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)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
# 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 servoNum 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)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
# 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 payload to an from the MQTT bindings is in the JSON format.

If an error occures, the bindings publish a JSON object containing the error message as attribute "_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 payload:
 
  • servo_num -- int

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 payload:
 
  • 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.

request/servo_brick/<UID>/is_enabled
Request payload:
 
  • servo_num -- int
Response payload:
 
  • enabled -- bool

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

request/servo_brick/<UID>/set_position
Request payload:
 
  • 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 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 payload:
 
  • servo_num -- int
Response payload:
 
  • position -- int

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

request/servo_brick/<UID>/get_current_position
Request payload:
 
  • servo_num -- int
Response payload:
 
  • position -- int

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 payload:
 
  • 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 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).

The default value is 65535.

request/servo_brick/<UID>/get_velocity
Request payload:
 
  • servo_num -- int
Response payload:
 
  • velocity -- int

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

request/servo_brick/<UID>/get_current_velocity
Request payload:
 
  • servo_num -- int
Response payload:
 
  • velocity -- int

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 payload:
 
  • 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.

request/servo_brick/<UID>/get_acceleration
Request payload:
 
  • servo_num -- int
Response payload:
 
  • acceleration -- int

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

request/servo_brick/<UID>/set_output_voltage
Request payload:
 
  • 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.

request/servo_brick/<UID>/get_output_voltage
Response payload:
 
  • voltage -- int

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

request/servo_brick/<UID>/set_pulse_width
Request payload:
 
  • 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.

request/servo_brick/<UID>/get_pulse_width
Request payload:
 
  • servo_num -- int
Response payload:
 
  • min -- int
  • max -- int

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 payload:
 
  • 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 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.

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.

request/servo_brick/<UID>/get_degree
Request payload:
 
  • servo_num -- int
Response payload:
 
  • min -- int
  • max -- int

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 payload:
 
  • 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).

request/servo_brick/<UID>/get_period
Request payload:
 
  • servo_num -- int
Response payload:
 
  • period -- int

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

request/servo_brick/<UID>/get_servo_current
Request payload:
 
  • servo_num -- int
Response payload:
 
  • current -- int

Returns the current consumption of the specified servo in mA.

request/servo_brick/<UID>/get_overall_current
Response payload:
 
  • current -- int

Returns the current consumption of all servos together in mA.

request/servo_brick/<UID>/get_stack_input_voltage
Response payload:
 
  • 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.

request/servo_brick/<UID>/get_external_input_voltage
Response payload:
 
  • 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

request/servo_brick/<UID>/set_spitfp_baudrate_config
Request payload:
 
  • enable_dynamic_baudrate -- bool
  • minimum_dynamic_baudrate -- int

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 send/received and decreased linearly if little data is send/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.

The minimum dynamic baudrate has a value range of 400000 to 2000000 baud.

By default dynamic baudrate is enabled and the minimum dynamic baudrate is 400000.

New in version 2.3.4 (Firmware).

request/servo_brick/<UID>/get_spitfp_baudrate_config
Response payload:
 
  • enable_dynamic_baudrate -- bool
  • minimum_dynamic_baudrate -- int

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 payload:
 
  • communication_method -- int (has symbols)
Response payload:
 
  • timeout_count -- int

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
  • "SPIStack" = 2
  • "Chibi" = 3
  • "RS485" = 4
  • "WIFI" = 5
  • "Ethernet" = 6
  • "WIFIV2" = 7

New in version 2.3.2 (Firmware).

request/servo_brick/<UID>/set_spitfp_baudrate
Request payload:
 
  • bricklet_port -- string
  • baudrate -- int

Sets the baudrate for a specific Bricklet port ('a' - 'd'). The baudrate can be in the range 400000 to 2000000.

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 you applications we recommend to not change the baudrate.

The default baudrate for all ports is 1400000.

