Optional 2S Setup (2600-3500 RPM) - The Trifecta!

Okay, so 3900 RPM is as low as Castle recommends with a 3S pack (at 3900 on a 3S pack the Talon15 is down to 70% power output and they recommend not going any lower - otherwise the ESC can get very hot and possibly cause serious problems).  As it turns out you can go lower with a 2S pack as long as you modify the settings in the Talon15 and get 'usable' headspeeds down in the 3000-3500 range. Actually you can go as low as 2600 (while keeping the Talon15 happy power-wise) but I've found anything less than 3000 doesn't work very well - the collective response becomes extremely poor with stock or Lynx plastic blades.  However,  at these 'usable' headspeeds the heli will be much quieter, less intimidating, and you'll get longer flight times and incur less wear and tear (barring any crashes that is).  I got a 9 minute flight at 3000 RPM using an 800mAh pack - casual backyard flying that is.  Obviously you'll get longer flights with an 800mAh pack (around 7+ minutes) , but 460s, 500s and 610s work very well to get you 4, 5 and 6+ minutes too - all depending on your type of flying and collective management skills.

2S LiPo Battery Packs
You'll need to acquire some 2S LiPo battery packs.  The 2S packs need to be relatively the same size and weight as the stock 3S lipo.  I've got 460mAh, 500mAh, 610mAh and 800mAh packs, all within 30g - 46g range:

Glacier 800mAh 2S 25C Lipo

Rhino 610mAh 2S 20C Lipo

Nano-Tech 460mAh 2S 25C Lipo

Gforce 500mAh 2S 30C Lipo

Typical 2S LiPos that can be used with the 180 CFX (weight 30-46g).

It's also a good idea to keep the overall power capacity of the 2S pack nearly equal to that of the 3S pack supplied with the 180 CFX by Blade, to start with that is, so we're comparing apples to apples.

All of the packs shown above are approximately the same size, and weight (or less) than the stock 3S pack. Good. But what about capacity, or mAh? We need to consider the Watt-Hours of the packs, where Volts times Amps = Watts. The stock 3S pack is a 5 Watt-hour pack (3.7V x 3 x .450Ah = 5Wh). Going backwards with a 2S pack we need at least 675mAh to be an equivalent power source (5Wh / 2 / 3.7V = .675Ah = 675mAh). For those using 3S 500mAh packs the capacity of those packs is 5.55 Watt-hours. An equivalent 2S pack would be 750mAh in capacity. So the 610s (36g, but a little shy in capacity) and 800s (42g, with a little extra capacity) above are good choices in keeping overall power supply capacity of the 2S packs fairly equivalent (obviously a 750mAh pack would be optimal - I just don't have any). The 2S 460mAh (3.4Wh) and 2S 500mAh (3.7Wh) packs can also be used, but you have to realize those 'gas tanks' are smaller than the stock 3S 450mAh (5Wh) pack, thus have less power available for flight.

The reason I mention comparing apples to apples is because MANY times I see pilots go from (for example) a 2S 2200mAh pack to a 3S 2200mAh pack (just add an extra cell, keep the mAh rating the same) and report amazingly longer flight times because they simply 'switched to 3S'. Yes, they switched to 3S, but they also increased the overall power capacity, and weight, of the pack. In actuality, they went from a 16.28 Watt-Hour pack (3.7V x 2 x 2.2Ah)  to a 24.42 Watt-Hour pack (3.7V x 3 x 2.2Ah) , a 67% larger pack!  THAT'S the real reason for the longer flight times. If they would have kept the Watt-Hour rating of the new pack similar (3S 1500mAh or 16.65 Watt-Hours, which would also be similar in weight) then their results would have been less spectacular, but way more realistic and meaningful when discussing 'switching to 3S'. Then, other pilots wouldn't be confused into thinking that increasing cell count alone somehow magically increases flight times ... it doesn't!

So keep the comparisons honest - match the weights and Watt-Hours of the packs (or get as close as possible) before reporting unbelievable benefits (or horrible penalties if reducing the number of cells) when modifying RC helicopter power systems.

Modify Cutoff Settings
Using CastleLink you need to make some changes to the Talon15's settings.  The first and most critical thing that needs to be changed is the "Cutoff Voltage".  Set it to "Auto Li-Po (*)".  This allows you to use both 2S and 3S packs with the Talon15.  When you plug your battery in from now on listen to make sure the number of beeps from the Talon15 matches the number of cells in the pack you're using.

Next set the "Auto-Lipo Volts/Cell" to "3.2 Volts/Cell". This sets the cutoff voltage to 3.2V per cell, as opposed to the default of 3.0V per cell.  You can change this later if you like, but for now give your pack a little buffer.  Better yet, figure out a power budget and use a countdown timer and stop flying when the alarm sounds.

