Robot Scan Time

FIRST General Forum
1

I am trying to find the scan time of my robot. As in how long the gap is in between each command processed by the robot itself.

Thanks in advance.

2

What language are you using? In LabVIEW you can set custom loop times, and in Java/C++ the loop interval for the scheduler is defaulted to 20ms (noted here: https://wpilib.screenstepslive.com/s/4485/m/13809/l/241892-what-is-command-based-programming).

3

Note that he is referring to code written in Periodic Tasks, code written in Teleop will be executed only when a packet from the driver station is received.

4

We are using java to program our robot and we would like to know the scan time if the scan time were ever to fluctuate.

5

It shouldn’t fluctuate unless you start dropping packets and experience sporadic ping timings. What are you going to use this information for?

6

We want to have acceleration for our drive train.

My idea was to increase the speed of a motor at a constant rate multiplied by the scan time of the robot.

if(maxSpeed > currentSpeed)
{
    currentSpeed += ACCELERATION * SCANTIME;
}
7

The time elapsed is going to be approximately 20ms, but it will fluctuate depending on network latencies.

Just perform the calculation each time through the loop.


currentTime = Timer.getFPGATimestamp(); //time in seconds
elapsedTime = currentTime - lastTime;

//do your math

lastTime = currentTime;

More info on what the getFPGATimestamp method does here: http://team2168.org/javadoc/edu/wpi/first/wpilibj/Timer.html#getFPGATimestamp--

8

Thank you all for your help!

-3098