Thursday, March 8, 2012

Biomechanics Midterm

For our midterm, Eric Hagan and I decided to take two elements of natural human gait (knee flexion and extension, and heel strike) and track them using sensors (potentiometer for the knee, and FSR for the heel strike). Using data from the sensors, we then created graphs and laser-cut them into acrylic mementos.

The first hurdle was getting the knee flexion and extension data. We purchased a knee brace and took apart one of the side supports, which was basically a lever that tucked into two neoprene pockets. We punched out the rivets holding them together and drilled out the holes to accept the shaft of the potentiometer.

Once completed, we secured the base of the potentiometer to one lever arm using the threads and nut already on the potentiometer. For the other arm, we stabilized the shaft on either side with shaft collars, and epoxy'd it all together.

For the FSR, my wife made a small pouch with elastic that secures to the sole of the foot. This became the base of our second data set.

We wrote Arduino code to make sure we were outputting serial data for both sensors, plus a millis column as the X axis on our graph.

We used an ethernet shield's micro SD slot to record the serial data.

We perfboarded the additional wiring and components, and it all fit into a pouch connected to the user's calf.

Now it was time to take a few walks.

After getting data for both our right legs and left legs, we plugged the data into excel and graphed it. This was then moved into Illustrator, ready for some creative license.

There was much more variation in the FSR, while the movement from the potentiometer was more subtle. For viewers to better understand the relationship between the knee movement and the heel strike, we raised the amplitude for the knee, and lowered it for the heel. This created a more aesthetically satisfactory shape.

Then it was on to cutting. For each of us, one piece is red, and another is clear, allowing us to overlay them and visually compare the difference in movement between the right leg and the left leg.

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