ME370 AUTOMATON WALKER ENGINEERING PORTFOLIO BY JOHN HUTCHINSON
Low-fi Prototype
Initial Concept
Intense Labor
Finished Automaton!
More Intense Labor
The purpose of the project was to create an intriguing and intricate automaton that would be integrated to a walking base. The thematic basis of our groups project was a medieval dragon. Dragons themselves have inspired and sparked the imaginations of many in a fantastic way, so they make for a great theme for the automaton walker.
The objective of the walker automaton was to have a walking and animated dragon. The automaton portion consists of the head, flapping wings, and swinging tail. The walker consists of the moving legs of the dragon.
The final product was successful in that the defining features of the dragon were present and moving. As the dragon’s legs propels the automaton forward, the wings flap and the tail sways side to side like something out of a movie.
PVA ANALYSIS BASIS: FOURBAR LINKAGE ANALYSIS
The Jansen Linkage can be broken into three 4-bar mechanisms, each of which can be analyzed using the Analytical Closure Equations
Single Fourbar Mechanism Analysis: Analytical Closure Equation Because fourbar linkages have a single degree of freedom, one input, namely the crank angle, can be used to determine the output angle, namely the rocker. Closure equation determines the relationship between crank angle and rocker angle for a given fourbar system Link lengths, crank angle and velocity are known
Single Fourbar Mechanism Analysis: Analytical Closure Equation Cont.
Single Fourbar Mechanism Analysis: Analytical Closure Equation Cont.
A similar equation can be developed for the second fourbar linkage system as shown
Single Fourbar Mechanism Analysis: Analytical Closure Equation Cont. The final fourbar equation can be developed assuming that link c is the ”ground” link and link e is the ”crank” link.
Angles 7 and 9 can be determined with the addition of the fixed angle from the triangular links
Single Fourbar Mechanism Analysis: Analytical Closure Equation Cont. Now that all of the required angles are known, all of the node positions can be determined using vector summation. For example:
Because the equations generated are for any given crank position, the entire mechanism configuration can be determined.
Single Fourbar Mechanism Analysis: Velocity and Acceleration
Given a time step dt and crank angular velocity, the continuous rotation of the crank can be simulated as discrete steps
The velocity of the nodes is given by:
Solving the three fourbar equations results in the positions of all nodes in the Jansen mechanism at a given step n=1,2,3,‌ for nodes k=1,2,3,‌,8
Acceleration is similarly given by:
Instant Center Analysis
Instant center analysis of this mechanism can be useful for quick estimate, however, for complete analysis, it can become unwieldy due to the procedure of finding the instantaneous centers, since there are 66 possible instant centers Once a comprehensive PVA/DFA is implemented, it is much more useful and robust than the instant center method
Dynamic Force Analysis In order to analyze the torque requirements and link forces, a DFA is required. The crank link m is shown as an example. Similar procedure can be carried out for all links.
In order to perform the DFA, Newton’s 2nd Law for forces and torques are developed for each link.
Dynamic Force Analysis Cont.
Next, all of the equations for each link are arranged into a matrix format, where there is a dimensions matrix, a column matrix containing all of the forces of interest, and the dynamics matrix
The dimensions and dynamics matrices are all known values based on the physical geometry of the linkage mechanism, so in order to obtain the forces, the inverse of the dimensions matrix is multiplied by each side to solve for the forces matrix
PVA/DFA Implementation PVA was implemented using Matlab software, resulting in the following analysis as shown on the right side. The top graph shows the position, velocity, and acceleration of the foot (node 8) and the bottom graph shows the foot motion contour.
PVA/DFA Implementation Cont. From the PVA, DFA is implemented in order to quickly solve for the force matrices for each crank position.
Foot F o
rces
Ground L ink Forces
PVA/DFA Implementation Cont. As a result of the analysis performed, the walker designed was able to move sufficiently quickly, around 20 cm/s, while running at a low enough torque so that the motor could drive the both the walker and the automaton with any problems! Fully Functional Automaton with performance requirements met!
CAD Model with theoretical performance
PVA/DFA Analysis to check performance
Design Thinking Process
Project Statement: “Children need to be immersed in engaging applications of science and technology, because physically interacting with things that elude a child’s understanding encourages them to be more inquisitive.�
User Needs: Children
Design Thinking Process Cont.
Ways/features to meet Children’s (user) needs
Dragon must be “LIFELIKE”
Design Thinking Process: Legs
”Motion must be smooth and elegant, while looking like dragon’s legs.”
Design Thinking Process: Wings
“Wings must be look like dragon wings, while emulating realistic flapping motion.�
Mechanism animation design in SAM
Design Thinking Process: Head and Tail
“The tail must swing side to side as the dragon lumbers.”
