Spirit Brushless Blaster Prototype Helmholtz Resonator Chamber

This modification adds a series of Helmholtz Resonator (HR) chambers to a modified enclosed flywheel cage for the Spirit brushless blaster

The chambers have precisely-sized holes and volumes targeting the following frequencies:

2x 2000.4 hz
1x 1947.6hz
1x 2056.3hz
1x 4002hz  (thinner wall, large hole)
1x 1khz (tiny hole)

These frequencies were selected based on audio analysis of a Spirit in tournament mode running Roboman's machined acetal 4/8 spoke wheels. Different blaster configurations and different speeds will have different frequency spikes, conduct your own audio analysis and determine what is best for your use case and modify the resonator chambers accordingly.

Printing Instructions

TL;DR: for HR chamber-support required, use PETG and 0.4mm nozzle, 0.42mm line width

The lid should be simple to print, and the modified cage and cage cover print just like the original ones. 

The walls of the resonator are precisely sized to 0.865mm (2 walls at the default Bambu 0.4mm nozzle line width of 0.42mm). One of the resonator walls with the large hole is only 0.42mm wide. Any deviation of the hole diameters or the chamber volumes resulting from printing inaccuracy WILL change the resulting resonant frequency. 

If you can't print accurately, that's ok because you can change dimensions and iterate. If you can't print precisely, you will not be able to get good results from this device as you'll have no idea what frequencies your device is actually resonant at.

The resonator itself should print in a T configuration with major support required underneath the ceiling of the resonator. You can also try printing it with the open face against the bed, but you'll need to ensure that all support interface used to support the roof is removed from the chamber as it will affect the chamber volume and change the resonant frequency.

I recommend a sparing amount of manual tree support used to support the overhangs in each hole, especially the single wall large hole. Clean up the holes with an xacto knife to remove support interface without changing their dimensions after printing. 

Assembly Instructions

Assemble the cage and cage cover to the Spirit just like the original one.

Use CA glue to attach the lid to the resonator, enclosing the chambers by giving them a “floor”. I recommend using sparing amounts of glue to avoid affecting the chamber volumes, but ensuring glue is used on each wall where it touches the lid to isolate the chambers fully.

Press fit the resonator into the hexagonal hole in the cage cover. To remove the resonator, take the cage cover off the blaster and press on the hexagonal duct from the inside; pulling on the resonator from the outside is likely to cause a layer line break.

If you are done testing different resonators and happy with the one you have printed, you can glue it to the cage cover permanently by placing glue on the large flat surface of the resonator and pressing it to the cage cover. This will make it more resistant to damage than the thin attachment point walls alone.