20.3 Design Process and Prototyping
Iterations
Started with calculations to determine lengths and angles needed.
2D drawing of the full linkage to help visualize movement paths.
Used the TPU printer to make iterations of our compliant joint.
This is a CAD representation of our linakges, no electronics. Here we can view the full path of our joints.
Unfortunately, at this scale the TPU allowed to much shear (i.e. too compliant) and did not act like a pin joint. With this in mind, we shifted towards using a film joint. Moving towards film we faced challenges with how to hold the film and tolerancing all the tiny pieces. Especially with a 5mm link these challenges took many hours of iteration. To maximize the strength of the small pieces and prevent snapping, we also geometrically shaped the links at the joints, maximizing the volume according to the extremities of the desired motion. Thus, at the extremes links side by side have faces with full contact near the joint. Additionally, almost all of our prototyping revolved around the mini four bar because this was the most geometrically complex and constrained part of the linkage.
For all the small pieces, we used SLA to print resin parts with a 50 micron layer height. The film was then clamped between resin prints and inserts snapped in to prevent the pieces from separating. Rigidly connecting these to FDM printed parts, we ended up with a singular leg consisting of 29 pieces.