180 lines
6.3 KiB
Markdown
180 lines
6.3 KiB
Markdown
# my_robot — Motor Controller Node
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ROS 2 package for differential-drive motor control on the Yahboom Raspbot V2 platform.
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---
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## Architecture
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```
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┌──────────────────────────────────┐
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│ MotorControllerNode │
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│ │
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/cmd_vel ──────────>│ Twist → differential kinematics │
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(geometry_msgs/Twist)│ left = linear − (angular × wb/2)│
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│ right = linear + (angular × wb/2)│
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│ │
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/wheel_speeds ──────>│ Direct per-wheel override │
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(Float32MultiArray │ [FL, FR, RL, RR] │
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4 × float32) │ │
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│ ▼ │
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│ raspbot_v2_interface │
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│ I²C bus 1, addr 0x2B │
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│ ▼ │
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│ /dev/i2c-1 ─────────> Motors │
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│ │
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/current_wheel_speeds│<─ telemetry @ 10 Hz │
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(Float32MultiArray) │ [FL, FR, RL, RR] │
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└──────────────────────────────────┘
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```
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### Topics
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| Topic | Direction | Type | Description |
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|---|---|---|---|
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| `/cmd_vel` | Subscribed | `geometry_msgs/Twist` | Velocity command — `linear.x` (m/s) and `angular.z` (rad/s) |
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| `/wheel_speeds` | Subscribed | `std_msgs/Float32MultiArray` | Direct per-wheel speed override `[FL, FR, RL, RR]` in library units (0–255) |
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| `/current_wheel_speeds` | Published | `std_msgs/Float32MultiArray` | Current wheel speeds read from hardware, published at 10 Hz |
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### Parameters
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| Parameter | Default | Description |
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|---|---|---|
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| `wheel_base` | `0.3` | Distance between left and right wheels in metres |
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| `max_speed` | `1.0` | Maximum motor speed in library units |
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### Hardware interface
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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`.
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---
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## Setting up the robot
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### 1. Flash Raspberry Pi OS
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Use the [Raspberry Pi Imager](https://www.raspberrypi.com/software/) to write Raspberry Pi OS (64-bit, Lite recommended) to a microSD card.
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Before writing, open the imager's **Advanced options** (⚙) and configure:
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| Setting | Value |
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|---|---|
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| Hostname | `raspbot-v2.local` |
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| SSH | Enabled |
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| Username / Password | Your preferred credentials |
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| Wi-Fi | Your network SSID and password (if not using Ethernet) |
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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.
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### 2. Provision with Ansible
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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.
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---
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## Deploying
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Once the image is built, pipe it directly to the target over SSH — no intermediate file or registry needed:
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```bash
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docker save my_robot:latest | ssh matt@raspbot-v2.local docker load
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```
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Replace `matt` with the username configured in [ansible/inventory.ini](ansible/inventory.ini).
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---
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## Building
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### Prerequisites
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- Docker (with BuildKit enabled)
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- 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:
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```bash
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docker run --rm --privileged tonistiigi/binfmt --install arm64
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```
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### Build the image
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The Raspberry Pi is `arm64`, so the image must be built for that platform. On an amd64 host use `docker buildx`:
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```bash
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docker build --platform linux/arm64 -t my_robot:latest .
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```
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`--load` exports the built image into the local Docker image store so it can be deployed with `docker save`.
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The build is split into two stages:
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1. **builder** — installs the Raspbot hardware library, then compiles the ROS package with `colcon`
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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
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---
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## Launching
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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:
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```bash
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docker run --rm \
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--device /dev/i2c-1 \
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my_robot:latest
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```
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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`).
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### Overriding parameters at launch
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ROS 2 parameters can be passed through `--ros-args`:
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```bash
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docker run --rm \
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--device /dev/i2c-1 \
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my_robot:latest \
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ros2 run my_robot motor_controller \
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--ros-args -p wheel_base:=0.25 -p max_speed:=0.8
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```
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### Sending velocity commands from the host
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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):
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```bash
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# Drive forward at 0.2 m/s
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ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
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"{linear: {x: 0.2}, angular: {z: 0.0}}"
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# Turn on the spot
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ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
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"{linear: {x: 0.0}, angular: {z: 0.5}}"
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# Stop
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ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist \
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"{linear: {x: 0.0}, angular: {z: 0.0}}"
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```
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### Verifying telemetry
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```bash
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ros2 topic echo /current_wheel_speeds
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```
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---
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## Project layout
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```
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.
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├── Dockerfile # Two-stage production image
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├── docker-entrypoint.sh # Sources ROS overlays before exec
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├── package.xml # ROS package manifest
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├── setup.py # ament_python build definition
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├── my_robot/
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│ ├── __init__.py
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│ └── motor_controller_node.py
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└── raspbot_v2_interface/ # Vendored Yahboom hardware library
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└── Raspbot_Lib/
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└── Raspbot_Lib.py # I²C driver (smbus, bus 1, addr 0x2B)
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```
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