2. The Challenge. 1. Introduction. 3. Rover Prototype NASA Research Space Grant Page 1

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1 Self-Orientating Autonomous Pathfinder (S.O.A.P.) Matt Bird, Tina Sandaval, Matt Wicke, Mark Nenninger, Metropolitan State College of Denver Professor Aaron Brown and Dr. Megan Paciaroni April 19 th, Abstract The NASA Space Grant Robotics Challenge put forward an opportunity to further college students understanding of the theory of autonomous vehicle design. For our team, our purpose was to gain insight into the process of design and better learn how to engineer from concept to construction.the challenge specifically is to design and construct an autonomous vehicle capable of navigating an obstacle course while locating a radio beacon. 1. Introduction The term robot was first used introduced by the Czech playwright Karel Capek in his 1920 play Rossum s Universal Robots i. Historically, robots have been used to replace the jobs of human when a human life doesn t want to be sacrificed. One of the jobs that can be completed by a robot is exploration. One type of robot commonly used for exploration is known as a rover. Due to the robustness of a robots ability to function after being accelerated beyond what a human could survive, made robots the perfect candidate to perform the job of Mars exploration. In the summer of 2003 the delta rockets One and Two, carrying the rovers Spirit and Opportunity,were launched from Cape Canaveral Air Force Base. After traveling three hundred million miles, the rovers had landed on Mars in January of These rovers were responsible for the discovery of high silicon content in the soil of our neighboring planet, which happens in the presence of water. This means the Rovers are responsible for proving the existence of water on Mars. More recently, in August of 2011 another exploration rover named Curiosity was launched with the intent of Mars exploration. Curiosity is larger than the original rovers, giving it the ability to travel greater distances. Curiosity is also capable of some sophisticated soil testing and time will tell what new discoveries the rover will make. 2. The Challenge This year was the sixth year for Adam s State College and N.A.S.A. s Colorado Space Grant Consortium robotics challenge at the Great Sand Dunes near Alamosa Colorado. The challenge was to build an autonomous robot capable of navigating through sandy terrain of the dunes and locate a central beacon, the Yagi antenna. The Yagi antenna transmitted a heading using a 433Mhtz RF signal that the robots then used the heading to travel towards the beacon. The sandy dunes provided a perfect testing site on earth similar to the extreme environment not unlike some conditions on an alien planet like Mars. Not only is the sand challenging to travel over, it also has an negative effect on moving parts an electronics therefore providing the teams with a real challenge in order for their robot to succeed. 3. Rover Prototype 1 While the end result of the project seemed to model the rover Curiosity, the original goal was to build an autonomous rover suitable for Adam s State College and NASA s Colorado Space Grant Consortium robotics challenge at the Great Sand Dunes in southern Colorado. The first problem was designing a wheel for the rover capable of providing traction in the deep sand. The robot also needed some sort of suspension system that could provide the rover with stability on the uneven surfaces of the wind blown sand. The team started with a prototype of the rover in December that consisted of a Tupperware box for the main body to house an Adriano Uno controller board, a rocker-bogie suspension system constructed of L-brackets and JB weld, six 6 volt dc motors, and six 20 fl. ounce Gatorade bottles for wheels complete with layered hot glue paddles for traction in the sand NASA Research Space Grant Page 1

The rocker-bogie suspension system was chosen due the low speed of the rover negated the use of a spring suspension and to its ability to allow the rover to climb over objects that are twice the

The prototype rover as shown in figure 1 also had servos on the front and back wheels providing four wheel steering capabilities and the possibility for zero- point turns which are useful in object

