Nitro to Electric conversion

duke.johnson wrote:Here's a good starting point, this is how I sized my Akromaster. And it work great..

First figure out what motor to get:

You'll need about 11 watts per ounce of airplane weight.  So for a 20 ounce airplane, that's 220 watts.  So look at motors that are rated for no less than 220 watts peak power
For this sized airplane you want to spin the prop between 10000 and 12000 RPM (that drops to about 9000 for a "full sized" stunter)
For this sized airplane you probably want a 3-cell pack (bigger airplanes = more cells).  This isn't a general rule -- you could probably make this work with two cells, or with four, if you size your motor and ESC right
A 3-cell pack is an 11.1 volt pack (there's 3.7 volts per cell, and it adds up -- 3.7V/cell * 3 cells = 11.1V)
You want to spin 12000 RPM at the end of the flight and at full current -- this means you can only count on 8.3V or so (that's 75% of full voltage -- (11.1V)(0.75) = 8.3-ish volts)
The motor speed is the motor Kv times voltage.  So you want to find Kv from Kv = (target speed) / (voltage).  In our case that's (12000 RPM) / (8.3V) = 1450 RPM/volt
Now you know enough to go motor shopping -- woo hoo!  Look for motors that can handle 220W peak, and have a Kv of 1450 or better
If you just can't find a suitable motor, go back to the step where we decided on the number of cells, and try it again with four

Now figure out what ESC to get:

power equals current times voltage.  We can turn that around: current equals power divided by voltage.  So when we're asking for 220 watts from the motor, we need a current of (220W) / (11.1V) = 19.8-ish amps -- call it 20A (more cells means higher voltage, which means less current for the same power -- this is why bigger planes have more cells)
So you know that you need a 20A ESC that can handle three cells
If you are using a KR timer, or if you don't care about a "perfect" run, then almost any ESC will work (there's some really cheapo ones that the KR timer doesn't like)
If you are using a Hubin timer then you need to get an ESC that has a governor mode (the KR timer has a governor -- the Hubin timer depends on the ESC)
Go select an ESC

Now you need a battery pack:

You're going to use about 0.6 or 0.7 watt-hours per flight if you do a full six minutes.
Watt-hours can be calculated like power: watt-hours = amp-hours * volts.  You can turn that around: amp-hours = (watt-hours)/(volts)
You have a 20 ounce plane, so you need about 14 watt-hours.  You have an 11.1V battery, so that works out to (14W-h)/(11.1V) = 1.26 amp-hours, or 1260 mA-h (1 amp = 1000 mA, so 1 amp-hour = 1000 mA-hour)
You only want to discharge the battery by 75%, so you need more than 1260 mA-h: (1260mA-h) / (0.75) = 1680 mA-h
So you need a 3-cell pack with better than 1680 mA-h capacity.  1800 would be plenty.  You could probably squeak by with 1600, because the Acromaster will probably fly the whole pattern in less than six minutes
You want at least a 20C discharge rate, and mo is betta
Go buy a 20C or better 3-cell pack with more than 1680mA-h of capacity

crankbndr wrote:Yes the way you explained it even a caveman could do it!!