# US 11,993,370 B2 · Coaxial tilt-rotor unmanned aerial vehicle and control method thereof

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- Number: US 11,993,370 B2
- Document ID: US11993370B2
- Status: Granted
- Kind: B2
- Application number: 17/414,715
- Filed: 2020-05-13
- Published: 2022-04-28
- Granted: 2024-05-28
- Earliest claimed: 2020-05-13
- Assignees: Dalian University of Technology
- Applicants: Dalian University of Technology
- Inventors: Yuhu Wu; Zongyang Lv; Ximing Sun; Xiangyu Shen; Rui Wang
- Web page: https://patentgrep.com/patent/US11993370B2

## CPC

- B64U 10/25: Fixed-wing aircraft (VTOL aircraft B64U10/20)
- B64C 11/48: Units of two or more coaxial propellers
- B64C 29/0033: {the propellers being tiltable relative to the fuselage}
- B64U 30/24: Coaxial rotors
- B64U 30/297: Tilting rotors
- G05D 1/0858: {specially adapted for vertical take-off of aircraft}
- B64U 70/80: Vertical take-off or landing, e.g. using rockets (rotorcrafts B64U10/10; VTOL aircraft B64U10/20)
- B64U 2201/00: UAVs characterised by their flight controls
- B64U: UNMANNED AERIAL VEHICLES [UAV]; EQUIPMENT THEREFOR
- B64C: AEROPLANES; HELICOPTERS
- G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES

## Abstract

A coaxial tilt-rotor unmanned aerial vehicle (CTRUAV) and a control method thereof. The CTRUAV includes three rotor modules, five rotors with motors and a control system. The three rotor modules are in an inverted triangle layout. The left and right coaxial tiltable rotor modules in the front of the CTRUAV can rotate around the plane of a fuselage. A rear rotor is installed on the rear fixed-axis rotor module. Two pairs of coaxial rotors are respectively installed on the left and right coaxial tiltable rotor modules. The left and right coaxial tiltable rotor modules include an upper rotor and a lower rotor respectively; the upper rotor and the lower rotor have opposite rotation directions and the same rotation speed during the flight. In the two pairs of coaxial rotors, the rotors on the same layers have opposite rotation directions, and the rotors on different layers have the same rotation directions.

## Claims

### Claim 1

A coaxial tilt-rotor unmanned aerial vehicle (CTRUAV), comprising:
three rotor modules positioned in an inverted triangle layout, the three to rotor modules comprising:
a left coaxial tiltable rotor module;
right coaxial tiltable rotor module located at a front of the CTRUAV; and
a fixed-axis rear rotor module located at a rear of the CTRUAV;
five rotors with motors, comprising:
a rear rotor installed on the rear fixed-axis rotor module and driven by a motor installed on the rear fixed-axis rotor module; and
two pairs of coaxial rotors respectively installed on the left coaxial tiltable rotor module and the right coaxial tiltable rotor module, each pair of coaxial rotors being driven by a pair of coaxial motors; and
a control system installed on the CTRUAV and used to receive position and attitude information of the CTRUAV, perform control operation, and drive the three rotor modules to control the motion of the CTRUAV,
wherein the left coaxial tiltable rotor module and the right coaxial tiltable rotor module are configured to rotate around a plane of a fuselage;
wherein the two motors of a pair of coaxial motors have a same rotation speed and opposite rotation directions,
wherein in the two pairs of coaxial rotors, rotors on same layers have opposite rotation directions, and rotors on different layers have the same rotation directions,
wherein the CTRUAV can roll around an X-axis, pitch around a Y-axis and yaw around a Z-axis, wherein, taking a positive direction of the X-axis as a forward direction; taking the positive direction of the Z-axis as a takeoff direction, and taking the positive direction of the Y-axis as a direction perpendicular to the positive direction of the X-axis,
wherein the CTRUAV has three modes comprising:
a vertical takeoff and landing (VTOL) mode;
a fixed-wing mode; and
a transition mode,
wherein the VTOL mode and the fixed-wing mode are switched through the transition mode,
wherein, when the CTRUAV is in the VTOL mode, the CTRUAV places the three rotor modules perpendicular to the plane of the fuselage, and uses the five rotors to provide lift forces to take off or land quickly, and
wherein, when the CTRUAV is in the fixed-wing mode, the CTRUAV tilts the left and right coaxial tiltable rotor modules parallel to the plane of the fuselage to provide horizontal forward thrust forces, and places the rear fixed-axis rotor module perpendicular to the plane of the fuselage to provide the lift force to ensure the smooth forward flight.

