Dynamixel

Latest revision as of 07:45, 26 October 2013

The plug-in interfaces to a number of dynamixel servos - build for version MX-28, but may work with others, as most registers in the servo interface is compatible.

[edit] Start sequence

The servos must have power before the a usb client is connected to the teensy controller, i.e. before RHD is started. The controller reads at start-up all registers from the servo, and assumes that all servos with no battery voltage reported is not connected, and thus stops receiving status from these servos.

[edit] Interface

The interface is through a microprocessor Atmel mega32u4 (teensy 2), the code for the microprocessor is in a subdirectory to the plugin code.

The microcontroller can be operated from a serial terminal (putty), and has on-line help. It is fully text oriented.

[edit] Read variables

The plugin has the following (configured for (up to) 5 servos)

servoPos[5]  Current angle of the servo in degrees x 10
servoMin[5]  Minimum servo angle (in degrees x 10) - defined in rhdconfig.xml - never updated
servoMax[5]  Maximum servi angle (in degrees x 10) - defined in rhdconfig.xml - never updated
servoVel[5]  Current servo velocity - as reported by the servo (i.e. not converted to degrees/sec)
servoLoad[5] Current servo load - as reported by the servo (motor current based)
servoVolt[5] Current battery voltage, measured by the servo (in volt x 10)
servoTemp[5] Current temperature in degrees C.
servoComErr[5] Count of communication errors (crc-fail, rx timeout, etc)
servoIntRef[5] Reference position in servo units (12bit unsigned)
servoIntPos[5] Current position in servo units (12 bit unsigned)
servoUpdCnt[5] Number of status updates received from each servo.

[edit] Write variables

The servos are controlled by an angle reference for each servo (in degrees x 10). The center position is defined in the rgdconfig.xml file.

servoref[5]

[edit] Sample rhdconfig entry

In this example only servo 0,3,4 of the 5 servos are connected. The actual servo ID (1,2,3,4,5) and interface speed (500kbit/s) is defined in the teensy firmware.

<! -- 
steering interface
* servo values (name from servo0 to servo10, value is "minpos centerpos maxpos scale",
* all positions in servo units, scale is used to and from RHD variable, set to 4096/360/10 = 1.1377778 to
* get sontrol and status in degrees (*10) relative to center position.
* dev is USB interface to teency 2 board
* dead zone (with no movement around target position) (0..255)
* safety > joystick (higher number, to get index to manual overwrite button - not used pt)
* debug if 1 then some errors during startup is ignored and more text printed
-- >
<dynamixel enable="true" lib="dynamixel.so.1"
 critical="true" 
 safety="2"
 dev="/dev/ttyACM0"
 servo0 = "1200 2450 3700 1.1377778"
 servo3 = "1300 2560 3800 1.1377778"
 servo4 = "300   800 1400 1.1377778"
 deadzone="3"
 debug="1">
 <dxlinit msg="i=0"/>
 <dxlinit msg="s=1"/>
 <dxlinit msg="j=0"/>
 <dxlinit msg="help"/>
</dynamixel>