Intro to Command Subsystem Programming for FIRST

8/13/2019 Intro to Command Subsystem Programming for FIRST

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Intro to Command/Subsystem

Programming

Ashbury Coltenoids 2013


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FRC Software Framework

You are responsible for creating a Robot java class

that does stuff.

FRC provides a software framework to communicate

with Driver Station and controloperating mode.

FRC writes the main()function.

Your robot class has functions that

FRC framework calls.


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Types of Robot Classes

SimpleRobot

When you Enablea mode a function is called.

autonomous(), operatorControl()

IterativeRobot A function is called periodically when a mode is

Enabled

autonomousPeriodic()

Command/Subsystem based Robot More complex framework provided by WPI Lib

But easier to use once you understand it.


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RobotBuilder App

FRC provides a very nice RobotBuilder

application.

Identify commands / subsystems, sensors,

actuators.

Execute commands from joystick buttons.

It creates basic code outline. You still need to write functionality.


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What is a Subsystem?

Subsystempart of the robot that doessomething: Claw, drive-train, Frisbee launcher

Subsystems have (specified in RobotBuilder): Sensorsswitches, encoders.

Actuatorsmotor controllers, pneumatics.

Subsystems are a State Machine (you need towrite):Current StateIs Frisbee loaded? Are launcher

motors running?

Change StateTurn launcher motors on/off


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State Machines

Parts you need to write:

Store internal state in class

member variables.

Public accessor functions to

get state (isMotorOn).

Public mutator functions to

change state (turnMotorOn).


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What is a Command?

A way to tell the robot to do something:

Fire a frisbee, load a frisbee, drive with joysticks.

Commands require a subsystem to execute on.

When a command is executed: Initialize(): Check if the command can be executed, change

state of subsystem.

Execute(): Periodic call to subsystem (joystick inputs to

drive-train). isFinished():Periodically check if the command finished?

Has the subsystem reached the desired state: isClawOpen()

Is the command a single-shot: true

Is the command time-based or running to long: isTimedOut()


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Motor Relay Example

1. Open RobotBuilder and create a new project.

2. Add a new subsystemMotorRelay

3. Add a Spike actuator to the subsystem Output Channel (PWM Sidecar pin) = 2

4. Add a command: toggleMotorRelayFwd Requires MotorRelay subsystem

5. Add a joystick to Operator Interface Add a buttonspecify command to execute and when to run

command.

6. Review Java Project Directory in MyRobot

7. Export -> Java

8. Open project in NetBeans


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MotorRelay.java

What state information do we need?

Motor on in forward or off.

Add state members and accessor methods to class:

What state changes to we want to happen?

Turn motor in forward or turn motor off.

Add mutator methods to change state.


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Toggle Motor Fwd Command

What is this command supposed to do?

If motor is off, turn it on. If motor is on, turn it off.

What type of command is it? When is it

finished?

Command is instantaneous (fire and forget)

Command is finished as soon as motor is on.

Motor is on as soon as we turn it on.


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toggleMotorRelayFwd.java

isFinished()return true, the command is always

finished (fire and forget).

End() and interrupted()empty

The command cant be interrupted and no special endstate is required (like turning off the motor).

Execute()empty

The command doesnt need to periodically check/change

anything.

Initialize()change the subsystem state.


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Things To Do

Make a timedMotorRelayFwdcommand: Have the command turn the motor relay on for 5 seconds.

Hintuse setTimeout in initialized and check isTimedOut for yourfinished condition.

Hintwith multiple commands using the same subsystem, youhave to worry about what happens when your command isinterrupted

Make a Servo subsystem with commands: Turn 5 degrees each button press.

When the Servo reaches its maximum or minimum angle, reverse

the direction. How do you figure out what the maximum/minimum Servo angles are?

Hintyou test them out!

Use a time based command to make the Servo dance.


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Hints

Use lots of System.out.println() for

testing/debugging.

Check out team2168.org/javadoc/for javadoc

info on WPILib

Check outhttp://wpilib.screenstepslive.com/s/3120/m/7952

Google it! (or look at Chief Delphi)
http://wpilib.screenstepslive.com/s/3120/m/7952http://wpilib.screenstepslive.com/s/3120/m/7952

Documents

Intro to Command Subsystem Programming for FIRST