arcticoder/spurious-force-balanceOpen, low-cost torsion balance for measuring the spurious forces (supply-lead Lorentz forces, heating, convection) that dominate small-force and thrust experiments: printable CadQuery mechanics, a validated force-noise model, and JLCPCB-assembled RP2040 electronics designed in KiCad and ngspice.
Heads panel is an open-source printed circuit board by arcticoder, from the arcticoder/spurious-force-balance repository on GitHub, published under the MIT licence. It is a 2-layer board of 76 × 70 mm with 58 parts on 18 nets, routed with 315 tracks and 29 vias.
Its parts include 10 capacitors, 6 ICs and 4 connectors. It belongs with the sensors and measurement boards and the RP2040 boards of this library.
An open, low-cost torsion balance for measuring the spurious forces that dominate small-force and thrust experiments, with printable mechanics, a validated force-noise model and fab-assembled electronics.
The question. On an open, fully SMT-assembled, low-cost torsion balance operating in air, quantify the forces that usually pass for thrust: the Lorentz force of supply-lead currents in the ambient magnetic field, and the thermal and convective forces of a dissipating device. Measure them as functions of current, lead geometry and dissipated power, with the balance's force noise floor, calibration constant and drift fully characterized. The instrument claim is a resolution of 0.4 nN or better (5σ on a 20 nN term) in a 1000 s measurement, at a parts cost to be filled in from the final bill of materials.
| Piece | State |
|---|---|
| G1 measurement goal | confirmed 2026-10-23 |
| G2 mechanics | an FR4 arm board on edge hung from a torsion head, collision-free over the swing, centre of mass solved onto the axis; JLC mechanical boards (Gerbers and DRC done); stock-size acrylic enclosure; field-modelled eddy damper; cutting jigs; fabrication decisions, assembly steps |
| G3 force-noise prediction | 0.108 nN (1σ, 1000 s, in air): a conditional go |
| WP1–WP3: requirements, 48 JLC-stocked parts, analog block simulations | done |
| WP4 schematic | done as checked netlists (main board + four head boards, 50 JLC parts); sheet rendering and WP5 layout wait |
| A5: prototype noise measurement | next; it decides layout and the board order |
The prediction is dominated by air currents (4.8 nN/√Hz), so the verdict flips at about 4 mm/s of air-speed fluctuation; the enclosure is the biggest noise control. The model reproduces six published numbers, from Soni and Roy (Rev. Sci. Instrum. 84, 095103, 2013) and the cryogenic torsion balance of arXiv:2206.02890.
| Path | What |
|---|---|
docs/plan.md | the plan: goal, mechanics, noise budget, environment control, calibration |
docs/fabrication.md, docs/assembly.md | how each part is made (fab boards, PLA, bought; JLC orders, coupons and parcels) and how to build it |
docs/bringup.md, docs/procedures.md | powering up the electronics step by step; the prototype check, calibration and measurement campaign |
docs/paper/ | the paper skeleton (LaTeX; results are placeholders) |
hardware/balance/ | parametric CAD (balance.py, STL and STEP in cad/), the FR4 boards for JLC (boards.py, boards/fab/), jigs, analytic model, parameters, checks |
hardware/instrument/ | the electronics: requirements, pin map, parts table, ngspice simulations, checks |
hardware/tools/jlc_query.py | search of the JLCPCB parts snapshot |
tools/force_noise_budget.py | the force-noise prediction and the anchor checks |
docs/TODO-agent.md, docs/TODO-arcticoder.md | the work lists (TODO-BLOCKED.md, TODO-backlog.md, TODO-completed.md beside them) |
Setup (Linux/WSL) is in hardware/README.md: KiCad 9, a Python venv with CadQuery, SKiDL and ngspice.
python3 tools/force_noise_budget.py # the noise prediction and anchor checks
~/.venvs/lab-hw/bin/python tools/run_all_smoke_tests.py # CAD, pin map, power budget, simulationsThe bench circuits this experiment uses for its prototype check (lock-in amplifier, optical shadow readout, R-2R signal generator) live in arcticoder/lab, which also holds the shared parts inventory and order ledger.
.py file is code (MIT)
whose output is hardware (CERN-OHL-P).| Qty | Value | Footprint | References |
|---|---|---|---|
| 38 | FID1, FID2, FID3, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB +22 | ||
| 8 | C0603 | C0603 | C1, C3, C4, C5, C7, C8, C9, C10 |
| 4 | CONN-SMD_4P-P1.00_SM04B-SRSS-TB-LF-SN | CONN-SMD_4P-P1.00_SM04B-SRSS-TB-LF-SN | J1, J2, J3, J4 |
| 4 | WSON-6_L2.0-W2.0-P0.65-TL-EP | WSON-6_L2.0-W2.0-P0.65-TL-EP | U1, U3, U5, U6 |
| 2 | C0805 | C0805 | C2, C6 |
| 2 | LGA-16_L3.0-W3.0-P0.50-BL_SQ | LGA-16_L3.0-W3.0-P0.50-BL_SQ | U2, U4 |
arcticoder/spurious-force-balance
Open, low-cost torsion balance for measuring the spurious forces (supply-lead Lorentz forces, heating, convection) that dominate small-force and thrust experiments: printable CadQuery mechanics, a validated force-noise…
arcticoder/spurious-force-balance
Open, low-cost torsion balance for measuring the spurious forces (supply-lead Lorentz forces, heating, convection) that dominate small-force and thrust experiments: printable CadQuery mechanics, a validated force-noise…
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The firmware/boards directory contains configuration for each board this firmware supports.
It measures 76 × 70 mm and has 2 copper layers, 1.6 mm thick.
58 parts. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
From the arcticoder/spurious-force-balance repository on GitHub, at the commit this page was made from: the board is hardware/instrument/heads_panel/out/heads_panel.kicad_pcb and its schematic hardware/instrument/schematic/out/sensor_head_2.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Its repository publishes it under the MIT licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).