bd-wax: SLAM setup technical plan — Jetson Nano + RealSense D435i + RPLIDAR #1
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projects/saltybot/SLAM-SETUP-PLAN.md
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# bd-wax: Jetson Nano + RealSense D435i + RPLIDAR SLAM Setup — Technical Plan
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**Bead:** bd-wax
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**Phase:** 2 (lower priority than Phase 1 balance)
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**Owner:** sl-perception
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**Hardware:** Jetson Nano 4GB + Intel RealSense D435i + RPLIDAR A1M8
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**Goal:** Indoor SLAM, mapping, and autonomous navigation (person-following)
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---
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## Hardware Summary
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| Component | Specs |
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|-----------|-------|
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| Jetson Nano 4GB | Quad-core ARM Cortex-A57 @ 1.43GHz, 128-core Maxwell GPU, 4GB LPDDR4 |
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| RealSense D435i | Stereo depth (0.1–10m), 848×480 @ 90fps, BMI055 IMU (accel+gyro) |
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| RPLIDAR A1M8 | 360° 2D LIDAR, 12m range, 8000 samples/s, ~5.5Hz scan rate |
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---
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## 1. OS & ROS2 Environment
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### Recommended: Docker on JetPack 4.6 (Ubuntu 18.04 / L4T 32.x)
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Jetson Nano ships with JetPack 4.6 (Ubuntu 18.04). Native ROS2 Humble requires Ubuntu 22.04, so **Docker is the correct approach**:
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- NVIDIA provides official ROS2 containers for Jetson via [dusty-nv/jetson-containers](https://github.com/dusty-nv/jetson-containers)
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- Container: `dustynv/ros:humble-ros-base-l4t-r32.7.1` (arm64, CUDA 10.2)
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- Compose file pins container, mounts device nodes (`/dev/video*`, `/dev/ttyUSB*`), and handles GPU access
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**Alternative: JetPack 5.x (Ubuntu 20.04)** allows native ROS2 Foxy but requires flashing newer JetPack — only worth it if we need direct hardware access outside Docker.
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**Decision:** Use JetPack 4.6 + Docker (Humble). Fastest path, avoids full OS reflash, proven for Nano.
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---
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## 2. SLAM Stack Recommendation
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### Recommendation: RTAB-Map (primary) with ORB-SLAM3 as fallback
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#### Why RTAB-Map
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| Criterion | ORB-SLAM3 | RTAB-Map |
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|-----------|-----------|----------|
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| Sensor fusion (D435i + RPLIDAR) | D435i only | D435i + RPLIDAR natively |
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| Output map type | Sparse 3D point cloud | Dense 2D occupancy + 3D point cloud |
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| Nav2 compatibility | Needs wrapper | Direct occupancy map output |
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| ATE RMSE accuracy | 0.009m | 0.019m |
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| Nano resource usage | Lower | Higher (needs tuning) |
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| Loop closure robustness | Good | Excellent |
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RTAB-Map's `subscribe_scan` mode uses the RPLIDAR A1M8 as the primary 2D odometry front-end (fast, low-CPU) with the D435i providing depth for loop closure and 3D reconstruction. This hybrid approach is well-documented for Nano deployments.
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**Note:** Cannot simultaneously use `subscribe_scan` (2D LIDAR) and `subscribe_scan_cloud` (3D point cloud) in RTAB-Map — use 2D mode.
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#### ORB-SLAM3 Role
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Keep ORB-SLAM3 as a lightweight visual odometry alternative if RTAB-Map proves too heavy for real-time operation. Can feed its odometry output into RTAB-Map's map management node.
