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Sonic Buggy (39 mm Dual-Engine Setup)

The Sonic Buggy merges two 39 mm sonic ramjet nozzles with a wheel‑bearing chassis to create a unique demonstration of acoustic propulsion. By resonating ~40 Hz waves inside precisely shaped nozzles, this buggy achieves measurable forward thrust—no mechanical propellers or fans required. While the instructions reference certain electronics, nearly any compatible amplifier, speaker, and battery can be adapted, so long as the original geometry is preserved. Experiment freely with voltage levels, speaker types, amplifiers, and signal sources.

Overview

Principle: Each 3D‑printed engine chamber compresses ~40 Hz sound into a focused jet. Placing two such engines side by side on a wheeled chassis doubles the available thrust, propelling the buggy forward.

Core Innovation: The design depends on wave resonance within a specialized shape. The exact choice of speaker or amplifier is flexible, provided it fits the 39 mm dimension (or is scaled appropriately).

Rolling Chassis: The buggy’s frame incorporates small wheels on bearings for reduced friction, with an upper platform to secure the amplifier, battery, and Bluetooth module.

Scaling

Though the design here specifies 39 mm speakers, it can be scaled up or down if other driver sizes are desired. The essential property is maintaining the ramjet’s shape and ensuring the speaker mount matches the driver’s outer diameter.

Bill of Materials (BOM)

Speakers (2×): 39 mm diameter, typically 4–8 Ω and around 5 W.
Amplifier: TPA3116 D2 XH‑M543 (or similar).
Bluetooth Receiver: XY‑BT‑Mini (3.7–5 V) or equivalent.
Battery: 2S Li‑ion (~8.4 V max) with suitable connectors (e.g., XT60).
Bearings (4×): 11 mm outer diameter × 5 mm inner diameter for the wheel hubs.
Misc. Wires & Fasteners: Electrical tape or M3 screws for the speakers, plus Velcro/hot glue for electronics.
Buck Converter (Optional): If supplying the BT module’s lower voltage from the main battery.
40 Hz Tone Source: Could be a smartphone, dedicated sine wave generator, or any audio player outputting low‑frequency signals.

Assembly Instructions

Printing and Wheel Setup

Print It
The buggy is all one piece except for the wheels. Standard print profile, PLA Basic, slim tree supports.

Attach Bearings and Wheels
Lube your bearings. Each wheel is designed to hold an 11×5 mm bearing. Press‑fit or snap the bearings into the printed wheels. Carefully push each wheel onto the small pins at the chassis base. A drop of lubrication can help if the fit is tight. Avoid excessive force. For real lube the bearings.

Mounting the Speakers

Each engine inlet is sized for a 39 mm driver. Align the speaker’s rim flush with the rear opening of the nozzle, ensuring no vents or waveguide holes are blocked. I used electrical tape around the speaker’s edge, creating a decent seal.

Electronics Placement

The amplifier (e.g., TPA3116) typically goes on the buggy’s flat top. A piece of Velcro or hot glue can secure it if desired. Position the Bluetooth module on the ledge just below the amp, so short wires run to the amplifier input. The battery can nest into the ovular slot or top surface, depending on the chassis design. I ran a single battery for both the amp and BT module (using a buck converter to step voltage down from 8.4v to 4.5v). If you are not familiar with working with batteries then power the BT module with a separate 3.7-5v lipo.

Wiring

Bluetooth to Amplifier: Identify the module’s L, R, G (left, right, ground) pads, then solder or connect them to the amplifier’s input.
Speakers to Amplifier: Each speaker is wired to its respective output channel (L+ / L–, R+ / R–), paying attention to polarity.
Power: The amplifier can handle ~8–24 V. Connect the 2S Li‑ion battery leads to the amp’s power input. If the Bluetooth board needs 5 V, a buck converter or separate power feed is recommended.

Operation

Once the system is wired, connect or power on the battery. Supply the Bluetooth module with 3.7–5 V (or verify its connection if using a buck converter). Pair a phone or play a 40 Hz sine wave through the amplifier. Slowly raise the amplifier volume until the engines begin to resonate with a distinct, low hum. On a smooth surface, the buggy should roll forward from the acoustic thrust alone, demonstrating the effect of properly channeled, low-frequency sound.

Safety & Notes

Sound Levels

Low‑frequency waves around 40 Hz can be quite intense; hearing protection is advisable, especially at higher volumes.

Component Flexibility

Though the reference design uses 39 mm speakers and a TPA3116 amplifier, many alternatives will work if the main ramjet geometry is preserved and parts are scaled appropriately.

High Voltage & Plasma

If future experiments involve high-voltage arcs or plasma, exercise appropriate caution and ensure no open wiring can interfere with the buggy’s plastic chassis.

Support Removal

The small wheel pins or arms can break during rough support removal. Proceed gently. Reprinting the entire chassis can be time-consuming.