Stackable drones

[0001] This invention relates to combining two or more flying machines into a vertically stacked unified flying assembly, especially the releasable stacking of multi-copter drones.

[0002] Multi-copter drones provide aerial delivery of packages. A drone can be overloaded by a large package and under-utilized by a small package. Using only large drones would result in unnecessary expense for most packages. This can be addressed with a fleet of different sized drones. However, the need for a given sized drone at a given location at a given time is largely unpredictable, resulting in wasteful relocating of unloaded drones or often using local drones that are larger than needed.

[0003] U.S. Pat. No. 9,457,899 and US patent application 2016/0378108 teach connecting multiple drones side-by-side into a collective unmanned aerial vehicle (UAV) that can carry larger packages but can separate into smaller or single vehicles for smaller packages. This prior art teaches connecting the drones to each other by connectors on their propeller guards and related peripheral parts.

[0015] FIG. 1 shows a top drone 4 landing on a bottom drone 2 for coupling in a vertically stacked drone configuration. A coupling protrusion 6 or convexity on the bottom drone will be received into a matching socket 8 or concavity on the top drone. A latch mechanism will connect the two drones together as a combined flying machine with more lift than a single drone. The drones are rotationally offset from each other by 45 degrees about a central vertical axis 10 so the propellers are staggered in the top view of FIG. 3. Other offsets are possible as later shown, including a 90-degree offset that provides coaxial counter-rotating propellers in the stack of drones.

[0016] FIG. 2 shows the top drone 4 coupled to the bottom drone 2 forming a combined flying machine 5A with approximately twice the lift of a single drone. Each drone may have a coupling protrusion 6 on top and a coupling socket 8 (FIG. 1) on the bottom so that any drone in a fleet can be a top or bottom drone. This allows a delivery package to be attached to any convenient drone in the fleet, then any other available drone in the fleet can be connected on top of the first drone as needed.

[0017] The lower drone propellers P6, P8 could hit the upper motors M3, M4 unless the drones are rotationally offset as in FIG. 3. Alternately, the drone bodies 2, and 4 can be taller so there is no interference in any position. With a taller body for example, the upper and lower drones can be rotationally offset 90 degrees to provide coaxial counter-rotating propellers as later shown.

[0018] FIG. 3 is a top view of the stacked drones of FIG. 2. The upper propellers are indicated by disks P1, P2, P3, and P4. The lower propellers are indicated by dashed line disks P5, P6, P7, and P8. Multi-copters normally have an even number of propellers, with half of them rotating clockwise, and the other half rotating counter-clockwise to neutralize net torque. In FIG. 3, the top drone 4 has two clockwise propellers P1, P3 and two counter-clockwise propellers P2, P4.

[0019] An objective of the invention is to minimize negative aerodynamic effects of the downwash from the upper propellers on the lower propellers. Rotationally offsetting the drones by 45 degrees as in FIG. 3 minimizes the total blade disk overlap. The upper and lower propeller disks may or may not partially overlap in this configuration, depending on the diameter of the propellers relative to their lateral distance from the drone center. The offset angle for minimal overlap depends on the number of propellers in the drones.

[0020] In the example of FIG. 3, blade P2 overlaps blades P5 and P6 in areas A1 and A2 respectively. In area A1, the upper and lower blades move in opposite rotational directions. In a top view the blades cross a line 12 drawn between the centers of rotation in opposite directions as shown by arrows. This can increase lift on the lower blade P5, since it can extract some of the rotational energy in the downwash of the upper blade P2 and can redirect the rotating downwash into a more vertical path. However, in overlap area A2, blades P2 and P6 move in the same direction, which can reduce lift on the bottom blade P6.

[0021] FIG. 4 shows an embodiment 5B with a drone rotational offset that maximizes blade overlap area A1 and minimizes area A2. The lower drone may be positioned such that the lower propeller disks P5, P6, P7, and P8 maximally overlap in beneficial areas (hatched) while not overlapping the motors 5 or motor arms 16 in the top view. Legs 18 may extend downward and outward from the motors 14 or motor arms 16 if wanted.

