Does the jaw-force bound still hold at arm accelerations of 100 to 800 m/s²?

What it found

A follow-up to robofab-graspmove and robofab-armaccel, which applied the bound m√((g+a_up)²+a_side²)/(2μ) beyond the 40 m/s² it had been tested to. Here a MuJoCo jaw assembly with prescribed constant acceleration (40 to 800 m/s²) holds three printed parts of a toy gripper. With a 0.05 ms timestep and 0.1 ms contact time constant the simulated minimum force is 0.89 to 1.02 times the bound over 39 cases (median 1.00); with the earlier settings no force up to 60 N holds a part at 400 or 800 m/s², a contact-lag artefact. Stylised: rigid box pads, one friction coefficient, no arm dynamics or trajectory.

A figure from its own output

Paper, code and results

• README and method
• White paper
• Experiments and results
• Code
• Tests

More in Robot manufacturing loops

• How fine must the MuJoCo contact settings be for a moving grasp?How fine must MuJoCo contact settings be for a moving grasp? On all seven toy-gripper parts, solref 0.2 ms and below reproduce the jaw-force bound (0.98–1.04×) at 100–800 m/s²; 0.5 ms fails at 400 and above, and the adequate value falls with acceleration (stylised, upward load only).
• Is it the contact time constant or the timestep that breaks a moving grasp?Is it solref or the timestep that breaks a moving MuJoCo grasp? On a 24-cell grid only 6 cells hold; a coarse step always fails, a finer step does not rescue a marginal solref, and solref 0.1 ms holds at steps of 0.1 ms and below (stylised).
• Is MuJoCo's refsafe clamp what breaks a moving grasp at a coarse timestep?Does MuJoCo's refsafe clamp break a moving grasp at a coarse timestep? Switching it off changes 7 of 32 grid cells' outcomes (11 hold on, 10 off), 10 runs go unstable, and the non-monotone timestep behaviour survives (stylised).
• Does an off-centre centre of mass need a harder grasp?Does an off-centre centre of mass need a harder grasp? Ball-pad elliptic-cone bound matches MuJoCo within 1.1% (5× force at 20 mm offset); flat-pad MuJoCo lies between an equal-split and a best-split corner-contact bound (stylised).
• Does the friction-grasp bound survive lift acceleration and an off-centre centre of mass?Does the friction-grasp bound survive lift acceleration and an off-centre centre of mass? Scaled bound matches MuJoCo within 6% over 66 cases; the torque bracket for an off-centre bar is inconclusive and depends on the rotation tolerance (stylised).
• Is the off-centre bar result in robofab-liftload a grasp effect or solver creep?Is the off-centre bar result in robofab-liftload a grasp effect or solver creep? The bar creeps at about 3.7 deg/s from 0.3 to 3 N in MuJoCo, with a rate set by contact settings, so the earlier verdict reflects the simulator (stylised).

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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.