P14231: UAV Aerial Imaging
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Sub Systems Design

Table of Contents

Mechanical Engineering Analysis

Since the scope of our project focused primarily on electronic and imaging system integration, and did not include designing a custom aircraft, there was little engineering design work done. Most of the following work details our selection criteria and process for our aircraft, and a basic explanation of how aircraft balance (Center of Gravity) is calculated and why it is important for flight.

Airframe Selection

Multiple commercially available Radio Control model aircraft were considered for the purpose of carrying our imaging equipment aloft. Our primary concerns were lifting capacity - how much payload weight the aircraft could carry, and internal volume. We elected from the outset to make every attempt to avoid mounting our electronics and camera externally on the aircraft. Doing so can seriously impact the aerodynamic qualities of an aircraft, and can lead to more severe component damage in the event of a crash. However, it soon became clear that most commercially available radio control aircraft are not designed to carry any internal payload beyond the basic components required for flight. We researched into a specific and emerging field of RC flying known as "First Person View" or "FPV" flying, where a video camera and transmission system provides a pilot's seat view from the model aircraft for the pilot on the ground. These aircraft typically are selected by hobbyists by trial and error, and certain models have become very popular for their flight characteristics and payload capacity.

A few notes about our selection information:

Existing Aircraft: Nexstar EP

Hobbico Nexstar EP

Hobbico Nexstar EP

A previous project team, P13231, purchased a Hobbico Nexstar EP trainer aircraft to carry their equipment. However, this aircraft had been seriously damaged when we inherited it. It had also been specifically modified for purposes outside the scope of our project.

Quick Specs:

Benefits:

Drawbacks:

Option 1: Telemaster 40 Kit/ARF

Hobby-Lobby Telemaster 40

Hobby-Lobby Telemaster 40

Hobby-Lobby Telemaster 40 ARF kit

Hobby-Lobby Telemaster 40 ARF kit

The Telemaster 40 was an obvious first candidate for a replacement aircraft. With significantly more wing area and a more robust power system, it would be able to handle any reasonable load we would be required to carry within the scope of this project. It retained the "trainer - style" high wing configuration of the existing aircraft, which is inherently stable and easier to fly. It is available from Hobby-Lobby, in two forms - a standard kit and an "Almost Ready to Fly" (ARF) kit. The standard kit would allow us to build the aircraft from scratch, and in the process build in any modifications our payload might require. The ARF would cut down on basic build time but would force us to modify the already constructed and covered aircraft components for our use. The Telemaster 40 kit is available here, and the Telemaster 40 ARF is available here.

Quick Specs:

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Additional Cost Estimate:

Option 2: Alpha 450 ARF/PNP

E-Flite Alpha 450 Sport Trainer

E-Flite Alpha 450 Sport Trainer

The E-Flite RC Alpha 450 sport trainer is an aircraft similar to the existing Hobbico Nexstar, but with a few advantages. It shares rough dimensional similarity with the Nexstar but features a larger wing and a better power system. The construction of the aircraft is of higher quality and is lighter weight. The Alpha 450 has similar internal volume, but is less cramped on the inside, allowing for easier modification. The stock motor features a lower 'kv' rating - meaning it can turn a larger, more aggressive pitch propeller, allowing this aircraft to produce significantly more thrust than the Nexstar. The Alpha 450 is available as an "Almost Ready to Fly" (ARF) or "Plug and Play" (PNP, Also known as "Plug and Fly," PNF) kit. PNP/PNF aircraft typically only require a receiver, and all other electronics are pre-installed, significantly reducing construction time. The Alpha 450 ARF is available here, and the PNP version is available here.

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Additional Cost Estimate:

Option 3: Mystique 2.9 ARF

E-Flite Mystique electric powered sailplane

E-Flite Mystique electric powered sailplane

Our Pugh analysis of different aircraft styles done during our System Design phase indicated that a sailplane - style aircraft would provide a superior platform for aerial imaging, with large amounts of lift, high aerodynamic efficiency and could be easily hand launched. However, it quickly became clear that most commercially available RC sailplanes lack internal volume, and the Mystique is no exception. Despite having enough lift and power to do what we want, and featuring high quality construction, simply did not have enough internal space to mount our electronics or cameras. The beautiful E-Flite Mystique is available as an ARF kit here.

