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# Ruby - Servo Brick

This is the description of the Ruby API bindings for the Servo Brick. General information and technical specifications for the Servo Brick are summarized in its hardware description.

An installation guide for the Ruby API bindings is part of their general description.

## Examples

The example code below is Public Domain (CC0 1.0).

### Callback

Download (example_callback.rb)

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    #!/usr/bin/env ruby
    # -*- ruby encoding: utf-8 -*-

    require 'tinkerforge/ip_connection'
    require 'tinkerforge/brick_servo'

    include Tinkerforge

    HOST = 'localhost'
    PORT = 4223
    UID = '9oTxLQ3d46C' # Change to your UID

    ipcon = IPConnection.new # Create IP connection
    servo = BrickServo.new UID, ipcon # Create device object

    ipcon.connect HOST, PORT # Connect to brickd
    # Don't use device before ipcon is connected

    # Use position reached callback to swing back and forth
    servo.register_callback(BrickServo::CALLBACK_POSITION_REACHED) do |servo_num, position|
      if position == 9000
        puts 'Position: 90°, going to -90°'
        servo.set_position servo_num, -9000
      elsif position == -9000
        puts 'Position: -90°, going to 90°'
        servo.set_position servo_num, 9000
      else
        puts 'Error' # Can only happen if another program sets position
      end
    end

    servo.enable_position_reached_callback

    # Set velocity to 100°/s. This has to be smaller or equal to
    # maximum velocity of the servo, otherwise cb_reached will be
    # called too early
    servo.set_velocity 0, 10000
    servo.set_position 0, 9000
    servo.enable 0

    puts 'Press key to exit'
    $stdin.gets
    ipcon.disconnect

### Configuration

Download (example_configuration.rb)

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    #!/usr/bin/env ruby
    # -*- ruby encoding: utf-8 -*-

    require 'tinkerforge/ip_connection'
    require 'tinkerforge/brick_servo'

    include Tinkerforge

    HOST = 'localhost'
    PORT = 4223
    UID = '9oTxLQ3d46C' # Change to your UID

    ipcon = IPConnection.new # Create IP connection
    servo = BrickServo.new UID, ipcon # Create device object

    ipcon.connect HOST, PORT # Connect to brickd
    # Don't use device before ipcon is connected

    # Configure two servos with voltage 5.5V
    # Servo 1: Connected to port 0, period of 19.5ms, pulse width of 1 to 2ms
    #          and operating angle -100 to 100°
    #
    # Servo 2: Connected to port 5, period of 20ms, pulse width of 0.95
    #          to 1.95ms and operating angle -90 to 90°
    servo.set_output_voltage 5500

    servo.set_degree 0, -10000, 10000
    servo.set_pulse_width 0, 1000, 2000
    servo.set_period 0, 19500
    servo.set_acceleration 0, 1000 # Slow acceleration
    servo.set_velocity 0, 0xFFFF # Full speed

    servo.set_degree 5, -9000, 9000
    servo.set_pulse_width 5, 950, 1950
    servo.set_period 5, 20000
    servo.set_acceleration 5, 0xFFFF # Full acceleration
    servo.set_velocity 5, 0xFFFF # Full speed

    servo.set_position 0, 10000 # Set to most right position
    servo.enable 0

    servo.set_position 5, -9000 # Set to most left position
    servo.enable 5

    puts 'Press key to exit'
    $stdin.gets
    ipcon.disconnect

## API

All methods listed below are thread-safe.

Every function of the Servo Brick API that has a servo_num parameter can address a servo with the servo number (0 to 6). If it is a setter function then multiple servos can be addressed at once with a bitmask for the servos, if the highest bit is set. For example: `1` will address servo 1, `(1 << 1) | (1 << 5) | (1 << 7)` will address servos 1 and 5, `0xFF` will address all seven servos, etc. This allows to set configurations to several servos with one function call. It is guaranteed that the changes will take effect in the same PWM period for all servos you specified in the bitmask.

