.
  • Check State: The VFD might be in a fault state or "Local" mode, rejecting remote commands.
  • Check IDs: Ensure the VFD Modbus ID matches $476 (or $460).