# my_robot — Motor Controller Node

ROS 2 package for differential-drive motor control on the Yahboom Raspbot V2 platform.

---

## Architecture

```
                      ┌──────────────────────────────────┐
                      │      MotorControllerNode          │
                      │                                   │
 /cmd_vel  ──────────>│  Twist → differential kinematics  │
 (geometry_msgs/Twist)│  left  = linear − (angular × wb/2)│
                      │  right = linear + (angular × wb/2)│
                      │                                   │
 /wheel_speeds ──────>│  Direct per-wheel override        │
 (Float32MultiArray   │  [FL, FR, RL, RR]                 │
  4 × float32)        │                                   │
                      │         ▼                         │
                      │   raspbot_v2_interface             │
                      │   I²C bus 1, addr 0x2B            │
                      │         ▼                         │
                      │   /dev/i2c-1 ─────────> Motors    │
                      │                                   │
 /current_wheel_speeds│<─ telemetry @ 10 Hz               │
 (Float32MultiArray)  │   [FL, FR, RL, RR]                │
                      └──────────────────────────────────┘
```

### Topics

| Topic | Direction | Type | Description |
|---|---|---|---|
| `/cmd_vel` | Subscribed | `geometry_msgs/Twist` | Velocity command — `linear.x` (m/s) and `angular.z` (rad/s) |
| `/wheel_speeds` | Subscribed | `std_msgs/Float32MultiArray` | Direct per-wheel speed override `[FL, FR, RL, RR]` in library units (0–255) |
| `/current_wheel_speeds` | Published | `std_msgs/Float32MultiArray` | Current wheel speeds read from hardware, published at 10 Hz |

### Parameters

| Parameter | Default | Description |
|---|---|---|
| `wheel_base` | `0.3` | Distance between left and right wheels in metres |
| `max_speed` | `1.0` | Maximum motor speed in library units |

### Hardware interface

The node drives the Yahboom Raspbot V2 motor controller over **I²C bus 1** (device address `0x2B`) using the bundled `raspbot_v2_interface` library. The only host device required is `/dev/i2c-1`.

---

## Setting up the robot

### 1. Flash Raspberry Pi OS

Use the [Raspberry Pi Imager](https://www.raspberrypi.com/software/) to write Raspberry Pi OS (64-bit, Lite recommended) to a microSD card.

Before writing, open the imager's **Advanced options** (⚙) and configure:

| Setting | Value |
|---|---|
| Hostname | `raspbot-v2.local` |
| SSH | Enabled |
| Username / Password | Your preferred credentials |
| Wi-Fi | Your network SSID and password (if not using Ethernet) |

Write the image, insert the card, and power on the Pi. Once it has booted and is reachable on the network (test with `ping raspbot-v2.local`), proceed to the next step.

### 2. Provision with Ansible

The [ansible/](ansible/) directory contains a playbook that handles the remaining setup (enabling SPI, installing Docker). See [ansible/README.md](ansible/README.md) for full instructions.

---

## Deploying

Once the image is built, pipe it directly to the target over SSH — no intermediate file or registry needed:

```bash
docker save my_robot:latest | ssh matt@raspbot-v2.local docker load
```

Replace `matt` with the username configured in [ansible/inventory.ini](ansible/inventory.ini).

---

## Building

### Prerequisites

- Docker (with BuildKit enabled)
- For cross-compilation from an amd64 host, QEMU user-space emulation must be registered with the kernel. If you haven't done this before, run once:

  ```bash
  docker run --rm --privileged tonistiigi/binfmt --install arm64
  ```

### Build the image

The Raspberry Pi is `arm64`, so the image must be built for that platform. On an amd64 host use `docker buildx`:

```bash
docker build --platform linux/arm64 -t my_robot:latest .
```

`--load` exports the built image into the local Docker image store so it can be deployed with `docker save`.

The build is split into two stages:

1. **builder** — installs the Raspbot hardware library, then compiles the ROS package with `colcon`
2. **runtime** — copies only the colcon install overlay and hardware library into a clean `ros:kilted` base; no build tools are included in the final image

---

## Launching

The container needs access to the I²C bus that the motor controller is wired to. Pass only that device rather than running the container in privileged mode:

```bash
docker run --rm \
  --device /dev/i2c-1 \
  my_robot:latest
```

If your board exposes the motor controller on a different bus (check with `ls /dev/i2c-*` on the host), substitute the correct device node (e.g. `--device /dev/i2c-0`).

### Overriding parameters at launch

ROS 2 parameters can be passed through `--ros-args`:

```bash
docker run --rm \
  --device /dev/i2c-1 \
  my_robot:latest \
  ros2 run my_robot motor_controller \
    --ros-args -p wheel_base:=0.25 -p max_speed:=0.8
```

### Sending velocity commands from the host

With the container running, publish a `cmd_vel` message from another terminal (requires ROS 2 installed on the host or a second container on the same network):

```bash
# Drive forward at 0.2 m/s
ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
  "{linear: {x: 0.2}, angular: {z: 0.0}}"

# Turn on the spot
ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
  "{linear: {x: 0.0}, angular: {z: 0.5}}"

# Stop
ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
  "{linear: {x: 0.0}, angular: {z: 0.0}}"
```

### Verifying telemetry

```bash
ros2 topic echo /current_wheel_speeds
```

---

## Project layout

```
.
├── Dockerfile                  # Two-stage production image
├── docker-entrypoint.sh        # Sources ROS overlays before exec
├── package.xml                 # ROS package manifest
├── setup.py                    # ament_python build definition
├── my_robot/
│   ├── __init__.py
│   └── motor_controller_node.py
└── raspbot_v2_interface/       # Vendored Yahboom hardware library
    └── Raspbot_Lib/
        └── Raspbot_Lib.py      # I²C driver (smbus, bus 1, addr 0x2B)
```