Long flight times are the result of efficiency,
and efficiency is a balance act.
Consider power input (current over voltage) and power output (thrust), and where those two variable relate best, that’s where you fly the longest. That’s not a secret, but what makes the difference is the patience and persistence to find the sweet spot on a very granular level.
The driver was not profit, but passion. We wanted the very best, without consideration for cost. So we started buying motors from every source we could find, and selected those that worked best, and then started testing their abilities to adjust.
Adjusting many variables, but most importantly the winding of the coils. Number of strains, thickness, structure. And then make many many small batches, again again. Fire up the machines, then fire up the quads. Make, fly, make, fly, repeat. It usually takes months, and in some cases years before we arrived at the coils that you now see for sale. An instrumental part of the process was this Community. Back in the days, it didn’t exist in the form of this forum yet, but the spirit of the people did. We got good and direct feedback from people who cared about flight, and the fine people in the factory always take that on board without hesitation.
So, to answer your question more directly: it’s just a source in China, but I consider it special.