ET-Quad Leg Design
Over The span of 9 months, along with a team of 20 students and professors, we built the first legged robot with the trimodal ability to walk, climb, and swim. I designed and fabricated the foot of the robot which enabled walking and climbing capabilities by having anisotropic compliance on individual "toes". ET-Quad can climb at 0.15 m/s which is on par with other legged modern climbing robots, but once again, ours could also walk and swim.
Prototype Foot
In my original design, I incorporated a flat ABS toe featuring a kerfing pattern (small cuts on the side of the toe) to precisely tailor the toe's stiffness. The flexibility to adjust stiffness is crucial, considering the distinct requirements for walking and climbing. We can effectively modulate the compression and tension stiffness of the C-curve of the toe, addressing the unique demands of both walking and climbing activities.
Prototype Failure
While the plastic toes demonstrated success in regular use, they fell short during stress testing. The video depicts the toes failing within the initial hops at maximum motor torque. This showed the necessity of adopting a more resilient material such as steel or aluminum to ensure durability and withstand rigorous real-world conditions.
Introducing Metal Toes
We instantly ran into complications in transferring our original design principles into metal. The laser cutter on lab was not able to cut metal therefore we would have to find a different way to make the kerfing pattern or we would have to change designs. We chose to use a water jet to cut the metal, however because of the nozzle size of the jet it would effect our kerfing. Including all of the diffrent designs and metals we tested over 120 metal unique toes.
Testing toe stiffness for compression cases (walking) and tension cases (climbing).
First batch of kerfed metal toes separated by material
While the plastic toes demonstrated success in regular use, they fell short during stress testing. The video footage depicts the toes succumbing to failure within the initial hops at maximum motor torque. This outcome showed the necessity of adopting a more resilient material to ensure durability and withstand rigorous real-world conditions.
Closer to Success
ET-Quad was able to climb effectively because of the individual compliance of each toe. However looking at the video on the right we can see how it struggles walking. The issue we determined was the lack of friction between the floor and the toes. We had dipped the toes in an abrasion resistant rubber however rubber would still scrape off.
Final Design
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The final design added spikes on the area the made contact with the ground to increase friction on rough terrain. This was the result of 9 months of work, and I am very proud of it considering ET-Quad was able to climb at rates on par with other legged climbing robots at 0.15 m/s. Please watch the video below to see the full results.