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---
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## 3. Software Architecture
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```
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┌─────────────────────────────────────────────────────┐
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│ Jetson Nano (Docker) │
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│ │
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│ ┌───────────────┐ ┌──────────────────────────┐ │
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│ │ realsense2_ │ │ rplidar_ros2 │ │
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│ │ camera node │ │ /scan (LaserScan) │ │
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│ │ │ │ 5.5Hz, 360°, 12m range │ │
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│ │ /depth/image │ └──────────┬───────────────┘ │
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│ │ /color/image │ │ │
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│ │ /imu │ │ │
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│ └──────┬────────┘ │ │
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│ │ │ │
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│ └──────────┬─────────────┘ │
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│ ▼ │
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│ ┌──────────────────┐ │
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│ │ rtabmap_ros │ │
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│ │ │ │
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│ │ subscribe_scan=true (RPLIDAR) │
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│ │ subscribe_rgbd=true (D435i depth) │
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│ │ │ │
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│ │ → /map (OccupancyGrid) │
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│ │ → /rtabmap/odom │
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│ │ → /rtabmap/cloud_map (3D) │
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│ └──────────┬────────┘ │
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│ │ │
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│ ▼ │
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│ ┌──────────────────┐ │
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│ │ nav2 stack │ (Phase 2b) │
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│ │ (reduced freq) │ │
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│ │ 5-10Hz costmap │ │
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│ └──────────────────┘ │
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└─────────────────────────────────────────────────────┘
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│ │
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USB3 (D435i) USB2 (RPLIDAR)
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```
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### ROS2 Node Graph
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| Node | Package | Key Topics |
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|------|---------|------------|
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| `camera/realsense2_camera_node` | `realsense2_camera` | `/camera/depth/image_rect_raw`, `/camera/color/image_raw`, `/camera/imu` |
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| `rplidar_node` | `rplidar_ros` | `/scan` |
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| `rtabmap` | `rtabmap_ros` | `/map`, `/rtabmap/odom`, `/rtabmap/cloud_map` |
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| `robot_state_publisher` | `robot_state_publisher` | `/tf` (static transforms) |
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---
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## 4. Implementation Phases
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### Phase 2a — SLAM Bring-up (this bead, bd-wax)
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**Deliverables:**
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- [ ] Docker Compose file (`docker/slam/docker-compose.yml`)
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- [ ] ROS2 Humble container with RTAB-Map + RealSense + RPLIDAR packages
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- [ ] Launch file: `launch/slam.launch.py` (RTAB-Map + both sensor nodes)
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- [ ] URDF/static TF: D435i and RPLIDAR positions on robot frame
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- [ ] `README.md` for Jetson setup instructions
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**Out of scope (Phase 2b):**
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- Nav2 autonomous navigation
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- Person-following
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- Integration with STM32 motor commands (needs Phase 1 balance complete first)
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### Phase 2b — Nav2 Integration (separate bead)
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- Nav2 stack with pre-built occupancy maps
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- 5–10Hz costmap updates (reduced from desktop default 20Hz)
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- Velocity command bridge: Nav2 `/cmd_vel` → STM32 via serial/ROS2 bridge
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- Person detection (YOLOv5 on Nano, or TensorRT-optimized)
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---
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## 5. Key Configuration Parameters
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### RTAB-Map Tuning for Jetson Nano
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```yaml
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# rtabmap_ros params — power/performance tradeoffs for Nano
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rtabmap:
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Rtabmap/DetectionRate: "2" # Process keyframes at 2Hz (not every frame)
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Rtabmap/TimeThr: "700" # Max processing time 700ms per iteration
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Kp/MaxFeatures: "400" # Reduce keypoints from default 1000
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Vis/MaxFeatures: "400"
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RGBD/LinearUpdate: "0.1" # Only update map if moved 10cm
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RGBD/AngularUpdate: "0.09" # Or rotated ~5 degrees
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Mem/STMSize: "30" # Short-term memory limit (saves RAM)
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Grid/3D: "false" # Use 2D occupancy only (lighter)
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Grid/RangeMin: "0.5" # Ignore points closer than 0.5m
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Grid/RangeMax: "5.0" # Limit to 5m (A1M8 is reliable to ~8m)
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```
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### RealSense D435i Launch Params
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```yaml
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# realsense2_camera — reduce load on Nano
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depth_module.profile: "640x480x15" # 15fps depth (not 90fps)
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rgb_camera.profile: "640x480x15" # 15fps color
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enable_gyro: true
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enable_accel: true
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unite_imu_method: 2 # Publish unified /camera/imu topic
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align_depth.enable: true
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```
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### RPLIDAR
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```yaml
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serial_port: "/dev/ttyUSB0"
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serial_baudrate: 115200
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scan_mode: "Standard" # A1M8 only supports Standard mode
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frame_id: "laser_frame"
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```
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---
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## 6. Static TF / URDF Robot Frame
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Robot coordinate frame (`base_link`) transforms needed:
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```
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base_link
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├── laser_frame (RPLIDAR A1M8 — top center of robot)
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├── camera_link (RealSense D435i — front, ~camera_height above base)
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│ ├── camera_depth_frame
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│ └── camera_imu_frame
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└── imu_link (STM32 IMU — FC board location)
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```
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Transforms will be defined in `urdf/saltybot.urdf.xacro` with measured offsets once hardware is physically mounted.
