030 lesson: turn the sticks into speeds

../_images/fig-l030-live.png

Turn each stick into a wheel speed, where forward is positive. Nothing on the robot moves yet.

Before you start.

  • L020 is done, so mytry holds L020SticksOpMode.

  • AdvantageScope is installed on the same laptop, and a gamepad is plugged into the laptop.

  • No robot is needed.

the steps

L030S010: copy the starter into mytry

Copy.

  • Open TeamCode/java/org.firstinspires.ftc.teamcode/lessons.

  • Click L030SpeedsOpMode once, and copy it: ⌘C on a Mac, Ctrl+C on Windows.

  • Click the mytry folder once, and paste.

  • The Copy Class box opens with Destination package already ending in mytry. Click OK.

  • If Android Studio asks whether to add the file to Git, click Add.

Check.

  • mytry holds L020SticksOpMode and L030SpeedsOpMode, and the new file is open.

L030S020: switch your copy on

Change. Find the line @Disabled, just under the comment that names this step, and delete the whole line, the way you did in L020.

Check.

  • Under the step’s comment, the next line reads // 'public' so the robot can run this OpMode. 'public' allows access from any code.

L030S030: the left speed

We are working toward tank drive, where the left stick drives the left wheels and the right stick drives the right wheels. Push a stick away from you and its wheels should turn forward. We call forward speeds positive and backward speeds negative. But in L020 a stick pushed away read -1.0, so its number has to be turned around to make a speed.

The starter already has the four lines you wrote in L020. They read the sticks and write them down.

Change. Under the comment that names this step, type double leftSpeed = -leftS. The list offers leftStickY, the name from the lines above. Press Tab, then finish the two lines:

../_images/fig-l030-complete.png 
        // When on L030S030, see
        // https://msb-stitt.github.io/ftc31459-26-27-biobuzz/guide/tasks/l030.html#l030s030
        // for what to do here.
        double leftSpeed = -leftStickY;
        Tracker.publish("speed/left", leftSpeed);

The minus sign turns the number around: -1.0 becomes 1.0, and 0.5 becomes -0.5. leftStickY is still what the stick says, and leftSpeed is how fast the wheels should go. Keeping two names for the two ideas means each name always says what it holds.

Simulator. In the Terminal, run:

./gradlew :TeamCode:simRun --args="mytry.L030SpeedsOpMode --pad"

AdvantageScope. Connect to the simulator as in L020. Type stick in the search box. Drag leftY from the stick folder, and left from the speed folder, into Left Axis.

Check.

  • Push the left stick away from you. stick/leftY goes to -1.0, and speed/left goes to 1.0.

  • The two lines are always mirror images of each other.

L030S040: the right speed

Change. Press Ctrl+C in the Terminal to stop the simulator. Under the comment that names this step, do the same for the right stick:

        // When on L030S040, see
        // https://msb-stitt.github.io/ftc31459-26-27-biobuzz/guide/tasks/l030.html#l030s040
        // for what to do here.
        double rightSpeed = -rightStickY;
        Tracker.publish("speed/right", rightSpeed);

Simulator. Run the same command again.

AdvantageScope. Drag rightY from stick and right from speed into Left Axis.

Check.

  • Push both sticks away from you. Both speeds read 1.0.

  • Pull both back, and both read -1.0.

What’s happening. E035 shows why each speed has a minus sign.

What you just did. Each speed is its stick with a minus sign in front, so forward is positive from here on. The stick and the speed have separate names because they are separate things: one is what the driver’s hand does, the other is what the wheels should do. A name like leftStick = -gamepad1.left_stick_y would hide that.

Where next. L040 sends leftSpeed and rightSpeed to the wheels and drives the robot in the simulator.