288 lines
10 KiB
Markdown
288 lines
10 KiB
Markdown
# my_robot
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ROS 2 package for the Yahboom Raspbot V2 platform — differential-drive motor control and pan/tilt camera orientation.
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---
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## Architecture
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Both nodes share the same I²C bus. The Linux kernel serialises individual transactions, so they can run as separate processes without additional locking.
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### Motor controller
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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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---
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### Camera orientation controller
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```
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┌──────────────────────────────────────┐
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│ CameraOrientationNode │
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│ │
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/joint_command ────────>│ JointState (names: pan, tilt) │
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(sensor_msgs/ │ position in radians │
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JointState) │ │
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│ pan → servo 1 (0°–180°) │
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│ tilt → servo 2 (0°–110°) │
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│ │
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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 ──────> Pan/tilt servos │
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│ │
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/joint_states <────────│ current angles @ 10 Hz │
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(sensor_msgs/ │ position in radians │
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JointState) │ │
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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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| `/joint_command` | Subscribed | `sensor_msgs/JointState` | Commanded pan/tilt angles. Joint names `"pan"` and `"tilt"`, positions in **radians**. Unknown joint names are ignored. |
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| `/joint_states` | Published | `sensor_msgs/JointState` | Current angles reflected from the last command, published at 10 Hz |
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#### Parameters
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| Parameter | Default | Description |
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|---|---|---|
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| `pan_servo_id` | `1` | Raspbot servo channel for pan |
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| `tilt_servo_id` | `2` | Raspbot servo channel for tilt |
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| `pan_min_deg` | `0.0` | Pan lower limit (degrees) |
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| `pan_max_deg` | `180.0` | Pan upper limit (degrees) |
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| `tilt_min_deg` | `0.0` | Tilt lower limit (degrees) |
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| `tilt_max_deg` | `110.0` | Tilt upper limit (degrees) — hardware cap |
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| `pan_center_deg` | `90.0` | Startup and shutdown park position for pan |
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| `tilt_center_deg` | `60.0` | Startup and shutdown park position for tilt |
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| `state_rate_hz` | `10.0` | `~/joint_states` publish rate |
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#### Hardware interface
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The node drives the pan and tilt servos over **I²C bus 1** (device address `0x2B`). The same `/dev/i2c-1` device used by the motor controller is sufficient — no additional device node is required.
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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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| 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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## 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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## 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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## 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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--network=host \
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--device /dev/i2c-1 \
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--env ROS_DOMAIN_ID=0 \
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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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### Camera orientation node
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Override the default `CMD` to run the camera orientation node instead:
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```bash
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docker run --rm \
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--network=host \
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--device /dev/i2c-1 \
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--env ROS_DOMAIN_ID=0 \
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my_robot:latest \
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ros2 run my_robot camera_orientation
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```
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#### Overriding parameters at launch
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```bash
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docker run --rm \
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--network=host \
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--device /dev/i2c-1 \
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--env ROS_DOMAIN_ID=0 \
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my_robot:latest \
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ros2 run my_robot camera_orientation \
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--ros-args -p pan_center_deg:=90.0 -p tilt_center_deg:=45.0
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```
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#### Commanding the camera from the host
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Pan to centre (90°) and tilt to 30°:
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```bash
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ros2 topic pub --once /joint_command sensor_msgs/msg/JointState \
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"{name: ['pan', 'tilt'], position: [1.5708, 0.5236]}"
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```
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You can command a single axis by omitting the other joint name:
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```bash
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# Pan only
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ros2 topic pub --once /joint_command sensor_msgs/msg/JointState \
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"{name: ['pan'], position: [0.0]}"
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```
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#### Verifying orientation state
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```bash
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ros2 topic echo /joint_states
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```
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---
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### Overriding parameters at launch (motor controller)
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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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--network=host \
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--device /dev/i2c-1 \
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--env ROS_DOMAIN_ID=0 \
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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: 0.02}, 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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├── src/
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│ └── my_robot/
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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 # Differential-drive motor control
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│ └── camera_orientation_node.py # Pan/tilt servo control
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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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