### Basic Functions

`BrickServo``::``new`(uid, ipcon) → servo

  Parameters:

  - uid -- str
  - ipcon -- IPConnection

  Creates an object with the unique device ID `uid`:

      servo = BrickServo.new 'YOUR_DEVICE_UID', ipcon

  This object can then be used after the IP Connection is connected (see examples above).

`BrickServo``#``enable`(servo_num) → nil

  Parameters: | servo_num -- int

  Enables a servo (0 to 6). If a servo is enabled, the configured position, velocity, acceleration, etc. are applied immediately.

`BrickServo``#``disable`(servo_num) → nil

  Parameters: | servo_num -- int

  Disables a servo (0 to 6). Disabled servos are not driven at all, i.e. a disabled servo will not hold its position if a load is applied.

`BrickServo``#``is_enabled`(servo_num) → bool

  Parameters: | servo_num -- int

  Returns true if the specified servo is enabled, false otherwise.

`BrickServo``#``set_position`(servo_num, position) → nil

  Parameters:

  - servo_num -- int
  - position -- int

  Sets the position in °/100 for the specified servo.

  The default range of the position is -9000 to 9000, but it can be specified according to your servo with `#set_degree`.

  If you want to control a linear servo or RC brushless motor controller or similar with the Servo Brick, you can also define lengths or speeds with `#set_degree`.

`BrickServo``#``get_position`(servo_num) → int

  Parameters: | servo_num -- int

  Returns the position of the specified servo as set by `#set_position`.

`BrickServo``#``get_current_position`(servo_num) → int

  Parameters: | servo_num -- int

  Returns the current position of the specified servo. This may not be the value of `#set_position` if the servo is currently approaching a position goal.

`BrickServo``#``set_velocity`(servo_num, velocity) → nil

  Parameters:

  - servo_num -- int
  - velocity -- int

  Sets the maximum velocity of the specified servo in °/100s. The velocity is accelerated according to the value set by `#set_acceleration`.

  The minimum velocity is 0 (no movement) and the maximum velocity is 65535. With a value of 65535 the position will be set immediately (no velocity).

  The default value is 65535.

`BrickServo``#``get_velocity`(servo_num) → int

  Parameters: | servo_num -- int

  Returns the velocity of the specified servo as set by `#set_velocity`.

`BrickServo``#``get_current_velocity`(servo_num) → int

  Parameters: | servo_num -- int

  Returns the current velocity of the specified servo. This may not be the value of `#set_velocity` if the servo is currently approaching a velocity goal.

`BrickServo``#``set_acceleration`(servo_num, acceleration) → nil

  Parameters:

  - servo_num -- int
  - acceleration -- int

  Sets the acceleration of the specified servo in °/100s².

  The minimum acceleration is 1 and the maximum acceleration is 65535. With a value of 65535 the velocity will be set immediately (no acceleration).

  The default value is 65535.

`BrickServo``#``get_acceleration`(servo_num) → int

  Parameters: | servo_num -- int

  Returns the acceleration for the specified servo as set by `#set_acceleration`.

`BrickServo``#``set_output_voltage`(voltage) → nil

  Parameters: | voltage -- int

  Sets the output voltages with which the servos are driven in mV. The minimum output voltage is 2000mV and the maximum output voltage is 9000mV.

  Note

  We recommend that you set this value to the maximum voltage that is specified for your servo, most servos achieve their maximum force only with high voltages.

  The default value is 5000.

`BrickServo``#``get_output_voltage` → int

  Returns the output voltage as specified by `#set_output_voltage`.

`BrickServo``#``set_pulse_width`(servo_num, min, max) → nil

  Parameters:

  - servo_num -- int
  - min -- int
  - max -- int

  Sets the minimum and maximum pulse width of the specified servo in µs.

  Usually, servos are controlled with a PWM, whereby the length of the pulse controls the position of the servo. Every servo has different minimum and maximum pulse widths, these can be specified with this function.

