This motor is being tested for optimal use with 3" props inside ducts. So far what we've found is that the smallest reasonable size motor that tends to work out reasonably well with any duct is 1506. Moving to 1507 is a significant improvement. 1606 was even better. We're testing three custom motors shortly and the best performing option will be produced. The Kv range that seems to be reasonable is between 3400-4000kv on 4S. Any more and the throttle control becomes even more difficult. So far on even a 600g AUW cinewhoop, we haven't really found much benefit to 6S. It's just unnecessary cost, complexity and drastically reduces component selection for now. We are also testing a new prop shaft design which saves a little weight. The mounting platform for this motor will be 12x12 M2.
Ducts pose a special set of circumstances with different requirements. The vast majority believe ducts to be a performance sucking vampire on a quad and are only a necessary evil to guard the props from injury when flying around people or in sensitive areas. While this is actually true the majority of the time, there are some benefits to ducts.
First off, it's important to make the distinction between ducts and just prop guards. Ducts will generally be a cylinder in which the entire propeller sits. It will also have some sort of curved shape to it's rim or the entire cylinder. This special shape can actually produce extra thrust which can be explained in part through Bernoulli's principle. Just know that it can actually produce thrust and that's the main difference between a guard and a duct. In addition, it has a few more effects that make it easier to fly slowly. Guards for the most part are just bumpers around props and don't have these effects at all. They actually are only performance vampires but again, a necessary evil sometimes. There is a lot more to ducts and how they function but that's the basic concept.
The main challenges with ducts and quad performance are two fold. The most significant impact is absolutely horrid throttle control. It's darn near impossible to change altitude smoothly without over correction when it's nearly effortless with an open prop design. This isn't the case with all duct designs however. The other issue is the efficiency of the quad with all this added weight. This is where the size of the prop compared to the duct can make a significant difference. The better fit the prop is to the duct without any excess space between prop and duct, the better the efficiency is and the more thrust is produced. Of course it isn't exactly reasonable to have a prop perfectly fit to a ducts that will ultimately flex and bend running into the prop...