### Claim 2 (depends on 1)

A control method of the coaxial tilt-rotor unmanned aerial vehicle (CTRUAV) of claim 1, comprising steps of:
step 1: according to target and current positing and attitude, obtaining error between the target and current value, and then getting a set of forces and torques vectors [Fx Fz τΦ τθ τψ]T after operation by the control system; wherein Fx is a resultant force of three rotor modules in the x direction; Fz is a resultant force of three rotor modules in the z direction; τΦ is a resultant torque of three rotor modules around the x direction; τθ is a resultant torque of three rotor modules around the y direction; and τψ a resultant torque of three rotor modules around the z direction;
step 2: calculating a set of forces [F5z F2z F2x F1z F1x]T which are produced by the left, right and rear rotor modules respectively through the equations (1);
[
F
x
F
z
τ
ϕ
τ
θ
τ
ψ
]
=
[
0
0
1
0
1
1
1
0
1
0
0
-
L
1
0
-
L
1
0
L
3
L
2
0
-
L
2
0
0
0
L
1
0
-
L
1
]
⁡
[
F
5
⁢
z
F
2
⁢
z
F
2
⁢
x
F
1
⁢
z
F
1
⁢
x
]
(
1
)
wherein F5z is lift force of the fixed-axis rotor module; F2z and F2x are component forces of the right coaxial tiltable rotor module in the z direction and the x direction respectively; F1z and F1x are component forces of the left coaxial tiltable rotor module in the z direction and the x direction respectively; CoG is center of gravity (CoG) of the CTRUAV; L1 is half of a distance between left and right coaxial tiltable rotor module of the CTRUAV; L2 is a distance from a midpoint of a connecting line between left and right coaxial tiltable rotor module to CoG; and L3 is a distance from the rear rotor module to the CoG;
step 3: calculating the rotation speed of the five motors of each rotor, tilt angles of the left and right coaxial tiltable rotor module in the front through equations (2); wherein in the equations (2), the force provided by each rotor is proportional to its rotation speed; k5, k2 k1 are respectively scale factors corresponding to the rear rotor module, the right rotor module and the left rotor module;
{
F
5
⁢
z
=
k
5
⁢
ω
5
2
F
2
⁢
z
2
+
F
2
⁢
x
2
=
F
2
=
k
2
⁢
ω
2
2
θ
2
=
arctan
⁡
(
F
2
⁢
z
/
F
2
⁢
x
)
F
1
⁢
z
2
+
F
1
⁢
x
2
=
F
1
=
k
1
⁢
ω
1
2
θ
1
=
arctan
⁡
(
F
1
⁢
z
/
F
1
⁢
x
)
(
2
)
wherein F1 is the force of the left coaxial tiltable rotor module; ω1 is the rotation speed of the coaxial motors on the left coaxial tiltable rotor module, and θ1 is the tilt angle of the left coaxial tiltable rotor module; F2 is the force of the right coaxial tiltable rotor module; ω2 is the rotation speed of the coaxial motors on the right coaxial tiltable rotor module, and θ2 is the tilt angle of the right coaxial tiltable rotor module; ω5 is the rotation speed of the motor on the rear rotor module;
step 4: the set of data ω1, θ1, ω2, θ2, and ω5 which has already obtained in step 3 can drive the CTRUAV directly so that the rotation speed of the rear rotor module, and the rotation speeds and tilt angles of the left and right coaxial tiltable rotor modules, i.e., changing five control inputs can change the motion state of the CTRUAV to approach the target position and attitude gradually.