The Zagi-FiXX is supplied with a balanced power system. Changing the prop will
change the load on the motor ESC and the battery. The Zagi-5 ESC is rated at 5
amps continuous. The Zagi-FiXX with a 370 mAh battery and the stock prop draw
2.5 amps at full throttle. So if the prop diameter or pitch is increased, the load
could exceed the range of the 5 amp ESC. This balanced system was tested with
over a hundred flights. Changing the pitch or diameter burn out the motor after
only a few flights. Using a 1000 mAh battery will burn out the GWS motor after
only a few flights. Trial and error can get expensive. The way to choose the correct
prop for an electric airplane is with the use of a watt meter. Astro Flight makes a
“Wattmeter for indoor R/C models” for $55.00 from Trick R/C. This device will
keep the smoke from escaping from the speed control. Another useful tool is a
tachometer. Cermark makes a good tach for cheap. A simple thrust meter can be
made with a small postal scale calibrated in ounces. A test stand setup with a
wattmeter, a scale and a tach will take the guesswork out of balancing electric
components.
Battery life is determined by two main factors; charging and discharging. Both of
these functions produce heat. Warm is okay, hot isn’t. A hot battery has either been
charged or discharged too fast. First, charging. Make sure that the charger is
designed to charge the number of cells being charged. The best type of charger is
the peak detector type. These chargers will charge the battery to peak at a pre-
selected rate then drops to a trickle. Chargers with timers will often over charge
batteries causing excessive heat. Manufacturers recommend charging batteries at
the rated capacity
i.e.
, a 500 mAh battery should be charged for one hour at 500
mAh. The exception to this is the batteries with the letter “R” at the end of the
designation (500AR, or 2000SCR). The “R” means rapid charge and discharge.
“R” cells are either very expensive or not available in small sizes. Hobbyists are
notorious battery abusers. Batteries that are not designed for rapid charge are
routinely over charged by charging and discharging them too fast. NiCad cells
have a finite number of cycles. Abuse will decrease the number of cycles. Electric
flight hobbyists are willing to accept the shortened life of the batteries for perfor-
mance. There are ways to cut these losses. Don’t charge at a rate more than twice
the designated capacity of the battery. Don’t charge a hot battery. Get enough
batteries to fly one, cool one, and charge one. A way to speed up the cycle is to
make a 12 volt field battery cooler. Tape a 12 VDC muffin fan to a 6 inch length of
2 inch PVC pipe. The muffin fan is available at Radio Shack or find an old com-
puter power supply fan (but make sure it’s designed for 12 VDC and not 110 VAC).
Air flow
1
1
1
1
12
12
6” Piece of 2” PVC
plumbing pipe
Battery
Muffin fan
12 VDC
20