Dynamixel Servo Driver

How to use the Dynamixel Servo Driver robot skill

Drives Robotis Dynamixel smart servos from ARCx's virtual servo ports, over a serial bus wired to an EZB.

Once configured, a Dynamixel behaves like any other servo in ARCx: Auto Position, the servo skill, Servo.SetPosition(), the Kinematics Service and everything else move virtual port V1 and this skill turns that into the right packet on the bus.

Supported: AX-12/18, MX-28/64/106 (protocol 1 firmware), XL-320, XL330, XL430, XC430, XM430, XM540, XH430, XH540.

Untested against hardware at the time of writing - treat the first bring-up with care.

Requirements

• A connected EZB.
• Dynamixel servos daisy chained on one bus, all set to the same baud rate, each with a different ID.
• Power for the servos at their own voltage - they do not run from the EZB's logic supply.
• Ideally a hardware UART, which is full duplex and therefore able to read servos. A transmit-only digital port can move servos but cannot read, ping or scan.

Adding it to a project

1. Wire the bus to a hardware UART on the EZB and connect.
2. Add the skill (Servo category).
3. On the Bus tab set the EZB index, the port and the baud rate. Dynamixels ship at 57600 (X series, XL-320) or 1000000 (AX series).
4. On the Tools tab press Scan bus to see which IDs answer.
5. On the Servos tab add an entry per servo: the virtual port other skills will use, the ID, the model, the operating mode and the position range.
6. Press Initialize and move a servo from the servo skill to check it.

Mapping ports to IDs

Each entry maps one ARCx virtual port (V0 to V255) to a Dynamixel ID. The ID does not have to match the port number - V3 can drive ID 17. Other skills only ever see the virtual port.

Setting	Meaning	Default
Port	The ARCx virtual servo port other skills move.	V1
ID	The Dynamixel ID (0-253) programmed into the servo.	1
Model	Decides the protocol and where every register lives, so it has to be right.	XL430
Operating mode	Position moves between the min and max. Wheel spins continuously, with the ARCx position choosing direction and speed (centre is stopped). ExtendedPosition is the X series multi-turn mode.	Position
Min position / Max position	The raw servo positions the lowest and highest ARCx positions map to. 1023 for a 1024 step servo (AX, XL-320), 4095 for a 4096 step servo (MX, X series).	0 / 4095
Invert	Reverse the direction, for a mirrored mounting.	off
Wheel velocity limit	Wheel mode: the raw velocity the extreme ARCx positions map to. Must not exceed the servo's own velocity limit register.	265
Default profile velocity	Raw moving speed (protocol 1, XL-320) or profile velocity (X series) applied on initialization, until a skill sets one. 0 is maximum.	0
Default profile acceleration	Raw profile acceleration (X series, MX) applied on initialization. 0 is maximum. Ignored by servos without the register.	0
Enabled	A disabled entry is kept but ignored, so a servo can be parked without losing its settings.	on

Bus settings

Setting	Meaning	Default
Board index	Which EZB the bus is wired to. The virtual ports of this EZB are the ones the skill listens to.	0
Port type	UART1 is the usual choice - full duplex, so servos can be read. UART0 on an EZ-B v4 shares the camera port pins. DigitalPort is transmit-only software serial: servos can be moved but not read, and only 4800 to 115200 are available.	UART1
Digital port	Which digital port to transmit from, when the port type is DigitalPort.	D0
Baud rate	Every servo on the bus must be set to this.	1000000
Response timeout (ms)	How long to wait for an answer to a read or ping.	250
Inter-command delay (ms)	Pause after every packet, so a servo has time to act before the next arrives. 0 sends as fast as the EZB can.	5
Initialize on connect	Open the UART and apply each servo's mode automatically when the EZB connects.	on
Set status return level on init	Tell every servo to answer only reads and pings, so writes are not slowed by replies. Turn off to see every acknowledgement in the debug log.	on
Debug logging	Write every packet sent and received to the log as hex. Useful when wiring a new chain, noisy once it works.	off

Telemetry

Background polling of every enabled servo's position, temperature, voltage, load and moving flag. It needs a hardware UART, and it is off by default because every poll is bus traffic that competes with movement.

Setting	Meaning	Default
Enabled	Poll the servos.	off
Interval (ms)	How often a full pass is started. A pass that takes longer simply runs back to back.	1000
Set global variables	Publish each reading as script variables.	on
Variable prefix	Start of every variable name.	Dynamixel
Over temperature limit	A servo reaching this many degrees Celsius is reported in the log. 0 disables the check. Dynamixels shut themselves down around 70-80 degrees.	70
Release on over temperature	Torque off a servo that reaches the limit, so it cools instead of tripping its own shutdown.	on

With the default prefix, port V1 publishes DynamixelV1Position, DynamixelV1Temperature, DynamixelV1Voltage, DynamixelV1Load, DynamixelV1Moving and DynamixelV1Online.

