Design and Implementation of an Unmanned Ground ... - IEEE Xplore

Proceeding of the 7th International Symposium on Mechatronics and its Applications (ISMA10), Sharjah, UAE, April 20-22, 2010

Design and Implementation of an Unmanned Ground Vehicle for Security Applications Abdelhafid Bouhraoua1, Necar Merah2, Mansour AlDajani3, and Mostafa ElShafei2 1 Computer Engineering Department, 2 Mechanical Engineering Department, 3 Systems Engineering Department, King Fahd University of Petroleum and Minerals P.O. Box 969, 31261 Dhahran, Saudi Arabia {abouh, nesar, dajani, elshafei}@kfupm.edu.sa ABSTRACT This paper describes the design and implementation of a prototype teleoperated unmanned guided vehicle (UGV) for security applications. A commercial Quad motorbike with a 1cylinder gasoline engine with a power of about 5 HP was reengineered and transformed into a fully automated vehicle that can be teleoperated. The designed UGV is remotely controlled using high speed secure wireless connection. The vehicle is provided with video cameras and controlled pan and tilt motion. The live video is transmitted to an operator in the command and control station who controls steering acceleration, braking, as well as gun positioning and firing using a joystick, a steering wheel and pedals. The command and control computer translates and sends the operator commands to an on-board computer which in turn activates a number of actuators and servo motors for full control of the vehicle. The developed UGV demonstrated clearly the potential application of this vehicle, and incorporated the necessary technology for local manufacturing of these types of vehicles for security applications, or for building less demanding UGV for civilian applications. 1.

INTRODUCTION

Unmanned mobile robots are actively being developed for both civilian and military use to perform dull, dirty, and dangerous activities. They proved to be effective in a large number of circumstances where the use of human labor is too expensive, the task is risky, or it is impractical for human capability. There are two general classes of unmanned mobile vehicles: Teleoperated, like the one described in the present work, and Autonomous. A teleoperated, or unmanned guided vehicle (UGV), is a vehicle that is controlled by a human operator at a remote location via a communications link. Fully autonomous UGVs have seen extensive development driven by the DARPA Grand Challenge competition [5,11]. Although some of these solutions are at a very advanced stage, they are still undergoing tests and their deployment is yet to be seen. On the contrary, remotely controlled UGVs have already made it to the deployment phase. This type of vehicles is also seeing a proliferation of developed solutions especially in the lightweight to medium weight sizes [1]. Many issues related to this category have been addressed in the literature [1-10]. These

issues can be grouped in the following aspects: communication aspect, control aspect, obstacle avoidance aspect, base station issues and vision systems development. Reliability and system robustness issues are also interesting aspects to consider. Although, some of the works relate to the autonomous branch of the UGVs (or UAVs), its nature applies perfectly to remotely controlled UGVs. Research and development of UGV is often focused on specific applications and are therefore designed accordingly. The ability to be customized or reconfigured and function in an unstructured, outdoor environment is a desired feature of robotic platforms. Among the recently proposed specialized applications are the military vehicles for tactical reconnaissance and explosive disposal missions. The US Department of Defense is planning to replace a third of its armed vehicles and weaponry with robots by 2015 [2]. Such systems are expected to minimize the operations cost and combat casualty. In reference [1], a survey of military use of UGVs has been presented. Several UGVs have made it to the field, like the PackBot [12] and the Talon family [13] which offer a large portfolio of different range and applications UGVs. Some of them like the Talon Sword has been deployed in Iraq. The Ripsaw [14] constitutes a typical remotely controlled UGV. It is fast reliable and can carry soldiers and safely help them withdraw from combat zones. The present paper describes the design, construction, testing and implementation of a UGV for security applications using the latest wireless computer communications and carefully designed mechanical and electronic systems for effective control and maneuvering. The system is supplied with two pan/tilt cameras, rifle/gun control, steering/speed/brake management, and many fail-safe features. The prototype was thoroughly and critically evaluated, and suggestions for the next generation design are discussed. 2.

BACKGROUND

2.1.

