Submission Format for IMS2004 (Title in 18-point Times font)



Advanced Remote Monitoring and Operated Reconnaissance Device (ARMORD)

Thomas Kehr, Andrew Lichenstein, Kevin Jadunandan

School of Electrical Engineering and Computer Science, University of Central Florida, Orlando, Florida, 32816-2450

Abstract — Unmanned ground vehicles are quickly becoming the first line of defense for US troops in conflicts around the world. Whether it’s disposing of unexploded ordinance, clearing buildings, or checking for IED’s, the military is quickly turning to robots to perform tasks deemed too dangerous for soldiers to engage in. There are currently more than 12,000 of these types of units being fielded by the US military and this number is projected to double in a matter of two-years. This increase in units outs a strain on the defense budget, as the average cost of an unmanned robotic vehicle is in the realm of $40K along with annual repair and maintenance costs. It was thereby taken upon us to develop a similar system, with identical capabilities, at only a fraction of the cost.

Utilizing cost-effective technologies and fabrication techniques, we were able to provide an extremely durable and reliable device capable of traversing a variety of terrains and collecting reconnaissance. In an effort to reduce training time, we have enabled full control of our device by means of an Apple iPhone or iTouch device. This gives soldiers a familiar platform that they feel comfortable with and allows them to spend more time pursuing more important duties.

Index Terms — Unmanned vehicle, remote control, iPhone, Zigbee, military

I. Introduction

The goal of this project was to develop an inexpensive, yet durable, un-manned ground based vehicle with similar characteristics and capabilities as those found being deployed currently by law-enforcement agencies and military units across the world. By using cost effective development practices and commercial off-the-shelf (COTS) products, we were able to develop the ARMORD system for under $3,000. While not as highly refined as some of the commercially available models, the ARMORD system delivers capabilities on par with most other units, such as video transmission, wireless control, GPS location, and exceptional durability. We have also implemented a state-of-the-art control system that utilizes the Apple iPhone/iTouch as a method of vehicle operation.

We decided from the beginning of this project we would not have a set leader, but would all take equal responsibility in the organization and completion of the project. We all knew what had to be done in order to complete our project and accompanying documentation. We scheduled weekly meetings in order to discuss updates with each section being worked on; this insured we were all on the same page with the project. Another way that we managed the project was by dividing it up into smaller pieces that each person could individually manage. Figure XX illustrates how the software and computer hardware was divided, and Figure XX has the electronic and chassis construction breakdown of the project. When splitting up the project, we looked at who had experience in certain systems and what people’s interests were. We knew that by allowing people to work on segments that they enjoyed more than they would be more enthusiastic with the project, which would result in a better system design and project outcome.

The paper is broken down into sections corresponding to the various sub-systems of ARMORD. Each section will discuss the design of that system as well as give some background information on why we chose to implement a certain component or element of design.

II. ENCLOSURE

We will start looking at ARMORD from the outside going in. The body is important to our system as it is the first line of defense against impact, debris, and the elements; simply put it is the armor of ARMORD. It would be easy to just build a box to encase our frame, but we needed to accommodate cameras, ventilation, antennas, etc. We also had to address the more basic functions, such as accommodating for wheel clearance and meeting height restrictions. In designing the enclosure, it was also important to design an efficient system to remove the enclosure in order to make repairs and charge batteries.

The enclosure was formed by creating a mold out of several layers of extruded polystyrene layered on top of each other. We then covered this in several layers of fiberglass matt and resin. Once the fiberglass set, we cut the mold in half and released and obtained the two halves of our enclosure. Once we had the initial enclosure pieces we could begin to make modifications for the peripherals and extremities of the system. Small holes were cut to accommodate the motor shafts for attaching the wheels and camera. The opening we cut for the camera hole was then fitted with 1/8” piece of Lexan (Plexiglass) and sealed with weather stripping to protect from the elements. The enclosure was then fitted with weather stripping along its perimeter to prevent debris and water from entering the vehicle.

For added strength we applied several layers of polyurea, truck bed liner, to the outside of our enclosure. This compound is extremely durability and has even been known to have certain ballistic and explosive resistant properties. We then gave the enclosure several coats of Army approved Olive Drab paint and a generous amount of clear coat to prevent abrasion.

[pic]

Figure 1 - Damage Sustained to Polyurea from Large Grade Explosives

Fiberglass was chosen as our enclosure material because it has a low price relative to its strength. Fiberglass is also easily layered, thus increasing its durability. We also found that fiberglass is permeable to all radio signals; making it the perfect medium for enclosing wireless communication infrastructure.

