P13231: UAV Ground Station
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Detailed Design

Table of Contents

Feasibility

The feasibility of our proposed solution is demonstrated in this section on a component-by-component basis. A portion of the design process is selecting the correct COTS products. For this, feasibility can be demonstrated through research and gathering information on the chosen components. For systems that are not available commercially off-the-shelf, appropriate engineering analysis is used to demonstrate the feasibility.

RC Aircraft

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Figure DD.1.1.1 (Click to enlarge) Image Credit: diydrones.com



Below is the plot of lift dependent on airspeed at various small angles of attack for the chosen aircraft. It is assumed that small angles have a linear correlation with the coefficient of lift. Airfoil was assumed to be a "plain airfoil." This gives an approximate load capacity of the aircraft, which was estimated to be 3 pounds or under.

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Figure DD.1.1.2 (Click to enlarge)

ArduPilot

A hardware-in-the-loop (HIL) simulation was performed on ArduPilot in order to verify that the system was working. By using the X-Plane Flight Simulator software, the main board was simulated with mathematical models of the GPS and the RC aircraft. This information was fed into ArduPilot via the GUI software called MissionPlanner. ArduPilot would then be able to control and fly the aircraft. Below is an image of the interactions between the components:

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Figure DD.1.2.1 (Click to enlarge)

Two simulations were run within X-Plane with ArduPilot in order to verify that MissionPlanner and X-Plane were exchanging information properly. From the screenshots below, the right program is X-Plane and the left program is MissionPlanner which show consistent parameters.

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Figure DD.1.2.2 (Click to enlarge)

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Figure DD.1.2.3 (Click to enlarge)

MissionPlanner is capable of logging all the data that is received from the ArduPilot board. Then, the software will store all the data in a telemetry log file where it will be able to replay the run, simulated or actual flight. The parameter data can be exported into a text, comma separated value (CSV), or graph file. The following is a link to an example CSV file from one of the simulations: Simulation Data

Video System

A cost and capability analysis was performed for the different options for a first person point of view (FPV) video system. The CN/P 26 camera was selected as the most feasible solution as the high definition Keychain #16 may require a more expensive transmitter and receiver to provide a real time feed with little lag. The FPV goggles were ruled out as they are too expensive for the needs of this project, the goggles may be implemented in the future.

Excel spreadsheet: Video System Analysis

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Figure DD.1.3.1 (Click to enlarge) Image Credit: diydrones.com
CMOS CN/P 26 camera ~ $31.95

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Figure DD.1.3.2 (Click to enlarge) Image Credit: diydrones.com
Transmitter for video feed. Included with receiver shown below in DD.1.2.3.

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Figure DD.1.3.3 (Click to enlarge) Image Credit: diydrones.com
Receiver and cables included with Tx/Rx kit ~ $189.99

Imaging System

The ideal imaging system utilizes a lightweight camera capable of capturing still images. Higher resolution (> 3Mp) is desirable to spark interest when displaying the project at the Imagine RIT festival.

Option #1:Mini HD camcorder, model #: YT-8001

Figure DD.1.2 shows the potential camera. This camcorder boasts 12Mp still image capabilities. It ships from mainland China and costs $29.00 excluded shipping and handling. Cost does not include microSD card needed for storing images. The camera claims a battery life of 1 hour, and can be recharge by provided USB charging cable. Click the link for PDF of user's manual for review: YT-8001 User's Manual

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Figure DD.1.4.1 (Click to enlarge) Image Credit: k-ding.cn

Option #2:Mini Smile Face button camcorder

Figure DD.1.3 shows the smile face button camera. This camera can capture still images at a resolution of 3Mp. It ships from the US and costs $60.00 excluded shipping and handling. Again, cost does not include microSD card required for storing images. Camera is charged via USB charging cable.

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Figure DD.1.4.2 (Click to enlarge) Image Credit: internetsiao.com

Option #3:Keychain Camera #18

Figure DD.1.4 shows the Keychain #18 camera. This camera captures still images at a resolution of 3Mp. Its price ranges between $27 and $50 and is sold from various eBay venders. More information about the keychain #18 camera can be found here

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Figure DD.1.4.3 (Click to enlarge) Image Credit: eletech086

Camera Trigger Option #1:NMOS pass transistor

The NMOS pass transistor will act like a short when a 'high' input is applied to the gate and an open circuit when a "low" signal is applied to the input of the gate. Figure DD.1.4.5 shows this configuration being used to emulate a button press to take a picture.

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Figure DD.1.4.5 (Click to enlarge)

Drawings, Schematics, Flow Charts, Simulations

Mechanical

Approximate dimensions for critical parts of the airplane are shown in figure DD.2.1.1 and DD.2.1.2 below.


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Figure DD.2.1.1 (Click to enlarge)
Dimensional drawing; viewed from underside of plane.


