Changelog

Unreleased

Mechanisms

• wobbl mechanism runs robot arms, four bar linkages, gear trains, impacts and things that tip in MuJoCo, from a template with --set values, a TOML spec of bodies, joints, drives, couplings, loops, loads and a move, or an MJCF or URDF model. Motors follow a straight torque speed line, and servos follow their move by computed torque up to it.
• An arm’s servos are judged for a stall against their line and for heat by their RMS torque over the cycle, a linkage gets its sweep, toggle positions, transmission angle and mechanical advantage, a gear train its output speed and torque with mesh losses, an impact its peak force and a stand its tipping point. Every fix is solved again before it is suggested.
• Each run is checked against a closed form wherever one applies, at half the time step and with an energy account over every force, and its contact depth and constraint drift are inspected. Runs write trajectory.csv and playback.json for replaying the run.
• MuJoCo installs itself on first use from its PyPI wheel, 7.8 MB to fetch and 18.3 MB on disk after pruning, or with wobbl setup --only mujoco. Agents get solve_mechanism, and plain questions about servos, linkages, gearboxes and tipping reach the new domain.
• Six validation cases against exact answers, all within 0.05%, and two examples, a desktop arm on hobby servos and a windshield wiper linkage.

Buckling, vibration and fatigue

• wobbl buckling finds the load factor and mode shapes with CalculiX’s buckling step and cuts the factor by an imperfection knockdown for the shape, the European column curves for struts, NASA SP-8007 for thin cylinders, none for flat plates and 0.5 for shapes with no test data, and by yielding. It checks Euler’s column, force balance, mode separation and the meshes.
• wobbl vibration finds natural frequencies, mode shapes and effective mass with attached masses, judges them against rotor speeds and tones, gives the peak stress of a sine sweep (checked against CalculiX’s steady state dynamics step) and the 3 sigma stress and fatigue of random input such as NASA GEVS. Each answer checks the mass, Rayleigh’s quotient and a single mode estimate.
• wobbl fatigue gives the cycles before a crack starts and a safety factor on stress from a strength or vibration result or from given stresses, with sourced S-N data per material, Marin factors, notch sensitivity, Goodman, Gerber or Soderberg and Miner’s rule for a duty cycle.
• Agents get solve_buckling, solve_vibration and fatigue_life. Nothing new is downloaded, since they run on the CalculiX strength uses.
• Five validation cases, Euler’s column, a cantilever’s and a plate’s modes, a sine peak on a tip mass and Shigley’s fatigue example, and three examples, a drone arm’s resonance, a strut’s buckling and a motor mount’s fatigue, each with a playback.json for the website to animate.

Rocket motors and combustion

• wobbl motor burns a solid motor design back to its thrust curve, from BATES, tube, end burner, star, finocyl, moon and X core grains, KNSB, KNDX, KNSU and MIT APCP propellants with their published burn rate laws, and a nozzle. It checks the time step, the mass balance, the closed form pressure and the propellant’s c* against equilibrium, judges the casing’s hoop stress at peak pressure, the port to throat ratio, core mass flux and nozzle separation, simulates each fix and writes thrust.csv and a RASP motor.eng. A rocket spec for motion flies a design with design = "motor.toml".
• wobbl flame and wobbl propellant give flame temperatures and CEA style c* and Isp from Cantera on NASA’s thermodynamic data, and agents get solve_motor, solve_flame and solve_propellant.
• Cantera installs itself on first use from its PyPI wheel, 6.3 MB to fetch and 15.7 MB on disk after pruning, or ahead of time with wobbl setup --only cantera.
• Eight new validation cases, against Turns, NASA CEA, Nakka’s PROPEP run, closed forms and two MIT static fires, and two examples, a KNSB motor and a propane flame.
• wobbl runaway finds the surrounding temperature at which a charged lithium ion cell’s own decomposition outruns its cooling, by Semenov’s criterion and a transient with the reactants used up, and can take its surroundings from a heat study. A LiCoO2 18650 runs away at 156 C against the published 155 C, and a new example checks the battery pack’s hottest cell. Agents get solve_runaway.
• Every motor, flame, propellant and runaway run writes playback.json, its own data thinned for a viewer to animate.

Motion

• A new motion domain flies a body from release or ignition to the ground through gravity that falls off with altitude, the 1976 standard atmosphere, drag that can follow Mach number, wind, a launch rail, a thrust curve and drogue and main parachutes, integrated with scipy one phase at a time between events. It needs nothing beyond scipy, so it downloads nothing.
• wobbl motion takes a round body as one line of flags or a rocket as a TOML spec with units, and agents get a solve_motion tool and a skill section on when to use it.
• Each flight is integrated again with a tolerance ten times tighter, compared with closed forms wherever the model reduces to one, closed with an energy balance and, for a rocket, with Tsiolkovsky’s delta v less its gravity, drag and steering losses. Rockets also get Barrowman’s stability margin, rail exit speed, peak loads, apogee against a target, landing speed and drift, with fixes for nose weight, fin span, rail length and the main parachute.
• Two new examples, a falling rock and a rocket launch, and six motion validation cases against exact closed forms, which make 25 cases in all.

