Dobot's smallest industrial arm is named after a reach it does not have — and its wrist has quietly doubled

The DOBOT MG400 is a four-axis desktop arm with a base of 190 x 190 mm - smaller than a sheet of A4 - and its current datasheet gives it a working radius of 440 mm. The model is called MG400, and the launch announcement of 22 December 2020 described a 400 mm reach. Every product datasheet the manufacturer has published since at least March 2023 says 440 mm. Dobot has never marked the difference. The second change is larger and equally unannounced. The datasheet archived in March 2023 gives the tool axis J4 a range of plus/minus 180 degrees. The page live today gives the same axis plus/minus 360 degrees - a full turn in each direction, twice the travel, on a machine sold under an unchanged name. There is no revision note, no hardware suffix and no dated changelog; the numbers simply differ between two snapshots of the same page. Neither is a scandal, and both matter to anyone integrating the arm. A cell laid out from the 2020 press release assumes 40 mm less reach than the machine has. A tool path written against the 2023 datasheet leaves half of the wrist's travel unused, and a fixture designed to avoid cable wind-up at 180 degrees is solving a problem the current arm may no longer have. The rest of the specification is stable across both snapshots: 500 g rated payload, 750 g maximum, plus/minus 0.05 mm repeatability, 300 deg/s on all four joints, the controller built into the base, 8 kg of arm, 100-240 V mains. The MG400 was launched in Shenzhen alongside the CR3, CR10 and CR16 cobots, and Dobot's founder and chief executive Jerry Liu presented it there as the industrial successor to the DOBOT Magician, the desktop arm that had made the company's name in classrooms five years earlier. It remains in production and Dobot publishes no list price for it. wujec.ai publishes the current figures in its MG400 profile and records the discrepancies rather than presenting either number as if it had always been true.