Shell - Servo Brick

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

Examples

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

Callback

Download (example-callback.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XXYYZZ # Change XXYYZZ to the UID of your Servo Brick

# Use position reached callback to swing back and forth
tinkerforge dispatch servo-brick $uid position-reached\
 --execute "if   [ {position} -eq  9000 ];
            then echo 'Position: 90°, going to -90°' && tinkerforge call servo-brick $uid set-position 0 -9000;
            elif [ {position} -eq -9000 ];
            then echo 'Position: -90°, going to 90°' && tinkerforge call servo-brick $uid set-position 0 9000;
            else echo error; fi" &

# Enable position reached callback
tinkerforge call servo-brick $uid 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
tinkerforge call servo-brick $uid set-velocity 0 10000
tinkerforge call servo-brick $uid set-position 0 9000
tinkerforge call servo-brick $uid enable 0

echo "Press key to exit"; read dummy

tinkerforge call servo-brick $uid disable 0

kill -- -$$ # Stop callback dispatch in background

Configuration

Download (example-configuration.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XXYYZZ # Change XXYYZZ to the UID of your Servo Brick

# 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°
tinkerforge call servo-brick $uid set-output-voltage 5500

tinkerforge call servo-brick $uid set-degree 0 -10000 10000
tinkerforge call servo-brick $uid set-pulse-width 0 1000 2000
tinkerforge call servo-brick $uid set-period 0 19500
tinkerforge call servo-brick $uid set-acceleration 0 1000 # Slow acceleration
tinkerforge call servo-brick $uid set-velocity 0 65535 # Full speed

tinkerforge call servo-brick $uid set-degree 5 -9000 9000
tinkerforge call servo-brick $uid set-pulse-width 5 950 1950
tinkerforge call servo-brick $uid set-period 5 20000
tinkerforge call servo-brick $uid set-acceleration 5 65535 # Full acceleration
tinkerforge call servo-brick $uid set-velocity 5 65535 # Full speed

tinkerforge call servo-brick $uid set-position 0 10000 # Set to most right position
tinkerforge call servo-brick $uid enable 0

tinkerforge call servo-brick $uid set-position 5 -9000 # Set to most left position
tinkerforge call servo-brick $uid enable 5

echo "Press key to exit"; read dummy

tinkerforge call servo-brick $uid disable 0
tinkerforge call servo-brick $uid disable 5

API

Possible exit codes for all tinkerforge commands are:

  • 1: interrupted (ctrl+c)
  • 2: syntax error
  • 21: Python 2.5 or newer is required
  • 22: Python argparse module is missing
  • 23: socket error
  • 24: other exception
  • 25: invalid placeholder in format string
  • 26: authentication error
  • 201: timeout occurred
  • 209: invalid argument value
  • 210: function is not supported
  • 211: unknown error

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.

Command Structure

The common options of the call and dispatch commands are documented here. The specific command structure is shown below.

tinkerforge call servo-brick [<option>..] <uid> <function> [<argument>..]
Parameters:
  • <uid> -- string
  • <function> -- string

The call command is used to call a function of the Servo Brick. It can take several options:

  • --help shows help for the specific call command and exits
  • --list-functions shows a list of known functions of the Servo Brick and exits
tinkerforge dispatch servo-brick [<option>..] <uid> <callback>
Parameters:
  • <uid> -- string
  • <callback> -- string

The dispatch command is used to dispatch a callback of the Servo Brick. It can take several options:

  • --help shows help for the specific dispatch command and exits
  • --list-callbacks shows a list of known callbacks of the Servo Brick and exits
tinkerforge call servo-brick <uid> <function> [<option>..] [<argument>..]
Parameters:
  • <uid> -- string
  • <function> -- string

The <function> to be called can take different options depending of its kind. All functions can take the following options:

  • --help shows help for the specific function and exits

Getter functions can take the following options:

  • --execute <command> shell command line to execute for each incoming response (see section about output formatting for details)

Setter functions can take the following options:

  • --expect-response requests response and waits for it

The --expect-response option for setter functions allows to detect timeouts and other error conditions calls of setters as well. The device will then send a response for this purpose. If this option is not given for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

tinkerforge dispatch servo-brick <uid> <callback> [<option>..]
Parameters:
  • <uid> -- string
  • <callback> -- string