Requirements The teleoperated UGV is composed of: • A Quad motorbike used as the vehicle. The Quad is a commercial grade vehicle. • The base station which consists of a PC with a wireless connection running the application that allows the operator to remotely control the vehicle. The base

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station receives video streams from the different on board cameras. To provide means to control the quad vehicle remotely the following requirements need to be fulfilled: 1. Efficient control of the means used to drive the vehicle (Ignition, Steering, Acceleration, Brakes and trigger) 2. The operator will need: • Relayed video to be able to see where the vehicle is and to drive it adequately • To transmit the driving control orders from the remote operator to the control system 3. The sniper will need: • Relaying video to see where the gun is pointing and act accordingly • Providing a means to control the gun trigger to allow the sniper to remotely start shooting • The gun must be mounted on an omni directional platform to allow for added freedom of action when the vehicle is moving. 3. DESIGN AND MANUFACTURING OF MECHANICAL SYSTEMS The first steps of the design consisted on evaluating the existing Quad by analyzing the different functions to be automated and measuring the available space for mounting the required motors and drives. Several design configurations were developed and evaluated. This lead to the selection of an optimal configuration that was implemented with the following criteria: 1. The modifications to the quad should be minimal so that it can be easily brought back to its initial state. 2. Modular system design should be adopted for ease of maintenance. 3. Simple part configuration designs should be made so that they can be manufactured locally and at low cost. 4. Materials available locally should be used. 5. Automated control of only the rear brake, given that the quad is not expected to travel at high speed. 6. Automated control of acceleration 7. Automated control of steering. 8. Use of two cameras; one at the back of the vehicle and one at the front 9. The cameras will be mounted on commercial pan and tilt 10. The gun will be mounted at the front and provided with an automated triggering system. 11. 12-V-55A batteries will be used to supply all of the required power. 12. A sturdy and stable platform is to be designed to support the cameras, the gun and ammunition and the computer. 3.1.

non-permanent joints to allow easy assembly and disassembly of the base. The front end corners of the sheet are chamfered to allow maximum travel of modified steering system and the side edges of the plate were rounded for safety.

Figure 1: A 3-D representation of platform with mounted poles. The rear and front cameras are mounted on commercial pan and tilt systems that allow a rotation of 360° and 180° for the tilt. The rear pan and tilt system is secured on an antenna-type pole with manually adjustable heights. The lower part of the pole was machined from a 40x40x2 square tube of aluminum for light weight. The height is adjusted to allow full view of front and side obstacles. The rear pole assembly is designed to allow for a maximum height of 2.0 m above ground and the front camera will be mounted at an approximate height of 1.5 m. 3.2.

The front pole is designed to support both the camera and gun support and triggering system. The camera is mounted on top of the gun, which in turn is supported by the front pan and tilt system. The fixture that holds the gun along with the triggering system is illustrated in Figure 2. The triggering device is constituted of a servo motor (1), an aluminum wheel (2) mounted on the motor shaft and triggering finger (3) which passes through the specially designed groove on the left side gun mount stand (4). The trigger is mounted on the wheel by two M4 screws. Actuating the servo motor will trigger the shot through the quick action of the finger. The mechanical finger returns to its initial position after the action. The butt of the gun is held in place by a fixture composed of vertical plate (5) bolted to the base, two side brackets (6) and one back clip (7) that holds the side brackets. The fixture helps hold the gun butt in the desired position and serves as a shoulder reacting to thrust force from gunshot. The front camera is mounted on plate (8). 3.3.

Platform and Supports

In order to adhere to the above criteria, the mechanical design begun with measurements of available space dimensions and estimation of required torque for steering, and force for brake and accelerator actuation. This lead to the establishment of the platform (base) configuration. A 2-mm thick steel sheet was selected to be used as base to support the computer and electronic equipment as well as the poles and pan and tilt systems for cameras and gun and ammunition system. Figure 1 is a 3-D view of the designed base plate and poles. This plate is mounted using

Gun support and trigger system

Accelerator and Brake Actuating Systems

The accelerator and brake will be driven by two identical commercial servo motors supplied by a 12 volt DC battery and mounted on the quad’s handgrips using specially designed fixtures. A3-D representation of the brake drive is illustrated in Fig. 3. High-torque model motors (1) with a maximum capacity of 380 kg-cm were selected based on required torque and available space. The motors which are controlled by pulses generated by the slave microcontroller are mounted on handgrip by a specially designed fixture (2). Both the accelerator and brake are actuated

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by the servo motor through the actuating wheel (3) and a flexible steel wire (4). The complete brake and accelerator driving systems were manufactured, assembled and successfully tested. The actual brake and acceleration systems are illustrated on the photographs of figures 4 and 5, respectively. It can be seen that the original quad design was not altered and that designed automatic brake and accelerator actuation systems can be easily assembled and disassembled using the specially designed mounting fixtures.

