Write a tutorial about using transport parameters with systems

[scpeters]

Desired behavior

A new feature was added in gazebosim/gz-transport#305 to declare and use parameters. An interface to this functionality was added for gz-sim systems in #1431, with a demo in the parameters-component-wheel-slip-demo6 branch and gazebosim/gz-msgs@e19f8e5. This demo should be merged to a release branch along with a tutorial.

Alternatives considered

Implementation suggestion

Demo instructions from #305:

Steps to run the demo:

• Build from source ignition fortress checking out the two branches specified above (I can provide PRs for another version if needed).
• Launch the trisphere cycle world:

  ign gazebo trisphere_cycle_wheel_slip.sdf
  

• In another terminal with the workspace sourced:

  • List available parameters:

    ign param -r /world/wheel_slip -l
    

    Expected output

    systems.wheel_slip.trisphere_cycle1.wheel_front [ignition.msgs.WheelSlipParameters]
    systems.wheel_slip.trisphere_cycle1.wheel_rear_right [ignition.msgs.WheelSlipParameters]
    systems.wheel_slip.trisphere_cycle0.wheel_rear_right [ignition.msgs.WheelSlipParameters]
    systems.wheel_slip.trisphere_cycle1.wheel_rear_left [ignition.msgs.WheelSlipParameters]
    systems.wheel_slip.trisphere_cycle0.wheel_rear_left [ignition.msgs.WheelSlipParameters]
    systems.wheel_slip.trisphere_cycle0.wheel_front [ignition.msgs.WheelSlipParameters]

  • Get the systems.wheel_slip.trisphere_cycle1.wheel_front parameter:

    ign param -r /world/wheel_slip -g -n systems.wheel_slip.trisphere_cycle1.wheel_front
    

    Expected output

    Getting parameter [systems.wheel_slip.trisphere_cycle1.wheel_front] for registry namespace [/world/wheel_slip]...
    Parameter type [ign_msgs.WheelSlipParameters]

    ---

    slip_compliance_lateral: 1
    slip_compliance_longitudinal: 1

  • Set the systems.wheel_slip.trisphere_cycle1.wheel_front parameter to a different value:

    ign param -r /world/wheel_slip -s -n systems.wheel_slip.trisphere_cycle1.wheel_front -t ign_msgs.WheelSlipParameters -m "
      slip_compliance_lateral: 1
      slip_compliance_longitudinal: 2"
    

    Expected output

    Setting parameter [systems.wheel_slip.trisphere_cycle1.wheel_front] for world [wheel_slip]...

    Parameter successfully set!

  • Get the systems.wheel_slip.trisphere_cycle1.wheel_front parameter again, its value should have changed:

    ign param -r /world/wheel_slip -g -n systems.wheel_slip.trisphere_cycle1.wheel_front
    

    Expected output

    Getting parameter [systems.wheel_slip.trisphere_cycle1.wheel_front] for registry namespace [/world/wheel_slip]...
    Parameter type [ign_msgs.WheelSlipParameters]

    ---

    slip_compliance_lateral: 1
    slip_compliance_longitudinal: 2

Additional context

[Gaurang-1402]

Hi @scpeters and @azeey I have made a PR to the Gazebo tutorials repo that resolves this issue: osrf/gazebo_tutorials#175

I'm curious to hear your feedback and improvise!

[knmcguire]

So just to add on that (@Gaurang-1402 noticed it first on his PR), is that ign param -r /world/wheel_slip -l lists no parameters in this example. I confirm that this is also the case with gazebo harmonic with gz param -r /world/wheel_slip -l

I'm currently trying to build harmonic from source to see if this is still the case on the latest development branch but if this is the case than I assume we need to make an issue on gz-transport github repo right?

[azeey]

The description mentions that the demo is in the parameters-component-wheel-slip-demo6 branch along with a specific commit in gz-msgs. Can you give that a try?

[knmcguire]

yes... I should really learn to read the whole description in not a hurry. Thanks for notifying me.

Absolutely I'll try that out as soon as I manage to build source without my pc freezing. I'll report back once I do.

[knmcguire]

wait, it seems that that branch was made from the gz-sim-6 era so that's probably not going to work unless I rebase the changes (if that is still possible).

Perhaps the easiest now is I'll use it as a reference to work on the example for the multicopter velocity control tuning that I've been working on: https://github.com/knmcguire/gz-plugin-multicopter-velocity-tuning. Bit of 2 birds one stone scenario since I'll need to work on this anyway for my work's project

[knmcguire]

or option 3.... I look in the code of gz_sim8 and find out that most of the branch has already been implemented 😄

Except for the wheel-slip plugin, of which I made a draft pull request for: #2518. There are still some iffy things happening so I'd need some help with that, but once that is merged than we are one step closer of making this tutorial a reality at least.