# Your first RoboSoccer bot

First lesson · One file · Drive, turn, watch

## 1. Get a match running together

Your teacher helps install Python and the kit first. In the unzipped kit folder:

```sh
python -m pip install .
robosoccer new my_bot.py
robosoccer check my_bot.py
```

No local setup yet? Use **My bot → Load starter → Check my bot** on the website.
Choose one route with your teacher; save installation troubleshooting for the setup session.

## 2. Copy this chaser into my_bot.py

```python
def act(robot_id, sensors, memory):
    balls = [obj for obj in sensors["camera"]
             if obj["kind"] == "ball"]
    if not balls:
        return {"move": (0.0, 1.0)}  # Turn to search.

    ball = min(balls, key=lambda obj: obj["distance"])
    bearing = ball["bearing"]
    speed = 0.8 if abs(bearing) < 0.4 else 0.0
    return {"move": (speed, 4.0 * bearing), "kick": 0.0}
```

The same function controls robots 0, 1 and 2. It turns toward the ball, drives
when roughly facing it, and searches when it cannot see it. Leave `memory`
unused for now. Kicking and team roles come in later lessons.

## 3. Which way should it turn?

![Robot bearings: straight ahead is zero, positive 0.5 is left and negative 0.5 is right. Positive turn rate turns left.](bearing-diagram.svg)

Radian is an angle unit: **0.5 rad ≈ 29°**. Use the sensor's bearing directly;
you do not need to convert it. `4.0 * bearing` sets how quickly to turn.
`move` means `(forward metres/second, turn radians/second)`, not x/y movement.

## 4. Watch one small experiment

```sh
robosoccer check my_bot.py
robosoccer run my_bot.py --vs chaser --perfect-sensors --half-seconds 5 --watch
```

Change only `4.0 * bearing` to `1.0 * bearing`. Predict: faster or slower turns?
Watch both replays. Then remove `--perfect-sensors`. What changes when the ball
is missed? Short matches test behavior; the score alone is not your grade.

## Stuck? Check these first

| What happened? | Try this |
| --- | --- |
| Turns the wrong way | Positive bearing and turn both mean left. Do not use 90 for a turn rate. |
| Crashes when the ball disappears | Keep the `if not balls` branch before using a ball reading. |
| Nothing moves immediately | Kickoff freezes movement for the first second. Keep watching. |
| Command not found | Try `python -m robosoccer check my_bot.py`; ask your teacher about the Python setup. |

Next: [short lessons and experiments](student-lessons.md).
Keep the [full handbook](student-guide.md) nearby as a reference; you do not need to read it all today.