Configure a gpio motor

The gpio model supports DC motors (both brushed and brushless).

Encoders can be configured to work with gpio motors. Find more information in the encoded motor documentation.

To configure a DC motor as a component of your robot, first configure the board to which the motor driver is wired. Then add your motor:

{
  "components": [
    {
      "name": "<your-board-name>",
      "type": "board",
      "model": "<your-board-model>",
      "attributes": {},
      "depends_on": [],
    },
    {
      "name": "<your-motor-name>",
      "type": "motor",
      "model": "gpio",
      "attributes": {
        "pins": {
          <...>
        },
        "board": "<your-board-name>",
        "max_rpm": <int>,
        "min_power_pct": <float>,
        "max_power_pct": <float>,
        "pwm_freq": <float>,
        "dir_flip": <float>,
        "en_low": <float>
      },
      "depends_on": []
    }
  ]
}

{
  "components": [
    {
      "name": "local",
      "type": "board",
      "model": "pi",
      "attributes": {},
      "depends_on": []
    },
    {
      "name": "example-gpio",
      "type": "motor",
      "model": "gpio",
      "attributes": {
        "pins": {
          "dir": "36",
          "pwm": "32"
        },
        "board": "local",
        "max_rpm": 500
      },
      "depends_on": []
    }
  ]
}

The following attributes are available for gpio motors:

Refer to your motor and motor driver data sheets for specifics.

pins

There are three common ways for your computer to communicate with a brushed DC motor driver chip. Your motor driver data sheet will specify which one to use.

• PWM/DIR: Use this if one of your motor driver’s pins (labeled “PWM”) takes a pulse width modulation (PWM) signal to the driver to control speed while another pin labeled “DIR” takes a high or low signal to control the direction.
  • Configure pwm and dir.
• In1/In2: Use this if your motor driver has pins labeled “IN1” and “IN2” or “A” and “B,” or similar. One digital signal set to a high voltage and another set to a low voltage turns the motor in one direction and vice versa. Speed is controlled with PWM through one or both pins.
  • Configure a and b.
• In1/In2 and PWM: Use this if your motor driver uses three pins: In1 (A) and In2 (B) to control direction and a separate PWM pin to control speed.
  • Configure a, b, and pwm.

Inside the pins struct you need to configure two or three of the following, depending on your motor driver:

Wiring examples

Brushed DC motor

Taking a 12V brushed DC motor controlled by a DRV8256E Single Brushed DC Motor Driver Carrier wired to a Raspberry Pi as an example, the wiring diagram would look like this:

The signal wires in the diagram run from two GPIO pins on the Pi to the DIR and PWM pins on the motor driver. Refer to a Raspberry Pi pinout schematic to locate generic GPIO pins and determine their pin numbers for configuration.

Brushless DC motor

Brushless DC motor drivers work in much the same way as brushed DC motor drivers. They typically require a PWM/DIR input or an A/B (In1/In2) and PWM input to set the motor power and direction. The key difference between a brushed and brushless motor driver is on the motor output side. Brushless motors typically have three power connections (commonly referred to as A, B and C; or sometimes Phase 1, 2 and 3) and 3 sensor connections (commonly referred to as Hall A, Hall B, and Hall C) running between the motor and driver.

The configuration file of a BLDC motor with Viam is the same as that of a brushed motor. Only the output side of the driver board is different in that more wires connect the driver to the motor.

Test the motor

Once your motor is configured and 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 check whether it moves as expected.

If the motor does not appear on the Control tab, or if you notice unexpected behavior, check your robot’s Logs tab for errors, and review the configuration.

Next steps