Stanford Online – Introduction to Haptics
I enrolled in Prof. Okamura’s course in order to expand my knowledge of haptics. It provided excellent detail about human haptics with some interesting experiments. The course also included basic experiments with a single degree-of-freedom haptic device designed specifically for the course called the HapKit, that was constructed from a combination of commercially available parts as well as 3D printed parts.
I successfully completed the course with a 100% grade based on video quiz questions and automatically graded lab results.
HapKit
The HapKit consists of a handle that moves freely in an arc with variable resistance (impedance) provided by a meshing motor controlled with an Arduino-based board. Positioning of the handle can be deduced via a hall effect sensor that reads the orientation of the magnet on the drive shaft. Based on the handle position, the motor can be driven to simulate a virtual spring, damper, wall, and/or texture.
Original
Following the plans graciously provided by the course staff produces the device shown below. Despite several attempts, I was unable to find a height adjustment that provided acceptable low and high impedance performance. Either the drive shaft slipped under high impedance conditions or the rolling friction was too great and uneven under low impedance conditions. It is quite likely that the problem was related to printing quality or the characteristics of the rubber. Regardless, I needed to modify the design in order to complete the course.
Modified
Subsequent to capstan wire failures in my exoskeleton prototypes, I have had great success with gear transmissions. Granted, my device’s gear transmission is mostly isolated by the series elastic elements, but I suspected that I could sufficiently minimize cogging. As the gear mesh was constrained by the design, I eliminated the height adjustment. I also replaced the shoulder screw and bushing shaft design with a more familiar dowel pin and ball bearing design. With the original design, I had found the flex in the vertical part of the stand to be marginally acceptable, and I expected the gear drive to be less tolerant; I therefore increased the rigidity by building thicker triangle braces into the stand. To support fault tolerant printing practices, I also split the base into five parts, but included tabs to utilize adhesive for fastener free assembly.
I was able to successfully complete the course lab assignments with my modified HapKit, and as a small thank you to the course staff and fellow students, I posted model files and assembly instructions on the course forum. Links to the files are also provided below:
Coursera – Georgia Tech – Engineering Systems in Motion: Dynamics of Particles and Bodies in 2D Motion
I enrolled in Prof. Whiteman’s course in order to learn two dimensional dynamics in the hopes of applying the knowledge to modeling, and with additional knowledge, robust control of my exoskeleton. It covered both kinematics and kinetics for particles, systems of particles, and bodies in rigid planar motion. The real-world examples were quite insightful while the practice and quiz questions were helpfully challenging.
I successfully completed the course with a 100% grade based on weekly quizzes.
Coursera – University of Michigan – Introduction to Thermodynamics: Transferring Energy from Here to There
I enrolled in Prof. Woodridge’s course in order to refresh my undergraduate knowledge of thermodynamics in preparation for graduate level fluid mechanics and heat transfer coursework. It covered the zeroth through second laws of thermodynamics, thermodynamic properties and phase diagrams, conservation of energy and mass, as well as power, refrigeration, and heat pump cycles. The course also provided insight into real-world applications in power plants, engines, and heat exchange systems with a view to global energy concerns.
As I started the course after the hard deadline for the first homework, I was unable to receive credit. Despite starting just hours before the second homework’s hard deadline, I sucessfully completed the course with full credit for every weekly homework after the first.
