TMC Stepsticks

Why SPI

TMC drivers can run standalone, where a small potentiometer (Vref) sets the current and a few pins set the microstepping. In SPI mode, which is how the FluidBoard uses them, all of that comes from the configuration file instead: current, microstepping and chopper mode are written to the driver at startup. There is no potentiometer to adjust, and you can change the current by editing one line.

Some modules come in separate SPI and standalone/UART versions, or have a solder jumper to select the mode. Make sure you buy, or configure, the SPI version.

Selecting stepstick voltage

There are two switches for selecting the voltage of the stepsticks. When using TMC stepsticks, select the 3.3v position.

The 5v position is only for external drivers and can destroy your FluidBoard when used with TMC stepsticks.

If you don't install your TMC stepstick correctly, there's a high chance you destroy both your stepstick and the FluidBoard. Always double check if your pin layout matches the board.

Each switch is used for 2 stepsticks. You cannot select different voltages for individual stepsticks.

Wiring

The wiring depends on the stepstick you are using. Not all TMC stepsticks use the same layout for A and B coils, and the coils are routed to the screw terminals. Even different versions of the same stepstick might use a different layout. Check your vendor for the correct pinout!

From the stepper end, you can easily determine which coil is A and B by using a multimeter and measuring the resistance. If the resistance is almost zero, the two wires are connected to the same coil. If the resistance is higher, the wires are connected to different coils. Wire two wires of the same coil to A and two wires to B.

A coil typically measures a few ohms; between wires of different coils you will see an open circuit. If the motor turns the wrong way, swap the two wires of one coil, or invert the direction pin in the configuration with :low.

Some practical rules for installing the modules:

• Power off before inserting or removing a stepstick, and before connecting or disconnecting a motor. Unplugging a motor from a powered driver can destroy the driver.
• Check the orientation against the markings on the board before powering up. The warning above is not exaggerated.
• Fit a heatsink and give the drivers some airflow. TMC drivers reduce or shut off current when they overheat, which shows up as an axis that randomly loses steps after a while.

Configuration

The YAML configuration for TMC stepsticks is as follows:

tmc_5160: # or tmc_2130:
  step_pin: i2so.14 # z axis; see the pinout below for the other sockets
  direction_pin: i2so.15
  disable_pin: i2so.12
  cs_pin: i2so.13
  r_sense_ohms: 0.050
  run_amps: 1.8
  hold_amps: 1.0
  microsteps: 8
  run_mode: CoolStep
  homing_mode: CoolStep

This block goes under motor0 of the axis it drives, in the same way as the external driver example.

What the settings do:

• r_sense_ohms — the value of the current sense resistors on your module. The driver calculates current from it, so a wrong value means a wrong motor current. Check your module's documentation or the marking on the resistors (R050 = 0.050 Ω, R075 = 0.075 Ω, R110 = 0.110 Ω).
• run_amps — motor current while moving. Start at about 70% of the motor's rated current, then raise it if the axis loses steps. Stay within what your module can handle; the TMC2130 runs out of headroom much sooner than the TMC5160.
• hold_amps — current at standstill. Lower than run_amps keeps motor and driver cooler, but the axis has to hold against whatever force is on it, such as a turret being clamped.
• microsteps — as with external drivers, more microsteps make motion smoother but don't add torque, and every extra microstep is a step pulse the board has to generate. Remember that steps_per_mm for the axis changes with this value.
• run_mode / homing_mode — the chopper mode used while running and while homing.

Choosing a mode

The FluidBoard does not route the drivers' DIAG pin, so sensorless homing with StallGuard is not supported. That's deliberate: on CNC mills and lathes, which typically run their motors hard, stall detection is more trouble than it's worth. Use real endstops for homing.

For the auxiliary axes these sockets are meant for, CoolStep as in the example is the safe default. If you only care about noise and the axis is lightly loaded, try StealthChop and check that it doesn't stall at your maximum rate.

Checking the drivers

At startup, the FluidBoard talks to each TMC driver over SPI. Type $SS in the console to see the startup messages and check that every configured driver was found and passed its test. A driver that doesn't respond is almost always a wrong cs_pin, a module that is not in SPI mode, the wrong voltage switch position, or a stepstick that isn't seated properly.

Troubleshooting

Pinout

The pinout for the 4 stepsticks is as follows:

Related guides

• External stepper drivers — for the main machine axes
• Automatic tool changer — a typical use for a TMC-driven axis
• Endstops