OpenSlip is a portable dual-purpose instrument.

One battery-powered, solderless, travel-sized machine does both:

  1. Tribometer. Variable-incidence / inclined-strut walkway meter. Mast incidence θ is from vertical on a level floor. Slip index is a transparent function of that angle: SI = tan θ, reported to 0.01. Worked example: 0.50 SI = 26.57°.
  2. Penetrometer. The same stack infers surface or ground resistance while a lead screw drives a probe or the mast. StallGuard and/or coil current is the signal. Subtract a zero-load stroke so lead-screw friction is not reported as ground strength. Do not report raw StallGuard as “ground strength.” This path is designed; it is not in firmware 0.2.0.

Angle is read at the hinge. Firmware is inspectable. CAD, when it exists, will be inspectable.

This is not a certified instrument. It is not a legal-opinion instrument. It is not a clone of any commercial tribometer. Experimental, provided AS IS. Numbers it produces are functions of measured geometry and a documented method; they are not automatically comparable to a branded meter or a published safety threshold.

The physics lineage, as published, is English XL principles (variable incidence, distal weight, heel-strike). Utility patents are understood to have expired. This project copies physics, not appearance, branding, trade dress, or any copyrighted manual.

What exists now

Firmware 0.2.0 is public (Arduino, LilyGO TTGO T-Motor / ESP32). Wi-Fi AP, phone UI, CSV, OTA. Motor stays disabled until armed. SI = tan θ to 0.01 works. The sketch still talks to the onboard MT6816; Phase 1 design puts an AS5600 on the hinge as angle truth.

Phase 0 is an electronics-only prototype (public 22 Aug 2026). Phase 1 (27 Aug 2026) discloses the machine as designed. Mechanical CAD does not exist yet. That absence is a named phase of the same object. CAD files are not required to practice the invention: the architecture note plus the public firmware and the worked example are enough to build a first unit.

Worked-example stack (first example, not a fence)

  • Controller: LilyGO TTGO T-Motor (ESP32-PICO-D4, onboard TMC2209).
  • Angle truth (as designed): AS5600 on I2C at the hinge.
  • Mast actuator: NEMA 17 linear stepper, 310 mm Tr8×8.
  • Power: 65 W USB-C PD bank, detachable (travel method).
  • Structure: PETG / ABS / ASA printed struts; PLA banned for load-bearing parts; internal M8 rod in pre-tension.
  • Hinge: M8 bolt through two 608ZZ bearings.
  • Incidence: hardware-store turnbuckle.
  • Travel envelope (example): about 17.3 in retracted, about 7 in width.

Honest gaps

No CAD. No photos of a complete Phase 1 machine. Firmware still electronics-first. OLED on the first public unit did not ACK. Mechanical shopping SKUs TBD. No wet protocol, no second-build validation, no inter-lab data. Penetrometer method is designed, not in 0.2.0.

Where the art is stamped

License

Firmware and in-repo docs: AGPL-3.0. Written disclosure: CC BY-SA 4.0. CAD: CERN-OHL-S when it exists.

Author: Michael Vredenburgh. OpenSlip is an independent open-hardware and open-firmware project for walkway traction measurement. It is not affiliated with, endorsed by, or derived from any commercial tribometer brand.