  If you have a datasheet for your servo that specifies the minimum and maximum pulse width, you should set the values accordingly. If your servo comes without any datasheet you have to find the values via trial and error.

  Both values have a range from 1 to 65535 (unsigned 16-bit integer). The minimum must be smaller than the maximum.

  The default values are 1000µs (1ms) and 2000µs (2ms) for minimum and maximum pulse width.

`BrickServo``#``get_pulse_width`(servo_num) → [int, int]

  Parameters: | servo_num -- int

  Returns the minimum and maximum pulse width for the specified servo as set by `#set_pulse_width`.

  The returned array has the values `min` and `max`.

`BrickServo``#``set_degree`(servo_num, min, max) → nil

  Parameters:

  - servo_num -- int
  - min -- int
  - max -- int

  Sets the minimum and maximum degree for the specified servo (by default given as °/100).

  This only specifies the abstract values between which the minimum and maximum pulse width is scaled. For example: If you specify a pulse width of 1000µs to 2000µs and a degree range of -90° to 90°, a call of `#set_position` with 0 will result in a pulse width of 1500µs (-90° = 1000µs, 90° = 2000µs, etc.).

  Possible usage:

  - The datasheet of your servo specifies a range of 200° with the middle position at 110°. In this case you can set the minimum to -9000 and the maximum to 11000.
  - You measure a range of 220° on your servo and you don't have or need a middle position. In this case you can set the minimum to 0 and the maximum to 22000.
  - You have a linear servo with a drive length of 20cm, In this case you could set the minimum to 0 and the maximum to 20000. Now you can set the Position with `#set_position` with a resolution of cm/100. Also the velocity will have a resolution of cm/100s and the acceleration will have a resolution of cm/100s².
  - You don't care about units and just want the highest possible resolution. In this case you should set the minimum to -32767 and the maximum to 32767.
  - You have a brushless motor with a maximum speed of 10000 rpm and want to control it with a RC brushless motor controller. In this case you can set the minimum to 0 and the maximum to 10000. `#set_position` now controls the rpm.

  Both values have a possible range from -32767 to 32767 (signed 16-bit integer). The minimum must be smaller than the maximum.

  The default values are -9000 and 9000 for the minimum and maximum degree.

`BrickServo``#``get_degree`(servo_num) → [int, int]

  Parameters: | servo_num -- int

  Returns the minimum and maximum degree for the specified servo as set by `#set_degree`.

  The returned array has the values `min` and `max`.

`BrickServo``#``set_period`(servo_num, period) → nil

  Parameters:

  - servo_num -- int
  - period -- int

  Sets the period of the specified servo in µs.

  Usually, servos are controlled with a PWM. Different servos expect PWMs with different periods. Most servos run well with a period of about 20ms.

  If your servo comes with a datasheet that specifies a period, you should set it accordingly. If you don't have a datasheet and you have no idea what the correct period is, the default value (19.5ms) will most likely work fine.

  The minimum possible period is 1µs and the maximum is 65535µs.

  The default value is 19.5ms (19500µs).

`BrickServo``#``get_period`(servo_num) → int

  Parameters: | servo_num -- int

  Returns the period for the specified servo as set by `#set_period`.

`BrickServo``#``get_servo_current`(servo_num) → int

  Parameters: | servo_num -- int

  Returns the current consumption of the specified servo in mA.

`BrickServo``#``get_overall_current` → int

  Returns the current consumption of all servos together in mA.

`BrickServo``#``get_stack_input_voltage` → int

  Returns the stack input voltage in mV. The stack input voltage is the voltage that is supplied via the stack, i.e. it is given by a Step-Down or Step-Up Power Supply.

`BrickServo``#``get_external_input_voltage` → int

  Returns the external input voltage in mV. The external input voltage is given via the black power input connector on the Servo Brick.

  If there is an external input voltage and a stack input voltage, the motors will be driven by the external input voltage. If there is only a stack voltage present, the motors will be driven by this voltage.

