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Old 03-04-2010, 04:56 PM   #1
heli-cuzz
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Default 120 ccpm or 140 ccpm???

What are the advantages and disadvantages?
I have the option of either one and would like to know if one is better than the other.
I remember asking Scott Gray about 140 ccpm at the heli jamboree a few years ago, if I remember correctly, he said, it gives a smoother elevator response.
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Old 03-04-2010, 04:58 PM   #2
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You just answered your own question, lol
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Old 03-04-2010, 05:50 PM   #3
heli-cuzz
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Quote:
Originally Posted by DarkTherapy View Post
You just answered your own question, lol
Just making sure but there's a little more to it than what I posted.
BarracudaHockey linked me to a very informative article on the subject.

This is a much better answer than my own.
C&P from the link


120 vs. 140 degree CCPM

I'll start by saying, if your radio supports 140 degree CCPM by all means use it. The combination of 8717 servos, lightning fast response time of the X9303 radio and the 9 channel receiver, and the interaction free 140 degree CCPM setup make the Vibe 50 a thrilling helicopter to fly. This is on par with or better than my Avant EFX 90 was, and it uses half the fuel.

120 degree CCPM spaces the 3 swash plate balls evenly around the perimeter of the swash plate. Even spacing around a 360 degree circle means the balls are spaced 120 degrees apart, hence the moniker, 120 CCPM. The distance between the center of the main shaft and the balls is equal.

The problem is with the servos. There are 3 servos that move to control the elevator function. One (normally referred to as the elevator servo) moves down while the other two move up, or vice versa. You can see from the left hand picture that while the swash balls are equal in distance from the center of the swash plate, the single elevator servo is twice as far from the center of the elevator pivot point (distance A) as the two front servos (distance B). This means that during an elevator only command the elevator servo has to move twice as far to complete its command as the two front servos. Since the servo has to move twice as far, and the servos are the same speed, it takes twice as long to get to where it was told to go. The result is a momentary collective pitch change until the elevator servo reaches its position. This collective change, during an elevator only command, is a perfect example of CCPM interaction.

In a 140 degree system, the front swash balls have been extended so that the distance between the center of the ball to the center of the main shaft is identical AND the distance between the center of the balls and the fore/aft tilt axis (Distance A and Distance B) are identical. Now the aileron balls are spaced approximately 138 degrees apart from the elevator ball, so they rounded it off to 140 degree CCPM. When an elevator command is given all three servos move the same distance and you don't get any interaction.

The system was developed by team pilot Curtis Youngblood (you may have heard that name before) and JR for the JR Vigor. Its since been adopted by several manufacturers and as an upgrade by third party vendors for some kits. If you want to see the interaction I'm talking about on a 120 degree CCPM machine simply stir the cyclic stick very quickly and watch the swashplate ball. You will notice that it jumps up and down a bit. Do the same thing to a 140 degree CCPM machine and the ball stays still.

How much of an effect you feel in flight from the interaction depends on a number of factors. Pilot skill chief among them. Also servo quality and speed, and the speed at which your radio system processes CCPM functions. If given the option though, I prefer 140 degree CCPM.

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