III. Chassis and Drive Train

Every part of ARMORD’s drive train and chassis has been custom built and designed by our group. ARMORD utilizes a four-wheel drive design and is propelled by four heavy duty IG42 geared DC motors. These motors provide 252 rpm’s of speed and approximately 10 kgf-cm or torque. The motors will then be connected via custom wheel shafts to 4 all-terrain 10-inch wheels. Based on our wheel size and motor speed we are able to calculate the maximum no-load speed of ARMORD as seen in the following equation.

Speed (fpm) = (Diameter of wheel (in) x π x rpm of motor) /12 = (10” x π x 252) /12 = 659.7 fpm = 7.59 mph

[pic]

Figure XX - IG42P DC Geared Motor

By our estimates, the wheels and axel are going to take the brunt of the impact from drops, thus it was important to design a reliable suspension system to stand up to the forces expected. ARMORD utilizes an original and custom suspension system to absorb impacts and protect the motors. The suspension system consists of large gauge wire clamps supported by springs surrounding smooth shaft hex bolts. This system is then sandwiched between 1/8” aluminum to provide the necessary compression in the springs. It was also important to make sure that there was no metal on metal contact in the suspension in an effort to cut down on friction and vibration.

[pic]

Figure XX - Custom Motor Suspension

Aluminum was chosen as the primary material for our chassis material because of its affordability and light weight. Aluminum also proved to be a much better material for fabrication as it takes a considerably less effort to cut and drill then steel.

Suspension

In an effort to protect the electronics contained within our system, we have implemented a system to dampen the forces experienced by internal components. One method we have utilized to reduce vibration is using rubber washers at all places components are screwed into the frame.

We will also be implementing a secondary mounting system for smaller electronics and components. While not as dramatic as the previous method it will still provide appropriate levels of shock absorption. This mounting solution utilizes bolts surrounded by springs that are embedded into the top and bottom of the aluminum chassis to suspend the components. Figure XX illustrates this mounting solution. This solution can also be used to mount batteries, voltage regulators, and other secondary electronics.

[pic]

Figure XX – Concept for Mounting Components to ARMORD

IV. Power System

ARMORD will consist of two different power circuits; a 24V drive circuit and a 12V control circuit. The 24V drive circuit will consist of a single 4500 mAHr 24V NiMH battery. This battery will power the motor controller and the four DC geared motors. We estimate the battery life of this system of approximately 45 minutes based on a 2300mA current draw from 4 DC geared motors. The 12V control circuit will be comprised of a single 4000 mAHr 12V NiMH battery. The control battery will be powering all of our peripherals and control logic. Because we have components that are utilizing several different voltages, we will be required to implement voltage regulators to get the correct voltages to our components. Figure XX illustrates the method for connecting voltage regulators in our system. Based on a total current draw of 795 mA for this circuit, we estimate a battery life of approximately 5 hours for the control battery. Table XX shows the current draw of the control circuit broken up into the various components.

[pic]

Figure XX - Control Circuit Regulator Bank

|Component |Current |Operating |Power Consumption |

| |Draw |Voltage | |

|XBee Pro |55mA |3.3 V |0.18 Watts |

|Falcom FSA03 |40mA |3.3 V |0.132 Watts |

|PIC18F4520 |200mA |5 V |1 Watt |

|Mini-Wireless Camera |500mA |9 V |4.5 Watts |

|Total |795mA | |5.812 Watts |

Table XX - Distribution of Current Draw in Contol Circuit

In an attempt to reduce maintenance times of removing batteries for charging, the two batteries will be wired to a double-pole double-throw switch so that in the “On” position, the circuit will be powered as normal and in the “Off” position, the batteries will be connected to a military style power plug for easy charging via NiMH battery chargers. Figure XX illustrates this circuit.

[pic]

Figure XX - Schematic of Power Supply and Distribution

Cooling System

ARMORD will utilize total of four mini PC fans for its ventilation and cooling system, two intake and two outtake fans. Each fan is 12V and will be powered by the battery hooked to the control circuit. A separate switch will be included for independent control over the ventilation system, thus helping to save power during idle testing times where cooling is not required. Another benefit of independent ventilation control is the ability to more stealthfully navigate an environment; however the fan units for our design are rated for ultra quite operation. Figure XX illustrates the ventilation systems ability to cool internal electronics and motors.

