THE ENGINEERING RECORD, FILE 08 OF 19

The chest mount and the camera alternative

Every file of the record The engineering hub

The chest cradle: a back plate with strap slots and a dovetail rail, the soft cradle with four spring jaws, and the rain cover, lifted apart. Outer dimensions: back plate 90 by 70 by 10 mm with its rail, cradle 75 by 70 by 21.9 mm with its jaws, rain cover 88 by 30 by 14 mm. — The chest cradle, from the OpenSCAD part. A back plate with slots for the elastic strap, 40 mm wide in this design (the record gives the strap's length in two sizes, not its width), and a dovetail rail; a soft TPU cradle with four spring jaws that take a phone 65 to 80 mm wide and 7 to 11 mm thick, gripping the edges only so the camera stays clear; and a rain cover hood. Quick release on the dovetail. Rendered by Blender from the STL files; dimensions are design values until a printed part is measured. Outer dimensions, design values until a printed part is measured: back plate 90 by 70 by 10 mm with its rail, cradle 75 by 70 by 21.9 mm with its jaws, rain cover 88 by 30 by 14 mm. Strain relief channels and service loops are not yet drawn; every enclosure dimension here is a design choice, not a measurement. Source: hardware/scad/chest-cradle.scad, drawn from docs/08 and docs/11.

Blueprint, isometric view of the chest cradle with its outer dimensions written under it, design values to be measured on the printed part. — The chest cradle, from the OpenSCAD part. A back plate with slots for the elastic strap, 40 mm wide in this design (the record gives the strap's length in two sizes, not its width), and a dovetail rail; a soft TPU cradle with four spring jaws that take a phone 65 to 80 mm wide and 7 to 11 mm thick, gripping the edges only so the camera stays clear; and a rain cover hood. Quick release on the dovetail. Rendered by Blender from the STL files; dimensions are design values until a printed part is measured. Outer dimensions, design values until a printed part is measured: back plate 90 by 70 by 10 mm with its rail, cradle 75 by 70 by 21.9 mm with its jaws, rain cover 88 by 30 by 14 mm. Strain relief channels and service loops are not yet drawn; every enclosure dimension here is a design choice, not a measurement. Source: hardware/scad/chest-cradle.scad, drawn from docs/08 and docs/11.

Decision: a quick release printed cradle on an elastic chest strap that shares the belt anchor so it does not pull. Holds the wearer's own phone in portrait or landscape with a rain cover option. Wireless to the Spine over Bluetooth; no cable to snag. Breathing and bounce are absorbed by a compliant TPU cradle face.

Camera alternative for wearers who cannot spare a phone: a low cost module driven by the Spine, clipping into the same mount. Candidates: Grove Vision AI V2 or OpenMV class modules. The phone path is the default because it is free to a wearer who already has a qualifying phone.

Roadmap, on the roadmap, planned after the tests: a smart glasses scene layer (an open OpenGlass class build on a XIAO ESP32-S3 Sense first, commercial frames such as Brilliant Labs Frame to demo and Halo when it ships) and, for wearers without a qualifying phone, a waist pouch in the Raspberry Pi 5 class with an AI accelerator hat. An optional stereo depth camera (OAK-D Lite class) stays a research rig instrument. The head camera pick for the scene layer is a wide module in the Raspberry Pi Camera Module 3 Wide class, run at 1 to 2 MP and 30 to 60 fps, because motion, field, and latency beat pixel count for obstacles; full resolution stills are taken only for reading text, on request. The scene layer describes and never warns.

Source: docs/08-chest-mount-and-camera.md, the engineering record. Every number on this page is read from that file. If a fact is not in the record, it is measured on the bench, or it stays off this site.