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Additional Cost Estimate:

Option 4: Radian RTF/Radian Pro BNF

Parkzone Radian electric powered sailplane

Parkzone Radian electric powered sailplane

Parkzone Radian Pro electric powered sailplane

Parkzone Radian Pro electric powered sailplane

Our Pugh analysis of different aircraft styles done during our System Design phase indicated that a sailplane - style aircraft would provide a superior platform for aerial imaging, with large amounts of lift, high aerodynamic efficiency and could be easily hand launched. Both of these aircraft are popular among RC enthusiasts in First Person View flying, and both have been proven capable of carrying equipment similar to what we will be implementing. However, like the E-Flite Mystique, both of these aircraft suffer from a lack of internal space. The Radian is a "trainer" sailplane, and features only rudder and elevator control (hence the curved wings), while the Radian Pro features full aileron control. The Radian Pro is available as a "Bind - 'N - Fly" (BNF) (only a compatible Spektrum brand radio transmitter is required) package here. Since the Radian is marketed as a trainer aircraft, it comes only in a "Ready - To - Fly" (RTF) configuration, available here.

Quick Specs:

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Drawbacks:

Additional Cost Estimate:

Option 5: Phoenix 2000

Phoenix 2000 electric powered sailplane

Phoenix 2000 electric powered sailplane

Our Pugh analysis of different aircraft styles done during our System Design phase indicated that a sailplane - style aircraft would provide a superior platform for aerial imaging, with large amounts of lift, high aerodynamic efficiency and could be easily hand launched. The Phoenix 2000 is an inexpensive electric glider platform that meets these requirements. Unlike the Radian Pro or the Mystique, the Phoenix appears to have enough internal space to mount the GoPro camera, or at minimum our extra electronics. It is used by some First Person View flying enthusiasts, carrying similar equipment to the Radian or Radian Pro. However, reports of shoddy manufacturing and stock electrical components make this aircraft a bit of a gamble. Another issue was the prospect of drilling a camera lens hole in the fuselage, which is made out of "blow moulded nylon." An article on machining nylon materials is available here, the process is similar to working with moulded fiberglass. The Phoenix 2000 is available from as an "Plug & Fly" (PNF/PNP) package here, and as an ARF (no electronics) here.

Quick Specs:

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Additional Cost Estimate:

Option 6: Penguin

Finwing Hobby Universeye Penguin FPV aircraft

Finwing Hobby Universeye Penguin FPV aircraft

During our aircraft selection process, we created an account on the popular Radio Control modelers' web forum RCGroups. We posted our requirements and asked other modelers' opinion of our proposed aircraft and if they had any suggestions. One suggestion that we received was the Finwing Universeye Penguin, an aircraft designed specifically for First Person View flying and aerial photography. Based on photos on other forums, we determined that the aircraft would have enough space for either our GoPro or our multispectrum camera system. Since our other top choices - the Alpha 450 and the Phoenix 2000 - did not have enough internal volume, the Penguin seemed to be a perfect alternative. Research into reviews on this aircraft revealed that while it was a decent airplane, its enormous canopy, designed for protecting an FPV camera system, caused some undesirable handling characteristics. This can be easily corrected by not flying with the canopy attached; the aircraft will fly just fine without it. The Penguin is available in many different packages here.

Quick Specs:

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Additional Cost Estimate:

Conclusion and Final Selection

Eventually, we narrowed our field of candidate aircraft down to the Alpha 450, Phoenix 2000 and Penguin. The Nexstar was not included because it was deemed too heavily damaged to be seriously used. The Alpha 450 was regarded as a superior base solution, and was used as a datum to compare the other aircraft in the Pugh chart below.
Criteria Alpha 450 RTF (DATUM) Penguin ARF Phoenix 2000 ARF Penguin ARF w/ motor & ESC Phoenix 2000 PNP
Lifting Capacity Datum + + + +
Internal Volume Datum + - + -
Modifiability (ease of modification) Datum - - - -
Initial Cost (+ is cheaper) Datum + + + +
Ability to Carry Either Camera (GoPro or Multispectrum) Datum + 0 + +
Out-of-box Build Quality Datum - - - -
Ruggedness Datum + 0 + 0
Flight Time Datum + + + +
Extendability (future use) Datum + - + -
Ease of Piloting Datum + - + -
Spare Part Availability Datum 0 - 0 -
Spare Part Cost (+ is lower) Datum + N/A + N/A
Additional Part Requirements Datum - - - -
Customization/Configurability Datum + + - 0
RC Community Recommendation Datum + + + +
Total Plus ~ 11 5 9 4
Total Minus ~ 3 7 4 7

Following this analysis, it was clear that the Penguin aircraft was the best solution for our needs.

