Documentation: "limit" key should be "limits" in "Exploring the Compiled Robot"

[jshprentz]

Code of Conduct

• I agree to follow this project's Code of Conduct

AI Policy

• I agree to follow this project's AI Policy, or I agree that AI was not used while creating this issue.

Versions

• Elixir 1.19.5-otp-28
• Erlang 28.4.1
• igniter_new 0.5.33
• bb 0.15.1

Operating system

Ubuntu 24.04.4 LTS running in 5.15.153.1-microsoft-standard-WSL2+

Current Behaviour

After completing Your First Robot steps 1-6, try Exploring the Compiled Robot. The expression robot.joints.pan_joint.limit.upper gives an error and suggests, "Did you mean :limits?" The modified expression robot.joints.pan_joint.limits.upper gives the expected result.

joel@Joels-Dell-XPS-8940:~/projects/foo_bar$ iex -S mix
Erlang/OTP 28 [erts-16.3] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.19.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> robot = MyRobot.robot()
%BB.Robot{
  name: MyRobot,
  root_link: :base,
  ...
}
...
iex(5)> robot.joints.pan_joint.limit.upper
** (KeyError) key :limit not found in:

    %BB.Robot.Joint{
      name: :pan_joint,
      type: :revolute,
      parent_link: :base,
      child_link: :pan_link,
      origin: %{position: {0.0, 0.0, 0.05}, orientation: {0.0, 0.0, 0.0}},
      axis: {0.0, 0.0, 1.0},
      limits: %{
        upper: 1.5707963267948966,
        lower: -1.5707963267948966,
        effort: 5.0,
        velocity: 1.0471975511965979
      },
      dynamics: nil,
      sensors: [],
      actuators: []
    }

Did you mean:

    * :limits

    iex:5: (file)
iex(5)> robot.joints.pan_joint.limits.upper
1.5707963267948966

Reproduction

Start with a new mix project ...

joel@Joels-Dell-XPS-8940:~/projects$ mix new foo_bar
...

Add Beam Bots to the project dependencies as described in Manual Installation.

joel@Joels-Dell-XPS-8940:~/projects$ cd foo_bar/

joel@Joels-Dell-XPS-8940:~/projects/foo_bar$ vi mix.exs

joel@Joels-Dell-XPS-8940:~/projects/foo_bar$ tail mix.exs

  # Run "mix help deps" to learn about dependencies.
  defp deps do
    [
      {:bb, "~> 0.1"}
      # {:dep_from_hexpm, "~> 0.3.0"},
      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
    ]
  end
end

Create a my_robot.ex file as described in Step 1: Create the Module. Copy the Complete Example robot definition into the file.

joel@Joels-Dell-XPS-8940:~/projects/foo_bar$ cat <<EOF >lib/my_robot.ex
defmodule MyRobot do
  use BB

  topology do
    link :base do
      visual do
        cylinder do
          radius(~u(0.04 meter))
          height(~u(0.05 meter))
        end
        ...
        end
      end
    end
  end
end
EOF

Get dependencies.

joel@Joels-Dell-XPS-8940:~/projects/foo_bar$ mix deps.get
Resolving Hex dependencies...
...

Explore the robot topology as described in "Exploring the Compiled Robot."

joel@Joels-Dell-XPS-8940:~/projects/foo_bar$ iex -S mix
Erlang/OTP 28 [erts-16.3] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

==> spark
Compiling 45 files (.ex)
Generated spark app
==> bb
Compiling 176 files (.ex)
Generating BB.Cldr for 2 locales named [:en, :und] with a default locale named :en
Generated bb app
==> foo_bar
Compiling 2 files (.ex)
Generated foo_bar app
Interactive Elixir (1.19.5) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> robot = MyRobot.robot()
%BB.Robot{
  name: MyRobot,
  root_link: :base,
  links: %{
    base: %BB.Robot.Link{
      name: :base,
      parent_joint: nil,
      child_joints: [:pan_joint],
      mass: nil,
      center_of_mass: nil,
      inertia: nil,
      visual: %{
        origin: nil,
        geometry: {:cylinder, %{height: 0.05, radius: 0.04}},
        material: %{
          name: :material_2,
          color: %{blue: 0.2, green: 0.2, red: 0.2, alpha: 1.0},
          texture: nil
        }
      },
      collisions: [],
      sensors: []
    },
    pan_link: %BB.Robot.Link{
      name: :pan_link,
      parent_joint: :pan_joint,
      child_joints: [:tilt_joint],
      mass: nil,
      center_of_mass: nil,
      inertia: nil,
      visual: %{
        origin: {{0.0, 0.0, 0.015}, {0.0, 0.0, 0.0}},
        geometry: {:box, %{x: 0.03, y: 0.03, z: 0.03}},
        material: %{
          name: :material_1,
          color: %{blue: 0.3, green: 0.3, red: 0.3, alpha: 1.0},
          texture: nil
        }
      },
      collisions: [],
      sensors: []
    },
    camera_link: %BB.Robot.Link{
      name: :camera_link,
      parent_joint: :tilt_joint,
      child_joints: [],
      mass: nil,
      center_of_mass: nil,
      inertia: nil,
      visual: %{
        origin: nil,
        geometry: {:box, %{x: 0.05, y: 0.03, z: 0.03}},
        material: %{
          name: :material_0,
          color: %{blue: 0.1, green: 0.1, red: 0.1, alpha: 1.0},
          texture: nil
        }
      },
      collisions: [],
      sensors: []
    }
  },
  joints: %{
    pan_joint: %BB.Robot.Joint{
      name: :pan_joint,
      type: :revolute,
      parent_link: :base,
      child_link: :pan_link,
      origin: %{position: {0.0, 0.0, 0.05}, orientation: {0.0, ...}},
      ...
    },
    ...
  },
  ...
}
iex(2)> Map.keys(robot.links)
[:base, :pan_link, :camera_link]
iex(3)> Map.keys(robot.joints)
[:pan_joint, :tilt_joint]
iex(4)> robot.joints.pan_joint.type
:revolute
iex(5)> robot.joints.pan_joint.limit.upper
** (KeyError) key :limit not found in:

    %BB.Robot.Joint{
      name: :pan_joint,
      type: :revolute,
      parent_link: :base,
      child_link: :pan_link,
      origin: %{position: {0.0, 0.0, 0.05}, orientation: {0.0, 0.0, 0.0}},
      axis: {0.0, 0.0, 1.0},
      limits: %{
        upper: 1.5707963267948966,
        lower: -1.5707963267948966,
        effort: 5.0,
        velocity: 1.0471975511965979
      },
      dynamics: nil,
      sensors: [],
      actuators: []
    }

Did you mean:

    * :limits

    iex:5: (file)
iex(5)> robot.joints.pan_joint.limits.upper
1.5707963267948966

Expected Behaviour

Iex should evaluate the final expression in Exploring the Compiled Robot, robot.joints.pan_joint.limit.upper, to 1.5707963267948966 (90 degrees in radians).

[jimsynz]

Thanks for the report. Fixed on main :)