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I'm pretty sure that it is generally considered a more reliable design in both small drones and such vechicles. Yes, there are 4 booms, but there are 8 ESCs, 8

I'm pretty sure that it is generally considered a more reliable design in both small drones and such vechicles. Yes, there are 4 booms, but there are 8 ESCs, 8 cable sets, 8 motors, 8 motor holders(they are the ones experiencing most vibrations), 8 props. All those 8x parts are much more likely to fail than the boom. How would the boom even fail mechanically if it's just a solid holding mechanical part that is well-built and tested? Would it just break off? Because of what? If so, in any regular normal airplane or a helicopter there are many other similar parts which are usually not redundant. This must be due to the fact that such solid parts fail very rarely, and perhaps more importantly, can be somewhat easily tested on the ground to check their structural integrity. Motors, ESCs, etc can fail due to many other reasons and are sometimes harder to test properly, there is much more risk in them. So yes there is redundancy. This configuration of props is called coax, and is specifically less effective than just putting 4 motors of higher power and bigger props. If there were no gains in reliability, no one would build drones like this, because they would just be less efficient and fly for less time. There is basically no other advantage in this setup than their better reliability due to redundancy. >And with co-axial counter-rotating props, a prop failure will almost certainly cascade to its partner Do you have a source for that? If a prop breaks, it will likely fly off onto sides due to centrifugal forces, not on the vertical axis into the other prop. Additionally if a bottom prop breaks, there is already a downward flow of air from the top prop, which will act as additional downward force on those breakaway parts which will force them to fly off downwards, not upwards into the remaining prop.

dTal 7y ago
My source is bitter experience designing and testing counter-rotating electric ducted fans for distributed propulsion drone applications. You have to consider specific failure modes. You might have an object strike, like a bird. You might lose sealing and get water in somewhere, frying anything electronic inside. You might have a loose bolt, a fatigued bracket, or a frayed wire. When you start considering scenarios rather than parts lists, it becomes clear that consolidating things together spatially costs you most of the advantage of redundancy. This is especially true in the case of props. In point of fact, if a prop breaks the net force is upwards, because that's the direction it was pushing in when it failed. However it's basically irrelevant - unless you perfectly and flawlessly detach the blades symmetrically with explosive bolts, with impeccable timing such that no detached blade hits the airframe, so much energy is released with a moving-part failure that anything in the vicinity is pretty well destroyed. Experience you might have with normal-sized drones is not applicable if you scale it up even a little - big props make a big mess, and you're lucky if the airframe survives at all. You certainly won't be able to count on that shared pod. We can only guess at why they chose to design it this way - personally I think they're a bunch of cowboys who will kill someone the way they're going. I suspect it's because they want to keep the footprint small, and because it's kind of uncool to have to pick your way through a dense ring of props to get to the cockpit (if you look at some of their videos you'll see that they've experimented with non-coaxial x8 configurations in the past). But stacking the props two-by-two like that only costs you reliability.

dTal 7y ago

My source is bitter experience designing and testing counter-rotating electric ducted fans for distributed propulsion drone applications. You have to consider specific failure modes. You might have an object strike, like a bird. You might lose sealing and get water in somewhere, frying anything electronic inside. You might have a loose bolt, a fatigued bracket, or a frayed wire. When you start considering scenarios rather than parts lists, it becomes clear that consolidating things together spatially costs you most of the advantage of redundancy. This is especially true in the case of props. In point of fact, if a prop breaks the net force is upwards, because that's the direction it was pushing in when it failed. However it's basically irrelevant - unless you perfectly and flawlessly detach the blades symmetrically with explosive bolts, with impeccable timing such that no detached blade hits the airframe, so much energy is released with a moving-part failure that anything in the vicinity is pretty well destroyed. Experience you might have with normal-sized drones is not applicable if you scale it up even a little - big props make a big mess, and you're lucky if the airframe survives at all. You certainly won't be able to count on that shared pod. We can only guess at why they chose to design it this way - personally I think they're a bunch of cowboys who will kill someone the way they're going. I suspect it's because they want to keep the footprint small, and because it's kind of uncool to have to pick your way through a dense ring of props to get to the cockpit (if you look at some of their videos you'll see that they've experimented with non-coaxial x8 configurations in the past). But stacking the props two-by-two like that only costs you reliability.