Realistic hovering mechanism for my sci-fi drone

Question

What realistic mechanism could be utilized to allow my drone to hover and move around in a visually pleasing and non distracting way?

I am currently working on a short sci-fi film, which, among other things, includes maintenance drones that will be present on a space ship. My goal is to have a fair amount of realism. (There are certain things, like FTL and ship-wide artificial gravity that will be hand-waved, but besides that I want to incorporate as much science as possible.) The drones are designed to operate on a civilian transport ship (basically a combination of a cruise ship and a commercial airplane) where they provide repairs, aid passengers, and just generally maintain the ship. (They do also happen to be useful for taking care of unwanted guests, if you catch my drift...) They need to be able to move freely anywhere in the ship, at any height, and at a relatively fast speed, while still looking cool and not being extremely distracting, without any obtrusive propellers or exhausts, using a scientifically plausible method of propulsion.

---

The Drone:

The main body is round, about the size of a basketball, and made of some kind of durable composite. I don't have any particular material in mind, so feel free to use what every might be necessary. The bottom half of the drone has multiple mechanical arms, (most likely 2 - 4) with different tools and gadgets. This is also where I assume the hovering system would be located. The top half has various sensors and lights. The exact weight isn't important, but it should be enough to make a sizable clank when it hits the ground.

---

The Ship:

The exact details of the ship shouldn't be too important, but here is some basic information. The ship is around 0.5km tall, and 2km long. Of course, not all of this will be habitable, but there is still more than enough space for hundreds of drones to be at work. Any area inside the ship will have near perfect artificial gravity, and otherwise be identical to earth as far things like air pressure and temperature are concerned.

---

Specifications:

Here is a list of all the requirements the propulsion system should meet. Some exceptions can be allowed, but the system should be as close as possible to these specifications.

• The drone should to be able to hover in place for at least a 30 seconds.
• It should be capable of traveling at least 20mph, although 50mph would be more desirable.
• It needs to be maneuverable and capable of quickly changing direction.
• It needs to be capable of functioning in the ideal conditions for human habitation. (As in: temperature, atmosphere, etc.) The ability to operate at higher temperatures would also be welcome.
• It has to be safe to use around humans; no radiation or excessive heat.
• It needs to be usable in close proximity to at least 3 other drones using the same system. (Ideally there should be no limit.)
• It should be able to move freely anywhere on the ship, without being confined to certain areas. If a specific component is required in the drone's environment, it has to be easily implementable throughout the ship.
• It needs to be quiet. Some small, sci-fi-y noise is acceptable, but nothing that will drown out any dialogue.
• It can't be bright or distracting. It's fine if there is no visual indication of any propulsion, but it would certainly be nice if it had some cool effects. (I will be animating this.) There can be no huge rocket thrusters, or propellers. This isn't a quadcopter. Something small, that's visible but not eye-popping would be ideal.

---

Some things to note:

• The ship itself may have artificial gravity, but this can not be utilized for the drone. (The idea is that the ship has some gigantic power source, unlike the drone.)
• The drones will also operate outside the ship in the vacuum. Some simple RCS thrusters should suffice, but it would be a bonus if the mechanism also works in space.

---

Is there a plausible propulsion system that suits my needs?

Answer 1

You can use ionocraft lifter, formally electro-hydrodynamic thrust like the one seen, for example, here: https://www.instructables.com/id/High-Voltage-Lifter-Ionocraft/ - yes, you can build one, too!

It works by using an negative anode to charge air particles. These charged particles or ions are drawn down to a positively charged cathode. As the ions move toward the cathode, they bump into other air molecules and push them down, creating the ionic wind.

Only drawback, but potentially aestheticslly pleasing, is that your drones can send dust or paper flying, and may make balloons stick to walls, if some ions escape.

In space this would obviously not work, because it uses air as reaction mass. Still, this ionocraft engine can use rcs exhaust as its reaction mass, making them noticeably stronger, and thus saving chemical fuel that's probably harder for you to replenish than electricity.

As for drones operating next to each other, there is no limit, except maybe don't let a drone take in exhaust of another one.

Only thing that's not quite doable right now is on-board power source, but we are getting better at that, so you can believably ignore it.

---

Note: If you will allow discharge to happen, you will have nice blue light (SF classic!) but also O₃ and NO₂ production. In smaller quantities, ships scrubbers can probably deal with them. In larger these may cause adverse health effects and corrosion. Thus, I'd suggest limiting it for emergency, and operation outside hull.

Answer 2

Quantum levitation.

Get a superconductor close to a magnetic field and you get some really cinematographic effects, though in real life.

You're seeing smoke because superconductors nowadays mostly exist in very cold temperatures. I mean liquid nitrogen cold. Every nerd who knows their materials dreams of the day we will have cheap, viable room temperature superconductors, which would be non-smoky and wouln't give you ice burns.

Anyway, these things will hover over tracks defined by magnetic fields. I believe that if you are doing FTL, it should be trivial to manipulate such fields, inside and outside the ship.

Last but not least, the science for this form of levitation has been known from since 1933, so it's no strerch at all seeing it applied for ordinary things such as drones in the future.

