TaleGator Nyal Jennings 4/22/13 University of Florida Email: Magicman01@ufl.edu TAs: Ryan Chilton Josh Weaver Instructors: Dr. A. Antonio Arroyo Dr. Eric M. Schwartz
Table of Contents Abstract...3 Executive Summary...4 Introduction... 5 Integrated System...6 Mobile Platform...7 Actuation...8 Sensors...9 Behaviors...10 Experimental Layout and Results...11 Conclusion...12 Documentation...13 Appendices...14
Abstract: Of all the popular activities to do on a college campus the favorite is tailgating. The experience of watching a great game outside while grilling some burgers is an experience most people will remember the rest of their lives. One of the biggest issues with arranging these events is getting all the supplies together and carrying them across campus to the picnic. To solve this problem a robot was proposed that would lighten the load. The robot will have a cooler mounted to it and drive around behind the user. The mount will have to support a heavy load and will be designed of strong material. The robot will have an onboard computer to process the image of a webcam that will seek a specific colored shirt. The TaleGator will also keep an eye out for pedestrians and other random obstacles with three sonar sensors. One of those sensors is mounted in the front to tell the distance between the TaleGator and the user with the colored shirt to keep it from running over the user. The robot will have to carry a heavy load and drive over rough terrain and so it will be equipped with four high torque motors and four off road tires. To handle the small bumps and holes in the grass low level shock absorbers will be placed between the frame and the wheels.
Executive Summary: TaleGator is an autonomous robot created to carry a cooler down a sidewalk. In addition to following the user the robot must avoid hitting pedestrians whenever they get in the way. Propulsion is provided by a two wheel drive system driven by two large dc motors mounted in the front.an Omni directional caster wheel is placed near the center back which takes most of the load off the drive wheels. Using only three wheels creates a single plain ensuring all wheels are on the ground at all times. Two ultrasonic sensors were placed in the front of the robot for obstacles avoidance. Each tower the ultra-sonic s mounted to have a led for feedback to tell were the color is. A third ultrasonic sensor was put in the center back of the robot to ensure when backing up it doesn t hit someone. To track the color a CmuCam was mounted to the center front at an angle so as to see the person s shirt. To command all these things an epiphany board was mounted to the robot powered by a 12 volt battery. To power the motors a large eighteen volt drill battery was wired to the board. The power for the motors and the power for the board are controlled by two different switches. When first booted up the robot waits 5 seconds before starting its tracking giving the user a chance to get out in front of it.
Introduction: I m from a beach town where my friends and I constantly go to picnics and beach celebrations. At these celebrations carrying he cooler was always a pain either carrying too much stuff or the cooler itself was too heavy. From this pain the TaleGator was born a robot that will carry a cooler for the user. In the original plan was a robot that will support about a hundred pounds divided amongst four wheels each with its own motors. Once construction is completed the true capacity of the drive wheels will be determined and the robot will be adapted.
Integrated System: The TaleGator makes use two ultrasonic sensors to avoid obstacles on either its left or right side. When not avoiding obstacles the TaleGator was guided by a web camera and color tracking software on a laptop onboard. The block diagram below shows the basic idea for the software.
Mobile Platform: The size of the cargo as well as its weight demanded a large body for the robot as well as a three wheel design to ensure the drive wheels always make contact. The TaleGator will need to drive over different terrains so large wheels were chosen. Each of these wheels was powered by a high powered low gear motor to support the high weight. A piece of aluminum L shape was cut into four two foot pieces and then welded together. The welding formation was set up so one set of parallel L shapes points up while the other parallel pair point downward. To keep the body simple a small sheet of wood was cut into a 2x2 sheet and trimmed until it fit between two of the upward shaped L s. The sheet was then bolted to the frame. The motors were mounted to the underside of the frame against the downward L s to protect the motors. Between the caster and the frame there are several soft rubber sheets to act as shock absorbers. To protect the circuit board a tool box was mounted to the back of the robot. The tool box also had two large switches to control the flow of power to the board and the motor drivers. A 2x4 was cut into two extremely small pieces to be used as towers to attach the ultrasonic sensors. Two holes were drilled into these 2x4 pieces that the led s were then mounted to show feedback. Finally the CmuCam is affixed to an angled piece of aluminum in the front with several bolts. The basic body setup allows for either Velcro or bungee cords to be used to hold a cooler.
