Watt's Up Applications
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10
WATT'S UP APPLICATIONS
10.1
On Board Use
The Watt's Up is compact and lightweight compared to other Watt meters on the market.
This allows the Watt's Up to be mounted on board in larger models. This can be convenient
and can also allow the determination of peak Amps, peak Watts and minimum Volts while
in flight due to the unique features of the Watt's Up. During short test flights, the peak
Amps peak Watts and minimum Volts generally occur simultaneously under heavy load.
These values can help give insight into the dynamic performance of the prop or explain
erratic operation or failures.
10.2
Flight Time
You can calculate flight time at various throttle settings by taking note of the Amps reading
on the Watt's Up and making some simple calculations. Divide the Ah rating of your
battery pack by the Amps reading to determine the flight time in hours. If your battery pack
is rated in mAh multiply the Amps reading by 1000 to convert it to mAh before dividing.
10.3
Basic Component Selection
You just finished your new model plane and want to select a battery, motor, prop, etc.
Where do you start? A useful metric for initial component selection is the power to weight
ratio or power loading. Power loading can be measured in watts/pound. Typical power
loading ranges from 20 W/lb to 200 W/lb depending on the type of model. Park flyers and
trainers are on the low end, while acrobatic and 3D models are on the high end.
Select a motor recommended for your model by the manufacture as a starting point. If the
manufacture does not recommend a motor, select a motor capable of putting out the power
required for a reasonable power loading for your model. Select a prop that looks suitable
from the motor manufactures recommendations and the prop manufactures data. Now
choose a suitable ESC and battery pack of the appropriate voltage.
10.4
Initial Testing
Now that you have chosen components to start with, it’s time to bench test things and do
some tuning. Keep in mind that a prop performs differently when tested statically on a
bench compared to dynamically when moving through the air. The faster a prop moves
through the air, the less thrust it produces. Bench testing can help select well-matched
components, but should not be taken as the final word. For bench testing, the complete
system can be assembled on a rolling sled (if you want to make thrust measurements), or
rigidly mounted. Connect the Watt's Up between the battery pack and the ESC.
Start by taking a baseline measurement at full throttle for comparison. Your battery pack
should be fully charged for each test. Run the motor up to full throttle and make note of the
Amps, Volts, and Watts readings on the Watt's Up at 30 seconds into the test then turn the
motor off. Readings at the beginning of the test are not typical due to the initial punch of
the batter pack, which quickly fades. The Watt's Up captures the peak Amps and peak
Watts readings which you can compare to the 30 second readings to see how much initial
punch your pack has.
Divide the Watts reading by the weight of your model to get the power loading. Compare
this to the desired power loading for your model. Compare the Amps reading to the
maximum Amps rating of your motor. If it is higher, your motor is being overloaded. If it is
much lower, your motor is larger than you need for the given prop. Now change one of the
system components such as the prop and run the test again. Continue this procedure until
you have a well-matched system that provides the desired power loading for your model.
10.5
Balancing Battery Pack Cells
You don't want battery pack cells going below their minimum safe voltages for safety and
battery life reasons.
"Watt's Up" & "Doc Wattson" Watt Meter and Power Analyzer User's Manual
RC Electronics, Inc.
