Multidisciplinary Senior Design Conference Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York 14623 Project Number: P12201 RIT “Tigerbot” Humanoid Platform for Future Expansion Charles Borrello Chris Rabnovich Andrew Jabrucki ME/Co-Project Manager CE/Lead CE EE/Co-Project Manager Ernest Danzo Joe Noble EE/Lead EE ME/Lead ME Danny Lee Jon Zaman Tony Burnette CE/Quality and Test Engineer EE/Integration Officer ME/Resource Engineer Abstract The objective of this project is to introduce a platform for a humanoid robot that could be built upon in future projects. The robot was designed with the ability to humanly move, be controlled autonomously, resist a fall with the ability to recover, and have at least twenty degrees of freedom in motion. Dr. Ferat Sahin, of the Electrical Engineering Dept. at Rochester Institute of Technology, facilitated the project with specific product requirements and team guidance. The team was split up into three disciplines of Mechanical, Electrical, and Computer Engineering. A robust control system was designed to process commands, sensing, and servo motion. The electromechanical body is comprised of link and joints that use servo motors to ensure complete human motion. The final product is comprised of three control devices, an aluminum sheet metal body, motion libraries with linked commands, and various sensors. In this paper, the design concept, control development, fabrication, and final product testing will be discussed for complete understanding for future developers. Proceedings of the Multidisciplinary Senior Design Conference Page 1 Nomenclature Degrees of Freedom (DOF), General Purpose Input Output (GPIO), Inter-Integrated Circuit (I2C), Inertial Measuring Unit (IMU), Multidisciplinary Senior Design (MSD), Rochester Institute of Technology (RIT), Serial Peripheral Interface (SPI), Universal A-synchronize Receiver Transmitter (UART) Introduction The development of robotic systems is a widely researched and important field in engineering. Robotic systems are used throughout industry to automate processes and advance product creation. Humanoid robot creation and manipulation of motion development has become a research area of interest in recent years. These robot types are utilized in environments where human motion and sensing is required to accomplish a task. Motion should not be mechanically limited and should be refined to human precision. The Rochester Institute of Technology Robotics Department headed by Dr. Ferat Sahin has previously begun research in the development of humanoid robot motion and sensing. This project named “Tigerbot” was derived as a platform to advance RIT’s development and research in humanoid robots. Tigerbot will help develop learning for future students and help display to the public the opportunities developing at the university. This Humanoid Platform is characterized into four main areas for development: electromechanical body, control system, intelligence, and sensing. The electromechanical body is comprised of aluminum links and joints that will be mounted to servo motors. Specialized brackets and differently torqued servos allow for complete unrestricted motion of the robot. The control system is divided into two specific devices: a servo controller and a sensor processor. The servo controller is used to provide human-like motion to the body. The sensor processor is used to process information from sensors and update the intelligence system of the external environment. The intelligence system is used to perform more complex functions of a human such as receiving voice commands or written commands (WIFI commands) and control the flow of information throughout the system. Finally, sensors are used to update Tigerbot about the external environment. The Multidisciplinary Senior Design team was constructed to combine Mechanical, Electrical, and Computer Engineering students. Mechanical Engineers used their skills in torque analysis and 3D modeling to design link material and select servos. Electrical and Computer Engineers used their combined skills in programming, power management, and control systems to help form communication and sensing framework. The advantage of the multidisciplinary team was the ability to learn in parallel with other disciplines by helping in the design and building processes. Throughout the process all disciplines had the opportunity to contribute in motion programming, link construction, and power management. The project was split into two ten week sections. The section of MSDI was spent designing all aspects of the Tigerbot, while Proceedings of the Multidisciplinary Senior Design Conference Page 2 the section of MSDII was used to realize the design by constructing and testing. This will be developed with explanation in the following sections. Design Methodology Customer Needs and Specifications Electromechanical Body These requirements consist of basic human functionality of the robot. The robot should be able to balance, walk, get up from falls, walk over small objects