models: Add an alternate model for the VPE

3d models/TagTuner VPE Notes.md

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+# VPE TagTuner stand
+An alternative enclosure for the VPE and PN532 NFC reader.
+
+I didn't want to completely disassemble the VPE, so I created this stand 
+to allow plugging the grove connector into the VPE through the snap-off hole
+in the bottom of the VPE.
+## Files
+- `TagTuner VPE Notes.md` - These Notes
+- `TagTuner VPE.scad` - VPE + NFC reader OpenSCAD design
+- `TagTuner VPE.stl` - VPE + NFC reader stand STL
+- `TagTuner disc with B-XD002.stl` - Disc with cavity for NFC chip 
+- `TagTuner disc.stl` - Disc without cavity
+- `TagTuner VPE.jpg` - Photo of assembled unit
+- `TagTuner VPE w-disc.jpg` - Photo of assembled unit with sample disc
+
+## OpenSCAD design
+I used the BOSL2 OpenSCAD library as part of the design. 
+https://github.com/BelfrySCAD/BOSL2/wiki
+
+The file contains both the stand and a simple disc design that fits the stand.
+To switch between them, you comment the appropriate line at the bottom of
+the file.
+
+The stand is made for a 100mm disc, but other sizes should sit there just
+fine. The disc module takes a true/false parameter that enables a cavity in the
+disc for a 25.4mm diameter x 1mm thick NFC chip (e.g. MakerWorld B-XD002). Or
+you can disable the cavity and just use stick-on tags.
+
+Many of the dimensions of the stand are parameterized such that relative
+positions will adjust as needed. So it's relatively easy to adjust if  you
+don't like my aesthetics.
+
+## Slicing Notes
+I enabled tree supports with "On build plate only" enabled. If you allow
+supports within the object they will obstruct the internal channel for the NFC
+reader wire and are very difficult to clean out.
+
+I set max bridge size to 10mm. Using a 10mm bridge size permits the through 
+holes for the VPE feet to be printed without supports. Supports here are 
+difficult to clean up and are not needed.
+
+I set the bridge direction manually, to 45 degrees. The default attempted 
+to create a diving board 50mm long with no support at one end over the 
+channel that the NFC reader wire runs through. There will be some amount 
+of stringing where the VPE base and the reader plate intersect, but it's 
+all internal and not visible.
+
+When slicing the disc, I used the Archimedian Chords surface pattern for top
+and bottom (gives a vinyl record-like appearance). If embedding an NFC chip
+in a cavity, you will need to set a pause point at the layer just prior to
+covering the cavity.
+
+## Assembly
+Run the grove cable from the back of the NFC reader plate down through the 
+channel and into the VPE base. Some jiggering is required to coax it through 
+the channel, but it will go.
+
+Attach one end of the grove to the NFC reader then slide the reader into
+the slot in the cavity on the back of the reader plate (with grove connector
+down and bottom side of reader toward the face of the plate). I would
+wait to snap in the back cover plate till everything is tested. It can be 
+difficult to remove.
+
+Snap off the plastic tab that covers the grove connector on the bottom of
+the VPE. Plug the grove connector into the bottom of the VPE. Snake the
+excess cable in the recessed area and set the VPE into the base.
+
+Optionally, you may remove the rubber feet and bolts in the bottom of the 
+VPE and screw the VPE down to the base. You will require 4 M3x16 bolts for
+this. The rubber feet can be reused in the bottom of the base.