The <callback> to be dispatched can take several options:

  • --help shows help for the specific callback and exits
  • --execute <command> shell command line to execute for each incoming response (see section about output formatting for details)

Basic Functions

tinkerforge call servo-brick <uid> enable <servo-num>
Parameters:
  • <servo-num> -- int
Output:

no output

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

tinkerforge call servo-brick <uid> disable <servo-num>
Parameters:
  • <servo-num> -- int
Output:

no output

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.

tinkerforge call servo-brick <uid> is-enabled <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • enabled -- bool

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

tinkerforge call servo-brick <uid> set-position <servo-num> <position>
Parameters:
  • <servo-num> -- int
  • <position> -- int
Output:

no output

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.

tinkerforge call servo-brick <uid> get-position <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • position -- int

Returns the position of the specified servo as set by set-position.

tinkerforge call servo-brick <uid> get-current-position <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • position -- 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.

tinkerforge call servo-brick <uid> set-velocity <servo-num> <velocity>
Parameters:
  • <servo-num> -- int
  • <velocity> -- int
Output:

no output

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.

tinkerforge call servo-brick <uid> get-velocity <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • velocity -- int

Returns the velocity of the specified servo as set by set-velocity.

tinkerforge call servo-brick <uid> get-current-velocity <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • velocity -- 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.

tinkerforge call servo-brick <uid> set-acceleration <servo-num> <acceleration>
Parameters:
  • <servo-num> -- int
  • <acceleration> -- int
Output:

no output

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.

tinkerforge call servo-brick <uid> get-acceleration <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • acceleration -- int

Returns the acceleration for the specified servo as set by set-acceleration.

tinkerforge call servo-brick <uid> set-output-voltage <voltage>
Parameters:
  • <voltage> -- int
Output:

no output

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.

tinkerforge call servo-brick <uid> get-output-voltage
Output:
  • voltage -- int

Returns the output voltage as specified by set-output-voltage.

tinkerforge call servo-brick <uid> set-pulse-width <servo-num> <min> <max>
Parameters:
  • <servo-num> -- int
  • <min> -- int
  • <max> -- int
Output:

no output

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.

tinkerforge call servo-brick <uid> get-pulse-width <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • min -- int
  • max -- int

Returns the minimum and maximum pulse width for the specified servo as set by set-pulse-width.

tinkerforge call servo-brick <uid> set-degree <servo-num> <min> <max>
Parameters:
  • <servo-num> -- int
  • <min> -- int
  • <max> -- int
Output:

no output

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.

tinkerforge call servo-brick <uid> get-degree <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • min -- int
  • max -- int

Returns the minimum and maximum degree for the specified servo as set by set-degree.

tinkerforge call servo-brick <uid> set-period <servo-num> <period>
Parameters:
  • <servo-num> -- int
  • <period> -- int
Output:

no output

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).

tinkerforge call servo-brick <uid> get-period <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • period -- int

Returns the period for the specified servo as set by set-period.

tinkerforge call servo-brick <uid> get-servo-current <servo-num>
Parameters:
  • <servo-num> -- int
Output:
  • current -- int

Returns the current consumption of the specified servo in mA.

tinkerforge call servo-brick <uid> get-overall-current
Output:
  • current -- int

Returns the current consumption of all servos together in mA.

tinkerforge call servo-brick <uid> get-stack-input-voltage
Output:
  • 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.

tinkerforge call servo-brick <uid> get-external-input-voltage
Output:
  • 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

tinkerforge call servo-brick <uid> set-spitfp-baudrate-config <enable-dynamic-baudrate> <minimum-dynamic-baudrate>
Parameters:
  • <enable-dynamic-baudrate> -- bool
  • <minimum-dynamic-baudrate> -- int
Output:

no output

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 set-spitfp-baudrate. If the dynamic baudrate is disabled, the baudrate as set by 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).

tinkerforge call servo-brick <uid> get-spitfp-baudrate-config
Output:
  • enable-dynamic-baudrate -- bool
  • minimum-dynamic-baudrate -- int

Returns the baudrate config, see set-spitfp-baudrate-config.

