FeasibilityThe 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.
- To be a feasible solution, the selected aircraft must be large enough to house ArduPilot within the fuselage. Figure DD.1.1 shows our selected aircraft (the Nexstar Mini EP) with the ArduPilot board installed. This verifies that integrating the Mini EP with ArduPilot is feasible.
- The aircraft is constructed of balsa wood which is advantage over foam construction when making modifications and implementing the seeded faults.
- Aircraft wingspan = 3.7ft which meets the specification that the wingspan be < 5ft. It is also contains an electric power plant.
- The ailerons are independently controlled which allows an aileron failure to be initiated while the aircraft is in flight.
- Total cost for Ready-to-Fly version (w/ shipping): $170.00
- To view the user's manual for the Nexstar Mini EP in PDF format, click the following link: Mini EP User's Manual
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.
ArduPilotA 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:
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.
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
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
Figure DD.1.3.1 (Click to enlarge) Image Credit: diydrones.com
CMOS CN/P 26 camera ~ $31.95
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.
Figure DD.1.3.3 (Click to enlarge) Image Credit: diydrones.com
Receiver and cables included with Tx/Rx kit ~ $189.99
Imaging SystemThe 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
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.
Option #3:Keychain Camera #18Figure 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
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.
Drawings, Schematics, Flow Charts, Simulations
MechanicalApproximate dimensions for critical parts of the airplane are shown in figure DD.2.1.1 and DD.2.1.2 below.
Figure DD.2.1.1 (Click to enlarge)
Dimensional drawing; viewed from underside of plane.
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.
- Figure DD.2.1.3 shows a hidden line model with locations of ArduPilot and aileron relay.
- Hidden line model in Figure DD.2.1.4 shows the locations of ArduPilot and aileron relay.
- Figure DD.2.1.5 is a top view of the RC aircraft airframe with locations of ArduPilot and aileron relay.
- Cross-section of model with locations of ArduPilot and aileron relay is shown in ''Figure DD.2.1.6.
- Figure DD.2.1.7 shows the modified rudder with approximate location of guide wire to initiate fault. The rudder failure will be initiated by using a servo to pull a pin connecting the upper and lower rudder sections. This will allow the upper rudder portion to act as a free rudder.
- Figure DD.2.1.8 shows the proposed design of door for wing fault. A servo will keep the spring loaded door closed via the latching mechanism shown. The red cable shows the location of a wire which will cross the door, making an electrical connection with the airframe. This broken connection will indicate a fault has occurred. Once released, the door will spring down into the airstream (oriented such that the airstream pushes the door towards the closed position).
- The location of the wing section failure is shown in Figure DD.2.1.9. It is located on the underside of the wing. Door will drop down mid flight to simulate a hole in the wing.
Electrical SystemsThe 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.
SensorsThree 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.
Data LoggingAll 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 CircuitA 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.
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.
To download and view the Excel spreadsheet version of the BOM, click the following link: P13231 BOM
Test PlansTesting 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.
Risk AssessmentDuring 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.
Detailed Design ReviewThe 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 Presentation (PDF form)
DDR Notes & Action ItemsThe following items were discussed during the DDR and require further action.
- Add flight data logging to project goals
- Ensure design keeps CG at the 1/4 chord location
- Generate a UML flowchart
- Order PPM cables for simulations
- Check into possibility of simulating with a custom plane
- Investigate the possibility to avoid storing debugging file
- Plan for accelerometer testing on newly acquired shaker table
- For rudder fault, watch for sensor travel issues
- Electro-magnetic actuation for rudder fault?
- For aileron failure relay, make sure it is isolated from analog
- Use opto-coupler for aileron failure?
- Investigate need for second battery for video system power (could be too heavy)
- Get sample image from for HD mini camcorder
- If needed, can spend up to $200 dollars on still image sytem
- Fabricate PCB for imaging system to allow for easy plug-and-play in different aircraft
- Is servo position stored?
- Create flow diagram to accompany the system integration chart
- Note total budget = $2500 (intend to spend less to allow for future projects)
- Sign up for Imagine RIT
- Allot enough time for calibrating sensors
- Build breadboard circuits early for testing purposes
- Allot time in schedule for servo calibration
- Plan weekly Friday updates to take place during MSD II