Turn On, Burn In and Burn Out

In preparation for releasing AMOS into the wild on its own, some reliability testing was done with the air propeller running for extended periods of time. AMOS was placed on our pool deck in the hot sun and the air propeller was run at its maximum speed. A temperature probe was inserted into the electronics box containing the battery, speed controller and solar charge controller, and hooked up to an external Arduino board, which was in turn connected to a PC. Additional temperature sensors were in the other electronics box and connected to the sensor deployment arm, but there was some concern that the solar charge controller and battery might get too hot, hence the additional probe for that box.

It was found that the temperature within the power box would approach 45 degrees C in the mid-day sun. This temperature seemed to be more or less independent of whether or not the air propeller was actually running, so probably most of the heating was directly from the sun, not from the self-heating of the electronics. The moving air propeller might have helped to remove some of the heat as well, perhaps compensating for the electronic heating. This temperature is actually kind of close to the recommended maximum (120 degrees F or 49 degrees C) for the battery being used: https://dakotalithium.com/product/dakota-lithium-12v-10ah-battery/?v=3e8d115eb4b3. It was also noticed that the output voltage of the solar charge controller would fluctuate wildly (about + / 2 V) when it reached its floating charge level (about 13.6 V). Often this fluctuation would mess up the speed controller for the propeller, causing it to stop moving the prop and start beeping loudly. Other times the Raspberry Pi board would re-boot itself. The solar charge controller was replaced, but the fluctuation at the floating charge level remained about the same, although so far no strange speed controller behavior or rebooting was observed. Unfortunately this may mean that there is a problem with the battery (perhaps it got too hot?). A replacement lead acid unit will be swapped in tomorrow to see if that might be the case.

Here is a typical plot of the voltage while running the air propeller at full speed in bright sunlight:

 A couple of the voltage transitions in the above graph made sense (changing the prop speed from 6 to 7 and then back again) but the brief jumps near the 0.5 hour mark and the 0.5 V drop at the 2 hour mark are unexplained. An additional unexplained 0.5 V drop was noticed again this evening without the propeller running. Could be some weird stuff going on in the battery when it gets too hot. It'll be interesting to see what the less complicated lead acid battery does. The low-charge detection software was improved for AMOS this week too. Before it just used a fixed 11.3 V limit for the low-charge condition; now it looks for a slope in the voltage curve less than -1 volt / hour. So far this seems to work well, but it needs more testing.

Lastly, In Nature Robotics Ltd. now has a logo (thanks kids for recommending the logo-maker website: https://www.freelogoservices.com):

and a website: www.innaturerobotics.com (thanks kids for recommending wix.com). The website is quite preliminary right now, but will be updated gradually over time.