Figure XX - Schematic of Power Supply and Distribution

V. Microcontroller

We chose to use the Microchip PIC18F microcontroller to be the brain of our robot. We came down to this selection due to the vast amount of features and experience we had using this chips. The microcontroller we used is installed on a standard printed circuit board using a 40 pin IC socket. We used the socket contact so that we don’t solder the microcontrollers’ pins directly to the printed circuit board; this is in case the microcontroller burns out or has other issues.

The main part after the microcontroller is connected to the board is powering the device. We need to connect a voltage source that is between 3.3 to 5 volts to the two VDD pins on our microcontroller and the MCLR pin to cause the microcontroller not to reset. We also need to connect the VSS pins to the ground in on our voltage source. You can’t just connect any power to the microcontroller due to the signal not being clean and it probably not being a constant voltage, which is not good for the microcontroller.

The process of cleaning up the signal is first, taking in our higher voltage, which we will say is 9 volts, and passing it through a filtering capacitor. Next we take our filtered signal and put it through a voltage regulator in order to knock down the voltage to what we want. Figure XX below shows the completed circuit for our power supply. The output voltage should be within 100 mV, which is acceptable. We also put bypass capacitors in between the VDD and VSS pins to remove the AC signal that sometimes can cause issues with microcontrollers.

[pic]

Fig. 1. Power Supply to Microcontroller

VI. Motor Controller

We could have bought just a normal H-Bridge to use as our motor controller but we decided against this because the movement of our robot is crucial. So we bought the Sabertooth motor controller to insure stability and reliability with our robot. The motor controller we purchased allows you to control the motors with analog voltage, radio control, serial, and packetized serial. The connections for the motors are very simple. We simply connect motor 1 to M1A and M1B terminals and motor 2 to M2A and M2B terminals. It also has two terminals to connect your battery maximum of up to 24V using terminals B+ and B-. The best feature of this motor controller is that it has regenerative braking. The way regenerative braking works is whenever our robot stops or brakes, the wasted energy is sent back to the battery giving us more battery life.

After you connected the motor controller to the motors, we then connect a wire from the S1 pin of the motor controller to an arbitrary pin on our microcontroller. This pin on the microcontroller will be emulating a hardware UART pin, by using software, which is known as bit-banging. We used simplified serial setting on the motor controller to send data between our microcontroller and the motor controller. When we send the char value of 1 to 127 we control the left motor and when we send the value of 128 to 255 we control the right motor. The value of 0 sends a command to stop the motors. The value of 1 is full reverse on the left and the value of the 127 is full forward on the left. The value of 128 is full reverse on the right and the value of 255 is full forward on the right. The figure below shows the setup of the motor controller to the microcontroller. The motor controller also has LED's to show the status of the motors at all times, in case of errors.

[pic]

VII. GPS System

The GPS system is used for locating our robot in case of a communication failure and for following it on a map application by gathering latitude and longitude from the device. The GPS unit we bought is the Falcom FSA03 unit; we purchased it with its own breakout board for ease of use. We connected our 3.3Volt source to the VCC pin of the break out board and our Ground to its GND pin. We then connected the TXL (transmit line) to our USART receive line. This will allow data to flow between both the microcontroller and the GPS unit seamlessly. For programming the GPS System we connected the RXL (receive line) to our USART transmit line. In addition to following the robot with GPS, we will gather acceleration data to measure speed to send back to the controller. Below is a string that is sent from the GPS to the microcontroller.

$GPGLL,4916.45,N,12311.12,W,225444,A,*1D

VIII. XBee Controller

We purchased the XBee Pro for our communication in between the microcontroller and the gateway, due the better features than the normal XBee. Figure XX shows the complete differences between the two XBee’s. The XBee Pro has an outside range (Line of Sight) of 1 mile and indoor range of 300 feet. We set up the XBee’s via serial communication from a Laptop using XCTU application give by the XBee manufacturers. We need two different controllers for our project, one for the robot and one for the gateway. The first controller was the XBee Explorer, which is a breakout board which allowed us to use on a breadboard for the microcontroller. The second controller was the XBee Explorer USB version that we connected to our gateway with onboard USB port be connected to our gateway.

