Multidisciplinary Senior Design ConferenceKate Gleason College of Engineering

Rochester Institute of TechnologyRochester, New York 14623

Project Number: P12202

TIGERBOT: HUMANOID PLATFORM

Jeremy JensenMechanical Engineering

Eric WalkamaMechanical Engineering

Matt DeCapuaElectrical Engineering

Kyle BackerElectrical Engineering

Mike ThomasElectrical Engineering

Jon CormierComputer Engineering

John SeyboldComputer Engineering

AbstractThe objective of this Senior Design Project was to design and build a humanoid robot capable of various

actions. The robot, called TigerBot, has been designed to be a platform for future use and work, capable of being modified easily. This project is to serve as a starting point in the progression towards a mobile robot capable of giving campus tours autonomously. A few of the main goals include the ability to walk, balance, and take voice commands.

The first step in the design process was the design of the mechanical body with the aid of CAD and stress analysis software. Additionally, the search for appropriate electrical components yielded the current set of devices. The three subsystems of the TigerBot are the mechanical body, electrical hardware, and programming environment. The mechanical body consists of 23 servos connected with various aluminum rods and plates. The main electrical components used include a RoBoard embedded computer, custom power distribution board, and servo controller board. Additionally, a voice recognition module, accelerometer, gyroscope, wireless adapter, and multiple ultrasonic sensors and infrared sensors are utilized. The programming environment consists of the ROS operating system.

Currently, the TigerBot is capable of standing on its own as well as performing various actions involving the arms all while balancing. One of the well-known, and commercially available humanoid robots, is called Robonova. The TigerBot is 48% taller than Robonova, but cost only 40% more.

NomenclatureROS – Robot Operating SystemVRM – Voice Recognition ModulePCB – Printed Circuit BoardDOF- Degree of FreedomCAD-Computer Aided Design

IntroductionThe topic of Humanoid Robots has been addressed worldwide for decades. Countless hours have been spent

attempting to create a robot capable of mimicking human movement. In its current state, robotics is not capable of perfectly achieving this task. This is due to the strictly bi-directional capabilities of most servos. The muscles in the human body are much more flexible and capable of more complex movements.

The TigerBot project is another step closer toward a more humanoid robot. The objective of this project was to design, build, and program a mobile robot capable of mimicking the majority of human movement and behavior.

Copyright © 2012 Rochester Institute of Technology

Proceedings of the Multidisciplinary Senior Design Conference Page 2

Single joints, such as elbows and knees, are accounted for by just one servo. Ball joints, such as shoulders, hips, and neck are implemented with two servos with perpendicular, intersecting axes of rotation. Some of the more complex movements, such as rotational twists in the arms and legs, have been accounted for by adding servos in each limb in the appropriate places.

The Robot Operation System (ROS) is the brain of the TigerBot. This operating system is loaded onto the RoBoard embedded computer. The RoBoard processes the programmed commands and sends the appropriate signals to each of the servos. Furthermore, the various sensors send signals to the RoBoard, helping it understand its current state and environment. Based on information from sensors, the TigerBot can balance, avoid obstacles, and take voice commands.

Process

The initial design process consisted of drawing a basic skeleton of the robot. This skeleton included basic body shape, servo and joint locations as well as the placement of the boards and batteries. To aid in this phase, the Robonova humanoid robot was used as a basic template for overall layout, body shape, and joint mechanics. Also, the human form was used for determining correct proportionality. This can be seen in Figure 1. One of the main goals of the mechanical design was to end up with a body that can be changed if needed. This was done by make four custom brackets and using a tubular design that can be lengthened or shortened based on torque requirements. Stress analysis was performed for each of the brackets created as well as the assemble links of the body (figure 2)

Figure 2:ANSYS Stress analysis of arm Link (left) and the 3 DOF hip joint CAD model (right).

The next stage in the design process included a detailed overview of the customer needs and specifications. With each specification declared, corresponding components were chosen to fill the need. Due to the large number of components in each category (sensors, batteries, etc), care had to be taken to choose the correct devices. This was done through the use of selection matrices to subjectively determine which path was the best to take in terms of the selection of each component. The selection matrices were designed to take into account the most important aspects and specifications of each component being considered.

