I've added another blog entry on my large Kossel build, covering 24V conversion to get higher speeds, the new Duet 0.8.5 board, and the Robotdigg metal effector. It's at [miscsolutions.wordpress.com].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

About the effector tilt error:
With an aluminum effector it should be possible to clamp the e3d hotend at the lowest end of the heatsink. This way the tilt error wouldn't have such a long lever.
The effector would need a redesign to make it possible, but could also contribute to the cooling.

Gaining a few mm extra z-height is another benefit
-Olaf