听音乐的图片Project DIAS:Drexel’s Integrated ATV System Keith W.Sevcik,Shreyansh Shah,Jason Collins,Andrew Moran Robert Ellenberg,Michael Perreca and Paul Y.Oh∗
kws23@drexel.edu,sks39@drexel.edu,jc359@drexel.edu,atm28@drexel.edu rwe24@drexel.edu,mgp27@drexel.edu,paul.yu.oh@drexel.edu
Drexel University,Philadelphia,PA
Abstract
Recent disaster scenarios and military operations have un-derscored the need for robotic ground vehicles that can nav-igate harsh terrain that is too dangerous for humans to en-ter.Such vehicles could be ud to extract injured people, deliver supplies,or provide reconnaissance.The goal of project DIAS is to produce a group of robotic all-terrain vehicles(ATVs)that can still be operated as off-the-shelf ATVs.This paper describes the design and construction of a robotic retro fi t for an ATV.The realization is a vehicle that can be remote controlled,navigate GPS waypoints,or be driven by a person.
Introduction
Disaster scenarios and military operations often involve rough terrain that is dif fi cult and dangerous fo
r a human to traver.Missions executed in the environments such as arch and rescue,supply delivery and reconnaissance de-mand asts on the ground that can be quickly and effec-tively deployed.All terrain vehicles(ATV’s)have proven themlves as reliable platforms for conducting such mis-sion.However,a person must put their lf in harms way to drive the ATV.A robotic retro fi t for the ATV offers a means to achieve the same goals without risking the life of an indi-vidual.
The design and construction of unmanned ground vehi-cles(UGV’s)is thoroughly studied fi eld in the realm of robotics.UGV’s such as tho prented in(Trebi-Ollennu &Dolan1999)and(DARPA2006)have demonstrated the ability to construct a sturdy platform capable of traversing harsh terrain without a driver.Other vehicles such as Stan-ford’s Stanley(Thrun2006)and Carnegie Melon’s Sand-storm and Highlander(Whittaker2006)have solved the Address all correspondence to this author.The U.S.Army Medical Rearch Acquisition Activity,820Chandler Street,Fort Detrick,MD21702-5014is the awarding and administering acqui-sition of fi ce.This investigation was funded under a U.S.Army Medical Rearch Acquisition Activity;Cooperative Agreement W81XWH04-1-0419.The content of the information herein does not necessarily re fl ect the position or the policy of the U.S.Gov-ernment or the U.S.Army and no of£cial endorment should be inferred.
Copyright c 2007,American Association for Arti fi cial Intelli-gence(www.aaai).All rights
rerved.Figure1:Drexel’s Integrated ATV System(DIAS).Project DIAS is a robotic retro£t for a stock ATV.Pictured here is DIAS-2,a converted Polaris Sportsman90cc with electron-ics bay on the back rack.
problem of autonomous navigation through such environ-ments.However,all of the vehicles are heavily modi fi ed from the stock version and in some cas can no longer be driven by a person.
This paper outlines the design and construction of a robotic retro fi t for a stock ATV,shown in Figure1.The fol-lowing ction outlines the design requirements and method-ology.The Hardware ction describes the hardware im-plementation.Next,the electrical system and the robot’s controller are explained followed by and explanation of the software.The results are then prented with suggestions for future work and applications.
Design Criteria
The missions and operating environments propod demand speci fi c criteria of the robotic vehicle.Disaster scenarios and military missions are often executed in rough terrain. The environment could vary in elevation,ruggedness,ob-stacle density and obstacle size.ATV’s are designed to be versatile and durable,allowing them to be utilized in a wide range of missions.For eas
e of transportation and storage,
we cho to work with a Polaris Sportsman90cc ATV.
The Sportsman90cc has a2-stroke engine which burns a mixture of gasoline and oil(the are mixed inside the com-bustion chamber).The2-stroke engine prents a unique challenge in that the throttle position does not linearly effect engine speed.However,the Sportsman does have cable ac-tuated brakes,which are much easier to interface with than the typical hydraulic brakes.The shifting mechanism is a lever that connects directly to the transmission.The Sports-
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man shifts between forward,neutral and rever,a feature not common among90cc ATV’s.Another attractive feature of the Sportsman is a built in kill switch which turns off the engine when activated.
