How Do Gyros Work

[putt_13]

Hello,
I know that a gyro keeps something level and balanced, but how do the ones in RC helis work. I was reading an article, and I just wondered. Thanx Patrick

PS- Moderator, If this should be moved to like a helicopter area, please do so.

[AirVenture]

Does anybody know if they are similar to the ones used in full sized aircraft instrument, such as the heading indictor? I have a GY-240 on my Corona. One has to wonder how they fit all of that stuff inside that tiny thing.

-Brett :)

[putt_13]

Originally posted by AirVenture
One has to wonder how they fit all of that stuff inside that tiny thing.

What Stuff?????

PS- How does it work?

[FlyByMike]

Since no one's answering yet I'll tell what I <think> I know. :)
1. They're not really gyros (as in gyroscopes) with little spinney things that keep orientation due to the inertia of the rotatioin mass. Brett- the original type and maybe the current type in 1:1 planes were/are gyros.
2. They are accelerometers. That is to say they produce a signal as the device changes speed. The more it acceletates the larger the signal. I would imagine that the ones in model helis take this signal and use it to control a PWM that an ordinary servo can use.
3. Helis use gyros to keep the tail oriented in the correct direction similar to what a rudder does on a fixed wing. I don't imagine heli gyros do this on more than one axis though.

[Andy W]

What he said. You CAN still buy tiny versions with true 'gyros' inside, but the modern micro ones use a tiny piezoelectric sensor (similar material to our the crystals in our TX and RX) with a small weight bonded to it. As the gyro is moved, it senses the acceleration and compensates appropriately.
..a

[AirVenture]

I was going to say....it must me some really small gyro to fit inside such a small package. In an airplane a gyro is an an actual gyroscope that maintains it's position no matter what the airplane is doing. I believe the term is it "retains rigidity in space." The instruments in most general aviation planes that use gyros are the turn/bank indicator, attitude indicator, and heading indicator. The turn/bank is electrically driven while the other two are driven by a vaccum system from the engine. They're really cool to look at if you can get your hands on one.

-Brett :)

[Paul Susbauer]

Goin' to heli's although its a pretty good question for this forum.

--Paul

[marcinr]

The early gyros were a little spinning disc mounted in a frame that could swivel in one axis and had springs to return it to center. When the gyro is moved about the single axis that it is sensitive to (the frame restricts this), the disk tilts one way or the other and the tilt is picked up by a potentiometer. The little springs which return the gyro to center make it behave like an accelerometer. The faster the gyro is rotated, the more the deflection. Based on this deflection, you can adjust the signal going to a servo and you get your "gyro" behavior.

The next generation of gyro is the piezoelectric gyro.
Here, there are no spinning bits, only a rapidly vibrating crystal. This crystal wobbles along a particular axis, and as I understand it, turning the crystal will cause disturbances in this wobble which cause a small electric current. This current can be measured and used to adjust your servo position. Piezoelectric systems are very temperature sensitive since temperature affects some internal resistances. This is why they start to drift as the temperature changes. Most piezo gyros now have a temperature compensation circuit to avoid this.

The most modern kind of gyro is the MEMS gyro. MEMS = Micro Electric-Mechanical System. MEMS are molecule sized machines that are fabricated on top of a piece of silicon, along with the electronics to interface to them. I don't know how MEMS gyros work specifically, but they do some sort of differencing on some sort of moving bits :). AFAIK, only Futaba sells MEMS gyros at the moment; GY240, GY401, GY502 and GY602.

The behavior of all three gyros above is known as "rate mode". This means that they will control the servo such that they resist rotation in the direction they measure. "Heading lock" gyros are a conceptually simple extension of the above sensors. In a heading lock gyro, a computer monitors gyro drift over time, keeping an internal count of how far a gyro has drifted from its set position. Based on the deflection from the set position, the gyro will control a servo such that the gyro returns to the set position. On a heading lock gyro, the rudder channel will not directly control the servo but it will reset the gyro's internal "set position" towards the direction you've moved the stick.