Please note this model is for a single engine for you to create your own sonic resonance vehicle with. If you would like to make the whole vehicle click here. Check out sonicramjet.com to learn more about how it works!

I created an engine with no moving parts that generates enough thrust to move a small model craft. The engine is not ported, everything coming our of the jet are sound waves. This model is just the resonance chamber, aka "the engine". It works by feeding a 40hz signal through amplification, then resonating it 3x to compress the sound waves into a uniform, stacking jet. I was inspired by sonic booms, and annoying deep-bass from passing cars that rattles the whole house. The vibration of the chamber also helps greatly reduce the coefficient of friction. I borrowed that trick from water striders.

To make this work you need a 1.5"(39mm) speaker, an amp, and a way to provide a 40hz signal. A sine wave generator is by far the cheapest and best option for performance. A Bluetooth module is awesome for convenience. Any size speaker will work just scale accordingly. The attached 3in version design file is much more robust, start with this one to go larger than 3in.
 

BOM - these are the parts I used. Any small amp, 2in speaker, and audio receiver should work!

• Audio Amplifier: TPA3116 D2 XH-M543
• Bluetooth Receiver: XY-BT-Mini
• SOTAMIA 2Pcs 40mm Full Range Speaker Audio Glass Fiber Basin Anti-fog Waterproof Speaker 1.5 Inch 4 Ohm 5W Bluetooth Loudspeaker Note* I had a 52mm speaker here by mistake. If you downloaded this prior to 2/18 you will need to scale your print up if you have 52mm speakers. Scale the file to be 133% larger and ensure your speaker diameter matches the resonance chamber hole. 
• 3in speakers if you want to make the larger version. SOTAMIA 2Pcs 3 Inch Portable Full Range Speakers 2 Ohm 5W Midrange Woofer Speaker Bass Subwoofer Sound Home Theater Loudspeaker
• Battery: I used an 8.4v Li Ion 2S I made with 18650s. The amp supports a lot more than what I am providing it. Take note! The BT module above is 3.7-5v. You either need an independent supply or a buck converter.
• Bearings - optional but highly advised if you are ordering the other parts anyway. I used 11mm x 5mm in my sound buggy. Bearings can get expensive at the hardware store.
   

NEW:
I have added the 3in version to the files. You can download the STL by clicking the drop down and then “download STL”. You will see both file versions. This one will also scale if you have 4in or larger speakers. The 3in version features a mount in the middle for testing of plasma interactions with the engine. My goal was to use something like a electric range starter to pulse high voltage arcs at matching frequencies. I have not completed testing on this yet but that's what is next. I think this design is much more poorly optimized than the smaller version, the reason for that was I wanted it to be one piece print for testing. There is a surprising amount of force from this version at 8.4v and I think this could be greatly improved with a longer and more tapered chamber. These speakers are significantly more efficient than the smaller 1.5in, and you can drive a lot more than 8.4v safely to test different setups (use caution with all voltage, especially as you get higher than 12v). 

To assemble one engine: 

1. Tape the speaker to the back of the chamber with electrical tape. Easier to do with no wires. Try to not obstruct the open ports on the speaker. 
   1. If building the 3in version, use 4 x m3 nut/bolt to screw it on with the included holes.
2. For the bluetooth module solder wires to the L, R, and G (labeled on bottom of board). You will wire these leads to your amplifier in. 
3. Connect bluetooth receiver module to the amp. The amp probably came with wires, I just cut and soldered those to the bt module. 
4. Connect your speaker(s) to the amp. The audio out are pretty easy to find on the board.. Solder leads to the + and - on your speaker and hook them to the corresponding speaker out.
5. For power - it is important you note the operating voltage of your bt receiver. Your amp can take a lot more voltage than the receiver. I used an 8.4v Li Ion battery with 8.4v leads to the amp (via XT60 connector) and then 4.5v via independent leads and a small mini-360 dc-dc buck converter. I would highly recommend you power your amp and receiver separately if you are not familiar with working with batteries. Give the receiver a 3.7v makerforce lipo, maybe 800mah. Wire a XC60 connector to the “battery in” on the amp to make things easy. Solder the small lipo straight to the receiver. I plan on upping the voltage to the speakers for testing in the future via a dc-dc boost converter. 
6. For volume - you can adjust the L and R knobs on the board. You may end up cadding some knobs to make changing the volume easier. 
7. To operate, connect your speaker battery. Turn on the BT module and connect your phone. Play a 40hz tone. I used amazon music and found “40 hz frequency pure tone” by David Wong to work best. Amazon music seems to have the best quality audio output out of the bluetooth audio methods I tested. You can also use a sine wave generator app to easily test other frequencies, or build a small sine wave generator for a few bucks (this would replace the bt module)!
   
    I hope those instructions are clear! Drop me a comment if you have a question or have any feedback.
   
   The 1.5in and 3in versions are both very loud. Use protection, or understand your risks before engaging in loud noises.