Where C is the center distance between the driving and driven pulleys, d and D are respectively the pitch diameters of small and large toothed pulleys and θd and θD are respectively the wrap angles on the small and large pulleys calculated from Eq. 2.

θ = π − 2 sin

⎛ −1 ⎜ ⎜ ⎜ ⎝

D − d ⎞⎟ ⎟ 2C ⎟⎠

θ = π + 2 sin

⎛ −1 ⎜ ⎜ ⎜ ⎝

D − d ⎞⎟ ⎟ 2C ⎟⎠

d

D

(2)

8

6 4

7

2 5 1

3

Figure 4: Accelerator actuation system Figure 2: gun holder and triggering device.

4 3

5 2

1 Figure 3: 3-D Representation of the Braking system 3.4.

Figure 5: Brake actuation system

Steering System

A thorough analysis of the Quad front structure led to the selection of the lower front part for designing and installing the automatic steering system. The design took into account criteria 1 and 2 defined above. Steering will be performed through a high torque motor with gear-timing belt drive system. The motor and drive elements were selected to provide easily controllable and precise steering. A commercially available high torque stepper motor was selected in order to get precise desired positions. Specific gears and timing belts were selected based on the required gear ratio (torque) and strength. The photograph of figure 6 shows the actual drive. The selection of a 24-teeth driving XL-gearbelt pulley and 72-teeth driven XL-gearbelt pulley allowed a gear ratio of 3 and an amplification of the torque by the same factor. Power transmission is ensured by an extra light (XL) rubberized fabric timing belt with a standard pitch of 5 mm. The required pitch length of the belt was estimated by Eq. 1 to be 500 mm: (1) 1/ 2 ⎡ ⎤ L = ⎢4C 2 − (D − d )2 ⎥ ⎣

⎦

+ 1 ⎛⎜ Dθ + dθ d 2⎝ D

The choice of the XL timing belt is based on flexibility of assembly and the criterion of back drivability. Moreover, this type of belt does not stretch nor slip resulting in the transmission of power with a constant angular velocity. Timing belts are also known to have efficiencies varying from 97 to 99%. The 24-teeth driving XL-gearbelt pulley, which was selected from a commercial catalog, was bored and mounted on the motor shaft using two setscrews. The large pulley (72-teeth) is used to drive the steering shaft through a specially designed spindle. The spindle is mounted by press-fit inside the original hollow steering shaft at one end and in the driven pulley at the other end. Square keys are used to provide extra constraint from relative rotation between spindle and driving pulley and a pin is utilized between steering shaft and spindle. The lower end of the spindle is threaded and a nut is used to constrain the pulleys’ axial motion as shown on figure 6.

⎞ ⎟ ⎠

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Two adjustable position brackets were designed for mounting the motor such that the whole system will result in minimum reduction of empty space between quad and ground. Since the axis of original steering shaft is tilted by approximately 15° with respect to the vertical the motor


mounting brackets were designed to compensate for the tilt and provide good alignment between the driving and driven gearbelt pulleys. A special cover plate was designed to protect the whole system from any external impacts. The complete system was assembled and successfully tested.

Figure 7: Block Diagram showing the base station on the left and the UGV on the right 4.1.

The server PC is disassembled and then fixed on the platform as shown in figure 8. It is connected to the wireless router through the Ethernet port and to one of the two PIC microcontroller through the serial COM1 port.

Figure 6: Photograph showing the timing belt drive system. 4.

The Server PC

CONTROL SYSTEMS DESIGN

The UGV project is divided into two main systems (Figure 7). The first system can be called the controlled vehicle and the second system is the base station. The main components of the controlled vehicle are: • The four-wheel motorbike modified to support the necessary mechanical components to be electrically controlled. • A PC working as a server which constitutes the center of the control and communication with the base station is mounted on the platform • A WiFi wireless router used as the communication channel to communicate with the base station • A Microcontroller board, used to relay the commands received from the base station, via the PC server to the drivers of the actuators.