2 The rocker-bogie suspension system was chosen due the low speed of the rover negated the use of a spring suspension and to its ability to allow the rover to climb over objects that are twice the diameter of the wheels. The prototype rover as shown in figure 1 also had servos on the front and back wheels providing four wheel steering capabilities and the possibility for zero- point turns which are useful in object avoidance and tight turning abilities. While the prototype rover provided a great Figure 2. Rocker Bogie Suspension System Figure 1. Prototype One 3.1 Rocker-Bogie Suspension System Although the rocker-bogie suspension system uses no springs, the low speed design of the rover negated the need for a spring suspension. The rockerbogie suspension system also posses the ability to allow the rover to climb over objects that are twice the diameter of the wheels. In order to drive over an object, the front wheels are forced against the vertical face of the object. Once the front two wheels begin to climb over the object, the middle and rear wheels push the rover forward while still providing four points of stability. After the front two wheels have cleared the object, the middle wheels climb over the object while being pulled by the front wheels and pushed by the rear wheels and still providing four points of stability. Finally the rear wheels are pulled over the object by the front wheels and the middle wheels with four points of contact for stability. Another feature of the rocker bogie suspension system is that the right side works independent of the left side providing the ultimate chaises design for the rover. foundation for the team to start with, it had some design flaws. First the rover lacked the torque necessary to travel through deep sand. Another problem was that the original L-brackets used in the suspension system had some over lapping of pieces, which did not allow the rocker bogie suspension to reach its full potential. Still another problem was that the servos used to control the heading of the rover had a plastic shaft that was breaking under the lateral stress of turning against the momentum of the moving rover. There were also problems with the way the suspension attached to the body of the rover. The Tupperware body was not rigid enough to support the stress at the point of contact between the Tupperware and the rocker bogie suspension system. 3.1 Sensors Another important part of an autonomous rover is its sensors. The sensors provide input about the surrounding environment, telling the rover to turn if there is something in its path. A few options used in path finding methods are infrared sensors, whiskers and ultra-sonic range finders. One drawbacks of the infrared sensors in the desert is the fact that the receiver in the sensor has a tendency to saturate in the bright sunlight of the desert. In order to avoid this problem, the prototype was designed to use ultrasonic range finders. The first sensors were less expensive and after a long night of troubleshooting bad data the decision was made to purchase some Ping ultrasonic range finders shown in figure 3. The new sensors worked well and provided data about obstacles up to 300 cm away NASA Research Space Grant Page 2

Figure 3. Ping Ultra Sonic Range Finders The next version of the rover had more powerful motors to drive the vehicle forward.

on the left and right as shown in Figure 4.

Once the initial sets of legs were cut a series of holes were drilled to accommodate secure and precise connection to the body and to the servos and all calculation for bending were done with a

3 Figure 3. Ping Ultra Sonic Range Finders The next version of the rover had more powerful motors to drive the vehicle forward. The problem with the with the servo shafts snapping by a reinforcement found on servo city the issue of detecting objects and walls was solved by adding two more sensors at forty-five degree angels on the left and right as shown in Figure 4. Our first designs were laid out in AutoCAD and cut with the Industrial Design department s CNC plasma cutter out of 16 gauge mild steel as shown in figure 5. Once the initial sets of legs were cut a series of holes were drilled to accommodate secure and precise connection to the body and to the servos and all calculation for bending were done with a standard bench top sheet metal brake. 3.1 Problems While the prototype rover provided a great foundation for the team to start with, the prototype rover had some design flaws. First the rover lacked the torque necessary to travel through deep sand. Another problem were the original L-brackets used in the suspension system had some over lapping which did not allow the rocker bogie suspension to reach it s full potential. Still another problem was that the servos used to control the heading of the rover had a plastic shaft that was breaking under the lateral stress of turning against the momentum of the moving rover. There were also problems with the way the suspension attached to the body of the rover. The Tupperware body was not rigid enough to support the stress at the point of contact between the Tupperware and the rocker bogie suspension system. Finally, with only two sensors the robot had trouble determining if there were any objects or walls to the right or left sides 4. S.O.A.P. 1.0 Figure 4. CNC Plasma Cutter The first mockup of the rover used a small plastic bin for the main compartment and body that housed the electronics. The two sides of three wheels each were mounted separately. After the initial design phase we chose to make a slightly larger body from acrylic, using water thin solvent to construct. With access to the plastics lab, we were able to create a shape that would accommodate our long Lithium-Polymer battery, and the mounting of cooling fans, as well as feeding all thread through to each side to attach the legs As seen in figure 6. Figure 5. Ping Ultra Sonic Range Finders and Servo Supports 2011 NASA Research Space Grant Page 3

suspension and wheels. The all thread was secured with threaded rubber washer plugs; which sealed the holes into the body to prevent sand exposure to electronics.

A type of adhesive door insulator was used around the edges of the lid also, to prevent sand exposure, with which we experienced minor shrinkage.

