Linear alternator module tuning parts: add-on mass discs, the soft 0.5 mm leaf and its rim shim — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/linear-alternator-module-tuning-2in/ (CC BY 4.0) Basis: Natural frequency f = √(k/m) / 2π of the mover on its leaves and bounce gas spring (k_b = γ p A² / V_b, adiabatic); masses from the CAD at 7.9 g/cm³ (assumed); leaf stiffness from the generator's frame model (E 200 GPa assumed) Catalog version: 2026-10-20 Sizes: see table below - What moves the frequency, largest first: the charge behind the piston, the bounce volume, the leaves, the mass. The discs are the fine trim: four of them lower the frequency by about 5 %, because the mover already carries 865 g of magnets and return path. - Coarse tuning without new parts: a stock 2 in spool between face B and the cap (one more gasket and clamp) softens the bounce gas spring. With a 3 in spool: 295 cm³, 17.5 / 28.3 Hz (air 1 bar / helium 10 bar, standard leaves); with a 6 in spool: 430 cm³, 17.1 / 25.1 Hz. - Mass down, frequency down: each disc adds 24.1 g. Discs stack on the crown inside the cup (Ø26 bore on the hub boss) and are held by three M3 screws into the crown's tapped holes: 1 disc M3 × 8, 2 discs M3 × 12, 3 discs M3 × 16, 4 discs M3 × 20 (always 4 mm of thread in the crown; the heads stay inside the cup). - Spring down: the soft leaf is the 0.8 leaf's outline at 0.5 thick, 1135 N/m against 4426 N/m axially (stiffness goes with thickness cubed). Fit both leaves soft, each between two 0.6 half gaskets (0.6 + 0.5 + 0.6 = 1.7, the joint). One leaf per joint is the rule: two leaves in one joint would rub on each other, and a joint holds only 1.7. In the open-frame module each soft leaf sits on a 0.3 rim shim in the 0.8 seat. - Spring up: charge. With face B closed the bounce gas is the stiffest spring in the module: 3.0 kN/m at 1 bar air, 29.2 kN/m at 10 bar air, 34.8 kN/m at 10 bar helium (157 cm³ behind the piston). A stock 2 in spool between face B and the cap adds volume and softens it (k_b falls in proportion). - The table is the module alone. On an engine the working gas on face A adds its own stiffness (and the engine's power): the module's frequency on the engine is the engine's, and it is measured, not set. - Open-frame module: no bounce space, so the leaves and the mass are the whole module spring: 15.8 Hz with the 0.8 leaves and no disc, 15.0 Hz with four discs, 8.0 Hz on the soft leaves (moving mass 899 g, its tube rod is longer). The engine's own gas on face A adds to it; the datasheet lists that for engine volumes from 50 to 400 cm³. discs mass_g std_open_Hz std_air1_Hz std_air10_Hz std_He10_Hz soft_open_Hz soft_air1_Hz soft_He10_Hz 0 865 16.1 18.6 33.4 35.8 8.2 12.4 33.0 1 889 15.9 18.3 32.9 35.3 8.1 12.2 32.6 2 913 15.7 18.1 32.5 34.8 7.9 12.1 32.1 3 937 15.5 17.9 32.1 34.4 7.8 11.9 31.7 4 961 15.3 17.6 31.7 33.9 7.7 11.8 31.3 Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - Xem Studio: tools/gen_la_module.py: the module's geometry, masses, bounce volume, natural frequencies and every number on these pages — code — CC BY 4.0 — https://xemstudio.com/ - Xem Studio: tools/gen_fpse_gen.py: the free-piston generator whose stator, magnets, leaves and collars this module reuses; its leaf frame model and magnetic-circuit estimate — code — CC BY 4.0 — https://xemstudio.com/ - Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/ Free files (CC BY 4.0, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/index.json API: https://xemstudio.com/api/geometry?object=linear-alternator-module-tuning-2in