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---
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## 7. Power Budget Concern
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Jetson Nano 4GB maximum draw: **10W** (5V/2A barrel jack mode)
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| Component | Estimated Draw |
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|-----------|---------------|
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| Jetson Nano (under SLAM load) | 7–8W |
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| RealSense D435i (USB3) | 1.5W |
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| RPLIDAR A1M8 (USB) | 0.5W |
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| **Total** | **~10W** |
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**Risk:** Marginal power budget. Recommend:
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1. Use 5V/4A supply (requires Jetson J48 header, not USB-C)
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2. Disable Jetson display output (`sudo systemctl disable gdm3`)
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3. Use `nvpmodel -m 1` (5W mode) during mapping-only tasks
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4. External powered USB hub for peripherals
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---
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## 8. Milestone Checklist
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- [ ] Flash JetPack 4.6 on Nano (or verify existing install)
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- [ ] Install Docker + NVIDIA Container Runtime on Nano
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- [ ] Pull `dustynv/ros:humble-ros-base-l4t-r32.7.1` container
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- [ ] Verify D435i recognized: `realsense-viewer` or `rs-enumerate-devices`
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- [ ] Verify RPLIDAR port: `ls /dev/ttyUSB*`
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- [ ] Build/pull `realsense2_camera` ROS2 package in container
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- [ ] Build/pull `rplidar_ros` ROS2 package in container
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- [ ] Build/pull `rtabmap_ros` ROS2 package in container
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- [ ] Test individual sensor topics with `ros2 topic echo`
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- [ ] Run SLAM launch file — verify `/map` published
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- [ ] Record rosbag for offline tuning
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- [ ] Document measured TF offsets (physical mount positions)
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- [ ] Write Phase 2b bead for Nav2 integration
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---
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## 9. Repo Structure (to be created)
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```
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saltylab-firmware/
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└── projects/
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└── saltybot/
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├── SLAM-SETUP-PLAN.md ← this file
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├── SALTYLAB.md ← main design doc (TBD)
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└── slam/
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├── docker/
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│ ├── docker-compose.yml
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│ └── Dockerfile.slam
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├── launch/
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│ └── slam.launch.py
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├── config/
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│ ├── rtabmap_params.yaml
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│ └── realsense_params.yaml
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└── urdf/
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└── saltybot.urdf.xacro
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```
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---
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## 10. References
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- [dusty-nv/jetson-containers](https://github.com/dusty-nv/jetson-containers) — official NVIDIA ROS2 Docker containers for Jetson
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- [rtabmap_ros](https://github.com/introlab/rtabmap_ros) — RTAB-Map ROS2 wrapper
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- [realsense-ros](https://github.com/IntelRealSense/realsense-ros) — Intel RealSense ROS2 wrapper
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- [rplidar_ros](https://github.com/Slamtec/rplidar_ros) — Slamtec RPLIDAR ROS2 package
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- [reedjacobp/JetsonBot](https://github.com/reedjacobp/JetsonBot) — Nano + D435i + RPLIDAR reference implementation
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- [RTAB-Map D435 + RPLidar discussion](https://answers.ros.org/question/367019/using-2-d435-cameras-and-an-rplidar-with-rtabmap/)
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- [Comparative SLAM evaluation (2024)](https://arxiv.org/html/2401.02816v1)
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