Now that I have a Bezier tool: http://www.thingiverse.com/thing:8454 Everything looks like it needs some swoopy smooth lines on it.
This thing is an experimental variant of the effector tool base for the PolyBot.
One of the things I was after was being able to print without too much warping. The previous design has a lot of surface area in contact with the platform, so it tends to warp.
I think this one might work out well enough, but it needs some mounting holes. It is somewhat parametric. You can choose how long the arms are, and the size of the axle mounts. It is a bit hacky though.
1) Print one of these
2) Attach your PolyBot robot arms to it