Hi @noah-heinen,
Thanks for the very detailed write-up and troubleshooting. There is a lot of useful information here, and this is a tough challenge. I hope we can help get it resolved with you.
The first thing that stands out to us is the custom extended-length USB harness between the Doodle Labs radio and VOXL 2 Mini. Before digging further into software, ESC firmware, or platform parameters, I would focus on that physical USB connection.
USB 2.0 High Speed is sensitive to cable construction and signal integrity. Extending the MCBL-00080 interface using discrete, untwisted, unshielded JST-GH conductors is not equivalent to extending it with a properly constructed USB cable. The added length also increases susceptibility to both radiated and common-mode noise, particularly in an electrically noisy environment such as a high-current multirotor.
We should also acknowledge that our standard development cables are not necessarily optimized for the highest-noise or final-production UAS environments. They are primarily intended to help get systems connected and operating during development. For final aircraft integrations, we generally encourage additional cable optimization where appropriate, including shielding, ruggedization, strain relief, and dedicated cable routing or cable channels that keep sensitive interfaces away from high-current and high-noise paths.
We have seen USB stability issues on aircraft when cabling and routing are not ideal, especially around ESCs, motors, and high-current battery wiring. The fact that your disconnects correlate strongly with motor current transients rather than steady-state current makes the custom USB harness and associated grounding/noise coupling particularly worth investigating.
I would recommend addressing the USB harness first:
Keep D+ and D- as a tightly coupled twisted pair and keep the run as short as practical.
Use a shielded USB-rated cable rather than individual discrete wires for the extended portion.
Adding shielding is absolutely a good approach here. Ideally, use the cable shield as a shield rather than simply adding another signal-ground conductor.
Keep the USB harness physically separated from ESC phase wiring, battery leads, and other high dI/dt paths.
Your plan to improve the ground path and experiment with ferrites is also reasonable, although I would first correct the basic USB cable construction before trying to solve the problem primarily with ferrites.
I would not assume there is a specific maximum J3 cable length where it suddenly becomes unreliable. Cable construction, impedance, routing, grounding, and the surrounding EMI environment all matter. A longer run made from discrete untwisted/unshielded conductors is certainly more susceptible than the stock harness, and yes, it could plausibly produce the transient-induced disconnect behavior you are seeing.
Moving the ESC bulk capacitor to the recommended location is also important, particularly on 6S, and I would still make that change. The improvement you observed when powering VOXL from a bench supply is another useful indication that conducted or common-mode noise may be contributing. There may be more than one coupling path here.
However, given the custom extended USB cable construction, I would correct that first and repeat your 0 -> 65% actuator transient test. That is actually a very good controlled reproduction test.
