Configure a fake motor

Configuring a fake motor can be convenient for testing software without using any hardware. For example, you can use a fake component as a placeholder while waiting on a hardware shipment, so that other components that depend on this motor (for example, a base) won’t fail to initialize, and your SDK code won’t throw errors when it fails to find a physical motor connected to your robot.

Navigate to the Config tab of your robot’s page in the Viam app. Click on the Components subtab and click Create component. Select the motor type, then select the fake model. Enter a name for your motor and click Create.

A fake motor config.

Edit and fill in the attributes as applicable.

{
  "components": [
    {
      "name": "<your-motor-name>",
      "type": "motor",
      "model": "fake",
      "attributes": {
        <...>
      },
      "depends_on": []
    }
  ]
}

{
  "components": [
    {
      "name": "fake-motor",
      "type": "motor",
      "model": "fake",
      "attributes": {
        "pins": {
          "dir": "",
          "pwm": ""
        },
        "board": "",
        "dir_flip": false
      },
      "depends_on": []
    }
  ]
}

Since a fake motor isn’t a physical piece of hardware, attributes are only representational and not required. However, if you would like to mock up a virtual placeholder for a real, physical motor, you can configure some or all of the following attributes:

NameTypeInclusionDescription
boardstringOptionalname of the board to which the motor driver is wired.
min_power_pctnumberOptionalSets a limit on minimum power percentage sent to the motor.
Default: 0.0
max_power_pctnumberOptionalRange is 0.06 to 1.0; sets a limit on maximum power percentage sent to the motor.
Default: 1.0
pwm_freqintOptionalSets the PWM pulse frequency in Hz. Many motors operate optimally in the kHz range.
Default: 800
encoderstringOptionalThe name of an encoder attached to this motor. See encoded motor. If an encoder is configured on a fake motor, ticks_per_rotation becomes required.
max_rpmnumberOptionalAn estimate of the max revolutions per minute (RPM) the motor will run at with full power under no load. The GoFor method calculates how much power to send to the motor as a percentage of max_rpm. If unknown, you can set it to 100, which will mean that giving 40 as the rpm argument to GoFor or GoTo will set it to 40% speed. For non-encoded fake motors, this is required or a default is assigned.
ticks_per_rotationintOptionalBecomes required for calculations if an encoder is configured (unlike on a real motor). For a stepper motor, the number of steps in one full rotation (200 is common). For an encoded motor, how many encoder ticks in one full rotation. See data sheet (for a real motor).
dir_flipboolOptionalFlips the direction of “forward” versus “backward” rotation.
Default: false
pinsobjectOptionalA struct that holds pin configuration information.

Nested within pins:

NameTypeInclusionDescription
astringOptionalSee Pin Information. Corresponds to “IN1” on many driver data sheets. Pin number of the GPIO pin this is wired to on the board.
bstringOptionalSee Pin Information. Corresponds to “IN2” on many driver data sheets. Pin number of the GPIO pin this is wired to on the board.
dirstringOptionalSee Pin Information. Pin number of the GPIO pin this is wired to on the board.
pwmstringOptionalSee Pin Information. Pin number of the GPIO pin this is wired to on the board.

Pin Information

There are three common ways for the computing device to communicate with a brushed DC motor driver chip. The driver data sheet (for a real, not fake, motor) will specify which one to use.

  • PWM/DIR: One digital input (such as a GPIO pin) sends a pulse width modulation (PWM) signal to the driver to control speed while another digital input sends a high or low signal to control the direction.
  • In1/In2 (or A/B): One digital input is set to high and another set to low turns the motor in one direction and vice versa, while speed is controlled with PWM through one or both pins.
  • In1/In2 + PWM: Three pins: an In1 (A) and In2 (B) to control direction and a separate PWM pin to control speed.

Test the motor

Once your motor is configured and your robot is connected, go to the Control tab and click on the motor’s drop-down panel. Use the buttons to try turning your motor forwards or backwards at different power levels and notice how the Position number changes.

Motor control panel.



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