The computing method chosen for the TigerBot was the RoBoard RB-110 embedded computer. This board contains the processing power and peripherals needed for the desired functions. The board has a 32bit x86 CPU with 256mb of DRAM. There

is also a serial port, adding another option for programming. The board is compatible with Linux, which was used to run ROS. Due to the lack of a sufficient number of

PWM ports, a Lynxmotion SSC-32 servo controller was used as well. This board only sent the signals to the servos. They were provided power from the custom PCB,

discussed later.The batteries chosen consist of two 5000mAh Lithium Polymer packs, capable of

providing a nominal 7.4 volts each. These were chosen due to their ability to provide a large amount of peak and constant current. This is important since it was hard to

Project P12202

Figure 1: Human-Robot Proportionality

Figure 1: Current TigerBot

Proceedings of the Multi-Disciplinary Senior Design Conference Page 3

determine how much current all the servos would draw at any particular time. Also, they provide a long lifetime and are very light-weight at just under a pound. Two low voltage alarms were also purchased as an easy and effective method to indicate a dead battery in either of the two packs.

Various sensors were included in the design of the TigerBot. Three infrared sensors were placed at the front, and both sides of the robot, providing a line of sight in almost all directions. Additionally, an ultrasonic sensor was placed in the chest, to provide more complete vision in the area in front of the TigerBot. A combination board containing an accelerometer and gyroscope is placed in the upper chest, providing very accurate position measurements. The data obtained from this chip is used for balancing and determining in the robot has fallen over. Finally, a webcam is mounted in place of the head, atop a pan and tilt configuration of servos. This allows the TigerBot to stream video to a computer of what it is currently viewing.

A custom PCB was designed and built to provide necessary power to different locations. Most importantly, this board is used to provide high currents to all the servos. It contains a 40 amp fuse as a safety measure. The board also provides the user with the capability of switching the robot main power between battery and a benchtop supply. Additionally, through switches the RB-110 board to be powered separately, while the servos are off. This is not only a power saving method, but a safety measure as well. The custom PCB can be seen in Figure 4.

The servos chosen are mid-range in terms of performance and torque. Higher torque servos would have been preferred, but were outside the budget range. The servos used are capable of providing approximately 486 ounces- inch of torque. They can run on voltages in the range of 6 to 7.4 and only weigh about two ounces each.

The build process started with the mechanical build. This required the assembly of the arms and legs, which consisted of servos and aluminum brackets and links. Considerable time had to be spent contemplating the position of the output spline. This was required since one of the requirements stated was “human movement”. This meant that no limb could move in such a way that was inconsistent with that of human movement. Due to this, servo and output spline placement was critical. Once the limbs were complete, they were attached to the torso, which consisted of aluminum plates and links. Once the mechanical assembly was complete, the electrical assembly began. This consisted of crimping and cutting wires to length and attaching the desired connectors. Also, since a custom PCB was made, the components had to be manual soldered in place. Once all the boards were available, the mounting process followed. This required significant brainstorming in order to fit all the necessary boards into the chest cavity of the torso. Considerations had to be made in terms of accessibility and overheating. The boards needed to be accessed while mounted, which led to the addition of a swivel on the RoBoard. The custom PCB was mounted in such a way that all necessary switches were accessible from the back of the TigerBot. The current TigerBot build is shown in Figure 2.

Experiments performed were mostly to test successful interfacing and movement algorithms. Interfacing tests had to be performed when attempting to utilize the wired and wireless internet connections of the TigerBot. Also, voice tests were conducted in order to test the functionality of the Voice Recognition Module. The majority of tests however, were to determine whether or not the movement sequences, such as walking and balancing, were functional. The movement tests eventually required the use of a test stand in order to elevate the TigerBot, taking stress off the legs and reducing current draw from the batteries or power source. With the idea of not requiring a helping hand to test walking, another test stand was created. This stand allowed the TigerBot's feet to be in contact with the ground, while supporting the majority of its weight. This allowed for a test of the walking algorithm to be performed that did not require a team member to support the TigerBot if it should fall while walking.

Results and DiscussionThe current iteration of the TigerBot is complete from a functional standpoint. Everything is operational,

but not all of the desired functions have been implemented in programming.The mechanical construction is finished and there are no fundamental problems with the physical body of the

robot. All joints function as previously designed and are only capable of moving in ways that mimic human movement. So far, the torque of the servos has been sufficient in allowing the TigerBot to stand on its own as well as lift its legs, with the batteries present. Another factor relating to the torque is weight. Since the links and frames were constructed using aluminum, the overall weight of the robot is minimal. This helps reduce the strain on the servos.