  Warning

  This means, if you have a high stack voltage and a low external voltage, the motors will be driven with the low external voltage. If you then remove the external connection, it will immediately be driven by the high stack voltage

### Advanced Functions

`BrickServo``#``get_api_version` → [int, int, int]

  Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

`BrickServo``#``get_response_expected`(function_id) → bool

  Parameters: | function_id -- int

  Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

  For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by `#set_response_expected`. For setter functions it is disabled by default and can be enabled.

  Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

  See `#set_response_expected` for the list of function ID constants available for this function.

`BrickServo``#``set_response_expected`(function_id, response_expected) → nil

  Parameters:

  - function_id -- int
  - response_expected -- bool

  Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled and callbacks it is always disabled.

  Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

  The following function ID constants are available for this function:

  - BrickServo::FUNCTION_ENABLE = 1
  - BrickServo::FUNCTION_DISABLE = 2
  - BrickServo::FUNCTION_SET_POSITION = 4
  - BrickServo::FUNCTION_SET_VELOCITY = 7
  - BrickServo::FUNCTION_SET_ACCELERATION = 10
  - BrickServo::FUNCTION_SET_OUTPUT_VOLTAGE = 12
  - BrickServo::FUNCTION_SET_PULSE_WIDTH = 14
  - BrickServo::FUNCTION_SET_DEGREE = 16
  - BrickServo::FUNCTION_SET_PERIOD = 18
  - BrickServo::FUNCTION_SET_MINIMUM_VOLTAGE = 24
  - BrickServo::FUNCTION_ENABLE_POSITION_REACHED_CALLBACK = 29
  - BrickServo::FUNCTION_DISABLE_POSITION_REACHED_CALLBACK = 30
  - BrickServo::FUNCTION_ENABLE_VELOCITY_REACHED_CALLBACK = 32
  - BrickServo::FUNCTION_DISABLE_VELOCITY_REACHED_CALLBACK = 33
  - BrickServo::FUNCTION_ENABLE_STATUS_LED = 238
  - BrickServo::FUNCTION_DISABLE_STATUS_LED = 239
  - BrickServo::FUNCTION_RESET = 243

`BrickServo``#``set_response_expected_all`(response_expected) → nil

  Parameters: | response_expected -- bool

  Changes the response expected flag for all setter and callback configuration functions of this device at once.

`BrickServo``#``enable_status_led` → nil

  Enables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

`BrickServo``#``disable_status_led` → nil

  Disables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

`BrickServo``#``is_status_led_enabled` → bool

  Returns true if the status LED is enabled, false otherwise.

  New in version 2.3.1 (Firmware).

`BrickServo``#``get_protocol1_bricklet_name`(port) → [int, [int, int, int], str]

  Parameters: | port -- str

  Returns the firmware and protocol version and the name of the Bricklet for a given port.

  This functions sole purpose is to allow automatic flashing of v1.x.y Bricklet plugins.

  The returned array has the values `protocol_version`, `firmware_version` and `name`.

`BrickServo``#``get_chip_temperature` → int

  Returns the temperature in °C/10 as measured inside the microcontroller. The value returned is not the ambient temperature!

  The temperature is only proportional to the real temperature and it has an accuracy of +-15%. Practically it is only useful as an indicator for temperature changes.

`BrickServo``#``reset` → nil

  Calling this function will reset the Brick. Calling this function on a Brick inside of a stack will reset the whole stack.

  After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

`BrickServo``#``get_identity` → [str, str, str, [int, int, int], [int, int, int], int]

  Returns the UID, the UID where the Brick is connected to, the position, the hardware and firmware version as well as the device identifier.

  The position can be '0'-'8' (stack position).

  The device identifier numbers can be found here. There is also a constant for the device identifier of this Brick.

  The returned array has the values `uid`, `connected_uid`, `position`, `hardware_version`, `firmware_version` and `device_identifier`.

