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Supported Hardware

Currently only the following Willow Garage hardware is supported:

WG005

These are the main motor controller boards used in the PR2. Each board has the following features:

• 1 quadrature incremental encoder input
• 1 limit-switch input (with on-board latching of encoder position at time of rising and falling edges)
• 1 digital output, used as to synchronize camera exposures with the realtime loop
• Closed-loop current control for 1 brushed DC motor up to ~3A

WG006

This motor controller board is used in the gripper on the PR2. Each board has the following features:

• Same as the WG005, but with a current limit of ~0.5A
• Additional LED to be used for finding position of hand in camera images
• 3-axis accelerometer with 3khz update
• Support for 2 SPI ports (compatible with 22-element tactile sensors for fingertips)

WG014

• 6-port EtherCAT hub

WG021

• Support for driving LED projector at 30hz, synchronized with motion control and camera exposures

ROS API

ethercat_hardware

ethercat_hardware is a driver for the EtherCAT motor controller boards (MCBs). The driver handles all initialization, communication, and diagnostic reporting for the MCBs. The driver currently supports four board types (WG005, WG006, WG014, and WG021)

Published Topics

diagnostics (diagnostic_msgs/DiagnosticStatus)

• Diagnostic status information.

accelerometer (pr2_msgs/AccelerometerState)

• Accelerometer data from a WG006 board (gripper)

pressure (pr2_msgs/PressureState)

• Fingertip pressure sensor data from a WG006 board (gripper)

motors_halted (std_msgs/Bool)

• A boolean value indicating if the motors have been halted

Command-line Tools

The ethercat_hardware package's primary purpose is to provide a library for communicating with motor controller boards. However, the package does provide the motorconf command-line tool for configuring these boards. In practice, this tool is used during robot assembly, and should not be needed after initial bring-up of the robot. NOTE: improper use of this tool could lead to hardware damage, motorconf usage is limited to system administrators only.

motorconf

motorconf

• Display the current configuration of motor controller boards, and allow boards to be programmed with new configuration information.

Usage: ./motorconf [options]
 -i, --interface <i>    Use the network interface <i>
 -a, --actuators <file> Get the actuator definitions from file (default: actuators.conf)
 -d, --device <d>       Select the device to program
 -b, --board <b>        Set the expected board type (wg005, wg006, wg021)
 -p, --program          Program a motor control board
 -n, --name <n>         Set the name of the motor control board to <n>
 -m, --motor <m>        Set the configuration for motor <m>
 -h, --help             Print this message and exit

When running motorconf, you must specify the interface used to communicate with the EtherCAT devices. Without any additional arguments, motorconf will enumerate all of the EtherCAT devices it can find.

# ./motorconf -i ecat0

[DEBUG] 1263333387.377268000: Device #00: WG014 (0x67d616)
[DEBUG] 1263333387.419128000: Device #01: WG014 (0x67d616)
[DEBUG] 1263333387.462366000: Device #02: WG05 (0x67d60d) Firmware Revision 1.20, PCB Revision F.02, Serial #: 1399
[DEBUG] 1263333387.463359000:             Serial #: 01399
[DEBUG] 1263333387.465986000:             Name: br_caster_r_wheel_motor
[DEBUG] 1263333387.509329000: Device #03: WG05 (0x67d60d) Firmware Revision 1.20, PCB Revision F.02, Serial #: 1414
[DEBUG] 1263333387.510322000:             Serial #: 01414
[DEBUG] 1263333387.512832000:             Name: br_caster_l_wheel_motor
 .
 . 
 .
[DEBUG] 1263333388.293608000: Device #20: WG05 (0x67d60d) Firmware Revision 1.20, PCB Revision F.02, Serial #: 1695
[DEBUG] 1263333388.294604000:             Serial #: 01695
[DEBUG] 1263333388.297113000:             Name: laser_tilt_mount_motor

In order to program an unconfigured device, or re-program a device, you must specify a name, motor type, and board type for this motor. If the name given (using the -n option) matches one of the names in the actuators configuration file (actuators.conf, by default), then the motor type and board type will be selected automatically. The motor type can be specified explicitly with the -m option, and the board type can be specified with the -b option. A list of valid actuator names and motor types can be found with the -h option. In addition to the name, motor, and board types, motorconf needs to know which device in the EtherCAT chain to program. The device number is specified with the -d option. Finally, the -p option tells motorconf to actually program the board. The following example programs device #2 to be the br_caster_r_wheel_motor:

./motorconf -i ecat0 -n br_caster_r_wheel_motor -d 2 -p

motorconf will respond with:

[ INFO] 1263334127.577301000: Programming device 2, to be named: br_caster_r_wheel_motor

actuators.conf

actuators.conf is an XML file that specifies the motor parameters and common motor names to be programmed into the motor controller boards. The file consists of a single <configuration> section. The <configuration> section contains two subsections: <motors> and <actuators>.

The <motors> subsection contains a series of <motor> definitions. Each motor requires a name attribute. The <motor> also requires child elements <params> and <encoder>. The <params> element contains the following attributes:

• Make
• Model
• Maximum current
• Speed constant
• Resistance
• Motor Torque Constant

The <encoder> element contains the following attributes:

• Pulses per Revolution
• Reduction

For example, this element specifies the Maxon RE40 motor used in PR2's elbow, shoulder and spine:

  <!-- Elbow, shoulder, spine -->
  <!-- http://pr.willowgarage.com/wiki/HardwareComponents/Motors?action=AttachFile&do=get&target=maxonRE40.pdf -->
  <motor name="148877">
    <params make="Maxon"
            model="148877"
            max_current="3.12"
            speed_constant="158"
            resistance="1.16"
            motor_torque_constant="0.0603" />
    <encoder pulses_per_revolution="1200" reduction="-1"/>
  </motor>

The <actuators> subsection contains a series of <actuator> definitions. An <actuator> has the following attributes:

• Name
• Motor
• Board

For example, the following <actuator> definition states that the l_elbow_flex_motor should be configured with the motor parameters specified in the previous example:

  <actuator name="l_elbow_flex_motor" motor="148877" board="wg005"/>