ISA Intimidator. July 6-8, Coronado Springs Resort Walt Disney World, Florida

Transcription

1 ISA Intimidator 10 th Annual Intelligent Ground Vehicle Competition July 6-8, Coronado Springs Resort Walt Disney World, Florida Faculty Advisor Contact Roy Pruett Bluefield State College

2 TABLE OF CONTENTS Introduction.. 3 Mechanical Systems. 4 Electrical Systems. 5 Control System Team Organization 9 Cost.. 10 Conclusion 11 2

3 1 Introduction In Fall 1998, the Electrical Engineering Technology Department at Bluefield State College began a Ground Robotic Vehicle project. The ELET Department began the design and construction of a Robot to be entered in the 8 th Annual International Ground Robotics Competition in July Thru an expansion of this initial project the ELET Department decided to begin construction of a second robot, the ISA Intimidator. This robot would be initially entered in the 10 th Annual Intelligent Ground Vehicle Competition of July The second vehicle s goal was to explore the feasibility of a Programmable Logic Controller (PLC) controlled robot instead of relying on a PC based system. The overall design theme was basically Success Thru Simplicity. We believed that by keeping the overall design as simple as possible we would greatly increase our chances of success in the competition, as well as reduce our time committed to design, troubleshooting, and problem solving. 3

4 2 - Mechanical Systems 2.1- Frame and structure The basic frame for the robot is simply a fabricated solid aluminum chassis that was custom built and donated by a local company. Most of the support structures for the necessary sensors and hardware were fabricated by the design team on an as needed basis. Support structures were constructed from aluminum angle stock. Aluminum was a good choice for construction material due to its light weight and ease of machining Drivetrain The drive train for the robot consists of two 24-volt 3.3-amp wheelchair motors mounted in a differential configuration and supplied with only 12-volts. This configuration greatly simplified many of the other design features of the robot. It allowed the robot to have an excellent turning radius while completely eliminating the need for any kind of independent steering system and related hardware. It also eliminated any need for a secondary mechanical braking system, as well as ensuring the robot stayed within the maximum vehicle speed of 5 mph. 4

5 3-Electrical Systems 3.1- Power Systems The power for the robot is provided by two Interstate, sealed gel cell, 12-volt batteries. One battery provides power for the two motors and the other is used in addition with a 600-watt power inverter to supply the necessary 120-Vac for the PLC and any other 120-Volt requirements. The batteries are sufficient to allow run times in excess of one hour which is more than adequate for our project Relays and Protection In order to switch the necessary power for the motors we used 4 Allen-Bradley 120-volt relays. The 120-volt relays were also necessary due to the fact that the output of the PLC is 120-volts. For protection of the motor power circuit we also used two 25-amp fuses wired on both the positive and negative leads between the batteries and the control relays. 5

6 4-Control System 4.1- Sensors To detect the road edges, the robot is using 6 Banner mini-beam diffuse sensors. The sensors are mounted parallel to each other on the front of the chassis and are mounted on an adjustable bracket to allow a slight adjustment of the vertical angle. The sensors are 12-volt devices and their outputs are directly wired to a 12-volt input card of the PLC. Due to the placing of the sensors on the chassis they should ensure that the robot would detect the lane markers before there is any possibility of the wheels going out of bounds on the course. For barrel detection we are using 5 Allen-Bradley diffuse photo switches. These sensors have a range of approximately 3 feet and their outputs are also wired directly to a 120-volt input card on the PLC. The sensors are placed on the front of the chassis in such a way that, even if one sensor was to fail, one of the adjacent sensors will be adequate for barrel detection Programmable Logic Controller All control logic and processing on the robot is controlled by an Allen-Bradley SLC slot PLC. The PLC is configured for 2 inputs cards, one 8 input 12-volt DC card and one 16 input 120-volt card, and one output card, an 8 output 120-volt AC card. This configuration allowed us to use both 120-volt AC and 12-volt DC sensors with outputs wired directly to the PLC. This is one of the major advantages of using a PLC as the processor. No interface or buffer circuits 6

7 are required. The system is easily reconfigured for different sensor types and expansion. It s simply a matter of switching the input or output cards. This type of system is also extremely easy to troubleshoot since there are no circuits between the sensors and processor Software Programming in a PLC is based on ladder logic. Initially one might think that this is very limiting in processing for navigation and control. Actually the simplicity of ladder logic is one of the advantages of this robot. Ladder logic is very easy to write and modify. By simply comparing sensor inputs the program has the ability to perform many complex tasks. Our goal for the control and navigation of the robot is simply to detect and avoid. Forward navigation of the robot will continue until an obstacle or lane marker is detected, or the robot is manually stopped via the remote E-stop or the on board E-stop. When an obstacle is detected, depending on which or how many sensors are tripped, the robot will initiate avoidance procedures. These procedures can vary from simply a right or left turn, or a stop, reverse, and turn, depending on the inputs from the sensors. For the Navigation Challenge we will simply use dead reckoning sending the robot on a set of predetermined azimuths and distances, until all waypoints are obtained or the vehicle run is terminated by infraction of the rules - as determined by the judges. 7

8 4.4-E-Stop System The E-stop on the robot is an industrial type mushroom head pushbutton mounted on the top back of the chassis. The E-stop is wired to interrupt the power between the batteries and the motor relays. The remote E-stop is designed to send a signal to the PLC input card shutting down the system. 8

9 5-Team Organization The ISA Intimidator team consists of the following four Bluefield State College Engineering students under the supervision of Professor Roy Pruett. Names Major Academic Level David Kinsley EET Senior Josh Fizer EET Senior Joni Law EET Senior James Pruett EET Senior The students spent approximately 250 person-hours on the design and construction of the robot. 9

10 6-Cost The robot was constructed of many donated and used parts for which values are undetermined at best. But for an identical design constructed with new parts the cost should include the following: Frame with wheelchair motors $ car batteries control relays with bases ZSRP-6005 Allen-Bradley sensors purchased on ebay at each 6 Banner sensors with cable DC to AC inerter Allen-Bradley E-stop switch remote E-stop switch Allen-Bradley 1746-PZ Power Supply Allen-Bradley 1747-L524 SLC 5/02 Processor Allen-Bradley 1746-A4 4 slot rack, modular hardway style 1 Allen-Bradley 1746-IA8 AC Digital Input Card Allen-Bradley 1746-IA16 AC Digital Input Card Allen-Bradley OA8 AC Digital Output Card Miscellaneous wiring and supplies Total Anticipated Cost of unit $3,

11 7-Conclusion This report highlights the major systems and design intentions of the BSC ISA Intimidator. Given the amount of time that was spent on this project (8 months) we feel that it will demonstrate the intelligence of a simple is better design philosophy and show that much can be accomplished with standard off the shelf products. 11