Basics

The Spindle is the main effector on your CNC Mill/Router. It holds the end mill or drill bit, makes it turn and remove material.

While manual control is sometimes fine ( turn it on before starting your G-code, off when you are done ), it is so much neater to have G-codes to control it automatically : simply put an ON G-code at the beginning of your G-code file, and a off G-code at the end of your G-code file, and you don't have to think about it any-more.

The spindle module supports different types of spindles which are described in the following subsections.

NOTE the spindle module is NOT compiled into the normal smoothie build, you need to use the CNC build.

General

The spindle module has an option which lets you enable or disable the entire module: 

spindle.enable                                   true   # set this to false to disable the spindle module

G-code

Available G-code commands:

  • M3 will start the spindle. M3 S5000 will start the spindle and set speed to 5000 RPM.
  • M5 will stop the spindle. Last set RPM is remembered and used for next M3 command if S argument is not given.
  • M957 will report the current spindle speed and PWM value. This returns not the actual value but the value that was set through M3.
  • M958 will report the current PID parameters. M958 Px.xxx Ix.xxx Dx.xxx will set them (to save the new values, you need to edit config file manually).

PWM Spindle

The PWM spindle is generic for all spindles that use a direct PWM signal to control the spindle speed directly with a MOSFet. It needs a feedback sensor to adjust the speed using a PID control.

Example config options

spindle.type                                 pwm               # sets the spindle module to PWM mode
spindle.pwm_pin                              2.5               # Big Mosfet Q7. Pin must be hardware PWM capable.
spindle.pwm_period                           1000              # default 1000, sets the PWM frequency
spindle.feedback_pin                         2.7               # Pin must be interrupt capable. 
spindle.pulses_per_rev                       1.0               # default 1. Defines the number of pulses occur for each rotation 
spindle.default_rpm                          5000              # default 5000. Defines a default RPM value in case no RPM value is provided.
spindle.control_P                            0.1               # default 0.0001. P value for the PID controller              
spindle.control_I                            0.1               # default 0.0001. I value for the PID controller
spindle.control_D                            0.1               # default 0.0001. D value for the PID controller
spindle.control_smoothing                    0.1               # default 0.1. This value is low pass filter time constant in seconds.
Check the pinout to verify if a pin is capable for a certain functionality!

Hobby servo ESC as spindle control

Since I'm expiriencing with hobby esc+motor combos (1:8 scale 3 phase 4068 like motor) I wanted to share it's config. ESCs act like hobby servos - 20 ms period time, 1.5-2ms duty cycle time -, so insted of having modified the spindle code, I've created a switch for commands M3/M5. Due to the very small duty cycle window you won't have much control over the motor: S7.5 is neutral, S12.5 is “fastest” after calibrating the ESC manually with bCNC (read ESC's manual; below S7.5 is breaking for now).

The following code is working, setting neutral upon boot - ESC init. 

switch.servo.enable                          true             # Servo module for PWM control
switch.servo.input_on_command                M3
switch.servo.input_off_command               M5
switch.servo.output_pin                      1.23o!             # spare pin with PWM capability, 3.25 should also work from EXP2, maybe needed to set it to 1.23o!
switch.servo.output_type                     hwpwm
#switch.servo.pwm_period_ms                  20                #set PWM period to 20ms (50 Hz)
switch.servo.startup_state                   true                # turn on the output to have neutral for ESC
switch.servo.startup_value                   7.5               # this is default_off_value
switch.servo.default_on_value                7.5
switch.servo.failsafe_set_to                 0

Going further

If you want to learn more about this module, or are curious how it works, Smoothie is Open-Source and you can simply go look at the code, here.

Analog Spindle

This module is used to control a VFD with an PWM that is converted to an 0-10V analog signal by an additional circuit. That circuit also provides an optocoupler for switching the VFD RUN signal. It is also the mode of choice if you run a brushless motor spindle driven by a ESC, in that case you will not need any additional circuitry.

The analog spindle is generic for all VFD's that use a 0-10V speed reference signal, so it doesn't need a special implementation for a certain VFD. The downside is that the signal is not completely linear and may be interfered by noise. If you can use a VFD that supports Modbus/RS485, its highly recommended to use that technique!

Example config options

spindle.type                                     analog   # set the spindle type to analog, can also be used for ESC spindles controlled by a PWM
spindle.max_rpm                                  24000    # set the max spindle speed that is achieved at 100% PWM
spindle.pwm_pin                                  2.4      # the pin which emits the PWM signal
spindle.pwm_period                               1000     # the PWM frequency
spindle.switch_on_pin                            2.6      # the pin which is used to enable the VFD (optional)

PWM to analog converter circuit

If you're using an brushless motor + ESC that takes the PWM directly as speed reference, you don't need an additional circuit.

VFD adapter board


Used to talk to your VFD via an analog signal

This is an example of a small extension PCB that contains a circuit to convert the 3.3V PWM signal into a 0-10V analog signal.

VFD adapter board schematic


For the curious

This is the related circuit diagram for the converter

VFD adapter board wiring


How to connect it to your Smoothieboard and vfd

This example shows how to wire the Smoothieboard to an Huanyang VFD using the PCB shown above.

Unfortunately the circuit does not create a completely linear output signal. As you can see in the graph, the signal is better at the beginning and at the end.

VFD analog signal linearity


Going further

If you want to learn more about this module, or are curious how it works, Smoothie is Open-Source and you can simply go look at the code, here.

Modbus Spindle

This module is used to control a VFD using a RS485 communication bus. It provides a Modbus implementation and is easily extendable to support a wide range of Modbus compliant VFDs. But is also can support VFD's that are not compliant with the Modbus standard such as the widely used Huanyang VFD that is popular and cheap on eBay.

The modbus spindle needs a separate implementation for every VFD model. At the time of writing only the Huanyang is implemented, but is very easy to extend the module for many other models.

Example config options

spindle.type                                     modbus   # set the spindle type to modbus/RS485
spindle.vfd_type                                 huanyang # set the VFD type, this is necessary because each inverter uses its own commands
spindle.rx_pin                                   2.6      # TX pin for the soft serial
spindle.tx_pin                                   2.4      # RX pin for the soft serial
spindle.dir_pin                                  2.5      # RS485 is only half-duplex, so we need a pin to switch between sending and receiving

Huanyang VFD Modbus Parameters

In order to get the Huanyang VFD accepting commands via ModBus, you need to change a few parameters:

PD001: 2 (Source of run commands: communication port) PD002: 2 (Source of operating frequency: communication port) PD163: 1 (Communication address: 1) PD164: 1 (Communication Baud Rate: 9600) PD165: 3 (Communication Data Method: 8N1 RTU)

RS485 extension board

Like an analog spindle, the Modbus spindle needs a external circuit, but that is much simpler.

VFD Modbus signal adapter PCB


Used to talk to your spindle over RS485 differential signals

This is an example of a small extension PCB that contains a circuit to convert the 3.3V UART signal into a RS485 signal.

VFD Modbus signal adapter schematic


for the curious

div This is the related circuit diagram for the converter

Wiring

VFD Modbus wiring


How to connect it to the Smoothieboard and the VFD

div This example shows how to wire the Smoothieboard to an Huanyang VFD using the PCB shown above.

Going further

If you want to learn more about this module, or are curious how it works, Smoothie is Open-Source and you can simply go look at the code, here.