# 030 lesson: turn the sticks into speeds

:::{figure} ../_static/figures/fig-l030-live.png
:name: fig-l030-live
:::

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

::::{only} mentor
**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.**

{.steps}
- 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:

:::{figure} ../_static/figures/fig-l030-complete.png
:name: fig-l030-complete
:::

```{code-block} java
:emphasize-lines: 4-5

        // 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:

```{code-block} java
:emphasize-lines: 4-5

        // 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](e035.md) shows why each speed has a minus sign.

::::{only} mentor
**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](l040.md) sends `leftSpeed` and `rightSpeed` to the wheels and drives the
robot in the simulator.
::::