The server/client software is written in Visual Basic. The server software runs at start-up in the server PC. The client software connects to the server and starts sending commands to control the vehicle. The server software forwards these commands to the PIC microcontroller that executes these commands. Video is relayed to the client PC using a streaming software installed on the server PC. A simple browser is used to display the relayed video on the client side. 4.2.

The control unit in is in charge of decoding and executing the user commands. It translates into sending the suitable signals to the various actuators of USAD-1. The control unit is also responsible for monitoring the integrity of the system and is in charge of taking the appropriate actions when the connection with the base station is lost. The control unit, figure 9, is composed of : • The microcontrollers boards, • The stepper motor driver and the stepper motor terminal connectors, • RS232-RS422 converter, • DC to DC adaptor, • Relays board and electrical connectors.

4.1. Power Requirements The vehicle has only a 12V battery used for ignition and to power some other vehicle features like lighting. Commercial Lead-acid batteries are used as budget constraints forbade us from seeking more reliable and power efficient batteries. The Server PC, is powered from a power-inverter that inverts the 12-V DC power supplied by the battery into a 110V AC power to which the PC power supply is connected. The Microcontroller and the router are both directly connected to the 12-V battery through some regulator or DC-to-DC voltage converters. The power supply of the actuators (servos and stepper motors) is taken from the additional batteries.

The Control Unit

Two PIC microcontroller boards, connected in a master/slave mode are used. The master PIC, connected to the server PC, is responsible for decoding the received commands and relaying them to the actuators. Commands related to the steering or servos are forwarded to the slave microcontroller while on/off types of actuations, using the relay board, are processed by the master PIC. The used relay board contains 16 relays. Each relay is controlled by a single digital signal. The master PIC microcontroller's parallel ports B and D are used to drive the relays. The two pan-and- tilt modules are connected to 4 relays

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each. The other relays are used to control various features like the ignition, the reverse drive and the lights. The steering stepper motor is controlled by the IMS 1007IE stepper motor driver. which is connected to the slave microcontroller through an RS232-to-RS-422 signal converter.

Figure 10: Videos from the UGV cameras as they appear in the client PC

6. Figure 8: The Server PC

PRELIMINARY TESTS

Extensive testing is required to demonstrate the viability of the developed prototype (Figure 11). However, this project aims at proving the technology transfer process and demonstrate local capabilities rather that producing a working product. Therefore, testing has been restricted to the functional aspect only. Performance testing has been excluded because of the limited budget and duration of the project at its current stage.

Figure 9: The Control Unit 5.

COMMUNICATION SYSTEMS

A regular IEEE 802.11n wireless LAN connection is used. However, this type of communication medium is not robust. A proprietary communication method that uses frequencies in the military reserved band will be more appropriate. The wireless LAN adoption is motivated by the sole purpose of fast prototyping. The client PC is a normal desktop PC that is connected to a USB Wireless 802.11n NIC (Network Interface Card),. The client control software requires the user to specify the static IP address of the server PC. Video can be viewed in the client PC monitor through a regular web browser as shown in Figure 10.

Figure 11: The UGV prototype (rear Camera not shown) Two test phases have been performed. While building the UGV, many modular and functional tests were conducted. Each module in the vehicle was tested separately. The breaking and acceleration modules, the communications module, the steering module, the visual system and other are all tested in the lab. These modules are then tuned and modified according to the observations. After the vehicle was fully functional in the lab, a field test was arranged in the main Stadium of KFUPM. The vehicle was transported to the test site and the tests were performed. The goal of the field tests is purely functional as mentioned earlier. The evaluation test results can be summerized as follows: •

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The range of communication is found to be around 250 meters. The reliability of the communication has been tested


•

•

•

• • 7.

under clear weather conditions and free space. Few packets were lost as a result of communication. Therefore, the range and reliability of communication is acceptable even when the vehicle is moving at moderate speeds (10 to 15 Km/h). The video stream takes a bandwidth of about 1.5 Mbits/s or less and uses MPEG-4. The resolution is quite acceptable given that the used camera is a regular webcam. However, it is clear that a better quality can be obtained by using more advanced cameras. The control system has been tested and shown that the response time is always less than one second which is mainly acceptable due to the reliability of the communication system. The bandwidth used by the control messages is quite small due to the size of the messages and the human speed. The acceleration and breaks servo motors are reliable. They have been extensively tested and found to produce sufficient torque and speed to respond promptly. However, some problems are observed with the triggering servo motor. It needed to be replaced with a more reliable one. Although the vehicle is provided with six batteries, the power issue was found to be the most challenging. The main cause for drainage of power was the on-board computer. The electronic system on the vehicle is quite stable as no failures were noticed due to vibrations during the field test.

