Software / API Bindings / MQTT / API Reference and Examples / Bricks (Discontinued) / Servo Brick

MQTT - Servo Brick¶

This is the description of the MQTT 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 MQTT API bindings is part of their general description.

Examples¶

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

Callback¶

Download (example-callback.txt)

# Change XXYYZZ to the UID of your Servo Brick

setup:
    # Use position reached callback to swing back and forth
    subscribe to tinkerforge/callback/servo_brick/XXYYZZ/position_reached
        if a message arives
            # message contains the current servo_num and position as int
            if position is 9000
                # Position is 90°, going to -90°
                publish '{"servo_num": 0, "position": -9000}' to tinkerforge/request/servo_brick/XXYYZZ/set_position
            elseif position is -9000
                # Position is -90°, going to 90°
                publish '{"servo_num": 0, "position": 9000}' to tinkerforge/request/servo_brick/XXYYZZ/set_position
            else
                # Another program has set the position, print an error
            endif
        endif
    endsubscribe

    publish '{"register": true}' to tinkerforge/register/servo_brick/XXYYZZ/position_reached # Register position_reached callback

    # Enable position reached callback
    publish '' to tinkerforge/request/servo_brick/XXYYZZ/enable_position_reached_callback

    # Set velocity to 100°/s. This has to be smaller or equal to the
    # maximum velocity of the servo you are using, otherwise the position
    # reached callback will be called too early
    publish '{"servo_num": 0, "velocity": 10000}' to tinkerforge/request/servo_brick/XXYYZZ/set_velocity

    publish '{"servo_num": 0, "position": 9000}' to tinkerforge/request/servo_brick/XXYYZZ/set_position

    publish '{"servo_num": 0}' to tinkerforge/request/servo_brick/XXYYZZ/enable

cleanup:
    # If you are done, run this to clean up
    publish '{"servo_num": 0}' to tinkerforge/request/servo_brick/XXYYZZ/disable

Configuration¶

Download (example-configuration.txt)

# Change XXYYZZ to the UID of your Servo Brick

setup:
    # 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°
    publish '{"voltage": 5500}' to tinkerforge/request/servo_brick/XXYYZZ/set_output_voltage

    publish '{"servo_num": 0, "min": -10000, "max": 10000}' to tinkerforge/request/servo_brick/XXYYZZ/set_degree

    publish '{"servo_num": 0, "min": 1000, "max": 2000}' to tinkerforge/request/servo_brick/XXYYZZ/set_pulse_width

    publish '{"servo_num": 0, "period": 19500}' to tinkerforge/request/servo_brick/XXYYZZ/set_period

    publish '{"servo_num": 0, "acceleration": 1000}' to tinkerforge/request/servo_brick/XXYYZZ/set_acceleration # Slow acceleration

    publish '{"servo_num": 0, "velocity": 65535}' to tinkerforge/request/servo_brick/XXYYZZ/set_velocity # Full speed

    publish '{"servo_num": 5, "min": -9000, "max": 9000}' to tinkerforge/request/servo_brick/XXYYZZ/set_degree

    publish '{"servo_num": 5, "min": 950, "max": 1950}' to tinkerforge/request/servo_brick/XXYYZZ/set_pulse_width

    publish '{"servo_num": 5, "period": 20000}' to tinkerforge/request/servo_brick/XXYYZZ/set_period

    publish '{"servo_num": 5, "acceleration": 65535}' to tinkerforge/request/servo_brick/XXYYZZ/set_acceleration # Full acceleration

    publish '{"servo_num": 5, "velocity": 65535}' to tinkerforge/request/servo_brick/XXYYZZ/set_velocity # Full speed

    publish '{"servo_num": 0, "position": 10000}' to tinkerforge/request/servo_brick/XXYYZZ/set_position # Set to most right position

    publish '{"servo_num": 0}' to tinkerforge/request/servo_brick/XXYYZZ/enable

    publish '{"servo_num": 5, "position": -9000}' to tinkerforge/request/servo_brick/XXYYZZ/set_position # Set to most left position

    publish '{"servo_num": 5}' to tinkerforge/request/servo_brick/XXYYZZ/enable

cleanup:
    # If you are done, run this to clean up
    publish '{"servo_num": 0}' to tinkerforge/request/servo_brick/XXYYZZ/disable

    publish '{"servo_num": 5}' to tinkerforge/request/servo_brick/XXYYZZ/disable

API¶

All published payloads to and from the MQTT bindings are in JSON format.