The window

• Bus status and counters: packets sent, status packets received, servo errors and response timeouts.
• Initialize - open the UART and put every servo into its configured mode.
• Scan bus - broadcast ping on both protocols and list every servo that answers, configured or not.
• Read all - read position, temperature, voltage and load once.
• Torque on / Release all.
• A row per configured servo with its live values and last error.

Sync writes

When several configured servos are moved in the same operation, the driver sends a sync write - one packet for the whole group - rather than one packet per servo. That is what makes a whole-arm Auto Position frame arrive at the servos together.

Tools tab

Scan the bus, ping a servo, change an ID, reboot a servo that has shut itself down on a hardware error, and factory reset.

The Window tab sets the robot skill's window title, its size on the workspace and notes about what it does in this project.

Troubleshooting

Symptom	Cause
Nothing answers a scan	Wrong baud rate, wrong UART, the bus is not powered, or the data line is wired the wrong way round.
Some servos answer, others do not	Duplicate IDs on the bus, or a bad link in the daisy chain.
Servos move but cannot be read	The bus is on a DigitalPort - transmit only. Move it to a hardware UART.
A servo moves the wrong way or to the wrong angle	Wrong model (so wrong control table), wrong min/max, or Invert needed.
Movement is jerky when several servos move	Raise Inter-command delay, or turn telemetry off or slower - it competes for the bus.
A servo stops responding and gets hot	It has shut down on a hardware error. Let it cool, then Reboot it.
Response timeouts in the counters	Raise Response timeout, check the baud rate and the wiring.
Positions jump when the mode is changed	Torque is turned off to change the operating mode; the servo may sag.

See also

• Feetech Rs485 servo Driver / Feetech Bus servo Driver - the same idea for Feetech servos
• Servo, Auto Position (movement panel), Kinematics Service - things that move these ports

Control Commands for the Dynamixel Servo Driver robot skill

There are Control Commands available for this robot skill which allows the skill to be controlled programmatically from scripts or other robot skills. These commands enable you to automate actions, respond to sensor inputs, and integrate the robot skill with other systems or custom interfaces. If you're new to the concept of Control Commands, we have a comprehensive manual available here that explains how to use them, provides examples to get you started and make the most of this powerful feature.

Control Command Manual

This robot skill has 36 control commands, listed below. Send them from a JavaScript or Python script, from Blockly, or from another robot skill.

The first value is always the window title, which is the name in the title bar of the robot skill on your workspace. It starts out as Dynamixel servo Driver, which is what every example below uses. If you rename the robot skill, or add a second copy of it to the project, use the title as it appears on that window instead.

ControlCommand() can be shortened to CC(), and both spellings work in JavaScript and in Python. The examples are JavaScript; Python is the same call, except that true and false are written True and False.

ChangeID

Program a new Dynamixel ID (0 to 253) into the servo and update the configuration entry to match

Syntax

ControlCommand("Dynamixel servo Driver", "ChangeID", (String)servoPort, (Number)newId)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	newId	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "ChangeID", "servoPort", 0);

FactoryReset

Restore factory settings. Option: ExceptIdAndBaud (default, protocol 2 only), ExceptId (protocol 2 only) or All. Protocol 1 always resets everything, which sets the ID to 1 and the baud rate to 1000000

Syntax

ControlCommand("Dynamixel servo Driver", "FactoryReset", (String)servoPort, (String)ExceptIdAndBaud|ExceptId|All)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	ExceptIdAndBaud|ExceptId|All	Text	Your text, in quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "FactoryReset", "servoPort", "ExceptIdAndBaud|ExceptId|All");

GetBusStatus

A one line description of the bus and whether it initialized

Syntax

ControlCommand("Dynamixel servo Driver", "GetBusStatus")

Returns: String

Example

var result = ControlCommand("Dynamixel servo Driver", "GetBusStatus");

GetFirmwareVersion

The firmware version the servo reports

Syntax

ControlCommand("Dynamixel servo Driver", "GetFirmwareVersion", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetFirmwareVersion", "servoPort");

GetHardwareError

The hardware error status bits (XL-320 and X series). 0 is healthy. Reboot clears a shutdown

