The First-Month Complaint List
For home service robots, the source reports that the top three complaints within the first month of ownership are oil leak, smell, and squeak. None of these is a catastrophic failure, but all three drive returns and negative reviews. The home scenario therefore inverts the usual priority order: instead of chasing maximum load capacity, the design must first avoid anything that stains a floor, smells, or makes noise in a quiet living room. The grease is no longer a hidden component; it becomes a customer-facing feature.
High-Frequency Micro-Motion
Home robots do not run continuously at high load; they perform thousands of small, high-frequency motions per hour as fingers adjust a grip, open a drawer, or pick up a cup. These micro-motions are precisely the regime where boundary lubrication dominates and where a stiff or starved grease squeaks. The grease must keep a thin, replenishing film at very small amplitudes, which puts shear stability and oil-release behavior ahead of raw EP load. A grease that is excellent on a gear test rig can fail this test within a week in a living room.
Parameter Targets for Home-Grade Grease
The source gives concrete selection targets: oil separation below 10% at 100°C for 24 hours, evaporation loss below 1.0% (tested per the GB/T 7325 method referenced in the source), and low starting torque to protect battery life, since every gram of drag in the joint costs runtime. A PTFE (polytetrafluoroethylene) thickener is recommended for its shear stability across long, low-amplitude duty cycles, and the working temperature range is set at -50 to 220°C to cover cold storage and summer heat.
Why Leak, Smell and Squeak Are Related
All three complaints trace back to the same root cause: excess free oil in the grease. High oil separation means free oil migrates out of the sealed joint and stains surfaces; the oil that wets the exterior picks up dust and oxidizes, producing odor; and once enough oil leaves, the remaining grease stiffens and the joint squeaks. Controlling oil separation therefore solves three complaints at once. Evaporation loss matters for the same reason: volatile fractions are what a user smells first.
Validation / Selection Conclusion
For home robots, validate the grease with an oil-separation test at 100°C, an evaporation-loss test, and a low-amplitude cycling test while listening for squeak and measuring start torque. Choose a shear-stable thickener such as PTFE, keep oil separation and evaporation under the source’s targets, and verify the grease survives the full -50 to 220°C envelope without hardening. The home scenario rewards restraint: a grease that quietly stays in place outperforms one with higher theoretical load capacity but visible side effects.