”The head must be fearsome and eye-catching, as if it will spit fire at any moment.”
Design Thinking Process: Culmination
This produce to not have come to fruition without the many tweaks and changes made during each iteration of the project. Initially, we had a very clear vision of what the end product should look like and behave like, so each part was created with that in mind. With flapping wings, flailing tail, fearsome head, and legs, our automaton is able to capture the essence of the mystical dragon and is very close to the original concept.
“The automaton is eye-catching and awe-inspiring at first glance. Its motion is smooth and graceful as a dragon’s.”
Design Thinking Process: Limitations Due to size constraints, the wings were not as large as they could have been. Ideally, the wings would be twice the wingspan to give the automaton a more impressive look. The head was not as animated as initially envisioned due to drive train routing issues. For future iterations, the drive train will be redesigned so that the mechanisms can be more easily powered by the central drive train. Time was wasted using wooden driveshafts, which kept breaking due to the high torque load. Instead, we should have used the metal shaft after the first or second shaft failures in order to better utilize time in other areas.
Individual Contributions
Jansen leg design Determine scale of leg links and assembly configuration
Swinging tail design Helped design alternative tail mechanism
Individual Contributions Cont.
D-Shaft to link connection
Shaft to gear Connection
Allowed for easier assembly compared to set screws. Very low chance of slip due to D shaped design. No adhesives.
Individual Contributions Cont.
Assembly and Troubleshooting
PVA/DFA Analysis
Reflection - I had good communication with my group members in a timely manner though GroupMe. As a result, we were able to meet as needed and decide on weekly goals and what needed to get done. When it came close to deliverables, I was also coordinating the synthesis of our team’s work, since each person was working on a single piece rather than all work on the same thing at the same time. When it came to assembly, I was able to make some quick solutions and decisions when our encountering minor setbacks. One example was the D hole and shaft connection used to connect our crank links to the driving shaft. Initially, we were planning on gluing the links to the shaft, but the glue was not able to connect the shafts and links permanently. I suggested using a d-hole and d-shaft connection, which would allow for the mating of the shaft and crank links without any slipping or need for extra adhesive.
Another example would be the wooden shaft fix. The wooden shafts used to turn the mechanisms were breaking due to the high amount of torque from the motor. I pitched the idea to use the d-shaft and filing slots to allow compatibility with the d-hole links already used. One thing we all could have done better would have been to commit to strict meeting times and dates. As the semester got busier, we found that not all of us could make it to regular team meetings. However, setting up specific days each week to meet and discuss the project would have been much more beneficial than setting up impromptu meetings. This more structured approach might have allowed one of our team members to be more committed and dedicated to the project.
Reflection Cont. - In this course, the subject that I learned the most about was linkages. I already had a good idea about gears and cams, but the more analytical information about linkages was new and interesting. It also helped that the majority of the project was based on linkages, rather than gear or cam systems. I obtained a lot of knowledge about linkage classification, PVA and DFA analysis, along with how to write computational programs to analyze a given linkage system. I found it the easiest to learn when there was some example problems or homework related to the material, or if it was applied during the project itself, such as performing PVA/DFA analysis. I also learned about the design process. Learning about what sort of things that professional designers do and look for helped me a lot. I now know that there needs to be extensive research put into the user base to determine the needs of the user and that there are many solutions for any given problem, and that the best to approach a design problem is to empathize and ideate based on the needs and wants.
- The things I learned from ME370 not only include knowledge of mechanical engineering, but also about team management and communication. The structured ideation exercises helped me and my team to produce a larger variety and higher quality ideas before narrowing down to the ones we thought were the best of the best. Working on a team-based project also bolstered my communication skills since each of us had our own opinions and methods of going about the project. We were able to decide on the best way to handle the project in and out of team meetings, which led to our final automaton outcome.
Reflection Cont. - However, nothing is without challenges. We had some design difficulties during assembly, such as the shaft breaking problem, but we were eventually able to find a suitable solution. Another challenge we had was meeting time management, since each of us had busy schedules, so meeting regularly as a group was difficult. Another challenge was that one of our group members was inactive for the latter half of the semester, putting undue burden on the rest of the group. We were able to overcome such adversity by better managing our project time together and re-delegating work that was done outside group meetings. Overall, every challenge and difficulty we faced did not stop our group’s progress.
- I think that the most applicable knowledge that would be applied in the real world would be the technical know-how and how to work in teams. Engineering is not a one-man job; any engineering problem is best suited to be taken on by a team and in industry, any project is team-based. Learning to work in teams now will only benefit me in the future and help me become a better and more holistic engineer and person.