Configure a Motor with an Encoder

Use an encoder with a motor to create a closed feedback loop for better control of your machine. Instead of sending speed or position commands without a way to verify the motor’s behavior, the encoder lets the computer know how the motor is actually rotating in the real world, so adjustments can be made to achieve the desired motor movement.

Some motors come with encoders integrated with or attached to them. You can also add an encoder to a motor. See the encoder component documentation for more information on encoders.

Viam supports gpio model motors with encoders. To configure an encoded motor, you must configure the encoder per the encoder documentation and then configure a gpio motor with an encoder attribute in addition to the standard gpio model attributes.

Here’s an example configuration:

An encoded motor config in the Viam app UI.

{
  "components": [
    {
      "name": "<your-board-name>",
      "model": "<your-board-model>",
      "type": "board",
      "namespace": "rdk",
      "attributes": {},
      "depends_on": []
    },
    {
      "name": "<your-encoder-name>",
      "model": "<your-encoder-model>",
      "type": "encoder",
      "namespace": "rdk",
      "attributes": {
        ... // insert encoder model specific attributes
      },
      "depends_on": []
    },
    {
      "name": "<your-motor-name>",
      "model": "gpio",
      "type": "motor",
      "namespace": "rdk",
      "attributes": {
        "board": "<your-board-name>",
        "pins": {
          <...> // insert pins struct
        },
        "encoder": "<your-encoder-name>",
        "ticks_per_rotation": <#>
      },
      "depends_on": []
    }
  ]
}

Here’s an example configuration:

{
  "components": [
    {
      "name": "local",
      "model": "pi",
      "type": "board",
      "namespace": "rdk",
      "attributes": {},
      "depends_on": []
    },
    {
      "name": "myEncoder",
      "model": "incremental",
      "type": "encoder",
      "namespace": "rdk",
      "attributes": {
        "board": "local",
        "pins": {
          "a": "13",
          "b": "15"
        }
      },
      "depends_on": []
    },
    {
      "name": "myMotor1",
      "model": "gpio",
      "type": "motor",
      "namespace": "rdk",
      "attributes": {
        "board": "local",
        "pins": {
          "pwm": "16",
          "dir": "18"
        },
        "encoder": "myEncoder",
        "ticks_per_rotation": 9600
      },
      "depends_on": []
    }
  ]
}

Same example JSON as on the JSON example tab, with notes alongside it. See attribute table below for all the same information.

In addition to the attributes for a non-encoded motor, the following attributes are available for encoded DC motors:

NameTypeInclusionDescription
encoderstringRequiredname of the encoder.
ticks_per_rotationintRequiredNumber of ticks in a full rotation of the encoder and motor shaft.
ramp_ratefloatOptionalRate to increase the motor’s input voltage (power supply) per second when increasing the speed the motor rotates (RPM).
Range = (0.0, 1.0]
Default: 0.2

Wiring example

Here’s an example of an encoded DC motor wired with the MAX14870 Single Brushed DC Motor Driver Carrier. This wiring example corresponds to the example config above.

Example wiring diagram with a Raspberry Pi, brushed DC motor, 12V power supply, and Pololu MAX14870 motor driver. The DIR pin of the driver is wired to pin 18 on the Pi. PWM goes to pin 16. The motor’s encoder signal wires (out a and out b) go to pins 11 and 13 on the Pi. The motor’s main power wires are connected to the motor driver while its encoder logic power wires are connected to the Pi.

Test the motor

Once your motor is configured and connected, go to the Control tab and click on the motor’s dropdown panel. Use the buttons to try turning your motor forwards or backwards at different power levels and check whether it moves as expected.

Motor control panel.

For example, a Viam Rover with encoded motors following both an angular and linear velocity command:

The position, orientation, and linear and angular velocity of the rover changing as it moves, as measured by a movement sensor:

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



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If you notice any issues with the documentation, feel free to file an issue or edit this file.