I got the idea for the Danaus from the QAV 250 with prop guards. It occurred to me that the prop guard structure, if extended, would form a rigid structure strong enough to be made out of 1.6mm G10 or carbon. That would make the whole thing light enough to be a viable mini airframe. The first drawing was…butt ugly. 

I already had a QAV 250, so the idea was to use its pdb and fpv cam plate and transfer the parts over. I wanted to try inverted motors to see if they were more efficient, and this box design was perfect for it – the pdb just had to go from the bottom to the top. It looked like a butterfly to me, so I thought it could be made beautiful in a ‘form follows function’ way. I really dislike quad designs that add cool looking elements that have no function and add weight.

The first prototype was cut by Nick Heppner (CNC Madness) out of carbon. I was happy to find that it was as rigid as I had hoped. The prop guards were only 5mm wide but it survived for quite a while, even as I was trying to break it. The first two cracks were simply taped up, but after that it became too floppy to fly and the props would hit the standoffs.

It was a little difficult to tune at first, pitching nose up in forward flight. I gave it more pitch I gain and then it flew perfectly, surprisingly nimble and quick. It did exactly what I hoped it would: embolden me to shoot for smaller and smaller gaps, rapidly improving my piloting skills.

One of the criticisms of the prop guards is it’s stupid to add the weight and drag just to save a $1 prop. What you don’t realize is how many gaps you don’t try because you don’t feel like crashing and taking the long walk to retrieve and fix your quad. It’s not about saving the $1 on the prop, it’s about the nuisance and wasted time. Here’s some flying that I’d never try otherwise.

I got Tim Nilson of Lumenier interested in licensing the design and we refined the next version. Tim wasn’t as keen on making it upside down, so I put identical cutouts on both plates to hold the battery, camera, and antenna so it could work either way. The prop guards were widened, and extra standoffs were added to the front and back. The prop guards were widened again in the next iteration, which became the final. It was drawn in Illustrator because a: I hadn’t learned Sketchup yet, and b: you can make pretty compound curves easily. I’m particularly proud of the organic shapes.

The size of the two pieces makes it much more expensive than a quad made of multiple small pieces – it just eats up a lot of material. We chose a carbon/fiberglass sandwich for the best balance of price and stiffness. A couple days after it was released someone got in touch with a copyright claim, so I did a little research and renamed it the Danaus.

You can buy the Danaus at Getfpv.com.