Amphibious Robot
Stanford ME112 Mechanical Systems Design
Team project, 6 weeks
Team members: Christina Martin-Ebosele, Janique Lee, Simone Wilcox
Spring 2019
Instructor: Prof. Mark Cutkosky
Skills:
3D printing
3D CAD Modeling
Solidworks
Research
Rapid Prototyping
Mechanical Engineering
Prompt:
Build a biologically-inspired autonomous machine that can navigate 1m of water, then climb a shallow ramp with 2cm tall obstacles within 1 minute.
Approach:
Make a robot that emulated the combined motion of a frog and a duck (fruck).
Additional Constraints:
The robot must be battery-powered, and use a provided Tamiya 6-speed motor and gearbox kit to power its motion.
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Diagram displaying robot's path. Courtesy of 'ME112 Final Project Spring 2019' teaching team
Description
Utilizing my skills in the humanities and previous research experience, I performed the majority of the initial research and summarized it for the team. From that grounding research, I was also in charge of the feet of the robot, from creating rapid prototypes, testing, iterating, through 3D printing the final feet used on our robot to pass the demonstration test.
It was a challenge to create "feet" that not only can dynamically swim through water but also climb onto an inclined ramp and successfully climb over obstacles.
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Choosing wheel legs was presented as a surefire option of passing the design challenge, but our team wanted to push ourselves further and use knowledge from the course to create a linkage based robot.
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Besides my responsibilities on developing the foot of the robot, I worked closely with my teammates every week to engage in team discussions, iterate through designs, prototyping, testing, design decisions, and solve issues that arose.
Research
I conducted a literature review for innovative biomimetic amphibious robots. From this research, we decided to prototype the motions and qualities of a frog, cockroach, duck, as well as a version of the researched robots wheel legs (Whegs) to see what worked best.
Left: Hinged duck foot model [source: Kashem S. et al. 2017]
Right: Cockroach whegs climbing an obstacle [source: Harkins R. et al. 2005]
Prototyping
I created prototypes out of pink foam to quickly sculpt and test different geometries of "feet" for the robot.
Using a water basin, I was able to quickly get a sense of the resistance when the different geometries paddled through the water. This let me iterate through ideas that were unlikely to work and identify shapes that had high potential.
Pink foam prototypes in a water basin for early testing.
"Wheg" design. 3 lasercut acrylic foot shapes, modeled loosely after the Naval Postgraduate School and Case Western Reserve University's bionic cockroach robot "whegs".
While I worked on getting the foot designed and printed, my teammates worked on the 4-bar linkages, the chain-gear mechanism separately. We worked on assembling the body and optimizing the robot together, and met testing milestones every other week.
CAD Modeling
Penultimate 3D model of foot.
Left highlights the trapezoidal bottom of foot that makes contact with land.
Right displays the rectangular back that functioned as the paddle in water.
Solidworks and Onshape assembly created in conjunction with team members.
Final 3D model of improved foot.
Solidworks model created with Christina Martin-Ebosele.
After testing and getting feedback with my teammates, course assistants and professor, we redesigned the foot to include both a curved foot similar to my earlier prototypes to easily move over obstacles, and a large, thin rectangular paddle to get through the water faster.
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Instead of bolting the foot to the linkage, as in the penultimate model, we used adhesive to attach the foot and linkage. The bolts often became loose in our testing so that the foot became misaligned, lost torque, and affected operation. We solved this with the redesign and by using adhesive on a large surface area to prevent loss of torque through rotation.
Summary
Final Amphibious (Frog +Duck = Fruck) Robot Design. Features a lightweight frame design, linkage bars, antlers, and a chain gear mechanism
At the final presentation, our robot traversed the water in 8 seconds and the ramp in 24s, well within the 1 minute limit.
We were pleased with the robot's performance, and if we had more time, we would have experimented with the use of a tail to let the robot travel in a straighter line in turbulent water. We also would experiment with more adventurous design, spend some more time on exterior aesthetics, and improve the efficiency of the motor through reducing weight and drag.
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This was most of our team's first robotics project, and we appreciated this opportunity to work on such a challenging project together.
Acknowledgements
Prof. Mark Cutkosky
Janique Lee
Christina Martin-Ebosele
Simone Wilcox
Katie Reinders
Ryan Lee
Esteban Meija
and others