Copyright © 2012 Rochester Institute of Technology

Figure 4: Custom Power PCB

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The electrical construction is also finished in that the boards and sensors are all interfaced and functional. The TigerBot is currently capable of sensing and reacting to voice commands. Also, the custom PCB designed works as designed and allows the TigerBot to be switched between running off of a power supply or off of the batteries. The capability of the TigerBot to run off of the batteries alone is also present. Additionally, voltage monitors have been attached to each battery pack as a safety measure. These monitors display the voltage of each battery pack and have audio alarms that indicate when the pack is approaching minimal voltage and needs to be charged. The gyroscope and accelerometer chip are interfaced with the RoBoard and are the essential tools needed when the TigerBot is balancing itself. Finally, a webcam has been attached as the head of the robot. This is not interfaced with the RoBoard, but can, however, be connected to a computer to provide a video stream of what the robot sees.

While the RoBoard is capable of being programmed effectively, not all predefined movement functions have been successfully implemented. The RoBoard of the TigerBot can be connected to and programmed through an ethernet cable, wireless network, or a serial connection. As of now, the TigerBot is capable of standing and balancing. Additionally, various actions involving the arms, such as waving, have been implemented. The main goal is to implement a successful walking algorithm, which has not been achieved yet. A walking algorithm has been implemented, but the TigerBot is not capable of walking effectively without falling.

Conclusions and RecommendationsOne of the main successes seen during the course of this project is that the TigerBot was actually built. The lead

time of the servos ordered was initially high and then the delivery date was delayed multiple times. Another success is the capability of wirelessly programming the robot. This is important because it is much faster and more convenient to wirelessly program a mobile robot while it is running on battery power. Additionally, the custom designed and built PCB for power distribution worked as planned, allowing the correct distribution of various voltages. The custom PCB also allows switching between the use of battery power and the use of a power supply. Having the robot run on battery supply only is also a big success seeing as the current draw from the servos is constantly changing. The voice recognition module was also successfully interfaced and programmed. It is currently capable of sensing and reacting to voice commands. It is also capable of outputting audio in response to voice commands. Finally, a walking algorithm has been implemented, and the different stages are successfully executed, but the TigerBot can not balancing effectively while walking yet. In summation, this project has proved to be a success in terms of the requirements given. The TigerBot, in its current state, is a fully functioning platform, capable of being programmed to perform various actions. Not only is the final product a good robotic platform for future use, it is successful in that it is a humanoid robot and is capable of mimicking the actions of a person. Another main success is that the TigerBot is 48% taller than Robonova, but cost only 40% more, meaning we were capable of designing and building a bigger robot, while using less money, proportionally.

The main failure of this project is the inability to implement a successful walking algorithm. When tested, the walking algorithm causes the TigerBot to sway excessive amounts and it is incapable of maintaining its balance. One of the solutions to this would be to used higher torque servos. This would allow the robot to balance more effectively while standing on one leg. Another solution would be to reduce the height of the robot. This would reduce the amount of torque needed to balance, while also increasing overall stability. A final solution to the failed walking algorithm would be to create and program a virtual robot in a virtual space. The virtual robot created can be made to perfectly copy the height and joint locations of the actual robot. After programming the virtual robot to walk, the same algorithm can be applied to the real robot and, in theory, it should walk the same as the virtual robot. Another one of the failures seen was a power issue. In some cases, when the servos were all turned on, the power to the RoBoard would drop low enough to cause the board to restart. This was rectified by adding capacitors to the custom power distribution board. Another failure was the breaking of one of the plastic servo horns. During start up, the TigerBot moved its right arm in a way that caused one of the plastic servo horns to break, breaking the arm off. This horn was replaced with another plastic horn, but a better solution would have been to use all metal servo horns. Finally, no input from the infrared or ultrasonic sensors is used, despite being able to interface with them.

