8. Relaxed Dual Rates, Expo, Pitch Curves & Final Words

Now it's time for some finishing touches :)

The previous page showed how to reduce the main rotor and tail rotor RPM by switching to a 2S Lipo and modifying the settings in the Talon15 using the CastleLink tool.  These changes will:
  1. Slow the heli down (somewhat).  Make no mistake, it can still MOVE if you tell it to!
  2. Quiet the heli down as there are fewer collisions per unit of time between the teeth of the pinion, main and tail drive gears.
  3. Increase the flight times as battery current draw drops SIGNIFICANTLY when RPM are reduced.  The ESC, motor and battery can run cooler as a result.
  4. Reduce the wear and tear on bearings, shafts, gears, etc. 
  5. Reduce crash damage (somewhat) as there is less energy being released by the aircraft during a crash.  Remember to cut power to the ESC if a crash is imminent.
  6. Improve the reliability of the ESC's BEC since it doesn't have to deal with as high of an input voltage. By switching to 2S the BEC has 33% less voltage to convert down to 5V for your servos and receiver.  Typically the BEC will now run cooler and may even be able to supply additional current to your gear because of the lower supply voltage!
Great!  Now we'll soften the controls, a bit.

Dual Rates and Expo
First, let's set some Dual Rates and Expo in your transmitter.  These settings will affect your Pitch (elevator), Roll (aileron) and Yaw (rudder) controls:
  1. Dual Rates = 50%, Expo = 40%, or
  2. Dual Rates = 70%, Expo = 30%
Use #1 for lower RPM, like 3100 or so, when you want more precise control of the heli.  Maybe you're flying in a back yard or small area where you want a more relaxed response to your stick movements.  This works great for hovering practice.

Use #2 for higher RPM, like 3500 or so, when you want crisper response from the heli.  Perhaps you're flying in a larger area, want to try some loops, rolls, flips, etc.  This works better for sport or aerobatic type flying.

Collective Pitch
Second, let's soften the collective pitch a bit:
  1. Pitch Curve: 0-30-50-70-100, or
  2. Pitch Curve: 5-30-50-70-95
Softer Pitch Curves for 3D/Sport/Aerobatic Flying (#1 Left, #2 Right)
Use #1 for lower RPM, like 3100 or so, where the collective response is starting to drop off and you want the entire pitch range at your fingertips. 

Use #2 for higher RPM, like 3500 or so, where the collective response is strong and you want to limit the upper and lower extremes to prevent the heli from climbing or dropping too fast.

Final Words
The above settings may or may not appeal to your tastes - feel free to experiment and decide what works best for you.  One thing's certain - out of the box this heli is VERY VERY responsive to cyclic and collective pitch controls, so I suggest you start out with what I've outlined first, then gradually make changes and dial them in to your liking.

At these lower headspeeds the rubber dampers in the rotor head should be softer, not harder.  Some 3rd party dampers are very hard - these are for the higher, smack 3D RPM.  If you attempt to use hard dampers at low RPM the heli will wobble terribly.  The stock dampers seem to work just fine at these lower RPM.

If you have wobbling (with the softer dampers) then there's a bent shaft or loose something or another problem somewhere on the heli.  Check to make sure things are fastened properly to the frame, servo control horns are seated firmly, pushrods attached correctly, the AR6335 isn't loose, blades are balanced and not too tight or too loose in the grips, battery properly secured, etc.

Keep in mind that the only time the throttle value equals the power output of the Talon15 is when in Fixed-Endpoints mode, that is, 75% throttle equals 75% power output (for example).  When using governor modes, this is no longer true and you must use the CastleLink tool (or the lists I've provided) to tell you what throttle value to use for a given desired power output.

Using flat throttle curves for the governor modes means you must use throttle hold to start/stop the rotors.  If you decide to use zero for the beginning of the curve (ie. 0-75-75-75-75) you would then use the throttle stick to start and stop the rotors (lowest position stops the rotors).  BUT - don't attempt to do inverted maneuvers with a throttle curve like this or your heli will loose power when inverted and drop like a rock, even though your pitch curve may support full positive and negative collective pitch.

2S lipo packs in the 30g weight range will work much better when running the lower RPM (3000-3200).  Heavier packs (up to 46g) are more suited for the higher RPM (3300-3500).

As a general guide when starting out with these lower head speeds, you can initially assume the following for easy-going non-aggressive flying:
  • 2S 460/500mAh 30g packs are good for 4-5 minutes of flight.
  • 2S 610mAh 38g packs are good for 5-6 minutes of flight.
  • 2S 800mAh 46g packs are good for 7-8 minutes of flight.
You can add a minute to each of the above if you really take it easy.  Be careful, use a timer, and check the mAh put back into your packs when you recharge them so you know how much you're actually using.  Make adjustments to your flight times as necessary.  Remember to leave at least 20% in your packs.

Once you've configured the Talon15 for Auto-Lipo and Governor High mode, you may freely switch between 2S and 3S packs when you fly.  Just make CERTAIN you're using the proper throttle curves that correspond to each pack (56.4% - 74.8% for 2S, and 79.9% - 92.2% for 3S).  For example I'll fly my first few flights on 2S at 3300 and 3500 RPM, so I'll set the throttle curves to 71.2% and 74.6% respectively.  Then for my next few flights I'll switch to 3S at 3900 and 4200, so I then change my throttle curves to 79.9% and 83.2% respectively.  Again, make sure the throttle curve values are appropriate for the number of cells in your pack!

If you're using Set RPM Governor mode you'll have to use CastleLink to reconfigure the Talon15 each time you change between 2S and 3S packs - a royal pain!  For this reason I prefer Governor High mode.

RPM above 3528 (2S) and below 3900 (3S) are in a 'grey area' not recommended by Castle Creations as they require the ESC to operate outside of the 70%-95% recommended power output range.  It's best to stay out of this RPM range using the techniques presented in this blog.

I've found that the default tail gyro gain setting of 50 (per the user's manual) isn't sufficient to hold the tail so I'm now using a tail gyro gain setting of 95.  Works much better.

I've also found it VERY helpful to adjust the pitch of the tail blades to 0° RIGHT BEFORE SPOOLING UP.  Typically, you'll plug the battery into the heli, wait for it to initialize, put on the canopy, then walk it out to your heli pad.  In doing so the tail gyro will attempt to compensate for all of the yaw movements you induced in getting it to the heli pad.  Most likely, the tail blades will be pegged at either maximum positive or maximum negative pitch when you set her down. And, since it's not a rate mode gyro, it will hold the position of those blades until it's forced to change it.  Spooling up with the tail blades like this is going to cause the tail to swing around (perhaps rather quickly) as the main rotors come up to speed and the gyro tries to erroneously fix the position of the tail (it doesn't know the heli is on the ground and not flying).  This is added drama that nobody needs!  Do yourself (and the heli) a favor by moving the rudder stick so the blades are at 0° before spooling up - you may just save yourself a tip-over as well as bunch of cussing!

Finally, try to keep your heli as close to it's stock AUW (all up weight) as possible, which is 190-195g.  Optional metal parts, fiberglass canopies, oversized Lipos, etc. all add weight.  Too much weight will cause poor performance especially at these lower head speeds.  Remember, light is right ;)  I like to keep my 180s close to stock AUW so I can attach things like cameras and navigation/strobe LEDs without bogging them down.

I hope this information has been helpful to you.  I appreciate all of the comments and feedback I've received.  I enjoyed writing it and having the opportunity to help others out, after all us "Blade Loosers" have to stick together :)  PM me on Helifreak or RCGroups...

Happy Flying, Happy Landings!