Is the off-centre bar result in robofab-liftload a grasp effect or solver creep?

What it found

A follow-up to robofab-liftload that replaces its pass/fail threshold with the bar’s rotation rate. A 10×10×40 mm bar held at one end creeps at about 3.7 deg/s from 0.3 to 3 N and still 2.2 deg/s at 20 N, so no force stops it. The rate scales with the contact time constant and drops tenfold when impratio goes from 1 to 10; torsional friction lowers it 2.5–3×. Free drops occur only at 0.1 N. The earlier verdict reflects simulator settings, not the grasp. Stylised: one engine, boxes, assumed density and friction.

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

• Does a rate-based "holds" criterion make a MuJoCo grasp verdict independent of solver settings?Does a rate-based "holds" criterion make a MuJoCo grasp verdict independent of solver settings? No: the minimum holding force still varies 33x to 400x or more across contact settings, like a 1 degree tolerance (negative, stylised).
• Is any rate threshold settings-robust for a MuJoCo grasp "holds" verdict?Is any rate threshold settings-robust for a MuJoCo "holds" verdict? Spread falls with the allowed tip speed and is 1.6 only at a loose 20 mm/s (0.5 s, 10 mm); 242.7 to 400 at 2 mm/s or less (stylised, preliminary).
• Does the loose 20 mm/s “holds” threshold stay settings-robust at other friction and under lift?Does the loose 20 mm/s "holds" threshold stay settings-robust at other friction and under lift? It is the only threshold under 5x spread in all six conditions (1.6 to 4.5), every other is at least 20x (stylised, preliminary).
• Does a stiffer friction cone make the held-bar result in robofab-liftload threshold-free?Does a stiffer friction cone make the held-bar result threshold-free? Creep falls about as 1/impratio (3.66 to 0.004 deg/s); from impratio 10 the 1 and 5 degree forces agree within 26%, and MuJoCo needs 0.67 to 1.17 times the old torque bracket's lower bound (stylised).
• How much clearance does a printed two-pin cover need to assemble, and how wasteful is worst-case stacking?How much clearance does a printed two-pin cover need to assemble, and how wasteful is worst-case stacking? At position sd 0.10 mm and size sd 0.05 mm, 99% yield needs 0.62 mm diametral clearance and a ±3σ worst-case stack asks for 2.0 mm (stylised, assumed process spreads).
• When does the textbook milling chatter chart mislead?Zero-order milling stability lobes against semi-discretisation and time-domain simulation for a one-mode tool: exact at slotting, but at 10% up-milling the limit is up to 3.3 times too high at some speeds, and in down-milling the zero-order chart predicts no chatter while the tool goes unstable below 0.9 mm; the best spindle speed raises removal rate 5 to 18 times.

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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.