This arm resembles a crane, with the first 3 degrees of freedom along cartesian x,y,z coordinates, and the last 3 degrees are angular azmuth, declination (from z axis), and rotation.
It is controlled by PyUltimateRobot software (available on source forge)
Components
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See BOM.ods spreadsheet in the drop box files
The total bill of materials is quite extensive, but comes in at less than $1000 total.
The grips are based on 3/4" aluminum square tubes. The predicted squeeze strength is around 40 pounds.
What about safety? Using PyUltimateRobot (see that Hackaday page), one can limit maximum force of any component of any movement. For example, you can program the robot to never use more than 1 pound of force unless explicitly commanded as needed for a particular movement.
I've finished making the bearing guides. They turned out well.
I've also updated a uploaded a lot more files into the dropbox area.
The design files are fairly complete now -- at least to the point that one could duplicate what I've done so far. I'm sure more revisions will follow as paper hits reality.