How to time an action in teleop without delaying teleop.

Technical Java
1

So me and my team are programming in java, and as head of programming I kind of have to have it together. (I don’t. I am a Sophomore and we are a 2nd year team.) What I’m trying to do is trigger a single solenoid, wait for a short time like 65-100 MS and then close the solenoid again, but I’m not sure how to do that without hitting my teleop routine with a 100 MS lag spike in which the whole teleop loop is delayed when the solenoid is opened up. Thanks!
-5683 Programming Dept.

2

Are you using the Command framework, or just SampleRobot?

If you are using commands, I would create a Command with a 100 ms timeout, which would open the solenoid in the initialize() method, and close it in the end() method.

If you are just using a simple teleop loop, then it is a little more complicated. Here is some psuedo code that should give you an idea of how to do it:


// Class variables (their values must persist between iterations of the loop)
boolean solenoidOpen = false;
long solenoidOpenTime;

// Runs on each iteration of the teleop loop
if (!solenoidOpen) {
    if(solenoidShouldBeTriggered) {
        openSolenoid();
        solenoidOpened = true;
        solenoidOpenTime = System.currentTimeMillis();
    }
} else {
    if (System.currentTimeMillis() - solenoidOpenTime > 100) {
         closeSolenoid();
         solenoidOpen = false;
    }
}

If you want more clarification, just ask.

3

You can use java.util.Timer and java.util.TimerTask to schedule something to happen in the future while your program still runs.


// local or class variables
final int solenoidDelay = 65; // milliseconds
final Timer myTimer = new Timer();
final TimerTask closeSolenoidTask = new TimerTask() {

    @Override
    public void run() {
        closeSolenoid();
    }
};

...

mySolenoid.open();
myTimer.schedule(closeSolenoidTask, solenoidDelay);
4

This method would work in this case (assuming the Solenoid methods are thread-safe), but I would be worried about possible race conditions if more complicated logic were to later be added in the TimerTask.

Also: Hi Sam!

5

Hey Ben!

Solenoid methods are thread-safe. I’d be more worried about scheduling a close, doing some stuff, then opening the solenoid (and expecting it to stay open) before the scheduled close happens. In this case, the methods for opening/closing the solenoid should have checks to see if it’s been claimed by a different call.


private boolean claimed = false;

public void openSolenoid() {
    if (!claimed) {
        claimed = true;
        // open it
    }
}

public void closeSolenoid() {
    if (claimed) {
        claimed = false;
        // close it
    }
}

But I don’t think it’s a problem for something this simple.

6

Definitely need to switch to command-based robot and don’t forget to use requires(); with your commands and subsystems, otherwise your whole robot will still pause. WPIlib documentation should be able to take it from there.

7

It can be solved by limiting the exposure of the solenoid to a class that governs the entire mechanism, then by calling TimerTask.cancel() to eliminate the auto-close when the mechanism is told to do something different.