Credibility evidence

• wobbl uncertainty carries load, material, geometry and boundary condition scatter through a finished run and returns the probability of failure with its 95% interval, the spread of the answer and Sobol indices. Strength runs scale exactly, several loads scatter one at a time through an exact sum of one solve per load on the final mesh, and Poisson’s ratio, geometry, heat and circuit inputs get new solves and a polynomial chaos surrogate with its leave one out error.
• wobbl validate-against compares a run with gauge, temperature, circuit or scope readings as ASME V&V 20 does, adds the area metric, calibrates the uncertain inputs and says which load attachment the readings favour.
• wobbl credibility writes a V&V 40 style assessment into report.html and a standalone credibility.html, and wobbl test-plan names the fewest physical tests that most reduce the risk. Wobbl supplies the evidence and certifies nothing.
• Four new agent tools and a skill section, five validation cases, and the cast mount credibility example with clearly synthetic readings.

0.1.1 (2026-10-13)

Heat

• A transient study whose held temperature differs from the part’s starting temperature now runs. A plate at 20 C set on a surface held at 120 C used to stop CalculiX with “increment size smaller than minimum”, because a face that jumps all at once moves its neighbors by a fixed amount however short the time step. The held temperature now ramps in a straight line from the starting temperature to its target over a tenth of the time heat takes to cross the smallest element at that face, or a thousandth of the run if that is shorter, and never quicker than CalculiX’s shortest time steps can follow. The result’s assumptions say how long the ramp was and why.
• A face that jumps gets extra saved times through the ramp and the fast flow of heat just after it, and a jump under 100 C gets smaller time steps in proportion, so a 20 C jump is followed as closely as a 100 C one.
• The transient energy balance integrates heat flows through a monotone cubic instead of straight lines between saved times, counts each held face on its own and is judged against the largest flow in the account. A hot face and a cold face pushing heat through a part now close within 2%, and the plate on the hot surface closes to 0.8%.
• A study that makes no heat says so in its assumptions, instead of saying the heat is spread through the part.
• A new validation case, sudden-face, compares the temperature 10 mm into an aluminum bar whose end jumps to 120 C with the erfc solution for a semi infinite solid. Two new end to end tests compare every node with the erfc solution and with the Fourier series for a bar between a hot face and a cold one.
• The battery pack example was run again, so its result shows the transient energy balance.

Install

• Installing on an Intel Mac no longer needs Rust and a C compiler, because cryptography stays below 49 there, the first version with no Intel Mac wheels.

0.1.0 (2026-10-13)

First release.

Strength

• STEP, IGES, BREP, STL and parametric .py parts, read through OpenCASCADE with healing only when a solid is broken, touching bodies bonded, tiny faces removed.
• Second order tetrahedral meshes (gmsh) with feature sizing, hotspot refinement, automatic fallbacks (another algorithm, straight sided elements, a finer size), and every mesh attempt isolated in a child process with a timeout.
• Loads can be forces, pressures, bolt bearing, gravity, or remote forces and moments through distributing (RBE3 style) or rigid couplings. Supports can be fixed (in all or some directions), bolted holes with washer rings, rollers, or wall contact solved by an active set loop with a coarse pre solve and warm starts.
• A face selector language picks sides, planes, normals, holes and fillets by size, nearest faces, spherical and box patches, and ids.
• 23 sourced materials, including sand cast A356-T6, plus custom properties. Each material says how it is made (printed, molded, cast or wrought), so its assumptions fit, and printed parts can be checked across layers.
• A bearing keyword for a bolt or pin pressing on one side of a hole, as in --load "300 N -x bearing @ hole d=6.6". Without it the force spreads evenly over the hole faces.

Verification on every answer

• Mesh convergence over at least three meshes, force and moment balance, a beam theory hand calculation through the critical section, singularity detection from exact CAD geometry, bolt bearing, units and deflection sanity, a large deflection re-solve when a part bends a good fraction of its wall, and the spread between rigid and distributed load attachment.
• Confidence (high, medium, low) with reasons, and never high after a failed check.
• The same input gives the same numbers on every run, because meshing runs on one thread with a fixed seed and every size comes from the CAD. When the rigid and distributed load attachments disagree, the other one is converged at its own peak before it is quoted.
• Bounded runtime, so the last finished level is returned when time or a solver runs out.

Seeing and fixing

• Heatmaps with the failure point marked (VTK off screen, matplotlib fallback), convergence plots, plain text summaries and a self contained HTML report.
• Fix suggestions with numbers. Fillets and gussets are applied to any STEP through OpenCASCADE, along with thickness and fillet parameters of parametric parts and material swaps, and each one is simulated again for a before and after table.

Heat and circuits

• Steady and transient conduction with convection, radiation, heat sources and held temperatures, with an energy balance on steady and transient runs and lumped hand calculations.
• ngspice checks for LEDs, RC networks, buck converter ripple and MOSFET junction temperature, plus arbitrary netlists, with textbook and time step checks.

Agents

• wobbl setup installs CalculiX and ngspice into ~/.wobbl with a pinned micromamba and registers an MCP server and skill for Claude Code, Codex, Cursor and Gemini CLI, with backups and wobbl uninstall. A test parses every command in the skill against the real CLI.
• A validation suite of 18 cases, with textbook solutions, NAFEMS LE1 and LE10, and five real parts against converged reference models. It runs in about 30 minutes on a 2018 six core laptop.