|XBee Comparison Chart |

| |XBee |XBee Pro |

|Indoor Range |133 ft |300 ft |

|Outdoor Range |400 ft |1 mi |

|Transmit Power |1.25 mW |50 mW |

|RF Data Rate |250 Kbps |250 Kbps |

|Supply Voltage |2.1-3.6 VDC |3.0-3.4 VDC |

|Transmit Current |35 mA |294 mA |

|Receiver Current |38 mA |45 mA |

|Power Down Current |< l uA |< 10 uA |

|FCC Approved |YES |YES |

The XBee explorer is a great solution to be able to add wireless communication to a robot. The XBee explorer allows easy access to the pins needed to receive, send, and give power to the XBee module. The controller also has LED’s in order to show if the unit is powered and if it sending and receiving data. This controller allows you to input 5 volts and it will regulate it to the necessary 3.3 volts. The DOUT pin will be directly connected to the RX pin of the microcontroller and the DIN pin will be directly connected to the TX pin of our microcontroller.

VIV Microcontroller Packet Structure

The data sent from ARMORD to the iPhone, consists of latitude, longitude, motor battery life, microcontroller battery life, motor temperature, microcontroller temperature, and speed. We send a packet with the format of $AAAAAA$BBBBBB$CC$DD$EEE$FFF$GG, where A represents the latitude, B represents the longitude, C represents the motor battery life, D represents microcontroller battery life, E represents the motor temperature, F represents the microcontroller temperature, G represents the speed of the robot, and the ‘$’ is used as a delimiter.

The data from ARMORD to XBee consists of all data the iPhone shows

VV. Temperature Sensors

We bought TMP37FT9Z temperature sensors to measure the temperatures of the motors and the microcontroller. These sensors are in a standard T0-92 package, which gives you easy to access pins. We will connect 3.3 Volts to the left pin and the ground to the right pin. The middle pin outputs a voltage that is connected to our microcontroller’s analog to digital pin. We then convert the voltage using the equation below to be able to get a temperature.

Temp in °C = [(Vout in mV) - 500] / 10

VVI. Battery Life

We needed to be able and watch the battery life of our two batteries. So we created two voltage dividers circuits to be able to watch the voltages of the batteries. The voltage divider circuits lower the voltage to safe level for our microcontroller to read. We then compare that value to the value of a charged battery and based off that we can estimate the remaining charge in our two batteries. The figure below shows how the setup of the basic voltage divider.

[pic]

VVI. Board Design

For the main part of our project we were using a bread board to test and design our hardware, but we were going to have a fabricated board in the end. Most groups decided to send out their materials and design to have their boards fabricated for them, but we decided this was inefficient in time and money. So we decided to create our own boards using a Pen Plotter, Copper Clad Plates, and Ferric Chloride. Figure XX shows the pen plotter with the copper clad plates.

The process does not take a long time to finish, but it is very tedious. The first process was to create our board design using CAD software. Next, we sent the data to a pen plotter, that we changed to have a etch resistant pen to be able to write on the copper clad plates. Finally, we took the finished board and put it in Ferric Chloride to remove everything but the pen lines. Figure XX shows a finished board that we created.

VVII. A/V System

ARMORD utilized a 2.4 GHz wireless camera mounted on its enclosure to capture video. This video system consists of the actual camera that acts as a transmitter and the video receiver. Both of these components run on 9V DC and draw very little current. The camera we chose, was chosen for its small size and light weight. Because real estate is scarce on ARMORD, we needed something with a small footprint and low cost in case of damage or malfunction. Figure XX shows the camera and receiver being used on the ARMORD system.

[pic][pic]

Figure XX - Wireless Camera and Receiver for ARMORD

In the original design of ARMORD, we planned to have video capabilities integrated with the iPhone device. The plan was to broadcast wireless video to a gateway PC with a video capture card and then transmit the captured video to the iPhone via WiFi communication. Figure XX shows a diagram of this initial concept. The problem with this design was that we experienced to great of a video lag to be used for any practical purpose.

[pic]

Figure XX - Overview of Original AMORD AV System

To remedy this issue, we decided to take video capability away from the iPhone and stream video directly to a separate LCD screen. This method of video capture limits our communication range, but provides more reliable video capture. Utilizing an external LCD screen required fabricating a custom controller which would allow mounting the iPhone, the video receiver, and the screen. The controller also contains a 9V rechargeable NiMH battery to power the video receiver. We did not have to worry about powering the screen, as the model we chose had a built in rechargeable battery. The only problem we had with this method of transmitting and receiving video was the lack of image processing. This meant that whenever ARMORD landed upside down, our video would also display upside down. To remedy this, we implemented a swivel mount for our LCD screen on the handheld controller. This allows the used to easily turn the screen 180 degrees and be ready to go. Figure XX shows an image of our wireless controller for the ARMORD system.

