UAV Autopilot Bode Plot Testing Without Flight Instability
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Solution Overview
Problem
Collecting information for Bode plot creation in UAVs is challenging due to stability issues, as multirotor UAVs are inherently unstable and require feedback loops for attitude control, making it difficult to apply Bode plot generation input signals without causing instability or crashes.
Innovation Solution
A method for collecting data by creating a Bode plot generation input signal, adding it to control inputs, collecting data from multiple points within the control system, calculating magnitude and phase, and recording these to create Bode plots for closed or open loop responses, allowing for safe and stable data collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Bode plot generation input signal is applied directly to the control system while feedback loops are engaged, then Bode plot data can be collected, but the UAV may become unstable and crash
Solution Approach 1:
The patent introduces an intermediary signal injection point at the output of the attitude controller, rather than directly at the motor controls. This allows the Bode plot test signal to be superimposed on the control output after attitude stabilization is maintained, enabling frequency response measurement without compromising flight stability. The intermediary approach separates the test signal path from the critical attitude control path.
Solution Approach 2:
The control system is segmented into distinct functional blocks (attitude controller, rate controller, motor control) with the Bode plot injection point strategically placed at the attitude controller output. This segmentation allows independent testing of the attitude control loop while the rate and motor control loops continue to maintain stability, enabling safe data collection.
2Measurement precision
If manual control is disabled to apply Bode plot generation input signal, then control system response can be measured, but position control is lost and UAV may crash into obstacles
Solution Approach 1:
The patent uses the attitude controller output as an intermediary injection point that allows Bode plot testing while maintaining position control through the rate controller and motor control loops. This approach enables measurement of control system response without disabling position control, preventing crashes into obstacles.
3Reliability
If feedback loops are engaged to maintain stability, then UAV can fly safely, but Bode plot generation input signal cannot be applied directly to controls
Solution Approach 1:
The patent places the Bode plot test signal injection at the attitude controller output, which serves as an intermediary point where the test signal can be added without interfering with the feedback loops that maintain flight safety. This enables Bode plot data collection while feedback loops remain engaged for stability.
Solution Approach 2:
The patent applies the Bode plot test signal locally at the attitude controller output rather than globally at the motor controls. This localized approach allows frequency response measurement of the attitude control loop while leaving other control loops unchanged and maintaining overall system stability.
4Measurement precision
If Bode plot test signal is applied to multirotor UAV controls, then frequency response can be measured, but UAV flips over and crashes due to inherent instability
Solution Approach 1:
The patent uses the attitude controller output as an intermediary injection point that allows frequency response measurement while the rate controller and motor control loops maintain flight stability. This prevents multirotor UAVs from flipping over and crashing during testing.
Solution Approach 2:
The patent applies the Bode plot test signal locally to the attitude control loop output, enabling frequency response measurement of that specific loop while leaving the rate and motor control loops unchanged to maintain overall flight stability.
Data Source
AI summary
A method for collecting information required for Bode plot creation of a UAV (Unmanned Aerial Vehicle) autopilot system is provided. The method comprises: creating a Bode plot generation input signal: adding the Bode plot generation input signal to control inputs; collecting data from multiple points within the control system; calculating magnitude and phase at the multiple points using the data collected; recording the magnitude and phase for the multiple points in a datalog; comparing the magnitude and phase for the multiple points to calculate the gain and phase margins for open loop responses in the control system; creating a Bode plot for at least one of the following: i) a closed loop response of the attitude and/or rate loops, ii) an open loop response of the attitude and/or rate loops and iii) a response of the UAV; and outputting the Bode plot.