Actuation: There are two high power low gear motors that control the motion of the robot. Each of these is mounted to the frame and directly controls one of the two drive wheels. These motors were chosen after much experimentation with higher gear motors. A caster wheel is used as the back support for the robot. The caster was chosen because it could adjust to any angle the drivers want to go. The circuit board regulates the speed and the direction of the motors. Some hard lessons were learned when it came to the motor choices. The original motors claimed to have enough torque to drive the robot but because they were high gear and made of plastic when pushed to their limits the gears would shear easily. After destroying many motors this problem was discovered and the motors were replaced.
Sensors: There are four sensors on the TaleGator three ultrasonic sensors and a CmuCam running color recognition software. The ultrasonic sensors run on 3.3v coming from the volt providing a signal to the board of 1v which decreases the closer an obstacle is to the robot. The ultrasonic sensors pick up any obstacle if they come within three feet of the robot. While the CmuCam runs off a separate 9v battery sending and receiving signals to the board. An interesting problem with the CmuCam is that the color threshold changes dramatically depending on the light requiring a new color command anytime the venue is changed. I learned a few things about designing the robot from trying to use the ultrasonic sensors like making sure to place them away from the robot or else the cone of vision it has will pick up itself and will always be sending signal announcing an obstacle. Also, depending on the floor strange signals can come back when there s no obstacle such as negative numbers. These oddities couldn t be fixed so they were merely accounted for in the software.
Behavior: The TaleGator has only one mode when booting up it waits for five seconds before beginning this program. The behavior of TaleGator can be broken up into two categories obstacle avoidance and color tracking. In obstacle avoidance mode the robot back away from potential obstacles. While reversing the TaleGator doesn t want any chance of hitting someone so he constantly checks if there is any obstacles behind it. If there are any obstacles behind it while backing up it immediately stops giving up on its backward motion. The second behavior color tracking involves the TaleGator recognizing were the color it seeks is in front of it from left to right on a scale of 1-160. He then recognizes any number below eighty as the color is on the left while eighty and up is considered to the right. The TaleGator takes this in to account and makes slight adjustments to the motor speeds so slight turns left or right can be made while still moving forward. The two Led s are on the right and the left side these give feedback illuminating whichever side the target color is on. The TaleGator will track its target forever only stopping if both an obstacle is both in front and behind it, an obstacle is in the center in front seen by both the sensors as an obstacle (this would most likely be the target) or if the CmuCam no longer sees the color. It is up to the target to help guide the TaleGator around obstacles the core of his design is to follow not to drive around on its own. With this in mind TaleGator only backs away from obstacles he doesn t try to drive around them.
Experimental Layout and results: My first thought for the design was to attach the motors and sensors directly to a cooler this was dismissed due to condensation issues and leaks from the cooler. Instead A mobile table design was chosen which would carry a cooler. With the table carrier design TaleGator can carry a cooler or anything else you need to tailgate. To support the weight the frame was made of sturdy aluminum L shape brackets and a sheet of plywood. After much consideration a four wheel design was chosen for the first prototype. The first design for the TaleGator included four low power high gear motors. This design was tested over and over it seemed to work properly during the initial stages. Once the platform tried to turn or do anything other than go full speed forward the motors in the back could not keep up. The combination of high gear and weak gears did not work with the high level of strain put on the motors when trying to turn. These motors would always shear when the TaleGator either turned or moved with the added weight of a cooler. To account for the added weight a caster wheel was placed where most of the weight of the TaleGator and cooler would be on it only about three or five pounds would be on each drive wheel in the front. To address the problem of the sheared gears new drive motors were chosen which were higher power and low gear.
Conclusion: After all the times I was unable to carry everything I needed to tailgate and was forced to make a second trip the idea of making the TaleGator was amazing. After building the first version of TaleGator I realized I needed a refined drive system. The older version constantly burned out the motors and constantly spun out. The four wheel design just could not meet the high demands of stress coming from the TaleGator. From building the TaleGator I learned allot and future models will be able to automatically adjust to lighting changes and will be able to handle all terrains much better.
Documentation: Image of a Tailgate http://taylortailgates.com/tailgating-at-florida/ Image of the motor http://www.pololu.com/ Image and data of maxbotic http://maxbotix.com/documents/mb1010_datasheet.pdf CmuCam v4 http://cmucam.org/projects/cmucam4/wiki/sparkfun_camera
Appendices: Software and other documentation can be found on https://sites.google.com/site/talegator01/