VVIII iPhone Application

The primary controlling device of our robot is an iPhone. We made a custom application in Objective-C specifically designed to allow users to control the robot, and view speed, distance, battery life, and direction.

When the iPhone application is launched, the user is presented with a login screen. After his/her credentials are verified, they are then sent to a connection screen to provide the IP address and Port of the gateway. Once a connection is made, the user is then presented with the main control screen.

[pic]

On the main screen, the user has two sliders that will allow control of the left and right motors of ARMORD. Pushing both sliders up, will result in the robot moving in full forward, both back, will move it in full reverse. In the middle of the screen, the user is presented with a map. The map displays the location of the user and the location of ARMORD.

Double tapping the bottom of the screen reveals the data view. Here the user can see other details of ARMORD, while still using the sliders at the left and right of the screen to control the robot.

[pic]

VVIII Gateway Application

Since the only iPhone communication port available to us was Wi-Fi, we had to create a computer application to relay data to and from the iPhone and ARMORD. This windows application, called “the gateway”, was written in C#. All the application does is initiating a connection to the iPhone, over a UDP server, and another connection to ARMORD, over a serial port. The serial port has a wireless XBee module connected to it, and is paired with another module sitting on ARMORD. Once the initial connection is established, the gateway will spawn two threads. The first thread will relay all data obtained from the serial port, to the iPhone. The second thread does the opposite, transmitting all data received from the iPhone, to the serial port. Figure XX shows the graphical user interface for the Gateway application.

[pic]

VIX iPhone Packet Structure

The data sent from the iPhone to ARMORD, consists of left and right motor values. We created a simple 8 byte packet with the format of $RRR$LLL, where RRR represents the right motor value, LLL is for the left, and the ‘$’ is used as a delimiter.

The data from the XBee to the iPhone consists of all data seen on the data view, and the latitude and longitude of ARMORD. It is transmitted in plain text and comma delimited.

Conclusion

Our group knew that this project wasn’t going to be easy when we picked it, but one thing we did know is that we would enjoy it and that is what mattered to us the most. To our group robotics is fun and interesting and was a big part of why we couldn’t say no to the opportunity of building our own robot. ARMORD was quite an amazing project for us because it included mechanical, electrical, and computer engineering aspects. We used all the skills we have learned from our courses as well as additional material we learned from the Internet, to get our project to where it needed to be. When we didn’t know about something we researched it fully to be able to understand the process, which made it easy to design later on. Our final design definitely was what we imagined when we first started this project, so we were happy with the fact we could create something that we pictured in our heads.

About the Authors

Thomas Kehr is currently employed as an engineering intern for the Department of Defense under the Program Executive Office for Simulation, Training, and Instrumentation (PEO STRI) where he supports the Target Modernization program in upgrading legacy live fire Army ranges to modern digital formats. Thomas will graduate with a bachelor’s degree in Electrical Engineering and upon graduation will go to work full-time for PEO STRI. Alongside work, Thomas will also be attending graduate school where he will be pursuing a MSEE with an emphasis on Signal Processing and Robotics.

Andrew Lichenstein is currently employed as a software engineer for L-3 Communications, where he works on simulation and training for Internal Research and Development. Andrew will graduate with a bachelor’s degree in Computer Engineering and a minor in Computer Science. Upon graduation Andrew will go to work full-time for L-3 Communications. Alongside work, Andrew will also be attending graduate school where he will be pursuing a MSCE with an emphasis on Embedded Systems and Robotics.

Kevin Jadunandan is a 21-year-old Computer Engineering student at the University of Central Florida. Kevin plans on pursuing a career in the engineering field and continuing his education to obtain a Masters degree in Computer Engineering.

References

[1] W. H. Cantrell, “Tuning analysis for the high-Q class-E power amplifier,” IEEE Trans. Microwave Theory & Tech., vol. 48, no. 12, pp. 2397-2402, December 2000.

[2] W. H. Cantrell, and W. A. Davis, “Amplitude modulator utilizing a high-Q class-E DC-DC converter,” 2003 IEEE MTT-S Int. Microwave Symp. Dig., vol. 3, pp. 1721-1724, June 2003.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download