EDIT: A new version of this that directly supports 1 inch square extrusion is coming very soon, along with instructions to build a removable square frame for the Robo using the stock mounting points.

This is a bracket that fits to the cover mounting points for the Robo3D so you can attach whatever you like, in my case arms for a spool holder.
I've included the spacer I designed to encase my timber upright for a tight fit though you'll likely need to design and print your own spacer for whatever you want to use.
The base bracket's internal dimension is 19.7mm by 44.2mm and 55mm high. The Robo3D cover mounting bracket is 25mm high so that leaves 30mm for mounting your uprights or whatever you like.

Printed in PLA with 3 perimeters/top/bottom and 33% infill.
Design your own spacer for a tight fit and drill your own mounting holes. The hole for the stock mounting bolt is included in the base bracket. Please see my spool hub design for mounting the spool.