Robotis

Driver for interfacing with Robotis Dynamixel servos.

This is a work in progress and currently only supports XL330 and devices with the same Control Table. It also only speaks Dynamixel protocol v2.

While it is possible to support GPIO-based switching for converting UART to the half-duplex signal required by Dynamixel, this library works best speaking UART over USB to another device that can do that conversion (such as and OpenR150 running the usb_to_dynamixel sketch.

Installation

def deps do
  [
    {:robotis, "~> 0.1.1"}
  ]
end

Usage

{:ok, pid} = Robotis.start_link(uart_port: "ttyAMA0", baud: 1_000_000)

Robotis.ping(pid, 1) # => {:ok, %{firmware: 49, id: 1, model: :xl330_m288, model_number: 1200}}
Robotis.read(pid, 1, :present_position) # => {:ok, 14.58984375}
:ok = Robotis.write(pid, 1, :torque_enable, true)
:ok = Robotis.write(pid, 1, :goal_position, 124.293)

Write or Write-and-Wait

The Robotis.write/5 function can work in either a write or write-and-wait manner:

# The default, this will send the command to the servo and not wait for a
# response.
:ok = Robotis.write(pid, 1, :goal_position, 180)

# This will send the command and wait for a status packet from the servo. This
# will block until that status packet is received or a timeout occurs
:ok = Robotis.write(pid, 1, :goal_position, 180, true)

It's important to consider the setting of :status_return_level when deciding which to use. In the case that :status_return_level is set to :all, the servo will respond with a status message after the write. If the Robotis.write call is not expecting this and another command is issued, it's possible the status message and the new command will conflict and have unintended consequences.

# The following may receive no data or invalid packets when reading present_position 
:ok = Robotis.write(pid, 1, :status_return_level, :all)
:ok = Robotis.write(pid, 1, :goal_position, 180)
:ok = Robotis.read(pid, 1, :present_position)

# The following will work
:ok = Robotis.write(pid, 1, :status_return_level, :ping_read)
:ok = Robotis.write(pid, 1, :goal_position, 180)
:ok = Robotis.read(pid, 1, :present_position)