The radar section sits at the top of the B9 robot, above the bubble dome. It’s the rotating sensor assembly — a distinctive piece of the robot’s silhouette with its characteristic spinning motion and integrated lighting. In the original series, the radar section was a practical mechanical assembly with actual rotation driven from inside the costume.
For replica builders, the radar section combines fabrication (the physical housing and arms), electronics (the motor drive and lighting), and mounting (attaching to the dome/head assembly with proper clearance for rotation).
Original Prop Reference
The radar section on the original B9 prop consisted of a central hub with extending arms and sensor elements. The configuration changed between seasons — Season 1 had a different arm arrangement than Seasons 2–3. Most replica builders target the Season 2–3 configuration.
Reference images from the B9 Builders Club forums document the arm count, approximate dimensions, and the sensor element shapes at the arm tips. The proportions relative to the dome diameter are critical for the correct visual — the radar section that’s too large or too small reads immediately as wrong.
Key reference dimensions to establish:
- Overall diameter of the radar assembly
- Hub diameter and height
- Arm length and profile
- Sensor element shape at the arm tips
- Height above the dome surface
Hub and Arm Construction
Machined Aluminum
The most accurate approach. The hub is turned on a lathe; the arms are milled or cut from flat stock and attached to the hub.
Advantages: Durable, accurate, appropriate weight and material feel Requirements: Lathe and mill access, or a machinist contact
For builders without machine shop access, the community has periodically produced run-of-show machined radar section components. Check the B9 Builders Club marketplace threads for availability.
Cast Resin
An alternative for builders set up for casting: sculpt the hub and arm assembly as a master, take a mold, and cast in rigid urethane resin. Finish with metallic paint.
Advantages: Accessible without machining; reproduces fine surface detail well Disadvantages: Less durable than aluminum; heavier for equivalent structural strength; less accurate to the original material
The casting process for components like this is covered in the plastic casting introduction and advanced techniques.
Fabricated from Commercial Stock
Arms cut from aluminum flat bar or rod, hub turned or purchased as a commercial tube fitting. Less precise than machined parts but achievable with basic hand tools.
Rotation Drive
The radar section rotates continuously in the show. Replicating this requires a motor drive at the base of the radar assembly.
Motor selection: A small 12V DC gear motor, 5–15 RPM output, provides appropriate rotation speed. The radar should rotate slowly — one revolution every 4–8 seconds looks correct.
Drive method options:
- Direct drive: motor shaft connects directly to the radar hub (simple, but motor must be coaxial with the rotation axis)
- Belt drive: motor offset from the rotation axis, connected via a small rubber belt or O-ring
- Friction drive: a rubber wheel on the motor shaft pressed against the radar base ring
Mounting location: The drive motor typically mounts inside the head assembly, below the dome, with the drive shaft passing up through the dome to the radar hub. This keeps the motor hidden while allowing rotation above the dome.
Control: The radar rotation can be run continuously from a switched power source, or integrated into the Arduino control system for on/off switching via remote. See B9 robot internal electronics for the overall control architecture.
Lighting
The original radar section had lighting elements — illuminated sensor tips and/or hub lighting that activated during the robot’s alert sequences.
Typical approach:
- LED elements at each arm tip, wired through the rotating hub
- Slip ring electrical connector at the rotation axis to carry power through the rotating assembly without wire tangling
Slip ring selection: A commercial slip ring (available from electronics suppliers, used in security cameras and wind turbines) with 4–6 conductors handles power and signal for LED lighting. Mount at the radar rotation axis, with fixed conductors on the stationary side and rotating conductors connected to the arm-tip LEDs.
Without a slip ring, wiring to rotating LEDs will wrap and eventually break. The slip ring adds complexity but is the correct solution for a robot that will operate regularly.
Mounting to the Dome
The radar section mounts to the top of the bubble dome. The mounting arrangement must:
- Support the weight of the radar assembly
- Provide the rotation bearing surface
- Allow motor access for the drive mechanism
- Seal cleanly to the dome surface visually
A central mounting post (aluminum tube) passes through a bearing in the dome top. The radar hub mounts to the top of the post; the motor and slip ring mount below the dome surface. The post/bearing arrangement handles the load while the motor provides the rotation.
The bearing can be as simple as a tight-tolerance aluminum tube inside an outer aluminum tube — or a proper radial ball bearing if available in the right size.
Integration with the Full Head Assembly
The radar section is the topmost element of the robot. Its weight and any motor/slip ring assembly inside the dome need to be accounted for in the brain and bubble dome construction, which covers the complete head assembly structure.
The completed radar section, rotating above the dome with illuminated sensor tips, is one of the most visually compelling elements of a finished B9 replica in operation.