This is a Lego-compatible cap for the Vorpal Hexapod http://www.vorpalrobotics.com/
You can replace the standard cap with this one to build custom structures with Lego on top of the robot.
More information about my design process and a video with the robot in action.
It needs support on the inside. If you can reduce the infill for the support to 10% or less this saves time and material. Support is only required to help with the long bridges.