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Quote: Originally Posted by Biff |
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Heading mode. Uhhhh,,,,? |
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I was in the same boat for while, these things seemed very complicated. Gyro technology has done wonders for the rc heli in the past 10 years. Gone are the days of revolution mixing (tail to collective). I couldn't imagine setting up a heli without a gryo.
Here we go, get your notebook. Cliff notes are at the end of the post.
First thing to start with is what does a gyro do, and how does it do it. Basically you have two types, mechanical and piezo. I do not think anyone still sells the old mechanical gyros. The mechanical gyros will have a buzzing sound coming from the sensor unit. They use an electric motor with two flywheels, one on each end of the motor shaft. And this is where the noise comes from. To understand how it works hold a spinning bicycle wheel by the axle and try to turn it, you will feel it resist you moving it. The flywheels in the mechanical gyro are mounted on a pivot and a sensor measures the deflection of the motor/flywheels when the helicopter makes a sudden movement. The piezo type gyros work with no moving parts. It uses a triangular crystal (or a silicon ring in the case of higher end models) with a piezo element on each side. The piezo element is used in a lot of watches to make the beep sound from the alarm function. The material not only can make sound but also sense it. So it is used in both speakers and microphones. Two of the piezo elements on the crystal are set to sense vibration and the third one is setup to vibrate. When the helicopter is not rotating the vibration traveling through the crystal hits the other two piezo elements at the same time. When the helicopter is rotating one sensor will have a stronger signal then the other. It is a very efficient design and has a lot finer degree of resolution then the mechanical type. In addition power consumption is greatly reduced as there is no spinning motor to power
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BIFF! WAKE UP! Here's you answer! I know this is a very dry subject but I find it interesting and it good to know what is going on inside that little plastic box.
Heading hold (hh) and standard rate or normal(non-hh).
In non-hh mode the gyro just dampens unwanted movements of the tail. To keep things simple lets say you are hovering and a constant wind hits the helicopter from the side, the gyro will keep the helicopter from suddenly swinging nose into the wind, but the helicopter will eventually drift nose into the wind. All the gyro does is to prevent any jerk type reaction.
In hh mode the gyro will keep the nose pointed in the same place until you tell it to move. You can fly sideways with the rudder stick in the center and the nose will remain pointed in the same direction.
If you have not used heading hold before then you will notice in fast forward flight that when you make a turn, the tail will not follow the helicopter, you have to give some rudder in your turns. Another thing is that you'll notice the rudder stick feels different. In heading hold, the amount you move the rudder stick from center tells the gyro how many degrees per second that you want the helicopter to rotate. The gyro moves the rudder servo however much it needs to obtain the requested rotation rate. With a standard rate gyro if you did a slow pirouette (one rotation) with the wind then to keep the helicopter spinning at the same rate you would have to move the rudder stick more as the tail is going upwind and less as the tail goes downwind. But with a heading hold gyro, it will tell the rudder servo to move more or less to maintain the constant rate, you just keep the rudder stick in one place.
Due to typical marketing ploys you will see many names for heading hold. They all are just different names for the same thing. The different names are just because each company wants to make it seem like their version is more special then another companies. AVCS = Tail Lock = Smart Lock = Heading Hold
Cliff and Biff notes:
Gyro's sense the yaw of the heli due to torque changes by the main rotor, and send a signal to the tail servo in the opposite direction to correct the movement and make it stay put.
Non heading hold will allow the heli to act like a weather vane (sp?) and point itself into the wind that is hitting the fins on the tail. Heading hold will keep the tail locked in one direction until stick input is entered (allows for easy sideways flight)