Document different use cases

[mikeferguson]

Collecting some notes here for future documentation:

Docking Use Cases

• Dock with a charge dock, providing configuration entirely in message
  • Dock information might be in map frame if provided from some other database/cloud solution
  • Dock information might be in odom or base_link in the case of "point the robot at a charge dock, press a button on the controller, and provide a pose directly in front of robot - maybe getting the distance from a laser scan/etc).
  • Dock with a charge dock, using dock_id and database (almost certainly done in map frame)

Plugin Implementations

• disableCharging() - if charger supports, should stop the flow of current so that the robot can disconnect without arcing
• isCharging() / hasStoppedCharging() - might be based on the charge current (from say sensor_msgs/BatteryState message) or could be based on battery voltage, etc
• isDocked() - keep in mind, this shouldn't block for an extended period of time, it is run inside the control loop at relatively high frequency:
  • If a charge dock communicates before charging starts, this should be done here. If the charge dock needs an "enable" message to be sent, this is a good place to send it.
  • If the charge dock doesn't use any sort of communications, you might still be able to detect contact with the dock by looking at the motor effort/current, or determining that velocity has dropped to zero
  • In the absolute simplest case, isDocked() might just call isCharging() if there is no other feedback to know when we are docked

Keep in mind: anytime isCharging() is true, isDocked() should be true

[SteveMacenski]

^ I'd also mention the new image pipeline node for april tags for the simple dock

If you think it would be helpful, you could make a package with the launch file for the apriltags + docking + script you're using to test with a demo video. I'm going to add something analog to that with the NV hardware, so multiple examples with multiple robot types might be nice. The NV one should be the most "showy" since they're funding this work and has an actual dock, but more examples never hurts

[mikeferguson]

As a note - I'm going to end up adding the motor current as an option for the SimpleChargeDock plugin (from a standard sensor_msgs/JointState) - so you might even be able to eventually drop the custom plugin for the NV hardware if you end up using the standard messages (and the Isaac April tag can be turned into geometry_mgs/PoseStamped).

[mikeferguson]

The information above is now in a PR - as for an example launch file - I'm gonna hold off on that, because I think we'll be able to use the simple plug-in for the NV robot (and so it will be an example there) and at the moment I still don't have any other robots that have a charge dock (when I get back from my class, I might try to fix that)