### Callback Configuration Functions

`BrickServo``#``register_callback`(id) { |param [, ...]| block } → nil

  Parameters: | id -- int

  Registers a callback with ID id to the given block. The available IDs with corresponding function signatures are listed below.

`BrickServo``#``set_minimum_voltage`(voltage) → nil

  Parameters: | voltage -- int

  Sets the minimum voltage in mV, below which the `::CALLBACK_UNDER_VOLTAGE` callback is triggered. The minimum possible value that works with the Servo Brick is 5V. You can use this function to detect the discharge of a battery that is used to drive the stepper motor. If you have a fixed power supply, you likely do not need this functionality.

  The default value is 5V (5000mV).

`BrickServo``#``get_minimum_voltage` → int

  Returns the minimum voltage as set by `#set_minimum_voltage`

`BrickServo``#``enable_position_reached_callback` → nil

  Enables the `::CALLBACK_POSITION_REACHED` callback.

  Default is disabled.

  New in version 2.0.1 (Firmware).

`BrickServo``#``disable_position_reached_callback` → nil

  Disables the `::CALLBACK_POSITION_REACHED` callback.

  Default is disabled.

  New in version 2.0.1 (Firmware).

`BrickServo``#``is_position_reached_callback_enabled` → int

  Returns true if `::CALLBACK_POSITION_REACHED` callback is enabled, false otherwise.

  New in version 2.0.1 (Firmware).

`BrickServo``#``enable_velocity_reached_callback` → nil

  Enables the `::CALLBACK_VELOCITY_REACHED` callback.

  Default is disabled.

  New in version 2.0.1 (Firmware).

`BrickServo``#``disable_velocity_reached_callback` → nil

  Disables the `::CALLBACK_VELOCITY_REACHED` callback.

  Default is disabled.

  New in version 2.0.1 (Firmware).

`BrickServo``#``is_velocity_reached_callback_enabled` → int

  Returns true if `::CALLBACK_VELOCITY_REACHED` callback is enabled, false otherwise.

  New in version 2.0.1 (Firmware).

### Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the `#register_callback` function of the device object. The first parameter is the callback ID and the second parameter is a block:

    servo.register_callback BrickServo::CALLBACK_EXAMPLE, do |param|
      puts "#{param}"
    end

The available constants with inherent number and type of parameters are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

`BrickServo``::``CALLBACK_UNDER_VOLTAGE`

  Parameters: | voltage -- int

  This callback is triggered when the input voltage drops below the value set by `#set_minimum_voltage`. The parameter is the current voltage given in mV.

`BrickServo``::``CALLBACK_POSITION_REACHED`

  Parameters:

  - servo_num -- int
  - position -- int

  This callback is triggered when a position set by `#set_position` is reached. The parameters are the servo and the position that is reached.

  You can enable this callback with `#enable_position_reached_callback`.

  Note

  Since we can't get any feedback from the servo, this only works if the velocity (see `#set_velocity`) is set smaller or equal to the maximum velocity of the servo. Otherwise the servo will lag behind the control value and the callback will be triggered too early.

`BrickServo``::``CALLBACK_VELOCITY_REACHED`

  Parameters:

  - servo_num -- int
  - velocity -- int

  This callback is triggered when a velocity set by `#set_velocity` is reached. The parameters are the servo and the velocity that is reached.

  You can enable this callback with `#enable_velocity_reached_callback`.

  Note

  Since we can't get any feedback from the servo, this only works if the acceleration (see `#set_acceleration`) is set smaller or equal to the maximum acceleration of the servo. Otherwise the servo will lag behind the control value and the callback will be triggered too early.

### Constants

`BrickServo``::``DEVICE_IDENTIFIER`

  This constant is used to identify a Servo Brick.

  The `#get_identity()` function and the `::CALLBACK_ENUMERATE` callback of the IP Connection have a `device_identifier` parameter to specify the Brick's or Bricklet's type.

The content of this page is licensed under Creative Commons Attribution 3.0 Unported License.