Manufacturing challenges –
To create a realistic technical CAD model that could be issued for manufacture of the watch, several important aspects needed to be considered. Firstly, draft angles were applied to the injection moulded pieces. Draft angles help ease the part from the mould once it has been injection moulded. To avoid breaks, cracks and marks left on the part, a minimum angle of half a degree should be added to the part (Schwartz, 2016 (reference 11 in appendix)). Secondly, thickness of the part. The thickness of a part dramatically affects its ability to mould without bulging or sinking and can lead to cooling problems (Schwartz, 2016 (reference 12 in appendix)). Finally, the part complexity in regards to mould part quantity was considered. In order to injection mould complex shapes multiple part moulds are required. The more parts required, the higher the cost of the mould. In order to keep costs realistic, the complexity of the moulded components was kept simpler and moulded primarily in one axis; reducing costs.
Water resistance –
As the watch will face all weather conditions and perspiration, it was necessary to make the watch water resistant. To ensure the watch was water resistant, an o-ring was sandwiched between the base and face of the watch. This o-ring will be “preventing an unwanted escape or loss of fluid” into the main compartment of the watch, housing the electronics (Whitlock et al, 2004 (Reference 9 in appendix)). The o-ring can be seen highlighted in blue in the technical CAD model. The step of the lid is orientated in this specific way to further increase the water resistance, as water will have to travel against gravity (depending on how the watch is orientated), up the wall of the base.
Finally the grill inlets of air for the PM2.5 sensor are water resistant through having holes so small that the water tension will not allow water droplets to pass. This is why the watch is water resistant and not water proof, as if the watch is submerged to any significant degree of pressure, the water pressure will overcome the tension keeping it from passing through the grill, and be forced into the sensor.
Watch app communication –
Bluetooth was chosen to transmit data between the phone and the app. The primary reason for choosing bluetooth resides in its energy efficient nature. When uploading a planned running route to the watch from the app, the phone will almost certainly be within 1 metre of the watch. At the 1 metre range, bluetooth only uses 1 milliwatt when transmitting the data (Huang et al, 2007(reference 7 in appendix)). As the battery life of the watch is a concern due to the small size of the battery, it was important for the transmission of data not to greatly impact the battery life. In the most common use case for the product, the user will upload their route to the watch before they set off from home, then leave their phone at home. This should not greatly affect battery life as this would only constitute 1 transmission, however, there is the potential for the user to take their phone with them. The watch allows for altering of routes manually while on a run by linking back to the phone. If a user has taken their phone and decides to alter their route while out with the watch, there will be significantly more data being transmitted and the lower energy consumption of bluetooth is the perfect solution.
Another two advantages of using bluetooth are that it is inexpensive and the technology is very small (Stlouis, 2011(reference 8 in appendix)). A cheaper component helps drive down the cost of production and the small size of the unit is vital for such a compact product.
Battery life –
The battery needs only to last 5 hours as this is half an hour over the approximate average time to run a marathon (Mcguire, 2019(reference 10 in appendix)). This being the case, the frequency of geolocation data transmission was decreased, from transmitting every 2 seconds to every 5 seconds. This reduction in data transmission ensures that the li-ion battery (3,000 mAh) of the watch has more than enough power for the duration of 5 hours. This reduction in data will have an impact on the smoothness of tracking the user however there is no functional impact, as the watch still tracks the location every 5 seconds. This was also a necessary change to ensure the battery life lasted the length of the run.
