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Evolution of a Leg Design

The leg design of Spot Puppy has already gone through a significant evolution based on iterative experimentation and learning. The early versions were design to be extremely light as shown in the picture below. This consideration was mostly due to our concerned about the available power of a micro servo. However after early testing it became clear that the design was too flimsy and with too much flex. We also discover the micro servo were more powerful than we originally thought.

With the knowledge we had acquired from testing our first generation of the leg we made significant design changes and moved on to generation 2 as shown below. This version of the leg design was much stronger and included screw holes for mounting the servos. We printed a pair of legs and using a cardboard box for a body and pencils for back legs we had our first moving prototype. Through testing we found some more design issues the biggest of which was the single attachment point for the servos.

With all of our learning from generation 1 & 2 we moved on to generation 3. This version of the leg included attachment points both sides of the servo which made it feel much stronger. To see how this version of the leg performed we decided to combine a test with an early version of our control library so we built a painting robot that used a Spot Puppy leg as its arm. Although we could still see flaws in both the leg design and the control library it was immensely satisfying to see our robot paint a simply picture.

Encouraged by the success of our painting robot we made a small modification to the foot and reprinted 2 more versions of the generation 3 legs. With the legs assembled we further developed the control library to include an early understanding of walking and running gaits and set about testing with the very satisfactory result shown below.

Generation 3 – Spot Puppy Legs demonstrating a running gait

We are still making refinements to the leg and completing further experimentation to determine the best foot design but we are very happy with the progress so far.

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