Modular Connectors
thingiverse
This connector system, designed for modular robotics projects, supports STL, IGES, STEP, and Alibre Design formats (original source). A robot utilizing this connection system is featured in a video at http://www.youtube.com/watch?v=wUivg15i2-Y. Further insights can be found in the paper "Simple Components for a Reconfigurable Modular Robotic System" available at https://rpk.lcsr.jhu.edu/Publications#Metamorphic_Robots. Initially, cast polyurethane was used; however, it may work well when printed. Both the pin taper and thread angle are 20 degrees.
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