Syntax

ControlCommand("Dynamixel servo Driver", "GetHardwareError", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetHardwareError", "servoPort");

GetLoad

The servo's present load as a signed raw value. Negative is clockwise. Units depend on the model (0.1% or mA)

Syntax

ControlCommand("Dynamixel servo Driver", "GetLoad", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetLoad", "servoPort");

GetLoadDirection

The direction of the servo's present load: CW or CCW

Syntax

ControlCommand("Dynamixel servo Driver", "GetLoadDirection", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: String

Example

var result = ControlCommand("Dynamixel servo Driver", "GetLoadDirection", "servoPort");

GetModelNumber

The model number the servo reports

Syntax

ControlCommand("Dynamixel servo Driver", "GetModelNumber", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetModelNumber", "servoPort");

GetPresentPosition

The servo's real position read back from it, scaled to the ARCx servo position range like any other servo

Syntax

ControlCommand("Dynamixel servo Driver", "GetPresentPosition", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetPresentPosition", "servoPort");

GetPresentPositionDegrees

The servo's real position in degrees from the start of its range

Syntax

ControlCommand("Dynamixel servo Driver", "GetPresentPositionDegrees", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Double [5.0e324 to 1.7e308]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetPresentPositionDegrees", "servoPort");

GetPresentPositionRaw

The servo's real position as the raw register value (0 to 1023 or 0 to 4095, wider in extended position mode)

Syntax

ControlCommand("Dynamixel servo Driver", "GetPresentPositionRaw", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetPresentPositionRaw", "servoPort");

GetServoPorts

The virtual servo ports configured as Dynamixel servos, as strings such as V1

Syntax

ControlCommand("Dynamixel servo Driver", "GetServoPorts")

Returns: Array of String

Example

var result = ControlCommand("Dynamixel servo Driver", "GetServoPorts");

GetTemperature

The servo's internal temperature in degrees Celsius

Syntax

ControlCommand("Dynamixel servo Driver", "GetTemperature", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetTemperature", "servoPort");

GetVoltage

The servo's supply voltage in volts

Syntax

ControlCommand("Dynamixel servo Driver", "GetVoltage", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Double [5.0e324 to 1.7e308]

Example

var result = ControlCommand("Dynamixel servo Driver", "GetVoltage", "servoPort");

InitializeBus

Open the UART and apply every servo's operating mode and default profile, as happens when the EZB connects

Syntax

ControlCommand("Dynamixel servo Driver", "InitializeBus")

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "InitializeBus");

IsMoving

True while the servo is still travelling to its goal

Syntax

ControlCommand("Dynamixel servo Driver", "IsMoving", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "IsMoving", "servoPort");

Ping

Ping the servo. Returns true when it answers, false when it does not. Needs a hardware UART

Syntax

ControlCommand("Dynamixel servo Driver", "Ping", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "Ping", "servoPort");

ReadByte

Read one byte from the servo's control table at the address

Syntax

ControlCommand("Dynamixel servo Driver", "ReadByte", (String)servoPort, (Number)address)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "ReadByte", "servoPort", 0);

ReadBytes

Read a number of bytes from the servo's control table at the address. Returns them as space separated hex

Syntax

ControlCommand("Dynamixel servo Driver", "ReadBytes", (String)servoPort, (Number)address, (Number)count)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes
3	count	Number	A number, without quotes

Returns: String

Example

var result = ControlCommand("Dynamixel servo Driver", "ReadBytes", "servoPort", 0, 0);

ReadInt16

Read a signed 16 bit value (2 bytes) from the servo's control table at the address

Syntax

ControlCommand("Dynamixel servo Driver", "ReadInt16", (String)servoPort, (Number)address)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "ReadInt16", "servoPort", 0);

ReadInt32

Read a signed 32 bit value (4 bytes) from the servo's control table at the address

Syntax

ControlCommand("Dynamixel servo Driver", "ReadInt32", (String)servoPort, (Number)address)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "ReadInt32", "servoPort", 0);

ReadUInt16

Read an unsigned 16 bit value (2 bytes) from the servo's control table at the address

Syntax

ControlCommand("Dynamixel servo Driver", "ReadUInt16", (String)servoPort, (Number)address)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes

Returns: Integer [-2,147,483,648 to 2,147,483,647]

Example

var result = ControlCommand("Dynamixel servo Driver", "ReadUInt16", "servoPort", 0);

Reboot

Reboot the servo, which clears a hardware error shutdown. Protocol 2 servos only

Syntax

ControlCommand("Dynamixel servo Driver", "Reboot", (String)servoPort)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "Reboot", "servoPort");

