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.

Configuration

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

Then assign your motor a name (to identify the motor), type (motor) and model (gpio), and fill in the attributes that apply to your particular hardware. Refer to your motor and motor driver data sheets for specifics.

An example configuration for a gpio motor:

• Config Builder
• JSON Template
• JSON Example
• Annotated JSON

{
  "components": [
    {
      "name": <board_name>,
      "type": "board",
      "model": <board_model>,
      "attributes": {},
      "depends_on": [],
    },
    {
      "name": <motor_name>,
      "type": "motor",
      "model": "gpio",
      "attributes": {
        "pins": {
          <...>
        },
        "board": <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": []
    }
  ]
}

Required Attributes

Nested within pins (note that only two or three of these are required depending on your motor driver; see Pin Information below for more details):

Pin Information

There are three common ways for the computing device to communicate with a brushed DC motor driver chip. The driver data sheet 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.

Optional Attributes

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.