Due to the extensive work applied to this project, many helpful recommendations can be made. The first, and most important recommendation, is to have a higher budget. While this may not be determined by the team working on the project, it is nonetheless important. The use of higher torque servos is required depending on the desired height and functions of the robot. Another recommendation is to make the robot shorter rather than taller. This would increase the success of the walking algorithm. Also, use metal servo horns. The plastic ones break too easily, and reduce robustness. Finally, if there is a deadline to meet, start programming as early as possible. It is highly recommended to program a virtual robot before the final robot is built. This gives an idea of how the final product will react to the walking algorithm used.

ReferencesWithin the text, references should be cited in numerical order, by order of appearance. The numbered reference

should be enclosed in brackets. For example: “It was shown by Prusa [1] that the width of the plume decreases

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Proceedings of the Multi-Disciplinary Senior Design Conference Page 5

under these conditions.” In the case of two citations, the numbers should be separated by a comma [1,2]. In the case of more than two references, the numbers should be separated by a dash [5-7].

References to original sources should be listed together at the end of the paper, and should include papers,

technical reports, books, prior team projects, personal discussions, websites (not Wikipedia), and software. References should be arranged in numerical order according to the sequence of citations within the text. Each reference should include the last name of each author followed by his or her initials.

(1) References to journal articles and papers in serial publications should include: last name of each author followed by their initials, year, full title of the article in quotes, full name of the publication (abbreviated), volume number (if any) in bold (do not include the abbreviation, "Vol."), issue number (if any) in parentheses (do not include the abbreviation, "No."), inclusive page numbers using “pp.".

(2) Reference to textbooks and monographs should include: last name of each author followed by their initials, year of publication, full title of the publication in italics, publisher, city of publication, inclusive page numbers using "pp.", chapter number (if any) at the end of the citation following the abbreviation, "Chap."

(3) Reference to individual conference papers, papers in compiled conference proceedings, or any other collection of works by numerous authors should include: last name of each author followed by their initials, year of publication, full title of the cited paper in quotes, individual paper number (if any), full title of the publication in italics initials followed by last name of editors (if any) followed by the abbreviation, "eds.", city of publication, volume number (if any) in boldface – include, "Vol." if part of larger identifier (e.g., "PVP-Vol. 254") – inclusive page numbers of using "pp.".

(4) Reference to theses and technical reports should include: last name of each author followed by their initials, year of publication, full title in quotes, report number (if any), publisher or institution name, city.

Example References:

[1] Taylot Veltrop at http://taylor.veltrop.com/robotics/khrhumanoidv2.php?topic=veltrop-ros-pkg[2] Ning, X., and Lovell, M. R., 2002, "On the Sliding Friction Characteristics of Unidirectional Continuous FRP

Composites," ASME J. Tribol., 124(1), pp. 5-13.[3] Barnes, M., 2001, "Stresses in Solenoids," J. Appl. Phys., 48(5), pp. 2000–2008.[4] Jones, J., 2000, Contact Mechanics, Cambridge University Press, Cambridge, UK, Chap. 6.[5] Lee, Y., Korpela, S. A., and Horne, R. N., 1982, "Structure of Multi-Cellular Natural Convection in a Tall

Vertical Annulus," Proc. 7th International Heat Transfer Conference, U. Grigul et al., eds., Hemisphere, Washington, DC, 2, pp. 221–226.

[6] Hashish, M., 2000, "600 MPa Waterjet Technology Development," High Pressure Technology, PVP-Vol. 406, pp. 135-140.

[7] Watson, D. W., 1997, "Thermodynamic Analysis," ASME Paper No. 97-GT-288.[8] Tung, C. Y., 1982, "Evaporative Heat Transfer in the Contact Line of a Mixture," Ph.D. thesis, Rensselaer

Polytechnic Institute, Troy, NY.[9] Kwon, O. K., and Pletcher, R. H., 1981, "Prediction of the Incompressible Flow Over A Rearward-Facing

Step," Technical Report No. HTL-26, CFD-4, Iowa State Univ., Ames, IA.

AcknowledgmentsWe would like to thank Dr. Ferat Sahin, Dr. Wayne Walter, Dr. Adriana Becker-Gomez, and George Slack for

their advice and guidance over the course of this project. We would also like to thank Phil Glasser for aiding in the debug process. Additionally, we owe thanks to the Robonova robot for being an inspiration in the design process. Finally, we would like to thank Veltrobot for his ROS work.

Copyright © 2012 Rochester Institute of Technology

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