Hardware Platform

• Base: iRobot Create 2 (Roomba)
• Structural frame: 3/4" Schedule 40 PVC pipe
• Custom parts: 3D‑printed base bracket and upper “blue” electronics enclosure
• Sensors and compute (upper assembly): Raspberry Pi 5 + active cooler, camera, MPU6050 IMU, top‑mounted LiDAR, 3S LiPo, 5 V regulator, wiring harnesses

Why iRobot Create 2 (Roomba) as the base

I chose the Create 2 because:

• It is a proven, rugged differential‑drive platform with integrated motor drivers, encoders, bump sensors, cliff sensors, and a charge dock interface.
• The Open Interface (OI) provides documented serial control for motion and telemetry, which simplifies bring‑up and reduces the number of custom PCBs I need to maintain.
• The chassis carries batteries low in the body, giving a naturally low center of mass that helps with the tall mast structure.
• Replacement parts and batteries are widely available; consumables (wheels, brushes) are inexpensive.

In short, it gives me reliable locomotion and power infrastructure so I can focus engineering time on perception and interaction.

Structural Framework: 3/4" Schedule 40 PVC

I built the superstructure as a four‑post mast using standard 3/4" Schedule 40 PVC with printed sockets at the base and a printed upper enclosure that captures the posts.

PVC framework rationale

• Cost‑effectiveness: PVC pipe and fittings cost a fraction of aluminum extrusion and require no specialty tooling. I can build and iterate for a few dollars per meter.
• Structural rigidity: For a ~1–1.2 m mast, four 3/4" PVC uprights provide adequate bending stiffness when posts are constrained at both ends; adding a single mid‑height brace eliminates noticeable sway.
• Lightweight: Low mass keeps the center of gravity near the Roomba deck, improving tip resistance during sudden stops or dock approaches.
• Modularity: I cut posts to length and swap elbows/tees to reconfigure sensor height in minutes. Printed collars give me mounting points exactly where I need them.
• Easy iteration: I can drill, ream, and solvent‑bond or simply screw into PVC without worrying about galvanic corrosion or thread wear in thin‑wall aluminum.

Practical tip: I lightly ream the pipe OD and size printed sockets with +0.3 to +0.5 mm clearance, then use two self‑tapping screws per joint. This holds under vibration and still allows disassembly.

Base Bracket (3D‑printed)

The base bracket is a circular plate that sits on the Roomba’s top deck and presents four vertical sockets for the PVC posts.

Design choices:

• I align the sockets on a square bolt circle to match the upper enclosure’s posts; this prevents torsion and keeps the mast square.
• The bracket uses the Create 2’s existing screw bosses for anchoring (no drilling in the shell). I embed heat‑set inserts in the print so I can torque fasteners without crushing plastic.
• Filleted ribs radiate from each socket into the center ring to distribute mast loads and survive side hits.

Material and print settings:

• PETG or ABS at 30–40% gyroid infill, four perimeters, 0.24–0.28 mm layer height. PETG gives enough ductility to absorb bumps without cracking.

Upper Assembly (“Blue Enclosure”)

The upper enclosure is a printed housing that integrates compute, power, and sensors while acting as the frame’s top plate. It also provides an easy surface for future sensors and user interfaces.

What I integrated

• Raspberry Pi 5 (8 GB) with the official active cooler
• 5 V buck regulator (≥ 5 A) from the 3S LiPo rail
• IMX219 camera module (front‑facing), recessed window
• MPU6050 IMU (mounted near the enclosure’s CG to reduce rotational noise)
• Top‑mounted LiDAR (clear 360° FOV, minimal occlusion from the mast)
• 3‑cell LiPo battery with inline fuse and master switch
• Cable glands and internal harnesses

Thermal management

• I treated the Pi 5 cooler as a forced‑air inlet and provided exhaust vents on the opposite wall. Short, straight flow paths are more effective than decorative perforations.
• Mounting bosses standoff the Pi to keep airflow under the board and let the radiator breathe.
• During sustained computer vision tasks, case temps stayed below ~72 °C with the fan at default curve.

Cable management and signal routing

• I routed all power and signal lines inside the PVC uprights. Two strategies worked best:
  • Slotted posts: A 6 mm slot near each end allows the cable to enter/exit without visible loops.
  • Printed clip rings: Snap‑on rings with zip‑tie slots prevent cable rattle.
• Power architecture:
  • 3S LiPo → 5 V buck (Pi 5 + camera + small peripherals)
  • LiDAR on a dedicated 5 V rail with its own inline fuse to prevent brown‑outs on Pi load spikes
• Roomba Interface:
  • I use a USB‑to‑TTL serial adapter (3.3 V logic) to the Create 2 Open Interface, routed through the mast. A small isolation board and a common ground tie keep noise out of the IMU.
  • UART wiring is strain‑relieved inside the enclosure; the connector is service‑looped for easy removal.

