Landing Mini 2 on a moving boat with many obstacles

[KiloMeater]

So I took the 3D printed legs i posted above and created this diy floater , since I will soon use it on a boat , I used pool noddles

Total weight is 28grams , the drone seems to handle it well
It will not behave good with wind but I have limited expectations just a few shots with my kids from the boat .
The idea is to be able to retrieve it if it comes to that…

I am considering a second version with the noodles cut in half and perhaps longer… I wonder how much buoyancy they produce and if it’s enough.

 

[scro]

Assuming the pool noodle is about 5cm diameter, then a single 14cm length will give you approx 250g uplift. With the current design it looks fairly unstable in the fore/aft direction, so could easily flip upside down with the drone hanging underneath the floats. Not ideal, but at least you don't completely lose the drone. 4 small bits of noodle further out would give it a better chance of staying upright - a bit like trainer skids for an RC helicopter. Best to keep the bulk of the buoyancy away from directly under the props too.

 

[KiloMeater]

Thanks for the figures , now I know how much material I need .
I will try for another version for more stability so in case it drops into water it may stay dry and not have to use the care refresh at all.
Indeed the current one is unstable but salvaging it seemed enough at the time

 

[KiloMeater]

Here we are
This is 3 gr more total 31 but can easily trim it

I have both versions to experiment

The noodles are cut in half cylinder shape this time

 

[RogerDH]

Here we are
This is 3 gr more total 31 but can easily trim it

I have both versions to experiment

The noodles are cut in half cylinder shape this time

As Archimedes discovered, the buoyant force acting on a body submerged or floating in water is equal to the weight of the water that's displaced, so if you want to float an object around 280g, you need to displace 280g of water. It's easiest to work in centimeters to take advantage of the fact that 1cc of water weighs 1g. So, just measure the diameter of your noodle and calculate the cross-sectional area, subtract the area of the hole in the middle if there is one, then divide 280 by that area to get the required length.

 

[scro]

Remember that calculating the required length like this will give you just enough buoyancy to keep the drone above the waterline. Theoretically you'd get some buoyancy from the plastic skids and drone itself, but the displaced volume will be very small and I suspect the objective is to keep the drone dry! I'd suggest doubling the number so there's plenty of spare buoyancy to deal with decelerating the drone if it falls or during landing so that it doesn't take an accidental dip on touchdown. ?

 

[RogerDH]

Remember that calculating the required length like this will give you just enough buoyancy to keep the drone above the waterline. Theoretically you'd get some buoyancy from the plastic skids and drone itself, but the displaced volume will be very small and I suspect the objective is to keep the drone dry! I'd suggest doubling the number so there's plenty of spare buoyancy to deal with decelerating the drone if it falls or during landing so that it doesn't take an accidental dip on touchdown. ?

Yep, I should have said minimum required length, which would be a starting point for minimum drag. I haven't tried the available floats, but I've read that they do have significant drag that makes a noticeable difference in performance. Whatever safety margin KiloMeater decides to use for buoyancy, before taking any such flotation device out on the water, I'd try to determine what kind of wind it can really handle. One problem with these type of floats (and actually, the shape of the Mini itself) is that drag increases considerably when the drone is tilted for maximum speed. For that reason, I've wondered if using four round styrofoam balls would be better. At least, their drag would be nearly constant, regardless of orientation or wind direction.

 

[scro]

I don't think there's an easy solution to making an aerodynamic shaped float, given that the drone tilts, can fly in any direction and the wind can come from any direction. Any shape that gives enough displacement for buoyancy to support itself and the drone will also provide a good bit of aerodynamic drag.

A possible good solution is to optimise the floats shapes for fwd flight aerodynamics so you can at least point the drone into the wind for the best chance of fighting through a gust without being blown away. Coincidentally the arrangement in post #44 isn't far off that.

 

[RogerDH]

I don't think there's an easy solution to making an aerodynamic shaped float, given that the drone tilts, can fly in any direction and the wind can come from any direction. Any shape that gives enough displacement for buoyancy to support itself and the drone will also provide a good bit of aerodynamic drag.

A possible good solution is to optimise the floats shapes for fwd flight aerodynamics so you can at least point the drone into the wind for the best chance of fighting through a gust without being blown away. Coincidentally the arrangement in post #44 isn't far off that.

Yeah, I hadn't done more than "wonder" about using four balls, but after looking into it some more, I now believe they would have more drag than two tubes of equal volume, in most orientations. You could round the front and taper toward the back -- like an airplane drop tank -- to reduce the drag when moving forward.

 

[scro]

Theoretically a sphere gives the best volume to surface area ratio so would give the smallest overall object that would give enough displacement. The cross section area is also not too bad, and the same in any direction. A sphere is also a reasonably aerodynamic shape, but where it fails miserably is in stability when the CoG is above the centre of the sphere. Going for 4 smaller spheres out on sticks (ie RC heli trainer gear) addresses the stability concern, keeps the drag force constant regardless of direction of travel, but increases the cross section area significantly.

After all that mathematical musing and disappearing down a rabbit hole, Kilomeater already acknowledged that sticking floats on will kill the wind resistance of the drone ?