4 Figure 6. New Acrylic Body The idea that the legs were attached to the same rod straight through the body was to give the rover s structure more rigidity and to allow the body to move independently from the suspension and wheels. The all thread was secured with threaded rubber washer plugs; which sealed the holes into the body to prevent sand exposure to electronics. The lid design was simply placed on top and secured with rubber bands for easy and quick access during trouble shooting. A type of adhesive door insulator was used around the edges of the lid also, to prevent sand exposure, with which we experienced minor shrinkage. Originally, two angled front corners would house the sonar sensors that were later repositioned atop the front servos. Initially it was thought that the acrylic might cause adverse reaction with the electronics due to static and the solution would be to treat the case with static dissipative epoxy paint; during testing, static never became an issue at this scale. S.O.A.P. version one is shown in figure Traction Figure 7. S.O.A.P. Version 1.0 Figure 8. New Tires 5. S.O.A.P. 2.0 After initial testing it was discovered that the chosen servomotor combo was powerful enough to bend the suspension made of 16-gauge steel due to wheels catching one another and having some issues with clearance. A second set was cut with 16 gauge after minor size and length adjustments and retested. The conclusion being strength issues, a new suspension was designed and cut out of 12-gauge steel. The choice of 12 gauges was in part restricted by weight concerns and the bending capacity of the sheet metal brake. This new set of legs was much more stable and after initial trials, holes for mounting were machined with a vertical mill rather than a drill press specifically for accuracy and speed. Tabs were built in to prevent over extension of the back two wheels on either side. Later, after testing, additional stop tabs were welded on for similar concerns. Another concern was a lack of traction provided by the Gatorade bottles alone. The decision was made to purchase some paddle tires for radio-controlled cars as shown in figure 8. The trouble was how to mount the tires to the motors already purchased for the rover. Luckily the wheel diameter of the wheels exactly fit the diameter of the Gatorade bottles and the new tires were added. 5.2 Controls S.OA.P. 2.0 used an Adriano Mega board for control and included some sophisticated code to accomplish the task of obstacle avoidance. It was checking for obstacles both in front of the rover and to the left and right. By comparing the values received by the ultra sonic sensors S.O.A.P. was able to determine the best way to go in real 2011 NASA Research Space Grant Page 4

time. Once an object had been avoided the path of the rovers turn was originally calculated using linear algebra to do a linear curve fit though this was latter replaced with a cosine function

5 time. Once an object had been avoided the path of the rovers turn was originally calculated using linear algebra to do a linear curve fit though this was latter replaced with a cosine function because of the functions curve one way then the other to return the rover to the original heading. The rover also included code that disabled it from turning sharply while traveling down steep inclines. In order to accomplish this the rover used an accelerometer to read the e angle normal to the rover. This allowed the rover to manipulate through a ditch instead of trying to avoid the bottom of the ditch. The Audrino Mega board interfaced with an Audrino Uno board that was used to receive the transmission signal transmitted from the Yagi antenna. The process of interfacing these two boards proved to be another challenge that the group was able to overcome. 6. References i Mark W. Spong, Seth Hutchinson, M. Vidyasagar Robotics Modeling and Control, Malloy Inc, United States of America, Bumper A bumper circuit was added to the rover s sensors as a failsafe to the ultra-sonic range finders. A screw, shielded by a spacer, surrounded by a sprig was used to create a normally open circuit that when closed caused the rover to reverse then turn forty five degrees, then read ultra-sonic sensors to determine the best path and proceed. 5.4 Conclusion The result was a Self-Orienting Autonomous Pathfinder that was capable of roving through the rugged dandy terrain of the Great Sand Dunes and also capable of finding the transmitter beacon using an RF heading signal and comparing it to the heading of the rover. The final project, S.O.A.P. 2.0 shown in figure 9, is the result of months of design, then testing then redesigning process improving the upon the weakness of the rover all the time. This was a valuable learning experience for all that could not be simulated in the classroom and the team will remember forever. Figure 9. S.O.A.P Version NASA Research Space Grant Page 5

roving on the moon Leader Notes for Grades 6 12 The Challenge Prepare ahead of time Introduce the challenge (5 minutes)

for Grades 6 12 roving on the moon Leader Notes The Challenge Build a rubber band-powered rover that can scramble across the room. In this challenge, kids follow the engineering design process to: (1)