Research Update (12/8/14): New Designs (some, even printed!)

Original Bio-Mimic Pylon (Left View)

Original Bio-Mimic Pylon (Angled View)

Secondary Bio-Mimic Pylon (Angled View)

Secondary Bio-Mimic Pylon (Left View)

Doubled Banded
Bio-Mimic Pylon (Left View)

Doubled Banded
Bio-Mimic Pylon (Angled View)

The intent of these designs is to mimic the natural flow of the leg and hopefully spread the pressure out better than a basic straight design. After consulting with my supervisor on the earlier bowed design (this design will not be printed. After designing and seeing the first set of parts print, it became apparent that this design is too bulky, both in weight and size, for practical application), he suggested designing a limb in this direction. Inspiration came from images on this site.

The series of events since the last post occurred chronologically as follows: 

• The first set of pylons (already posted) were designed,
• the straight elliptic pylon was printed, the first true bio-mimic pylon was designed,
• the bio-mimic pylon was printed at a percentage so as to copy the size of the other pylon (it was overshot and the bio-mimic pylon was slightly smaller),
• it was realized that the bows of the original bio-mimic pylon are on the wrong the axis of the ellipse (perpendicular to the minor axis rather than the major, which matches natural design better) and the pylon was not useful do to my accidentally including an ankle component, which is made superfluous by foot attachments,
• the second bio-mimic pylon was designed with the bow perpendicular to the major axis without the intent of production (this design was made primarily for cataloguing, creating a template for future designs on which to build, and visualization),
• the double banded pylon was designed,
• the first produced pylon was qualitatively evaluated under impact; it was determined an elliptic straight pylon of 16cm at 10% in-fill can withstand impact up to 3500-4000 N of pressure for showing serious damage,
• the double banded pylon and the elliptic straight pylon were printed at 10% in-fill with percentages that would produce pylons of approximately 20cm,
• the double banded pylon experienced a printing failure and was reprinted at 20% in-fill.

As you can see from the link and the first four pictures, I got lost in designing and forgot about actual functionality of the product. The first two bio-mimic legs are pretty much a waste due to them extending to ball of the ankle. This error was considered when designing the double-banded pylon.

The reasoning behind these designs (and some sketches for future designs) was the natural design of human legs externally (they match the outlines of the calf muscle, which may result in greater aesthetic appeal) and the structures of the tibia and fibula with respect to one another. The latter is why the central column in all three designs does not have a static circumference; rather, it's thin in the middle and largest at the top and base.

Qualitatively determined by just holding the two existing parts, is that the double banded pylon (20%) is much stronger than the elliptic straight pylon (10%). It is hard to judge whether this is solely due to the difference in in-fill (I am going to have the straight pylon printed with 20% in-fill next) or it could be due to either the presence of banded or a central column with dynamic radii.

The next step, which will occur before Thursday, is to test the pylons by applying sustained pressure (rather than impact). This will by done resting cinder blocks (weighing approximately 160 N each, which is approximately 36 lbs) and other modes of weight while the pylon is fixed to a force plate. The force plate will connected to a data logger, which will record all of this. Weight will be applied to the pylon until it shows signs of damage.