ReleaseAll

Release (torque off) every configured servo

Syntax

ControlCommand("Dynamixel servo Driver", "ReleaseAll")

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "ReleaseAll");

ScanBus

Broadcast ping the bus and return a line per servo found (ID, protocol, model). protocol is 1, 2 or 0 for both

Syntax

ControlCommand("Dynamixel servo Driver", "ScanBus", (Number)protocol)

Parameters

#	Name	Type	What to pass
1	protocol	Number	A number, without quotes

Returns: Array of String

Example

var result = ControlCommand("Dynamixel servo Driver", "ScanBus", 0);

SetGoalVelocity

Wheel mode: spin at the raw signed velocity. Positive is counter clockwise, 0 stops. Bypasses the ARCx position mapping

Syntax

ControlCommand("Dynamixel servo Driver", "SetGoalVelocity", (String)servoPort, (Number)velocity)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	velocity	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "SetGoalVelocity", "servoPort", 0);

SetHomingOffset

X series and MX: the raw offset added to the position, to shift where 0 is. Torque is turned off to write it

Syntax

ControlCommand("Dynamixel servo Driver", "SetHomingOffset", (String)servoPort, (Number)offset)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	offset	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "SetHomingOffset", "servoPort", 0);

SetLED

Turn the LED of the Dynamixel on the virtual servo port (for example v1, or id:5 to address by Dynamixel ID) on or off

Syntax

ControlCommand("Dynamixel servo Driver", "SetLED", (String)servoPort, (Bool)on)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	on	True or false	true or false, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "SetLED", "servoPort", true);

SetOperatingMode

Switch the servo between Position, Wheel and ExtendedPosition and remember it in the configuration. Torque is turned off to do it

Syntax

ControlCommand("Dynamixel servo Driver", "SetOperatingMode", (String)servoPort, (String)Position|Wheel|ExtendedPosition)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	Position|Wheel|ExtendedPosition	Text	Your text, in quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "SetOperatingMode", "servoPort", "Position|Wheel|ExtendedPosition");

SetProfileAcceleration

The raw profile acceleration for position moves (X series and MX). 0 is the servo's maximum. Same as setting the port's acceleration

Syntax

ControlCommand("Dynamixel servo Driver", "SetProfileAcceleration", (String)servoPort, (Number)acceleration)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	acceleration	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "SetProfileAcceleration", "servoPort", 0);

SetProfileVelocity

The raw speed limit for position moves (moving speed or profile velocity). 0 is the servo's maximum. Same as setting the port's velocity

Syntax

ControlCommand("Dynamixel servo Driver", "SetProfileVelocity", (String)servoPort, (Number)velocity)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	velocity	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "SetProfileVelocity", "servoPort", 0);

TorqueEnable

Turn torque on (hold position) or off (free to move by hand) for the servo. Off is the same as releasing the port

Syntax

ControlCommand("Dynamixel servo Driver", "TorqueEnable", (String)servoPort, (Bool)enabled)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	enabled	True or false	true or false, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "TorqueEnable", "servoPort", true);

TorqueEnableAll

Turn torque on or off for every configured servo

Syntax

ControlCommand("Dynamixel servo Driver", "TorqueEnableAll", (Bool)enabled)

Parameters

#	Name	Type	What to pass
1	enabled	True or false	true or false, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "TorqueEnableAll", true);

WriteByte

Write one byte to the servo's control table at the address

Syntax

ControlCommand("Dynamixel servo Driver", "WriteByte", (String)servoPort, (Number)address, (Number)value)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes
3	value	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "WriteByte", "servoPort", 0, 0);

WriteInt32

Write a signed 32 bit value (4 bytes) to the servo's control table at the address

Syntax

ControlCommand("Dynamixel servo Driver", "WriteInt32", (String)servoPort, (Number)address, (Number)value)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes
3	value	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "WriteInt32", "servoPort", 0, 0);

WriteUInt16

Write an unsigned 16 bit value (2 bytes) to the servo's control table at the address

Syntax

ControlCommand("Dynamixel servo Driver", "WriteUInt16", (String)servoPort, (Number)address, (Number)value)

Parameters

#	Name	Type	What to pass
1	servoPort	Text	Your text, in quotes
2	address	Number	A number, without quotes
3	value	Number	A number, without quotes

Returns: Boolean [true or false]

Example

var result = ControlCommand("Dynamixel servo Driver", "WriteUInt16", "servoPort", 0, 0);

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This list is read out of the robot skill itself each time its package is uploaded, so it matches the published version (v4).