Changing Stepper Motor Currents on the LaserBoard

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If you are experiencing stepper motors which are buzzing / whining, skipping, or they are not turning as expected, this guide will help you troubleshoot the onboard drivers. These steps are not relevant to external stepper drivers.

For the Trinamic Stepper Drivers used on the LaserBoard, the current limit for each built in driver is 1.2 amps RMS current. Review the stepper motor datasheet, which will probably provide a spec that is a PEAK current value and should not be exceeded.

Convert these numbers into the same units and make note of the values to apply to the config file:

  • Peak to RMS: Multiply by 0.707
  • RMS to Peak: Divide by 0.707

Reference Chart

RMS Current Peak Current
0.4 0.57
0.6 0.85
0.8 1.13
1 1.41
1.2 1.70

Example:

One stepper motor version is a Nema 17 with a 48mm long body by OpenBuilds.

On the datasheet, the peak current value is listed at 1.68 amps. Consult the chart above to compare. This is approximately 1.7, which corresponds to 1.2 amps on the Laserboard. This is the current value to input on the config file (see steps below). Alternatively, you can update the current values, incrementally increasing 0.2 amps at a time to fine tune your stepper motors until the issue no longer persists or start at 1.0.

Datasheet

Setup the Config File:

  1. Power off the C3D Board and remove the memory card. No lights should be on.
  2. Put the board’s memory card into your computer, using a MicroSD/ SD reader if necessary.
  3. Open the config.txt on the memory card using an editor such as Sublime Text. Do not use Notepad++.
  4. Find the # Stepper module pins section
  5. Change the below parameters using the previously determined value(s) or use the recommended default value to begin testing with.
    alpha_current 0.6 # X stepper motor current
    beta_current 0.8 # Y stepper motor current
    gamma_current 0.8 # Z stepper motor current
    delta_current 0.8 # A stepper motor current (may be under a different section)
  6. Ensure the motors are not overheating after increasing. Warm to the touch is acceptable, hot is not. Lower the setting until you get optimal performance.
  7. Save the config.txt file on the memory card.
  8. “Safely Eject” or “Unmount” the memory card.
  9. Put the memory card back into the board and power up.

Note: If you have previously changed your config file to disable Spreadcycle mode (set to false) to reduce motor noise, this could also be a determining factor, as Stealthchop mode is less powerful. Simply reverse the configuration to test: LaserBoard Stepper Motor Noise and Stepper Driver Modes

Nema 17 motors up to 48mm long should work fine with the built in LaserBoard drivers. Anything longer, and heftier motors like the Nema 23 or higher should use an external driver. See our Cohesion3D LaserBoard Buyer’s Guide for details.