Structure and principle of four-rotor aircraft

Structure and principle of four-rotor aircraft

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Preface: The year before the electric game left a set of four rotor aircraft now only four rotor and motor (do not know who was demolished, assembly parts can not find), while the National Day holiday, hope to be able to quickly re-DIY out. wherein the control and drive board can be temporarily welded by the bread plate, and so on to verify the success can fly in the re-design of integrated circuit board to achieve the machine.

Principle of rotor: the ins and outs of lift

This is the knowledge of aerodynamics, the research content is very extensive, this article only focuses on the general theory, elaborated on the airfoil lift and the rotor lift principle.

Wing type lift

According to the basic principle of fluid mechanics, the atmospheric pressure with slow flow is stronger, and the atmospheric pressure with fast flow is smaller. Because the wing is generally asymmetrical, the upper surface is relatively convex, and the lower surface is relatively flat ( airfoil ), the air flow through the upper surface of the wing is similar to the narrow area of the flow of water, the flow rate is faster, and the air flow through the lower surface of the wing is the opposite, similar to the wide area of water, The flow rate is slower than the upper surface. The pressure between the atmosphere and the lower surface of the wing (direction upward) is greater than the pressure applied to the upper surface of the wing (direction downward), and the pressure difference between the two forms a lift. [Excerpt from How Lift is produced].

So for the commonly said aircraft, it is necessary to run, when the speed of the aircraft reached a certain size, the wings of the aircraft generated by the lift to offset the gravity, so as to achieve flight.

The lift of the rotor

The three takeoff principles of aircraft, helicopters and rotary-wing machines are different. Aircraft rely on the approach to provide speed to achieve enough lift, and helicopters rely on the control of the rotor to achieve vertical lifting without running, the helicopter rotation is provided by the power system, and the rotor rotation will produce upward lift and air to the rotor reaction moment, In the design of the need to provide a balance rotor reaction torque method, usually a single-rotor plus tail propeller type (tail propeller is usually vertical installation), double-rotor longitudinal type (opposite to counteract the reaction torque), etc., while the rotor is between the aircraft and the helicopter, the rotor of the rotor is not connected to the power system, A lift (like a wind car) is generated by the forward airflow in the course of the flight, i.e. the rotor is rotated, and the torque transmitted to the machine is small and does not need to be specifically offset.

The design of the four-rotor aircraft is essentially a category of helicopters, need to be powered by the power system to provide four rotor rotation power, while the rotary rotor rotation generated by the torque needs to be offset, so the simple control of the structure is convenient, similar to the twin-rotor longitudinal type plus Heng Lie type helicopter model, The rotation direction of the two rotors and the other two rotors must be reversed in order to counteract the gyro effect and the power torque of the aircraft.

The structural form of four-rotor aircraft

Rotor symmetrical distribution in the body before and after, about four directions, four rotors in the same height plane, and four rotors of the structure and radius are the same, four of the motor is symmetrically installed in the aircraft's stent end, the middle space stent placement flight control and drive plate.

Operating principle of four-rotor aircraft

The four-rotor aircraft can control the attitude and position of the aircraft by adjusting the rotational speed of the rotor by regulating the speed of four motors to realize the change of lift. Four-rotor aircraft is a six-DOF vertical elevator, but only four input force, but also has six state output, so it is an under-driven system.

It can be seen from the motion posture provided in 6 that the movement of 6 degrees of freedom can be achieved by controlling the speed and direction of the motor. Therefore, the design of four-rotor aircraft mainly includes three aspects: one is the structure design, the other is the Motor drive design (ESC), and the third is the control program design.

Design and structure design of four-rotor aircraft

On the one hand, the balance is ensured by the structural design, while the structure design of the rotor is related to the lift size;

Motor Drive Design

Because the electric current of the motor is very large, usually when each motor is working normally, there is an average a Around the current, if there is no ESC, the flight control board can not withstand such a large current (also does not drive the function of brushless motor). The function of the ESC is to change the control signal of the flight Control Board to the current size to adjust the speed of the motor. The knowledge about ESC turned back to a blog post explaining.

Design of Control Program

The main control signal is generated. To enable the aircraft to achieve different flight attitude and function, usually with feedback control, you need to place a gyroscope on the flight Control Board, a four-axis accelerometer or a measuring height of the sensor (ultrasonic sensor) and so on. Through the feedback of the position, height or angle information, through a reasonable control algorithm to produce the appropriate control signal, through the ESC adjustment four motor rotation state, and then achieve a variety of posture and functions.

PS: Due to the actual implementation of the blog post, design considerations are certainly not comprehensive, when the real implementation of the various aspects of the content to supplement.

Reference documents:
http://blog.csdn.net/jbb0523/article/details/24198505

Http://zhan.renren.com/niuneine?gid=3602888498032410217&checked=true

Http://zhan.renren.com/worldofrobot?from=template&checked=true

Http://www.cnmox.com/thread-12460-1-1.html

2015-9-30 Less Art

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Structure and principle of four-rotor aircraft