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Figure DD.2.1.2 (Click to enlarge)
Dimensional drawing; viewed from side of plane. Red dimension is the location of the hole that the cable for the rudder fault will exit through.


The following CAD drawings show the placement of ArduPilot within the aircraft fuselage. The drawings also depict the faults to be implemented on the aircraft.

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Figure DD.2.1.3 (Click to enlarge)


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Figure DD.2.1.4 (Click to enlarge)


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Figure DD.2.1.5 (Click to enlarge)


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Figure DD.2.1.6 (Click to enlarge)


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Figure DD.2.1.7 (Click to enlarge)


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Figure DD.2.1.8 (Click to enlarge)


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Figure DD.2.1.9 (Click to enlarge)

Electrical Systems

The electrical system consists are an array of interconnected components as detailed in Figure DD.2.2.1. All power is delivered from the main 11.1 V battery. The ArduPilot power module contains a 5 V regulated output which is used to power the RC receiver as well as the electronics on board the ArduPilot itself. The planes Electronic Speed Control (ESC) module also has a 5 V regulated output which is connected to the ArduPilot PWM outputs, which are isolated from the power rails of the rest of the board through the disconnection of jumper JP1. This allows the planes servos to be powered from an isolated power supply, improving current delivery and reducing noise in the sensitive ArduPilot electronics and sensors. Besides power distribution, PWM signals are routed into the ArduPilot from the RC receiver and back out to the flight servos. This allows ArduPilot to pass along or intercept the PWM servo control signals. Additional PWM outputs are also connected to fault servos. These servos will be controlled in software to initiate the different mechanical plane faults. Analog to Digital Converters (ADC) are also utilized for additional accelerometer and airspeed sensors. The remaining General Purpose Input/Output (GPIO) pins are used for triggering or detecting additional faults. Finally, GPS and telemetry are digitally interfaced with the ArduPilot.

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Figure DD.2.2.1 (Click to enlarge)

Sensors

Three additional accelerometers are to be placed in the plane, one in each wingtip and one in the tail. The intent of these accelerometers is to capture a signature indicating a fault has occurred. The boards in Figure DD.2.3.1 are 5 V tolerant, carrying an onboard 3.3 V LDO regulator, however their analog output is ratiometric within the 3.3 V supply. Due to a fixed 5 V reference voltage being used on the ArduPilot ADC, an OpAmp gain stage will be employed to step the signal up to the full 5 V range. This ensures the full 10-bit resolution of the ADC is utilized.

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Figure DD.2.3.1 (Click to enlarge)

Data Logging

All data logging performed by the stock ArduPilot setup is left as-is. This includes facilities for real-time transmission of in-flight data to the MissionPlanner base station as well as on-board storage in a 16 Mbit (2 MB) data flash.

Additional logging facilities will be created to interface with the 9 channels of analog accelerometer data being read by the ADC. Logging will be performed at a rate of at least 50 Hz, satisfying the Nyquist Criterion for detecting vibration or movement up to 25 Hz. Storage of the samples on the on-board data flash is available along with real-time transmission to the MissionPlanner base station over the planes telemetry radio link. This logging rate will generate about 270 kbits of data per minute, allowing up to an hour of logging to be performed, assuming no other sensors are being logged simultaneously. Depending on available CPU time on the ArduPilot, higher data logging rates may also be possible, further raising the maximum frequency that can be measured.

Servo Fault Circuit

A servo fault can be induced by disconnecting the power connection using a relay. Figure DD.2.5.1 details the circuit used to drive the relay coil using a GPIO pin on the ArduPilot microcontroller.

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Figure DD.2.5.1 (Click to enlarge)

Bill of Material (BOM)

An Excel spreadsheet has been generated tabulating the material/component costs expected to complete the project. Major components are listed. Wiring, resistors, and other components for circuit fabrication are not individually listed and are instead lumped into one category with an estimated cost. Figure DD.3.1.1 is a snapshot of the BOM at the time of the detailed design review.

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Figure DD.3.1.1 (Click to enlarge)

To download and view the Excel spreadsheet version of the BOM, click the following link: P13231 BOM

Test Plans

Testing procedures for the systems and sub-systems of the UAV and ground station are described in the following document. Logistics, data collection methods, and data analysis techniques are outlined.

UAV and Ground-station Test Plan

Risk Assessment

During the detailed design process, project risks were re-assessed and added to. By this point in the design process, some risks have already been addressed (such as RC aircraft cargo space concerns and meeting project deadlines). Figure DD.5.1.1 is the list of risks generated during the systems design phase with additional risks that came up during the detailed design phase added at the bottom of the list.

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Figure DD.5.1.1 (Click to enlarge)

Detailed Design Review

The MSD I detailed design review was held on Friday, February 8, 2013 on the RIT campus. To view a copy of the presentation, click on the link below.

DDR Notes & Action Items

The following items were discussed during the DDR and require further action.

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