Multirotor Thrust Feedback Control for Air Density Variations
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Solution Overview
Problem
Existing multirotor aircraft control systems rely on assumptions about air density and other parameters, leading to mismatches between intended and actual thrust and torque, which affects stability and motion.
Innovation Solution
The method involves directly commanding thrust setpoints to drive units associated with each rotor, using thrust measurements as a controlled variable to adjust rotor speed, eliminating the need for assumptions about air density and other parameters, and implementing a cascaded control loop with thrust and speed control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rotor angular speed setpoints are used to control multirotor aircraft, then the control system is simple to implement, but mismatches between intended and actual thrust occur due to air density variations
Solution Approach 1:
The patent implements a feedback control mechanism where the actual thrust measured by the thrust measuring device is fed back to the thrust controller. The thrust controller adjusts the rotor speed command based on the difference between commanded and actual thrust, eliminating mismatches caused by air density variations while maintaining control simplicity.
Solution Approach 2:
The patent replaces the traditional mechanical/aerodynamic thrust estimation model with a direct electrical measurement approach using a thrust measuring device. This substitution eliminates the need for complex aerodynamic calculations and air density assumptions, providing direct and accurate thrust measurement regardless of environmental conditions.
2Device complexity
If air density assumptions are made for thrust calculation, then the control calculations are simplified, but errors occur when real air density differs from nominal values
Solution Approach 1:
The system becomes self-calibrating by continuously measuring actual thrust and using this information to automatically adjust rotor speed commands. The thrust controller adapts to real-time conditions without requiring external intervention or pre-programmed air density values, making the system reliable across varying environmental conditions.
Solution Approach 2:
The patent replaces aerodynamic models that require air density assumptions with direct electrical measurement of thrust. This substitution eliminates the source of errors related to nominal vs. actual air density differences while maintaining simplified control calculations.
3Ease of operation
If rotor speed is used as the control variable, then the control interface is straightforward, but thrust response varies with air density and inflow speed
Solution Approach 1:
The feedback loop continuously monitors actual thrust and adjusts rotor speed commands accordingly. This ensures that despite variations in air density and inflow speed, the system maintains consistent and reliable thrust response while keeping the control interface simple for the operator.
Solution Approach 2:
The system dynamically adapts the rotor speed command based on real-time feedback from thrust measurement. This dynamic adjustment allows the control interface to remain simple while the underlying control mechanism adapts to changing environmental conditions to maintain consistent thrust response.
4Device complexity
If nominal air density is assumed for flight controller design, then the controller design is simplified, but mismatches occur between intended and actual thrust
Solution Approach 1:
The flight controller becomes self-adjusting by using thrust feedback to automatically compensate for deviations from nominal air density. This eliminates the need for complex design considerations regarding air density variations while maintaining accurate thrust measurement and control.
Solution Approach 2:
The patent replaces aerodynamic modeling approaches with direct electrical measurement of thrust. This substitution eliminates the need for complex air density compensation algorithms in the controller design while providing accurate real-time thrust information for precise control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures precise control by making the aircraft motion and attitude deterministic, reducing errors in thrust and torque, and eliminating the need for air density measurements, thus simplifying the control process.
Implementation Method 1
a certain thrust force (T) in Newton (or an equivalent unit of measurement) is expected for a certain rotor angular speed (ω), which in turn generates a torque (τ) in Newton meter acting on the aircraft
Implementation Method 2
the rotor drag (D) can be expressed as where the drag coefficient cD is a function of air density as well
Implementation Method 3
measuring the thrust (T), preferably in Newton (or an equivalent unit) within said drive unit
Data Source
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AI summary
We propose a method of controlling operation of an aircraft with a plurality of n rotors (6), n ∈ , and a corresponding plurality of drive units (2), preferably a vertical take-off and landing aircraft with electrically powered rotors (6), comprising: a) determining, by means of a flight control unit (1), a respective desired resulting thrust setpoint, preferably in Newton (N) or an equivalent unit, for each of said plurality of rotors (6); b) directly commanding, by means of said flight control unit (1), a respective thrust setpoint to a drive unit (2) associated with a given rotor (6) of said plurality of rotors (6) by sending a corresponding thrust command to said drive unit (2); c) measuring a thrust (T), preferably in Newton (N) or an equivalent unit, within said drive unit (2); and d) processing said measured thrust (T) as a controlled variable.