A recent Consumer Reports tested the Moto 360 Sport smartwatch for water resistance with the IP67 water test simulating a submersion up to 1 meter deep for 30 minutes. Unfortunately the watch did not pass the test. From a pressure standpoint, this test is relatively benign (1.42 psi or 0.1 bar) and arguably represents the bare minimum sealing for a sport and GPS watch. As a point of reference my Suunto GPS watch is rated to 50 meters and 5 bar. So what what was the root cause of the Moto 360 Sport’s failure? To understand this we’d need to know what gasket material was used, the tolerance stack ups, the amount of gasket compression, the installation or dispensing method or if a gasket was even part of the design. Below are some common root causes of gasket design and IP67 failure modes.
- Gasket Stress Relaxation – this is when the gasket relaxes and stops pushing back, letting external pressures push past the gasket. Usually a result of improper gasket material selection for the specific application.
- Tolerance stack – if the variation in the sealing faces and gasket are not fully accounted for leaving minimal compression on the gasket
- Dispensing seam or flash – dispensed gaskets share a starting and ending point, it’s possible to have a small “bump” or “divot” that may not have been accounted for in a tolerance analysis or closure force. Similarly, a molded gasket with flash can make a minute gap and allow ingress.
- Closure force vs. rigidity – often in an at/custom-gasket-manufacturing/t to compress a gasket the housing flexes creating an ingress point
- O-ring roll – seen more often where an o-rings is installed into an non-matching gland, the gasket is worked into the gland and can be rolled or twisted
- Thermal cycling – the heating an cooling of the devices on/off mode creates internal pressures or vacuums that can “suck” in water.
The above are just a few, general causes we see with IP6X failures. The root cause of the Moto 360 Sport could be due to one of the above or one of many others. As Consumer Reports mentions, the other Moto 360 smartwatches passed the IP67 test and were rated very highly. Hopefully Motorola will get to the root cause and possibly raise the sealing bar on the sport category of the rugged smartwatch industry.