If an error occures, the bindings publish a JSON object containing the error message as member _ERROR. It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

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¶

request/servo_brick/<UID>/enable¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255]
Response:	no response

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

request/servo_brick/<UID>/disable¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255]
Response:	no response

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.

request/servo_brick/<UID>/is_enabled¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	enabled – Type: bool, Default: false

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

request/servo_brick/<UID>/set_position¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255] position – Type: int, Unit: 1/100 °, Range: ?
Response:	no response

Sets the position for the specified servo.

The default range of the position is -9000 to 9000, but it can be specified according to your servo with request/servo_brick/<UID>/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 request/servo_brick/<UID>/set_degree.

request/servo_brick/<UID>/get_position¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	position – Type: int, Unit: 1/100 °, Range: ?

Returns the position of the specified servo as set by request/servo_brick/<UID>/set_position.

request/servo_brick/<UID>/get_current_position¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	position – Type: int, Unit: 1/100 °, Range: ?

Returns the current position of the specified servo. This may not be the value of request/servo_brick/<UID>/set_position if the servo is currently approaching a position goal.

request/servo_brick/<UID>/set_velocity¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255] velocity – Type: int, Unit: 1/100 °/s, Range: [0 to 2¹⁶ - 1], Default: 2¹⁶ - 1
Response:	no response

Sets the maximum velocity of the specified servo. The velocity is accelerated according to the value set by request/servo_brick/<UID>/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).

request/servo_brick/<UID>/get_velocity¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	velocity – Type: int, Unit: 1/100 °/s, Range: [0 to 2¹⁶ - 1], Default: 2¹⁶ - 1

Returns the velocity of the specified servo as set by request/servo_brick/<UID>/set_velocity.

request/servo_brick/<UID>/get_current_velocity¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	velocity – Type: int, Unit: 1/100 °/s, Range: [0 to 2¹⁶ - 1], Default: 2¹⁶ - 1

Returns the current velocity of the specified servo. This may not be the value of request/servo_brick/<UID>/set_velocity if the servo is currently approaching a velocity goal.

request/servo_brick/<UID>/set_acceleration¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255] acceleration – Type: int, Unit: 1/100 °/s², Range: [0 to 2¹⁶ - 1], Default: 2¹⁶ - 1
Response:	no response

Sets the acceleration of the specified servo.

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

request/servo_brick/<UID>/get_acceleration¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	acceleration – Type: int, Unit: 1/100 °/s², Range: [0 to 2¹⁶ - 1], Default: 2¹⁶ - 1

Returns the acceleration for the specified servo as set by request/servo_brick/<UID>/set_acceleration.

request/servo_brick/<UID>/set_output_voltage¶

Request:	voltage – Type: int, Unit: 1 mV, Range: [2000 to 9000], Default: 5000
Response:	no response

Sets the output voltages with which the servos are driven.

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.

request/servo_brick/<UID>/get_output_voltage¶

Request:	empty payload
Response:	voltage – Type: int, Unit: 1 mV, Range: [2000 to 9000], Default: 5000

Returns the output voltage as specified by request/servo_brick/<UID>/set_output_voltage.

request/servo_brick/<UID>/set_pulse_width¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255] min – Type: int, Unit: 1 µs, Range: [0 to 2¹⁶ - 1], Default: 1000 max – Type: int, Unit: 1 µs, Range: [0 to 2¹⁶ - 1], Default: 2000
Response:	no response

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

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.

The minimum must be smaller than the maximum.

request/servo_brick/<UID>/get_pulse_width¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	min – Type: int, Unit: 1 µs, Range: [0 to 2¹⁶ - 1], Default: 1000 max – Type: int, Unit: 1 µs, Range: [0 to 2¹⁶ - 1], Default: 2000

Returns the minimum and maximum pulse width for the specified servo as set by request/servo_brick/<UID>/set_pulse_width.

request/servo_brick/<UID>/set_degree¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255] min – Type: int, Unit: 1/100 °, Range: [-2¹⁵ to 2¹⁵ - 1], Default: -9000 max – Type: int, Unit: 1/100 °, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 9000
Response:	no response

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 request/servo_brick/<UID>/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 request/servo_brick/<UID>/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. request/servo_brick/<UID>/set_position now controls the rpm.