New in version 2.3.2 (Firmware).

request/servo_brick/<UID>/get_spitfp_baudrate
Request payload:
 
  • bricklet_port -- string
Response payload:
 
  • baudrate -- int

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 payload:
 
  • bricklet_port -- string
Response payload:
 
  • error_count_ack_checksum -- int
  • error_count_message_checksum -- int
  • error_count_frame -- int
  • error_count_overflow -- int

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

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

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
Response payload:
 
  • enabled -- bool

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

New in version 2.3.1 (Firmware).

request/servo_brick/<UID>/get_protocol1_bricklet_name
Request payload:
 
  • port -- string
Response payload:
 
  • protocol_version -- int
  • firmware_version -- [int,int,int]
  • name -- string

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.

request/servo_brick/<UID>/get_chip_temperature
Response payload:
 
  • 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.

request/servo_brick/<UID>/reset

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
Response payload:
 
  • uid -- string
  • connected_uid -- string
  • position -- string
  • hardware_version -- [int,int,int]
  • firmware_version -- [int,int,int]
  • device_identifier -- int (has symbols)
  • _display_name -- 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 can be '0'-'8' (stack position).

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 payload:
 
  • voltage -- int

Sets the minimum voltage in mV, 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.

The default value is 5V (5000mV).

request/servo_brick/<UID>/get_minimum_voltage
Response payload:
 
  • voltage -- int

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

request/servo_brick/<UID>/enable_position_reached_callback

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

Default is disabled.

New in version 2.0.1 (Firmware).

request/servo_brick/<UID>/disable_position_reached_callback

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

Default is disabled.

New in version 2.0.1 (Firmware).

request/servo_brick/<UID>/is_position_reached_callback_enabled
Response payload:
 
  • enabled -- bool

Returns true if register/servo_brick/<UID>/position_reached callback is enabled, false otherwise.

New in version 2.0.1 (Firmware).

request/servo_brick/<UID>/enable_velocity_reached_callback

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

Default is disabled.

New in version 2.0.1 (Firmware).

request/servo_brick/<UID>/disable_velocity_reached_callback

Disables the register/servo_brick/<UID>/velocity_reached callback.

Default is disabled.

New in version 2.0.1 (Firmware).

request/servo_brick/<UID>/is_velocity_reached_callback_enabled
Response payload:
 
  • enabled -- bool

Returns true if register/servo_brick/<UID>/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 corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.

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.

register/servo_brick/<UID>/under_voltage
Request payload:
 
  • register -- bool
Response payload:
 
  • voltage -- int

A callback can be registered for this event by publishing to the .../register/servo_brick/<UID>/under_voltage[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/servo_brick/<UID>/under_voltage[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when the input voltage drops below the value set by request/servo_brick/<UID>/set_minimum_voltage. The callback payload is the current voltage given in mV.

register/servo_brick/<UID>/position_reached
Request payload:
 
  • register -- bool
Response payload:
 
  • servo_num -- int
  • position -- int

A callback can be registered for this event by publishing to the .../register/servo_brick/<UID>/position_reached[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/servo_brick/<UID>/position_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when a position set by request/servo_brick/<UID>/set_position is reached. If the new position matches the current position then the callback is not triggered, because the servo didn't move. The callback payload members are the servo and the position that is reached.

You can enable this callback with request/servo_brick/<UID>/enable_position_reached_callback.

Note

Since we can't get any feedback from the servo, this only works if the velocity (see request/servo_brick/<UID>/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.

register/servo_brick/<UID>/velocity_reached
Request payload:
 
  • register -- bool
Response payload:
 
  • servo_num -- int
  • velocity -- int

A callback can be registered for this event by publishing to the .../register/servo_brick/<UID>/velocity_reached[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/servo_brick/<UID>/velocity_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when a velocity set by request/servo_brick/<UID>/set_velocity is reached. The callback payload members are the servo and the velocity that is reached.

You can enable this callback with request/servo_brick/<UID>/enable_velocity_reached_callback.

Note

Since we can't get any feedback from the servo, this only works if the acceleration (see request/servo_brick/<UID>/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.