Summary

This is an 80mm IoT field mill. The field mill is usually located outside, a few feet above the ground and pointing towards the ground, where it measures the local E-field strength and polarity. This field mill has a place for a NodeMCU module that sends out the E-field measurements wirelessly.

Post-Printing

The non-3D parts needed to complete the field mill are some 3mm heat set inserts, 3mm screws, 4-40x1/4" set screws, 4-40 jam nut, 5mm shaft, 5x16x5 bearing, motor, flex tubing, copper foil tape, custom circuit board, NodeMCU module, and a printed label for the optical encoder.

The rotor is covered with self adhesive copper foil tape. A 4-40 x 1/4" set screw with a 4-40 jam nut on top holds the rotor in place and electrically connects the foil to the shaft. The 5mm shaft must be grounded; I used a repurposed motor brush as a contactor to the shaft. The faceplate and frame are bonded together to form one piece. I used ABS for these parts and solvent bonded them together. More copper foil tape goes on the faceplate sensor areas and is soldered to wires fed through the faceplate. The encoder wheel needs to be drilled out to 5mm for the shaft, and all set screw holes tapped for 4-40 threads. The motor shaft is about 2mm diameter, so a shaft adapter is used to bring it up to about 5mm and then a bit of flexible tubing is used as a shaft coupler.

80mm Field Mill