The minimum must be smaller than the maximum.

request/servo_brick/<UID>/get_degree¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	min – Type: int, Unit: 1/100 °, Range: [-2¹⁵ to 2¹⁵ - 1], Default: -9000 max – Type: int, Unit: 1/100 °, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 9000

Returns the minimum and maximum degree for the specified servo as set by request/servo_brick/<UID>/set_degree.

request/servo_brick/<UID>/set_period¶

Request:	servo_num – Type: int, Range: [0 to 6, 128 to 255] period – Type: int, Unit: 1 µs, Range: [0 to 2¹⁶ - 1], Default: 19500
Response:	no response

Sets the period of the specified servo.

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 will most likely work fine.

request/servo_brick/<UID>/get_period¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	period – Type: int, Unit: 1 µs, Range: [0 to 2¹⁶ - 1], Default: 19500

Returns the period for the specified servo as set by request/servo_brick/<UID>/set_period.

request/servo_brick/<UID>/get_servo_current¶

Request:	servo_num – Type: int, Range: [0 to 6]
Response:	current – Type: int, Unit: 1 mA, Range: [0 to 2¹⁶ - 1]

Returns the current consumption of the specified servo.

request/servo_brick/<UID>/get_overall_current¶

Request:	empty payload
Response:	current – Type: int, Unit: 1 mA, Range: [0 to 2¹⁶ - 1]

Returns the current consumption of all servos together.

request/servo_brick/<UID>/get_stack_input_voltage¶

Request:	empty payload
Response:	voltage – Type: int, Unit: 1 mV, Range: [0 to 2¹⁶ - 1]

Returns the stack input voltage. 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.

request/servo_brick/<UID>/get_external_input_voltage¶

Request:	empty payload
Response:	voltage – Type: int, Unit: 1 mV, Range: [0 to 2¹⁶ - 1]

Returns the external input voltage. 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¶

request/servo_brick/<UID>/set_spitfp_baudrate_config¶

Request:	enable_dynamic_baudrate – Type: bool, Default: true minimum_dynamic_baudrate – Type: int, Unit: 1 Bd, Range: [400000 to 2000000], Default: 400000
Response:	no response

The SPITF protocol can be used with a dynamic baudrate. If the dynamic baudrate is enabled, the Brick will try to adapt the baudrate for the communication between Bricks and Bricklets according to the amount of data that is transferred.

The baudrate will be increased exponentially if lots of data is sent/received and decreased linearly if little data is sent/received.

This lowers the baudrate in applications where little data is transferred (e.g. a weather station) and increases the robustness. If there is lots of data to transfer (e.g. Thermal Imaging Bricklet) it automatically increases the baudrate as needed.

In cases where some data has to transferred as fast as possible every few seconds (e.g. RS485 Bricklet with a high baudrate but small payload) you may want to turn the dynamic baudrate off to get the highest possible performance.

The maximum value of the baudrate can be set per port with the function request/servo_brick/<UID>/set_spitfp_baudrate. If the dynamic baudrate is disabled, the baudrate as set by request/servo_brick/<UID>/set_spitfp_baudrate will be used statically.

New in version 2.3.4 (Firmware).

request/servo_brick/<UID>/get_spitfp_baudrate_config¶

Request:	empty payload
Response:	enable_dynamic_baudrate – Type: bool, Default: true minimum_dynamic_baudrate – Type: int, Unit: 1 Bd, Range: [400000 to 2000000], Default: 400000

Returns the baudrate config, see request/servo_brick/<UID>/set_spitfp_baudrate_config.

New in version 2.3.4 (Firmware).

request/servo_brick/<UID>/get_send_timeout_count¶

Request:	communication_method – Type: int, Range: See symbols
Response:	timeout_count – Type: int, Range: [0 to 2³² - 1]

Returns the timeout count for the different communication methods.

The methods 0-2 are available for all Bricks, 3-7 only for Master Bricks.

This function is mostly used for debugging during development, in normal operation the counters should nearly always stay at 0.

The following symbols are available for this function:

For communication_method:

"none" = 0
"usb" = 1
"spi_stack" = 2
"chibi" = 3
"rs485" = 4
"wifi" = 5
"ethernet" = 6
"wifi_v2" = 7

New in version 2.3.2 (Firmware).

request/servo_brick/<UID>/set_spitfp_baudrate¶

Request:	bricklet_port – Type: char, Range: ["a" to "b"] baudrate – Type: int, Unit: 1 Bd, Range: [400000 to 2000000], Default: 1400000
Response:	no response

Sets the baudrate for a specific Bricklet port.

If you want to increase the throughput of Bricklets you can increase the baudrate. If you get a high error count because of high interference (see request/servo_brick/<UID>/get_spitfp_error_count) you can decrease the baudrate.

If the dynamic baudrate feature is enabled, the baudrate set by this function corresponds to the maximum baudrate (see request/servo_brick/<UID>/set_spitfp_baudrate_config).

Regulatory testing is done with the default baudrate. If CE compatibility or similar is necessary in your applications we recommend to not change the baudrate.

New in version 2.3.2 (Firmware).

request/servo_brick/<UID>/get_spitfp_baudrate¶

Request:	bricklet_port – Type: char, Range: ["a" to "b"]
Response:	baudrate – Type: int, Unit: 1 Bd, Range: [400000 to 2000000], Default: 1400000

Returns the baudrate for a given Bricklet port, see request/servo_brick/<UID>/set_spitfp_baudrate.

New in version 2.3.2 (Firmware).

request/servo_brick/<UID>/get_spitfp_error_count¶

Request:	bricklet_port – Type: char, Range: ["a" to "b"]
Response:	error_count_ack_checksum – Type: int, Range: [0 to 2³² - 1] error_count_message_checksum – Type: int, Range: [0 to 2³² - 1] error_count_frame – Type: int, Range: [0 to 2³² - 1] error_count_overflow – Type: int, Range: [0 to 2³² - 1]

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

ACK checksum errors,
message checksum errors,
framing errors and
overflow errors.

The errors counts are for errors that occur on the Brick side. All Bricklets have a similar function that returns the errors on the Bricklet side.

New in version 2.3.2 (Firmware).

request/servo_brick/<UID>/enable_status_led¶

Request:	empty payload
Response:	no response

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).

request/servo_brick/<UID>/disable_status_led¶

Request:	empty payload
Response:	no response

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).

request/servo_brick/<UID>/is_status_led_enabled¶

Request:	empty payload
Response:	enabled – Type: bool, Default: true

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

New in version 2.3.1 (Firmware).

request/servo_brick/<UID>/get_chip_temperature¶

Request:	empty payload
Response:	temperature – Type: int, Unit: 1/10 °C, Range: [-2¹⁵ to 2¹⁵ - 1]

Returns the temperature 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.

request/servo_brick/<UID>/reset¶

Request:	empty payload
Response:	no response

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!

request/servo_brick/<UID>/get_identity¶

Request:

empty payload

Response:

uid – Type: string, Length: up to 8
connected_uid – Type: string, Length: up to 8
position – Type: char, Range: ["0" to "8"]
hardware_version – Type: [int, ...], Length: 3

0: major – Type: int, Range: [0 to 255]
1: minor – Type: int, Range: [0 to 255]
2: revision – Type: int, Range: [0 to 255]

firmware_version – Type: [int, ...], Length: 3

0: major – Type: int, Range: [0 to 255]
1: minor – Type: int, Range: [0 to 255]
2: revision – Type: int, Range: [0 to 255]

device_identifier – Type: int, Range: [0 to 2¹⁶ - 1]
_display_name – Type: string

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 is the position in the stack from '0' (bottom) to '8' (top).

The device identifier numbers can be found here. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the Servo's name in a human readable form.

Callback Configuration Functions¶

request/servo_brick/<UID>/set_minimum_voltage¶

Request:	voltage – Type: int, Unit: 1 mV, Range: [0 to 2¹⁶ - 1], Default: 5000
Response:	no response

Sets the minimum voltage, below which the register/servo_brick/<UID>/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.

request/servo_brick/<UID>/get_minimum_voltage¶

Request:	empty payload
Response:	voltage – Type: int, Unit: 1 mV, Range: [0 to 2¹⁶ - 1], Default: 5000

Returns the minimum voltage as set by request/servo_brick/<UID>/set_minimum_voltage

request/servo_brick/<UID>/enable_position_reached_callback¶

Request:	empty payload
Response:	no response

Enables the register/servo_brick/<UID>/position_reached callback.

Default is disabled.