[0022] FIG. 5 is a sectional view taken on line 5-5 of FIG. 7 when two drones are coupled. The lower drone 2 has a coupling protrusion 6 that fits into a coupling socket 8 in the upper drone 4. A hook 22 on the upper drone 2 extends into a slot 24 in a first side of the coupling protrusion 6. The hook is urged by a spring 26 to fall into the slot. An actuator 28 is controlled by a control system in the upper drone to lock the hook in the slot and retract the hook from the slot for drone separation. A second hook 23 on the upper drone 4 extends into a second slot 25 on the opposite side of the coupling protrusion 6 from the first hook 22. The second hook is likewise urged by a second spring 27 and controlled by a second actuator 29. A first set of contacts 32 on the lower drone 2 engage matching contacts 34 on the upper drone 4 to communicate data and power sharing between the drones.

[0023] The upper and lower coupling parts 6, 8 engage two vertically stacked drones 2, 4 in a predetermined relative rotational orientation of the two drones about a common centerline 36 to offset the upper propellers from the lower propellers by a certain amount as seen from above. Each drone in a fleet of drones may have both a coupling protrusion 6 on the top of the drone and a coupling socket 8 on the bottom of the drone.

[0024] FIG. 5 is just an example of a specific coupling design. Other coupling designs may be used within the scope of the invention. In another embodiment (not shown) multiple hooks may be provided in a circular array around the bottom of the upper drone to latch into a circular array of slots on the upper surface of the lower drone. For example, four coupling hooks may be used in this embodiment. A separate indexing protrusion or key may be provided in the bottom of the upper drone to fit into a matching slot in the top of the lower drone to enforce a relative rotational orientation of the drones. The lower drone may have landing guidance markings on the upper surface that are analyzed by the control system of the upper drone via a camera in the bottom of the upper drone to guide landing of the upper drone on the lower drone in the correct orientation.

[0025] FIG. 6 is a perspective view of the bottom surface of body of a drone 4 with a coupling socket 8. A latch hook 22 is actuated by a control system of the drone 4. A second latch hook (hidden) may be provided on the opposite end 23 of the socket.

[0026] FIG. 7 is a perspective view of the top surface of body of a drone 2 with a coupling protrusion 6. A latch slot 25 is provided to receive a second latch hook (hidden) in the coupling socket 8 as shown in FIG. 5. Electrical contacts 32 are provided to connect with matching contacts in the coupling socket 8 of FIG. 5 (hidden) to provide data and power communication between the stacked drones 2 and 4. The shape of the coupling parts 6 and 8 enforces a predetermined relative rotational orientation of the upper and lower drones.

[0027] The upper drone 4 can land on the lower drone, self-center on the coupling protrusion 6, and automatically attach thereto by a springs in the opposed latch hooks. The stacked configuration serves not only for increasing lift with two active drones, but allows retrieval of a disabled drone, for example one having a disabled motor. A disabled drone in a prior art lateral array of drones can imbalance the lift of the array, making it inoperable. Such laterally connected drones require at least two drones to rescue a disabled drone, since the disabled drone must be in the center of the array. However, a disabled drone in a vertical stack does not imbalance lift, so the present invention requires only one drone to rescue a disabled drone.

[0028] FIG. 8 is a schematic view of a unified control system in the stacked drones. Each drone has an independent control system 38, 40 for independent flight. Each control system is connected to respective batteries 42, 44, a radio control antenna 46, and a GPS receiver 48 as known in the art. Each control system includes a power module that monitors the batteries and provides power to all other system components, including the motors (not shown). Control communication 50 and power communication 52 are established by respective interfaces 54, 56 between the drones, for example by electrical contacts (32, 34 in FIG. 5) that engage when the drones are coupled. Such interface may follow an established physical and/or electrical interface standard. For example, a USB electrical and power interface standard may be used in order to use existing USB circuit and driver designs in the controllers, while the physical interface for the contacts may be custom. Upon interconnection, the control systems perform a handshaking protocol that establishes one of the control systems 38 as master and the other control system(s) 40 as slave(s). Now the master control system controls all drones in the stack so they are coordinated and may share power as needed.

