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« on: January 29, 2013, 10:16:53 PM »
bhaveshsangani
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After reading this , the pitch curve setting were crystal clear to me. So just wanted beginners like me to understand it the simpler way


The normal Pitch  settings for a helicopter consist of 3 things.

A. Negative Pitch  for inverted flying and getting the heli down in high winds.
B. Zero Pitch  - the point of transition from negative to positive, and positive to negative Pitch 
C. Positive Pitch  for upright flying.

As we know, servos have limited travel. Picture a servo lying down horizontally with its servo arm pointing horizontally. In this position it would be at position B as listed above....Zero Pitch . From position B as the servo arm moves downward, it would be at position A....Negative Pitch  From position B as the servo arm moves upward, it would be at position C....Positive Pitch 

Most modern radios allow us to set Pitch  curves based upon a 5-7 point "Pitch  curve". Her we are going to base everything on a 5 point Pitch  curve. Todayís radio's think of a total servos travel as 0,25,50,75,100.

Think back to the horizontal servo, where the radio sees 0 as having the servo arm all the way down, 50 as dead level, and 100 as all the way up. So if we wanted a servo to move from position B to position C. We would have to tell the radio that we want the servo to move from 50 to 100...not 0 to 100. Get the idea? Remember the radio sees 50 as centered...not 0 and a properly set up head sees zero pitch.

Ok so where does this lead us.

Well on a collective Pitch  helicopter. Servo movement directly translates into blade Pitch . So when we set up a collective Pitch  helicopter we want to use what the radio sees to program and set it up. Now there are two basic different ways to fly a collective Pitch  helicopter.

1. Normal mode. - For upright flying, consisting of positive Pitch  only
2. Idle up (3D mode) - For inverted flying, consisting of positive and negative Pitch 

Lets look at Normal mode first. BUT...you want to keep thinking in terms of full collective...that is Negative to Positive Pitch .

Lets assume that Pitch  is controlled by a single servo. Since servo travel is directly translated into blade Pitch , we want the radio to understand that we only want the servo to move the blades into positive Pitch , and only a small amount of negative to fight high winds 4 degrees. This means that we want the servo to be limited to moving from lets say 40 to 100 not 0-100. So with the servo centered, and the servo arm centered at 50/ then 40 would give us that little bit of negative we need. Get it??

Point 1 would be 40.
The next point...Point 2 would be 45
The next point...Point 3 would be 50
The next point...Point 4 would be 75
The next point...Point 5 would be 100

The throttle curve would be set as
0,25,50,75,100

This means that when the throttle stick as at dead bottom. There is 0 throttle, and negative roughly-4% Pitch .
As you move the stick up, it increases throttle to 25%, and increases Pitch  to 45 (roughly negative 2+1 degrees Pitch  based on a max of +12)
When you get to mid-stick, throttle will be at 50%, and the Pitch  will be at 50 (0 degrees pitch)
...and so forth.

In this manner, when you have the heli sitting on the ground, the blades arenít spinning, and there is a very small amount of negative Pitch .
As you increase the throttle stick, the blades start spinning, and the heli lifts off around mid-throttle.


Now...on to Idle up or 3D mode.

Now we want to take things to the next level. In order for us to do this we have to tell the radio that we want to make use of the servos travel below 40. So how do we do that? Well via a switch on the radio. The Idle Up switch. When we flip this switch we are telling the radio that we now want to discontinue use of the normal mode, and that we want the throttle stick to now control the entire range of the servos travel

Remember the 5 point Pitch  curve. This is what really confuses beginners.
Now the 5 point Pitch  curve contains points for the entire servo travel instead of only roughly half of it and therefore, the 5 points have to represent the entire servos travel.

So the first point would be 0...full down on the servo, full negative Pitch  -12
Point 2 would be 25....mid-way down on the servo, half negative Pitch  -6
Point 3 would be 50...centered servo...zero Pitch 
Point 4 would be 75...mid-way up on the servo, half positive Pitch  +6
Point 5 would be 100...full up on the servo, full positive Pitch  +12

Notice also that the throttle curve changes. In idle up mode we never want the throttle below 50% or else the blade RPM  will get too slow and the heli could fall from the sky. This is where the collective Pitch  independent of throttle comes into play. In idle up, the blade Pitch  is no longer dependant on throttle. So throttle settings in Idle up often look something like this, 100,75,50,75,100.


Courtesy : http://www.rchelicoptertown.com/forum/showthread.php?t=3480
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« Reply #1 on: January 29, 2013, 10:39:06 PM »
bhaveshsangani
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I would like the experts to throw some light and correct if i am wrong here!!!
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« Reply #2 on: January 30, 2013, 01:02:57 AM »
Shannon
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thats good research bhavesh firstly throttle curve does not only mean 0 25 50 75 100 like pitch cuve where 50 s zero and say 75 is 6 degrees and 100 is 12 degrees the same way 0 25 50 75 100 corresponds to rpm and rpm depends upon the number of pinion teeth ,main gear teeth,motor kv and battery cell count u can use head speed calculator for this..just for example ur motor kv is 3800kv pinion is 13t main gear is 150t and ur using a 3 cell battery  at 100%throttle u will get 3600rpm not at all suitable for a clone it will rip apart so in order to get correct rpm say for normal mode u require 2700rpm so tht can be got only at 75% throttle using head speed calculater so in normal mode ur throttle curve will be 0 25 50 75 75 keep last two points same cause variation in the last 2 points of throttle curve ill cause major pitch changes ...the same way for stunt or 3d or idel up  mode same thing different names throttle curve has to be set correctly so say u require 3000pm so 3000 rpm is available at 84% throttle at 0 pitch so if u set 100 75 50 75 100 ur gonna get 1828rpm at mid stick 2742rpm at 75% and 3600 at 100% tis is not right ...so to maintaing 3000rpm throughout flight in any maneuver u need to set throttle as 90 88 84 88 90 ...the first two and last two points are set in excess so as to maintain rpm as he heli performs maneuvers the increased amount of pitch decreases rpm so to copensate and maintain 3000rpm we have to give a little more throttle at the extremes .....hope u have understood all this http://dhrc.rchomepage.com/calc.htm hsc link
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« Reply #3 on: January 30, 2013, 01:40:30 PM »
kumardasai
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beginners must read this thread. Its really intresting. Hats Off. And also, it will be a great help if you could have explained it with a small images or pictorial representations (blade directions and servo directions.) Bhavesh, Now you have become a master, Good going, keep it up, when r u posting your maiden video ?
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« Reply #4 on: January 30, 2013, 01:45:43 PM »
raja_mastana
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I agree, its interesting write up
Helicopter pitch settings from the pov of a servo.
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« Reply #5 on: January 30, 2013, 05:40:47 PM »
bhaveshsangani
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Kumardasai : Hi sir, i have not mastered anything as such , still in the struggling face . Just got these details from one similar forum...... this post , as i thought would be helpful for newbies like me so i reposted it here....
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« Reply #6 on: February 25, 2013, 02:48:33 PM »
avesh
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Shannon THe Great, is correct, i played with pitch curve but at end linear worked fine. +10 seems fine for me i usually play around with mid throttle ..
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