Serviceability

• The lid comes off with four machine screws. All boards mount to threaded brass inserts; nothing self‑tapped into plastic.
• The battery is strapped to a removable tray with a finger‑pull, so I can swap packs without touching the rest of the wiring.

Component Selection Rationale

• Raspberry Pi 5: Enough CPU for real‑time perception pipelines; strong community support; camera and LiDAR libraries are mature on Ubuntu.
• IMX219 camera: Small, easy to mount flush in the enclosure, validated at 30 fps with the libcamera stack.
• MPU6050: Commodity IMU with acceptable drift for mobile base stabilization and motion gating; easy to filter at 200 Hz on the Pi.
• Top‑mounted LiDAR: Clear line of sight above people and furniture; the mast keeps occlusions outside of the primary scan plane.
• 3S LiPo + buck: Keeps high current off the Roomba’s internal 5 V; isolates compute from base brown‑outs and gives me a clean power budget.

Mechanical Integration Details

• Fasteners: Almost everything is M3 or M4 to simplify spares. Steel washers are used where printed parts interface with PVC to prevent local crushing.
• Tolerances: I leave 0.2–0.3 mm clearance for printed‑to‑printed fits and 0.4–0.5 mm for printed‑to‑PVC sockets; this range consistently assembles without post‑processing on a 0.4 mm nozzle.
• Vibration: A single cross‑brace mid‑mast reduces LiDAR ringing and camera shake noticeably. If I add heavier sensors later, I’ll upgrade to a truss‑style brace that bolts to captured nuts in the posts.

Why PVC Instead of Aluminum Extrusion

Criterion	PVC (3/4" Sch 40)	2020/2040 Aluminum Extrusion
Cost	Very low	Moderate to high
Stiffness/weight for this height	Adequate with bracing	Higher
Tooling	Hand saw, drill, small screws	Chop saw, tapping, brackets
Modularity	Cut‑to‑length, printed adapters	Excellent with slot hardware
Iteration speed	Very fast	Moderate
Aesthetics	Utility‑grade	Professional

For a research robot that changes every week, the speed and cost advantages of PVC outweigh the stiffness and finish benefits of extrusion. When the design freezes, I can translate the printed sockets to aluminum adapters if needed.

Assembly Summary

1. Print base bracket, post sockets, and upper enclosure components with embedded heat‑set inserts.
2. Cut four PVC posts to length; drill cable entry/exit slots.
3. Mount the base bracket to the Create 2 using existing bosses; verify level.
4. Route the harnesses through posts, then seat posts into the base bracket and temporarily pin with screws.
5. Install the upper enclosure, capture the posts, and secure all joints.
6. Fit the Pi 5, regulator, IMU, camera, LiDAR, and battery; complete wiring with fuses and the master switch.
7. Bring up power rails, verify voltages, and perform sensor smoke tests before closing the lid.

Integration Challenges and Solutions

• EMI into IMU at motor start: I added a small LC filter and routed the IMU cable away from the main battery run; problem disappeared.
• LiDAR cable strain: A printed strain‑relief block under the top lid ensures the connector cannot back out with mast flex.
• Tip stability during docking: Adding a small cross‑brace reduced mast oscillations that could trigger the Roomba’s safety bumpers.

Design Goals vs. Outcomes

• Cost: Achieved. PVC + printed parts kept the mechanical BOM inexpensive.
• Functionality: Achieved. Clear FOV for the camera and LiDAR, with clean sensor cabling.
• Modularity: Achieved. I can reconfigure height and add shelves in under an hour.
• Ease of assembly/maintenance: Achieved. All fasteners are accessible; boards mount to inserts; battery swaps are fast.

Bill of Materials (mechanical/electro‑mechanical, major items)

• iRobot Create 2 (base)
• 3/4" Schedule 40 PVC pipe + self‑tapping screws
• 3D‑printed base bracket, post sockets, upper enclosure, strain‑reliefs
• Raspberry Pi 5 + official active cooler
• 5 V high‑current buck regulator (≥ 5 A)
• IMX219 camera module + acrylic window
• MPU6050 IMU breakout
• 2D LiDAR (top mount)
• 3S LiPo battery, inline fuse, master switch
• USB‑to‑TTL serial adapter (3.3 V) for Roomba OI
• Cable glands, wire, ferrules, heat‑shrink