[0029] FIG. 9 is a perspective view of an embodiment 5C with two drones 2, 4 stacked and offset rotationally by 90 degrees. Each upper propeller P1, P2, P3, P4 is paired with a coaxially counter-rotating lower propeller P6, P7, P8, P5 respectively. For example, upper propeller P2 is coaxial 58 and counter-rotating with lower propeller P7. This allows lower propeller P7 to extract rotational energy from the downwash of the upper propeller P2, providing aerodynamic synergy in the combined flying machine.

[0030] The offset that provides counter-rotating propellers depends on the number of propellers and how they are organized for clockwise and counterclockwise rotation. Adjacent propellers normally rotate in opposite directions on a drone. If drones with 6 propellers in this arrangement are stacked, the relative rotational offset for counter-rotating propellers in the combined flying machine is 60 degrees. If drones with 8 propellers in this arrangement are stacked, the relative rotational offset for counter-rotating propellers in the combined flying machine is 45 degrees. Going sequentially around an 8-propeller drone, the propeller directions can be represented as < > < > < > < >, where < represents clockwise, and > represents counterclockwise. Using drones with opposite rotation directions in adjacent propellers, the drone rotational offset for coaxial counter-rotation in stacked drones is an odd multiple of 360/N degrees, where N is the number of propellers. For example with eight propellers 1*360/8=45 degrees or 3*360/8=135 degrees.

[0031] This is different if the propellers are arranged differently on the drone. For example, a drone with 8 propellers may have four groups of two propellers rotating in the same direction. Going sequentially around an 8-propeller drone with this arrangement, the propeller directions can be represented as < < > > < < > >. With this arrangement, the drone rotational offset for counter-rotating propellers in the stacked drones is an odd multiple of 360/X, where X is the number of rotation groups. In the 8 propeller example above with 4 groups of 2 propellers, 1*360/4=90 degrees or 3*360/4=270 degrees.

[0032] FIG. 10 is a top schematic view of a drone body 4 with a top protrusion represented by arrow 6, and a bottom socket represented by dashed arrow 8. The bottom socket is offset from the top protrusion by 90 degrees, resulting in the configuration of FIG. 9. The unified master/slave control system previously described now controls the lower drone 90 degrees differently from the upper drone, so they both fly in the same direction. The bottom socket may be offset by another amount if a different embodiment such as 5A (FIG. 3) or 5B (FIG. 4) is wanted.

[0033] The present invention connects two or more drones in a vertically stacked configuration that provides more lift for larger packages than a single drone. A stacked drone configuration has the following advantages over a lateral array of drones:

[0034] a) Stacked drones are more rigid because coupling is made directly between the drone bodies instead of between propeller guards or other peripheral parts.

[0035] b) Stacked drones weigh less than a lateral array since peripheral walls and arms strong enough for side-to-side attachments are not needed.

[0036] c) Stacked drones use less wiring for interconnection because wires do not span from the periphery to the drone body.

[0037] d) Stacked drones provide a smaller footprint than a lateral array of drones, providing a smaller landing area requirement.

[0038] e) Stacked drones can provide aerodynamic synergy because the lower propellers can extract rotational energy from the downwash of the upper propellers that would otherwise be wasted.

[0039] f) A single stackable drone can rescue a disabled drone. Prior art lateral arrays require at least two drones to rescue a disabled drone.

[0040] While various embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Changes and substitutions may be made without departing from the invention. Accordingly, it is intended that the invention be limited only by the scope and intended meaning of the appended claims.