FS4 Mission update – Flight electronics package is ready for testing.
The Flying Squirrel #4 payload electronics package has been built and testing has started. The electronics are similar to the FS3 hardware, but a few changes were made to produce more heat inside the cabin and to clean up the board design.
FS4 has a new electric blanket that can be switched on and off to regulate the heat inside the payload container. The blanket is constructed with fifteen 220 Ohm resistors in parallel to form a 14.7 Ohm resistor. When switched on, this resistor will pull battery power and make about 0.75 watts of heat. Is that enough to keep warm? Further testing needs to be performed to confirm it will.
The goal is to keep FS4 warm at prolonged high-altitude cold outside temperatures. To further warm the insides, the GPS and Radio are left running, drawing battery current and producing more heat. FS3 and prior mission worked to save battery energy and while that was a success at prolonging the limited capacity of a small battery, it worked against the goal of staying warm. In effect prior squirrel missions were too efficient with energy and too cold as a result. Had FS3 stayed intact for another hour it would have likely frozen to death.
To support extra heat generation, a higher capacity battery is needed. FS4 will use an 18650 Lithium Ion battery cell to power the flight. This 3000 maH battery has about 7 times the energy of the AA sized LiFePo battery used on FS1-FS3 flights, but only weighs double.
The first outdoor battery test was performed and the run time on the battery, operating at full heating power consumption (i.e. worst case scenario) was 11 hours. On a real flight, the heater won’t be switched on until the cabin gets around freezing, which may be an hour or more into the flight. The heater, if it makes enough heat, can be switched on/off to maintain a minimum temperature and further saving battery power.
The next task is to build the payload cabin for our squirrel to enjoy a cozy ride. This cabin will be insulated and when ready, the payload with electronics will be placed in a cooler with dry ice for cold testing. This testing should verify (or not) that enough heat is being generated. FS4 will be a short flight, by design, but will be testing the ability to keep warm overnight, using battery power, for future longer-term missions.
73s de Don KJ6FO