Answer 3

Now, I know you said "not a Quadcoptor" - but you also said "The main body is round, about the size of a basketball". So, put the propellers (or impellers?) inside the casing, with vents to take air in the top, and push it out the bottom.

Then, for manoeuvring, have pulsed jets of compressed air, arranged around the drone (like the training drone in the original Star Wars!). As the drone travels, it will generate a characteristic "phut-phut" noise, to go with the whirring-drone of the propellers/impellers. It can push in any direction - multiple pulses will keep it going in one direction - since air resistance will try to slow it down, and faster pulses will make it travel faster. The pulse of compressed air can cause a visual effect - the refractive index of the air is changed, you may get water vapour because the gas is cold, etc.

While inside the ship, it can run a miniature compressor to suck in and store air, so it is limited only by power (And will add yet another noise that the drones sometimes make - it may even pause and hover or land/dock while it does this, possibly with lights to indicate that it has low manoeuvrability).

While outside the ship, it will have a limited air supply - but also no air resistance or gravity to contend with, so a single pulse can carry it as far as it needs to go. The propellers/impellers inside can then be used as gyroscopic reaction wheels, to allow turning without expending air. It may have an emergency supply of very compressed gas that can be swapped out when it returns to the ship, at whatever docking station it uses to recharge.

Answer 4

Gravity tech.

/ship-wide artificial gravity that will be hand-waved/

There you go! And you only needed to wave your hands once, so you didn't get all sweaty. Your gravity tech is granular. It is not generated centrally for the whole ship, but cell by cell across the floor, just as a series of rooms might be illuminated 1 room at a time. That conserves power; gravity is produced where people need it and where circumstances require (like a swimming pool) but no energy is wasted making gravity for an empty room.

Your drones leverage this tech. They have gravity capable cells in them. They orient and turn on the cells as needed, essentially pulling themselves through the air against the mass of the ship. Ships gravity under the drones will be off as they pass by, but the drones might choose to produce their own gravity to pull them closer to the ceiling or down to the floor. This would affect items in the vicinity of the drones as well, giving an effect similar to a gust of wind even though a drone might not be moving fast.

Having your gravity tech portable and granular like this also offers narrative potential. If a drone can pull itself, a tethered drone (or one which anchors itself) can attract a distant object by ramping up the gravity pointing that way.

Answer 5

Anti-Gravity

Before I get into it, let me clarify: What would be plausible technology in the Middle Ages? Metallic boxes running on some parts of oil via combustion (or short: cars) would be unthinkable to these times. So instead of attempting to apply currently known, but not sufficiently explored technology to a futuristic, fictional world, let's try to create something that is sufficiently plausible and on par with let's say FTL and, as in the question mentioned, artificial gravity. One metric which is important is consistency and keeping basic physical laws applied.

How would it work? Similarly to electro-magnetism, but with gravity instead and also reversed. It would be a module which could exert anti-gravitational forces if powered by electricity and which exerts force in a direction opposite to the current gravity. Now, gravity itself however is not just a force. It's a phenomenon which bends space (and time) in a way that for example stellar objects can orbit each other. Now, the anti-gravity module has the opposite effect - it bends space (and time) backwards in a relatively small, confined space, so that the space-time bending of gravity causes the drone to move upwards instead by being repelled. There would be a constant value which could entirely negate gravity, and anything above that would cause it to have opposite effects.

This effect would work gradually, meaning a drone has to continually adjust the efficiency in order to either move downwards, upwards or remain still. That goes also for moving horizontally - which could be achieved by simply using the anti-gravity module asymmetrically so that a part of the drone "falls" in the direction it intends to hover. This navigation requires a sophisticated AI in order to work properly, but that exists today already for normal drones.

The energy required for the module depends on the volume and mass of the drone and the magnitude of gravity it is in. But to what is the energy actually converted? Repulsion! It may defy gravity through its workings, but at the same time it would also push away whatever is exerting gravity to it. This means practically that the floor/artificial gravity modules would still have to carry their weight. The surplus energy, which couldn't be used effectively, would result in some heat which may require cooling.

Upsides: It could directly convert energy into propulsion without the need for fuel. The device would be harmless. It wouldn't require a lot of energy and the energy conversion could be much higher than that of fuel for example.

Downsides: It could not be used for space flight because it would be dependent on gravity and be too weak in general (navigation would be near impossible). It would be no easy tech, maintenance would require quite some technical knowledge and complex parts.

Note: Usage for vehicles on a planet are feasible, but quite sluggish to navigate in - braking would be the most difficult part as it would work the same as forward thrust, not like cars which use brake based on friction. Remember, it would not repel matter, only sources of gravity. That said, this propulsion might not be the only one used, but might get complementary methods or tech to accommodate for its shortcomings.

Answer 6

I know you want a flying drone, but I feel like this idea could do roughly the same

BB8 Drones with an extra magnetic connector so it can travel around on the walls, roof and floor. Whether its avoiding crowds or getting to hard to reach places, BB8 can do it.

BB8 is round and adorable

BB8 is a multiple purpose drone. Multiple grappling hooks, a torch and a terminal plugallow BB8 to be an all purpose maintenance bot and a deadly adversary.

BB8 is safe and friendly. No deadly rotor blades or thrusters that could hurt potential customers. BB8 is also environmentally friendly, running off a battery powered motor.