and resist a push. To accomplish this, further needs of at least four degrees of freedom per arm and leg, two degrees in the torso, and two degrees in the head were required. The DOF had to have human similarity. For example, elbows and knees could not hyper-extend. These requirements also implied that wiring and links would not get in the way of the DOF. In addition to the DOF, the robot had to be robust enough that it would not break either due to falls or torque on the joints. To accomplish this strong link design and securing the boards and wires are all important. Intelligence These requirements consisted of a PC or “brain” that should be present in the robot. One of the main requirements of Tigerbot is that it had to be expandable. To do this the intelligence system needed to be powerful and have many expandability ports. Requirements on the main PC or “brain” of Tigerbot are the presence of a 32-bit architecture, an operating system, a minimum of 2GB of memory, Wifi or Bluetooth capabilities and multiple expansion interfaces. Specifically related to expansion, the intelligence system needed to be able to control up to 32 servos and have SPI, UART, I2C interfaces. Sensing Tigerbot has to be able to detect its internal and external environment along with performing functions of a humanoid. Tigerbot needed the ability to detect body position and objects that it may come in contact with. To do this proximity, touch and IMU sensors would be used. To perform the functions of a humanoid, Tigerbot needed to respond to voice commands. Tigerbot was required to respond to a minimum of sixteen voice commands. Additional requirements were related to sensing. These included interacting with object and avoiding obstacles. The robot had to be able to avoid large objects, walk over small objects, walk up inclines, walk down declines and avoid shear drops. Tigerbot also had to detect and counter-act harmful forces such as a push. Human Characteristics Since this is a humanoid platform, Tigerbot had to have human characteristics. These included human proportionality, human-like movements, a height of 20 to 36 inches and weigh Proceedings of the Multidisciplinary Senior Design Conference Page 3 less than 30 pounds, as well as supporting 25% of its own weight and be functional for a minimum of two hours Human-like movements had to be possible through software libraries. These software libraries had to contain simple algorithms such as walk and get up from a fall. The voice commands could then be tied to some of these software libraries. Concepts Link Material and Servo Selection Worst case scenario torque analysis was performed to determine the torque values required by the servos in key locations. Due to budgetary constraints, the high torque servos selected for the robot could not be used for every joint, so these servos were only used on key joints such as the knee, forward leaning motion of the hip, and the elbow/shoulder bending servos. This can be seen in Figure 1, which displays a portion of the torque analysis. These were determined to be key joints in walking, balancing, and getting up from a fallen position. When the analysis was performed some general assumptions were made. These have the following link properties: weight acts at center, made of aluminum ( , thickness of at least 1/16’’, at least the width of the servo, and are on both sides of the servos. Figure 1: Torque Analysis: Leg Layout (left), Thigh Servo (right) An assumption was also made that the thigh servo would require higher torque. The torque calculations were made using equation (1) ( ( ( )) ( ( ( )) ( (1) where S is the Sress, F the Force, and L the Length of the link segments. The max torque was calculated and found to be 210.9 oz-in, which resulted in the selection of the higher torque servos. Each of the designed custom built links was analyzed in ANSYS for the worst case loading conditions to ensure that they would stand up to both normal robot operation and severe Proceedings of the Multidisciplinary Senior Design Conference Page 4 conditions such as a fall. The links were designed to be robust so that future expansion of the robot would not cause the robot’s links to sustain loads beyond their capabilities. The above conditions for “worst case loading” were used for the general worst case for normal operation. For the falls, an estimated load based on the mass of the robot falling from a height of about two feet was used. Degrees of Freedom The customer specifications on DOF were specific. The customer needs overall 20 degrees of freedom in the robot involving four per arm, four per leg, two degrees in the torso and two in the head. Figure 2 shows the final concept of the DOF for the robot. Figure 2: DOF Concept Diagram The final design involves two degrees of freedom in the upper arm to replicate the ball joint movement of a human shoulder. The other two degrees of freedom were placed at the elbow to simulate both the twisting motion of the shoulder ball joint and the bending of the elbow.