Drive Servos

The outputs DO2 and DO3 can drive standard hobby servo motors — for instance to move a lick spout or a door in and out of reach. Each servo has a period register (ServoMotor2Period) and a pulse-width register (ServoMotor2Pulse), both in microseconds, and the EnableServos and DisableServos registers switch the pulse train. The examples below use the servo on DO2.

The complete workflow is shown below:

Configure the Servo

• Insert a KeyDown operator and set the Filter property to A.
• Insert a CreateMessage operator and configure the following properties:
  • Payload - Select ServoMotor2PeriodPayload.
  • ServoMotor2Period - Set the period of the servo pulse train in µs (e.g. 20000 for the standard 50 Hz servo frame).
• Insert a MulticastSubject operator named Behavior Commands.
• Insert a CreateMessage operator and configure the following properties:
  • Payload - Select ServoMotor2PulsePayload.
  • ServoMotor2Pulse - Set the pulse width in µs (e.g. 1500 for the center position of a standard servo).
• Insert a MulticastSubject operator named Behavior Commands.

Run the workflow and press A to load the servo configuration. Check your servo's datasheet for its period and pulse-width range.

Enable and Disable Servos

• Insert a KeyDown operator and set the Filter property to S.
• Insert a CreateMessage operator and configure the following properties:
  • Payload - Select EnableServosPayload.
  • EnableServos - Select ServoOutput2.
• Insert a MulticastSubject operator named Behavior Commands.

In a separate branch:

• Insert a KeyDown operator and set the Filter property to D.
• Insert a CreateMessage operator and configure the following properties:
  • Payload - Select DisableServosPayload.
  • DisableServos - Select ServoOutput2.
• Insert a MulticastSubject operator named Behavior Commands.

Run the workflow, press S to start driving the servo and D to stop. The servo moves to the position set by the pulse width and holds it while enabled.

Adjust the Position

While the servo is enabled, writing a new pulse width moves it immediately:

• Insert a KeyDown operator and set the Filter property to F.
• Insert a CreateMessage operator and configure the following properties:
  • Payload - Select ServoMotor2PulsePayload.
  • ServoMotor2Pulse - Set a new pulse width in µs (e.g. 2000).
• Insert a MulticastSubject operator named Behavior Commands.

Run the workflow, enable the servo with S, then press F — the servo moves to the new position.

Warning

DO2 and DO3 share their hardware timers with the PWM generator. Don't run PWM and a servo on the same output at the same time.

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Last updated with:
Hardware v2.1
Firmware v3.3
Bonsai Package v0.2