New in version 2.3.4 (Firmware).

tinkerforge call servo-brick <uid> get-send-timeout-count <communication-method>
Parameters:
  • <communication-method> -- int (has symbols)
Output:
  • 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:

  • communication-method-none = 0, for <communication-method>
  • communication-method-usb = 1, for <communication-method>
  • communication-method-spi-stack = 2, for <communication-method>
  • communication-method-chibi = 3, for <communication-method>
  • communication-method-rs485 = 4, for <communication-method>
  • communication-method-wifi = 5, for <communication-method>
  • communication-method-ethernet = 6, for <communication-method>
  • communication-method-wifi-v2 = 7, for <communication-method>

New in version 2.3.2 (Firmware).

tinkerforge call servo-brick <uid> set-spitfp-baudrate <bricklet-port> <baudrate>
Parameters:
  • <bricklet-port> -- char
  • <baudrate> -- int
Output:

no output

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 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 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).

tinkerforge call servo-brick <uid> get-spitfp-baudrate <bricklet-port>
Parameters:
  • <bricklet-port> -- char
Output:
  • baudrate -- int

Returns the baudrate for a given Bricklet port, see set-spitfp-baudrate.

New in version 2.3.2 (Firmware).

tinkerforge call servo-brick <uid> get-spitfp-error-count <bricklet-port>
Parameters:
  • <bricklet-port> -- char
Output:
  • 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).

tinkerforge call servo-brick <uid> enable-status-led
Output:no output

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).

tinkerforge call servo-brick <uid> disable-status-led
Output:no output

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).

tinkerforge call servo-brick <uid> is-status-led-enabled
Output:
  • enabled -- bool

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

New in version 2.3.1 (Firmware).

tinkerforge call servo-brick <uid> get-protocol1-bricklet-name <port>
Parameters:
  • <port> -- char
Output:
  • 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.

tinkerforge call servo-brick <uid> get-chip-temperature
Output:
  • 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.

tinkerforge call servo-brick <uid> reset
Output:no output

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!

tinkerforge call servo-brick <uid> get-identity
Output:
  • uid -- string
  • connected-uid -- string
  • position -- char
  • hardware-version -- int,int,int
  • firmware-version -- int,int,int
  • device-identifier -- int (has symbols)

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

Callback Configuration Functions

tinkerforge call servo-brick <uid> set-minimum-voltage <voltage>
Parameters:
  • <voltage> -- int
Output:

no output

Sets the minimum voltage in mV, below which the 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).

tinkerforge call servo-brick <uid> get-minimum-voltage
Output:
  • voltage -- int

Returns the minimum voltage as set by set-minimum-voltage

tinkerforge call servo-brick <uid> enable-position-reached-callback
Output:no output

Enables the position-reached callback.

Default is disabled.

New in version 2.0.1 (Firmware).

tinkerforge call servo-brick <uid> disable-position-reached-callback
Output:no output

Disables the position-reached callback.

Default is disabled.

New in version 2.0.1 (Firmware).

tinkerforge call servo-brick <uid> is-position-reached-callback-enabled
Output:
  • enabled -- bool

Returns true if position-reached callback is enabled, false otherwise.

New in version 2.0.1 (Firmware).

tinkerforge call servo-brick <uid> enable-velocity-reached-callback
Output:no output

Enables the velocity-reached callback.

Default is disabled.

New in version 2.0.1 (Firmware).

tinkerforge call servo-brick <uid> disable-velocity-reached-callback
Output:no output

Disables the velocity-reached callback.

Default is disabled.

New in version 2.0.1 (Firmware).

tinkerforge call servo-brick <uid> is-velocity-reached-callback-enabled
Output:
  • enabled -- bool

Returns true if velocity-reached callback is enabled, false otherwise.

New in version 2.0.1 (Firmware).

Callbacks

Callbacks can be used to receive time critical or recurring data from the device:

tinkerforge dispatch servo-brick <uid> example

The available callbacks 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.

tinkerforge dispatch servo-brick <uid> under-voltage
Output:
  • 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.

tinkerforge dispatch servo-brick <uid> position-reached
Output:
  • servo-num -- int
  • position -- int

This callback is triggered when a position set by 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 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.

tinkerforge dispatch servo-brick <uid> velocity-reached
Output:
  • 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.