For this design iteration,the goal was to achieve GPS waypoint following in a fl at,open fi eld.Bad on the avail-able GPS technologies,DIAS was required to come within 1m of the speci£ed waypoint.We also wished to retain the ability of a person to drive the vehicle.For this reason,DIAS had to maintain75%of the stock capability.The criteria drove the design of the hardware and software systems that controlled DIAS.
Hardware
To achieve basic control of the vehicle,four axes need to be actuated:steering,throttle,brake,and shifting.The axes are actuated using a variety of motors connected to a central processing unit.The design and implementation of the systems is outlined in the following ctions.
Steering
Preliminary load tests were conducted to determine the amount of force required to steer the ATV.It was determined that an electric motor capable of producing10to13ft.-lbs. of force would be required to turn the steering shaft.The motor that was picked is an AME12VDC gear head motor capable of producing17.67ft.-lbs of force.
The torque is delivered through a magnetic clutch.This clutch is t to dingage the steering motor from the steer-ing shaft if a load over17.67ft.-lbs of force is applied,thus preventing the motor from being overloaded.The clutch also allows the drive motor to be disconnected when the ATV is t to manual mode,allowing a person to operate the vehicle in a normal fashion.To provide steering angle feedback,a potentiometer was attached to the steering column. Shifting
The shifting on the ATV is actuated via a linear actuator. This replaces the hand shifter creating an electronic shifting system.Limit switches are ud to n the position of the shifter arm and to act
as the feedback of the system.The fix ed end is mounted to a pivot point while the piston is con-nected to the shifter arm itlf,as shown in Figure b.Manual shifting is actuated with a three way switch mounted on the dash of the ATV,shown in Figure a.Using this switch,the operator can manipulate the gearing of the transmission. This design depicts a”shift-by-wire”system where the shifter does not mechanically shift the vehicle into gear but rather nds a signal to the central controller.The
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(a)
(b)
Figure2:DIAS implemented a”shift-by-wire”system in which shifting was controlled by a switch mounted in the dash,shown in(a).This switch controlled the linear actuator pictured in(b)which moved the shifting arm.
Figure3:A look inside the electronics bay for DIAS-2.The 12V battery on the left provides all power for the robotic retro fi t.The controller is located at the bottom.Mounted at the top,the12VDC to7.75VDC converter powers the lower level electrical system.
controller then controls the linear actuator to shift the vehi-cle into gear.Reed switches mounted near the shifting arm indicate when the vehicle is in forward,rever or neutral. Braking and Throttle
The braking and throttle systems on the Polaris are both operated by cables connected to switches on the handle bars.To automate the degrees of freedom,Hitec HSR5995 rvo motors were ud.The HSR5995is rated at2.2ft-lbs. torque at7.2VDC,which proved suf£cient to actuate the systems.Both rvos were connected in parallel to the the stock systems.This allowed the brakes and throttle to be controlled by a person or by the central processor.
The rvo has8-bit resolution,allowing for over50throt-tle positions in the range of motion ud.Limits were placed in both hardware and software to prevent the throttle from being fully actuated.This limited the top speed of the ATV.
Electronics
The electrical system for DIAS shown in Figure3involved both the low power control system and the high power sys-tem for driving motors and other actuators.The following ctions describe t h e individual subsystems that compo the electronics.
Control System
All of the actuation on the robot feeds into a central pro-cessing unit.The central component is the Mini Robot Con-troller(Mini RC)from Innovation First,Incorporated(IFI). The Mini RC provides16channels of digital or analog I/O’s, 8PWM outputs,6solenoid outputs,a TTL rial port,and DB-9rial port.
简单手抄报The rvo motors actuating the throttle and brakes are ca-pable of being controlled directly from the Mini RC outputs.To control the steering motor,pwm outputs are nt to a Vic-tor883speed controller.
The speed controller sources the power necessary to drive the motor.The shifting actuator is driven by a Spike H-Bridge Relay.Both of the compo-nents are available from IFI Robotics.
招投标管理The controller also handles all data input.Feedback such as limit switches on the shifting system and the potentiome-ter on the steering are read into the controller and procesd. The controller also communicates with three different pe-ripherals:the GPS nsor,the wireless modem and the Futaba receiver.
