First of all, you have to fix the PXFmini on the Erle-Rover with a Raspberry Pi Zero/Raspberry Pi Zero W, Raspberry Pi 2 and Raspberry Pi 3 with the 3D piece.

In the following links you will find the STL necessary for Raspberry Zero, Raspberry Pi 2B / 1B and Raspberry Pi 3:

Then connect the Erle-Rover components to the PXFmini: