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Sep 30 2010

Autonomous EasyStar (Oh the Possibilities)

Although the Hexakopter has been performing flawlessly over the past few weeks, knock on wood; the Ecosynth team is still searching for a less expensive alternative for gathering aerial photographs. As of now, the only way to do this consistently and reliably is through the use of autonomous technology. Throughout this semester I have decided to convert the EasyStar platform into an inexpensive yet fully autonomous airplane.

One of the most significant advantages of this platform will be its ability to fly long distances without having any range limitations. This feature will enable us to fly an entire site without having to plan multiple flight patterns or plan around the “home” position of the aircraft. In addition to this, the open source code will enable us to adjust the flight characteristics and create subroutines of our own that will enhance the airplane’s usability and effectiveness. 

The primary objectives for this project are as follows:

  1. -  Create an autonomous airplane for under $400 (US)
  2. -  Capable of carrying a standard digital camera
  3. -  Utilize GPS technology to allow for multiple 3D waypoint navigation
  4. -  Maintain safe and stable autonomous flights in winds up to 10mph
  5. -  Provide continuous flight for approximately 15 minutes
  6. -  Relay the planes geographic position, altitude and airspeed to a field computer
  7. -  Return to home on request and sustain a holding pattern

 

If I somehow manage to complete all of the primary objectives with time to spare then I will begin to work on the slightly more interesting secondary objectives:

  • -  Ability to take off and land autonomously in large fields 
  • -  Autonomous parachute deployment at a specified position and altitude to assist with landing in small fields
  • -  Use IR sensors to provide obstacle avoidance capabilities
  • Over the past week I’ve been researching the various autopilot systems available online. One of the most promising options is the ArduPilot from DIY Drones. The main advantage of this system is its use of open source code which can be modified to accommodate any airplane with three or more channels. The ArduPilot is also capable of controlling additional channels to support optional tasks, such as parachute deployment. In addition, the ArduPilot is capable of performing 3D waypoint navigation and two-way telemetry data transfer via the optional XBee modules. DIY Drones provides a free point and click style mission planner that enables users to easily create and upload 3D waypoints to the airplane (as illustrated in the figure above). The components required to use the ArduPilot include the following: 
  • ArduPilot Board                                24.95
  • Shield V2 kit w/ Airspeed Sensor       57.20
  • Breakaway header                              2.50
  • U-Blox5 GPS                                   87.90
  • U-Blox Adapter                                19.50
  • U-Blox Cable                                   1.95
  • X, Y and Z Sensors                           99.90
  • Female-to-female RC cables (x4)       1.50 per
  •  
  • The parts required for wireless telemetry are as follows:
  • Air XBee                                            42.95
  • Ground XBee                                      44.95
  • XBee Antenna                                  7.95
  • Adafruit adapter board                      10.00
  • XBee Explorer USB                          24.95

The total cost of the ArduPilot system, without wireless telemetry; is around $299.90 (US). The wireless telemetry brings the total cost to $430.70. Throughout the upcoming week I will continue to look for ways of reducing the cost of this system. If we decide to use the ground XBee, XBee Explorer USB and XBee Antenna included with the Hexakopter then the total cost could be reduced to $352.85, which is still a significant investment.

The EasyStar itself is a relatively inexpensive plane; an almost ready to fly (ARF) version can be purchased for around $120. Our prior experience with the EasyStar has led us to believe that the stock motor and ESC should be upgraded to a 400 speed brushless in-runner motor and brushless 25A ESC. In addition to this, the tail rudder should be extended by 1.5 in. to allow for a tighter turning radius. Over the next few weeks I’ll be creating a page which will contain all of the modifications made to our EasyStar as well as their overall effectiveness.

You can download the Arduino software here and the waypoint configuration tool here, both of which are free. The latest version of the autopilot code can be found here. I will be sure to post more blogs about the ArduPilot system as I continue to familiarize myself with its tools and capabilities.     


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