Wireless and GPS Solution
To link the ATV to the ba station computer,two Maxstream9XStream900MHz wireless radio modems were ud.The transceivers offer full duplex asynchronous -rial communication with miles of range outdoors and a bit rate of up to19200bps.Information nt from the ba sta-tion to the IFI controller is typically commands for the var-ious axes of the robot.Information nt from the controller to the ba station is predominately GPS data.
The Garmin GPS185Hz provides GPS position readings at a rate of5Hz.With a diameter of3in and a height of under1in,the nsor fi t neatly on the top of the electronics box.As a standard GPS nsor it has an accuracy of15m. However,it is DGPS enabled,permitting accuracies of under 3m.
Power
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To provide power to the entire autonomous system,an ex-ternal12volt DC electrical system was implemented.This system includes two12VDC aled lead acid batteries from Power Sonic.The two batteries were wired in parallel to give a run time of over an hour under full load.
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The12VDC system is then ud in conjunction with a 12V to8.5V step down converter to create an electrical sys-tem for the IFI Controller and the steering and braking r-vos.To reach the operating voltage of the components,the step down converter was adjusted to create an output of7.76 volts DC.As an added safety feature,all components were individually fud.An external kill switch cuts power to the entire robot when removed.
Software
To control DIAS,the ba station application pictured in Figure4was created in Visual Basic6.When the ATV was switched into autonomous mode,the ba station could be t to three different modes of operation:Futaba control, joystick control,or GPS waypoint navigation.In all modes of operation,the ba station can kill or start the ATV’s en-gine remotely.
The ba station utilizes GPS information to plot the po-sition of DIAS on a map.Under GPS waypoint navigation, waypoints can be added by clicking on the desired position on the map.Once a waypoint queue exists and the”En-gage Waypoint Following”button is clicked,the ba station will issue commands to the subsystems.The distance from a waypoint and the required heading to approach a waypoint
Figure4:The ba station application ud to control DIAS-2.The ur can lect between radio control,joystick con-trol,and GPS waypoint navigation.A map allows the ur t GPS waypoints.
are then calculated.Distance from a waypoint in¤uences throttle and the error in waypoint heading and true heading in fl uences steering(each utilize a form of proportional con-trol).
Results
The£nished product was tested outdoors under all operating modes.DIAS performed well,successfully navigating way-points mapped in an empty parking lot.The fi nished product met the threshold requirements t out at the beginning of the project.The only change to the stock ATV was the shift-by-wire system.The design still maintained the threshold70% stock capability.The vehicle was shown to operate in grassy fi elds with navigation within2m accuracy.The accuracy of the system was entirely dependent upon the GPS receiver. Greater accuracy could be attained if a more expensive GPS nsor was utilized.
A couple of design issues were encountered during test-ing.The IFI controller proved to be very nsitive to heat, and would often shut itlf down in environments with tem-peratures exceeding90◦F.The next deisgn iteration should include a cooling system or investigate new controlle
rs.It was also dif£cult to consistently regulate the speed of the two stroke engine.Future design iterations should include clod loop control of the speed.
Future Work
Currently two DIAS vehicles have been constructed,DIAS-1and DIAS-2.A third vehicle has been purchad and is awaiting robotic retro fi t.We have also acquired two robotic helicopter platforms from Rotomotion,Inc shown in Figure 5.This infrastructure paves the way for investigating higher level problems in heterogeneous robotic teaming.Missions such as cooperated arch and rescue,convoys,and terrain mapping can all be executed with this group of aerial and ground
asts.
(a)
(b)
Figure5:(a)The SR100from Rotomotion,Inc.can be ud in conjunction with the DIAS vehicles to investigate robotic teaming.(b)The helicopter fl ying above provides aerial surveillance for DIAS driving below.
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Acknowledgments
We would like to acknowledge Matthew Hardy,Colin Gra-ham,Jacob Warren and Chris Crudele for their work in de-signing and constructing DIAS-1.
References
DARPA.2006.Crusher unmanned ground combat vehicle unveiled.Technical report,Defen Advanced Rearch Projects Agency.
a.2006.Stanley,the robot that won the Darpa grand challenge.Journal of Field Robotics23(9):661–692. Trebi-Ollennu,A.,and Dolan,J.M.1999.An autonomous ground vehicle for distributed surveillance:Cyberscout. Technical report,Institute for Complex Engineered Sys-tems,Carnegie Mellon University.
a.2006.A robust approach to high-speed navigation for unreheard dert terrain.Journal of Field Robotics23(8):467–508.