Modify Pack Voltage Settings
Now we're going to change the Battery Pack Voltage under the Vehicle Setup Information section.  Change it from 3 series cells to 2 series cells.  The Nominal Battery Voltage should now display 7.4:

Verify Motor and Gearing Settings
Now we'll check the Motor and Gearing parameters under the Vehicle Setup Information section.  Make sure the values match the following:

Select Throttle & RPM Settings
At this point we can choose whether we want to use the governor modes or fixed endpoints mode.  The characteristics of each mode (advantages, disadvantages, etc.) are identical to those previously discussed when using a 3S pack.  I'm only going to cover 3 options here, but there are a few more in the Talon15 that can be explored on your own, if you like ;)

Option#1 - Governor Mode: Set RPM
(In this mode the battery pack voltage, motor and gearing settings are used throughout the Talon15's operation to keep the RPM constant.)

If you want to continue using throttle curve 'ranges' on your transmitter to select pre-defined head speeds then select Set RPM Governor mode.  Under Desired Head Speeds enter 3100, 3300 and 3500 (for example).  CastleLink will then tell you to use a flat 30% throttle curve for 3100, a flat 70% throttle curve for 3300, and a flat 100% throttle curve for 3500, just like when using the stock 3S setup.

If you want to change those head speeds to something else later on you'll have to re-connect the CastleLink and repeat the above procedure and set your new head speeds.

Option#2 - Governor Mode: Governor High
(In this mode the battery pack voltage, motor and gearing settings are used by the CastleLink tool to calculate throttle curve values based on your RPM inputs.  During flight the ESC uses this info to keep RPM constant based on your throttle curve value and the ESC's own predetermined RPM for those throttle curve values.  It's smart enough to allow you two switch between 2S and 3S packs, and various throttle curve values without having to go back into CastleLink and change the battery cell count.)

If you would rather use the value of the throttle curve to select pre-defined head speeds then select Governor High mode.  Under Desired Head Speeds enter 3100, 3300 and 3500 (for example).  CastleLink will then tell you to use a flat 67.6% throttle curve for 3100, a flat 71.2% throttle curve for 3300, and a flat 74.6% throttle curve for 3500.

If you want to change those head speeds to something else later on all you need to do is change your throttle curve in your transmitter to a value that corresponds to the new head speed you want.  You can go back into CastleLink to find out what those values are, or refer to the following - I've already done that for you for these head speeds:

• 2600 RPM = 56.4% Throttle.  ESC is at 70.0% output power.  (Minimum Recommended)
• 2700 RPM = 58.9% Throttle.  ESC is at 72.7% output power.
• 2800 RPM = 61.4% Throttle.  ESC is at 75.4% output power.
• 2900 RPM = 63.7% Throttle.  ESC is at 78.1% output power.
• 3000 RPM = 65.6% Throttle.  ESC is at 80.8% output power.
• 3100 RPM = 67.6% Throttle.  ESC is at 83.5% output power.
• 3200 RPM = 69.5% Throttle.  ESC is at 86.2% output power.
• 3300 RPM = 71.2% Throttle.  ESC is at 88.8% output power.
• 3400 RPM = 72.9% Throttle.  ESC is at 91.5% output power.
• 3500 RPM = 74.6% Throttle.  ESC is at 94.2% output power.
• 3528 RPM = 74.8% Throttle.  ESC is at 95.0% output power.  (Maximum Recommended)

As I mentioned, 3000 RPM is about a low as you want to go - any lower and the collective response becomes very poor.

Option#3 - Fixed Endpoints Mode
(In this mode the battery pack voltage, motor and gearing settings are not used at all and are grayed out in the CastleLink tool.)

If you would rather use custom throttle curves that you define in your transmitter (and not use a governor) then select Fixed-Endpoints.  In this mode the Talon 15A doesn't use any of the battery, gearing, motor KV, etc. information.  Instead it operates in a linear mode where (for example) a 50% throttle curve results in 50% output power.  Most head speed calculators can be used to estimate what the output will be for a given throttle value.  Assuming 90% overall efficiency you would end up with something like this:
 

2S throttle curve values and resulting RPM (Fixed-Endpoints Mode Only).

So for higher 3D RPM you might set your pitch curve to 0-25-50-75-100, and your throttle curve to 100-95-90-95-100.  This would give you approximately 3529 RPM on average, initially*

2S Higher 3D RPM

For lower sport RPM you might set your pitch curve to 0-25-50-75-100, and your throttle curve to 95-90-85-90-95.  This would give you approximately 3343 RPM on average, initially*

2S Lower Sport RPM

Or, you might want a more scale-like setup, where you won't be flying inverted and would like more stick movement (higher resolution) to control your positive pitch.  This would give you approximately 3200 RPM on average, initially*

2S Scale-Like Setup (No Inverted !!!)

It's a good idea to keep the output power (throttle value) between 70% and 95% as recommended by Castle Creations for their governor modes to avoid overheating the Talon 15A. 

*Keep in mind that in this mode the RPM will decrease over the duration of your flight as the battery voltage drops.  From start to finish typically the head speed will decrease by a few hundred RPM.