120 mm planetary, 8:1 reduction — torque and stiffness for servo axes
The GBX1200081102G is a 120 mm-diameter planetary gearbox from Schneider Electric's GBX series, built with straight-cut teeth for a balance of torque density and cost. The 8:1 reduction ratio transforms a servo motor's speed and torque — at 100 rpm input, the output delivers 120 N.m continuous and peaks at 192 N.m maximum (both at 30 °C). The 96 % efficiency means roughly 4 % of the input power is lost as heat inside the housing — for a 120 N.m output at 100 rpm, that's about 50 W of thermal load the black anodized aluminium housing must sink. In a tire-curing press environment, that heat adds to the ambient steam heat; the -25 to 90 °C operating range covers the typical press-side cabinet conditions.
Continuous vs maximum torque — the real working limit
The continuous output torque of 120 N.m at 100 rpm and 30 °C is the rating for sustained duty — this is the figure to size against your axis cycle's RMS torque. The maximum torque of 192 N.m at the same speed and temperature covers acceleration peaks and emergency stops, but repeated operation at this level shortens the 30000 h service life. Service life is specified at 30000 hours at 100 rpm and 30 °C — that's about 3.4 years of continuous 24/7 operation. The gearbox is lubricated for life, so no maintenance oil changes; the life limit is gear and bearing wear, not lubrication degradation.
Shaft loading — axial and radial force budgets
The output shaft, made of C45 steel, accepts a maximum axial force of 2100 N at 100 rpm over the 30000 h life, or 2800 N if you accept a 10000 h service interval. Radial force is limited to 1500 N at 100 rpm (30000 h life) or 2000 N (10000 h life), with the force applied at mid-distance from the output shaft. These limits govern belt-drive or direct-coupling applications — a belt tension that exceeds 1500 N radial will reduce gearbox life below the 30000 h target. The shaft output carries an IP54 rating, meaning it resists dust ingress and splashing water, adequate for most industrial environments but not washdown.
Backlash and torsional rigidity — positioning accuracy constraints
Maximum torsional backlash is 8 arc.min — this is the lost motion at the output when reversing direction. For a positioning axis, this 8 arc.min translates to about 0.12 mm of linear error on a 50 mm pitch circle, which matters for indexing applications but is acceptable for general conveying and positioning. Torsional rigidity is 12 N.m/arcmin — meaning a 12 N.m load twists the output shaft by one arc-minute. This stiffness figure lets you calculate the windup under peak load: at 192 N.m maximum torque, the torsional deflection is about 16 arc.min (192 / 12), which must be added to the backlash budget for the total positioning error.
The gearbox mounts in any position, which simplifies integration into existing machine frames. The 1.32 g.cm² moment of inertia is the reflected inertia at the input — a servo motor sizing tool will add this to the load inertia when calculating the total inertia ratio.