Where should PID live - subsystem or command? (Command-based)

Technical Programming
1

I’m curious on what’s considered the best practice for coding the PID.

Does it make sense to create several PIDs for a subsystem:

PIDController forwardController = new PIDController(P,I,D);
PIDController turnController = new PIDController(P,I,D);
etc…

and create getters for commands to retrieve and calculate in their execute block?

OR…

Should the PID Controllers be created in each command? If so does that mean every time a new command is created/scheduled that we’d be creating a new PID? My fear is that if for example I have a command bound to, say the A button, does that mean everytime I hold and release A I’m creating a new PID loop. Would that bog down the rio?

Thanks in advance for any help!

2

Generally all PID setup and configuration is done in the Subsystem, with the Commands using getters/setters to set setpoints, get current position, turn the PID off, etc.

3 Likes
3

Yep, this is a good practice. If defining commands inline as in-subsystem factory methods, you don’t even need the verbosity of all the intermediary methods.

Another option is PIDSubsystem/PIDCommand: PID Control through PIDSubsystems and PIDCommands — FIRST Robotics Competition documentation

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4

Wow that was so helpful! That read on in-subsystem factory methods sent me down a rabbit hole - awesome read!

This might be a misunderstanding of PID in general, but with a PID command do I need to end anything aside from the command to stop the PID loop. Does a PID loop only take up resources when the calculate method is called?

5

The PID runs from the command itself (as opposed to pre-2020 PID).