ACKNOWLEDGEMENTS

This work was supported by King Fahd University of Petroleum and Minerals (KFUPM) through grant # CCCR0000. The authors would like to thank the senior design students M. A. Al-Marouf and A. T. Fars and the lab engineer K. Sattar for their valuable contributions to the project.

REFERENCES

[1]

D. Voth, “A New Generation of Military Robots”, IEEE Intelligent Systems, Volume 19, Issue 4, Jul-Aug 2004, pp 2 – 3.

[2]

“Robot Wars,” The Economist, April 17, 2007, at http://www.economist.com/science/tq/displaystory.cf m?story_id=9028041.

[3]

S.S. Mehta et. al. “Adaptive Vision-Based Collaborative Tracking Control of an UGV via a Moving Airborne Camera: A Daisy Chaining Approach”, in Proceedings of the 45th IEEE Conference on Decision & Control, San Diego, CA, USA, December 13-15, 2006, pp 3867-3872 S.J. Lee, D. M. Lee and J. C. Lee; “Development of Communication Framework for Unmanned Ground Vehicle”, in Proceedings of the International Conference on Control Automation and Systems, Oct. 14-17, 2008, Seoul, South Korea, pp 604-607. A. Bacha, et al., “The DARPA Grand Challenge: Overview of the Virginia Tech Vehicle and Experience”, in Proceedings of the 2004 IEEE Intelligent Transportation Systems Conference, Washington DC, USA, Oct. 3-5 2004, pp 481-486 M. Sugiura, et. al., “Development of unmanned ground vehicle for IGVC JAUS challenge”, SICE Annual Conference 2008, August 20-22, 2008, The University Electro-Communications, Japan, pp 2719-2722. X. Feng et. al., “Enhanced Supervisory Control System Design of an Unmanned Ground Vehicle”, in Proceedings of the 2004 IEEE lntemational Conference on Systems, Man and Cybemetics, October 10-13, 2004, The Hague, The Netherlands, pp 1864-1869. J. Ortiz, et al.; “Description and tests of a multisensorial driving interface for vehicle teleoperation”, in Proceedings of the 11th International IEEE Conference on Intelligent Transportation System, October 12-15, 2008, Beijing, China, pp 616-621 L. Lo Belloy et al.; “Towards a robust real-time wireless link in a land monitoring application”, in Proceedings of the 11th IEEE Conference on Emerging Technologies and Factory Automation, EFTA’06, September 20-22, Prague, Czech Republic, pp 449-452. S. Lee, S. Yoon, H. J. Kim, and Y. Kim; “Wireless Stereo Vision System Development for Rotary-wing UAV Guidance and Control”, in Proceedings of the 3rd International Conference on Sensing Technology, Nov. 30 – Dec. 3, 2008, Tainan, Taiwan, pp 168-173. http://www.darpa.mil/grandchallenge/index.asp http://www.howeandhowe.com/ http://www.foster-miller.com/lemming.htm http://www.irobot.com/sp.cfm?pageid=325

[4]

[5]

[6]

CONCLUSIONS

An Unmanned Ground Vehicle has been designed and assembled using off-the-shelf, commercial grade components. The design of the mechanical systems followed a simple yet powerful approach where all the parts were integrated within the vehicle with the strict minimum modifications introduced. The control system has been designed using a systematic approach efficient in the context of fast prototyping. A server PC has been used as the main gateway for controlling and communicating with the vehicle. Besides the PC, two microcontrollers were used in a master/slave setting to control the different actuators that help control the vehicle. Regular wireless LAN technology has been used as the communication medium. Functional tests were carried out in the lab as well as in the field. The main findings were about power consumption and battery life which needs to be enhanced. All the other features and components showed an acceptable level of functionality except for the gun trigger subsystem which also needs improvement. The current project constitutes an excellent demonstrator of design, manufacturing and control capabilities that can be used to develop more sophisticated UGVs for different application in the future. 8.

9.

[7]

[8]

[9]

[10]

[11] [12] [13] [14]

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