Previously, our System Design process demonstrated that a sailplane-style aircraft would provide the most efficient platform for our aerial imaging suite. However, costs for sailplanes more capable than the Phoenix 2000 quickly rose into the thousands of dollars for the airframes alone, and were eliminated on a basis of cost, not capability. Should this imaging suite be put into actual commercial usage, a custom designed airframe in a sailplane style is recommended. It should be noted that the Penguin is not a sailplane-style aircraft. However, at this stage in the project the flexibility of the Penguin as a platform for our imaging equipment outweighs its inherent aerodynamic inefficiencies.

Weights and Balances

Aircraft CG diagram, courtesy of NASA

Aircraft CG diagram, courtesy of NASA

Another CG Diagram

Another CG Diagram

To ensure minimal effect on the aircraft's handling, it is important to locate the center of gravity (CG) of the aircraft within the aircraft's operating range. The operating range of the CG is different for every aircraft. Model aircraft typically come with a user manual that will include information regarding the CG range. Custom designed aircraft should be designed with CG location in mind.

CG Location Importance:

CG Validation Methods:

  1. Analytically, with calculations and schematics
  2. Experimentally, by balancing the airframe
  3. Procedurally, by following the aircraft instructions and standard operating proceedure

Weights & Balances Spreadsheet:

Full-size Aircraft vs. Model Aircraft:

Electrical Engineering Analysis

Camera Exposure

The Gopro hero three silver addition has a bus port on the back which is used by the Gopro to support hardware additions such as screens and batteries. This implies that it should be possible to at the very least trigger an image capture through this port. In addition it should be possible to obtain images as well as stream video and possibly sound through this same port. The pin out for this port is as follows according to research on forums. (This pin out is not confirmed as of yet)

Pin Out

The most promising avenue to trigger an image capture is by using the pin 12 and programmatically shorting this to ground. The schematics to be attempted to do this are :

Basic Functionality Schematic

Image:/public/Subsystem Design/assets/Gopro_Basic_Schematic.png

Advanced Functionality Schematic

Image:/public/Subsystem Design/assets/Go_Pro_Schematic_Adv.jpg

In order to have the camera recognize the external hardware, the hardware will need an EEPROM with is first memory location set to 9. This is a basic I2C check that the camera software does to ensure that what is connected is a valid attachment.

The breakout board that has been selected to expose the pins is:

Image:/public/Subsystem Design/assets/GoPro_Breakout_Board_wip_2.png

To realize these designs the following will be needed:

A more detailed explaination can be found: GoPro Exposure

Communications

In order to get the autopilot and ground station to communicate nicely, it is necessary to get a radio that can achieve meet all the requirements for a successful flight. These include, but are not limited to:

Radio option:

Image:/public/Subsystem Design/assets/3DR Radio Telemetry Kit.jpg

Quick Specs

Range booster:

Image:/public/Subsystem Design/assets/3DR Signal Booster.png

Quick Specs

Computer Engineering Analysis

Auto Pilot Interfacing

Hurdles

Interfacing Code

With the old Arduino system turning a pin out required the following code snippet:

digitialWrite(pin, val);

With the new system this translates to:

hal.gpio->write(pin, val);

Using this code snippet we would be able to activate a pin instructing the camera to activate.

Looking Ahead

A suitable auxiliary pin's digital identity needs to be located. Once this is found a test can be made to activate the camera on command. Afterwards a ground test with gps waypoints can be tested, verifying that the camera can be activated once a waypoint has been reached.

Telemetry & GPS Retrieval

Image:/public/Subsystem Design/assets/telem_uml.png Image:/public/Subsystem Design/assets/gps_uml.png

The ahrs struct contains the telemetry data and the gps_raw contains the gps data required for each photograph. Once the camera is triggered, these structs will need to be accessed and the data will have to be saved in chronological order. Every access will need to be thread safe as to not cause any race conditions.

Subsystems Design Presentation

Subsystems Design Review


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