The brain and bubble dome is the topmost section of the B9 robot — the clear acrylic hemisphere that reveals the robot’s illuminated “brain” unit inside. It’s one of the most visually distinctive elements of the B9 design and creates a dramatic focal point on a finished robot.

The Original Brain Section

On the original B9 prop, the dome section consists of:

  • A clear acrylic hemisphere (the bubble dome)
  • A mounting ring at the base of the dome
  • The brain unit — an illuminated assembly visible through the dome
  • The bubble lift mechanism — a device that made the robot’s bubble “brain” appear to rise and fall

The brain interior is illuminated and features what appears to be electronic components, tubes, and circuit board-like elements. The overall effect is an exposed mechanical brain visible through the protective dome.

Dome Sourcing

The clear acrylic dome is typically sourced rather than fabricated, as forming a perfect hemisphere requires vacuum forming equipment not commonly available to hobbyists.

Sources for acrylic domes:

  • Plastics distributors — Companies like TAP Plastics, Regal Plastics, and Port Plastics stock formed acrylic domes in standard diameters. Approximately 14–16 inches diameter fits the B9 proportions.
  • Scientific supply companies — Bell jars and vacuum domes are sometimes the right size and shape
  • Lighting suppliers — Pendant light globes in acrylic or polycarbonate occasionally match B9 proportions
  • Display dome suppliers — Museum and retail display domes are commonly available in acrylic

The dome should be optical-grade clear acrylic (not polystyrene, which yellows). UV-resistant acrylic is worth the premium for a display piece.

Mounting Ring

The dome sits on a mounting ring that:

  • Supports the dome’s weight and secures it against falling or being knocked off
  • Interfaces with the radar section above and the upper body below
  • Provides a clean visual transition between the dome and the robot body

Fabricate the mounting ring from aluminum plate or turned aluminum on a lathe. The inner diameter should match the dome base exactly with a small ledge to prevent the dome from sliding inward.

A rubber gasket between the dome base and the mounting ring prevents the acrylic from cracking against metal under point loads.

The Brain Unit

The brain unit is a sculpted and illuminated assembly visible through the dome. Key elements:

Structural base — A flat platform that holds all the brain components and mounts to the robot frame inside the dome. Aluminum sheet or rigid urethane.

Brain components — The original appears to include vacuum tubes, circuit board sections, coiled wire, and various electronic-looking components arranged in a visually interesting composition. Many replica builders use actual vintage electronic components (salvaged tubes, capacitors, etc.) for authenticity.

Illumination — Internal LED lighting illuminates the brain assembly from below or within. Warm white LEDs give a period-appropriate incandescent glow. Color-changing LEDs allow dramatic effects for display.

Scale — The brain unit should fill approximately 60–70% of the dome interior, leaving visible clearance on all sides.

Bubble Lift Mechanism

The original B9’s bubble lift made the brain appear to rise and fall inside the dome. The mechanism drove a platform up and down via a simple cam and motor arrangement inside the robot’s upper body section.

Modern replicas implement this with a vertical linear actuator or a lead screw mechanism:

  1. A stepper motor drives a lead screw
  2. A nut on the lead screw carries a lift platform
  3. The brain assembly sits on the lift platform
  4. An Arduino controls the stepper in slow up-and-down cycles (approximately 2–4 inches of travel)

The movement should be slow and deliberate — one complete up-and-down cycle over 10–15 seconds looks right.

Wire routing is the main challenge: power and signal wires for the lift motor and brain lights need to flex with the vertical movement without tangling. Use a small wire bundle with slack loops gathered by a light spring to allow movement while preventing tangles.

Final Assembly and Lighting

With brain, mounting ring, and lift mechanism complete:

  1. Mount the lift mechanism to the upper body armature
  2. Attach the brain assembly to the lift platform
  3. Wire lights and motor through the robot body (see the electronics guide)
  4. Set the mounting ring on the upper body
  5. Set the dome over the brain assembly onto the mounting ring

Final lighting adjustment: the brain should be clearly visible through the dome under normal room lighting, with the illumination giving a warm glow without washing out the detail.

For the complete build sequence, see the B9 robot construction overview.