How Do Gyros Work?

Gyros or gyroscopes are used in everything from full computer mice to the navigation system on the space shuttle to RC helicopters.

So what’s a gyro? In lamans terms, it’s a device that can sense and measure rotation or how quickly an object turns.

In helicopters, gyros are typically used to dampen the tail movements or in the case of the heading hold gyro, to keep the tail in a constant position.

However, the modern RC helicopter gyro isn’t really a gyroscope at all – it’s an accelerometer. Accelerometers produce a signal as they’re rotated about an axis just like a traditional gyro and the more it accelerates, the stronger the signal is.

For the purposes of this article and real life, we’ll still refer to accelerometers as gyros because they function similarly and the end result is much the same.

On your RC helicopter, gyros work by measuing yaw or rotational acceleration, then mixing that with the pilots rudder commands to add dampening to your helicopters yaw axis rotation. For example, if a gust of wind makes your helicopter turn counterclockwise in the yaw axis, the gyro senses this and moves the tail rotor in the opposite direction to slow or dampen the rotation.

The are three main types of gyros:

1. The first is the mechanical rate gyro uses an electric motor to spin a small disc or flywheel that can pivot on one axis and has springs to return it to center. When the gyro was moved about the axis that it’s sensitive to, the spinning disc tilts and this tilt is picked up electronically by a ptentiomenter.

The faster the gyro is rotated, the greater the deflection is and based on the deflection, the corrective signal can be fed into a servo.

(Mechanical gyro)

2. The second type of gyro is the piezoelectric gyro which uses a quickly vibrating crystal. As the crystal vibrates, an applied rotational force will casue disturbances in it’s wobble which create a small, but measurable electric current proportional to the rate at which the gyro is rotated.

The piezo element is similar to that used in a gas lighter system like those found on a barbeque.

Piezo electric gyros are much more sensitive than a mechanical gyro and because there are no moving parts, they are a lot smaller.

(Piezoelectric gyro)

A disadvantage of piezoelectric gyros systems is that they’re very temperature sensitive and going from hot to cold or vice versa will casue them to act erradictly. Most have built in temperature protection circuits, but they’re not perfect, so if you’re going to take a gyro from warm your car and fly in cold weather, give it 10 or 15 minutes to adjust before flying.

3. And the third and most modern type of gyro is the MEMS or Micro Electric-Mechanical System gyro.

MEMS are molecule sized machines that are fabricated on top of a piece of silicon, along with the electronics to interface to them. They vibrate at a high rate just like the piezoelectric gyro and the As the gyro rotates, so does the displacement of the mass and the signal generated by the gyro.

(Mems gyro)

Besides the different makups and types of gyros, there are two primary ways that gryo’s operate, rate and heading hold mode.

Rate Mode Vs. Heading Hold Gyros

There are two types of gyro functions, rate mode and heading hold.

Rate Gyros

Rate gyro’s are often used in scale RC helicopters because they lend themselves to a more realistic flying experience, while heading hold gyros are used by almost eveyone else because they make flying easier.

Rate gyros only sense the turn rate or angular acceleration of your helicopter, not the absolute orientation of the helicopter and do not provide a heading hold capability. For example, once the helicopter has been turned, it cannot return the helicopter to the original orientation, nor keep the helicopter facing a constant direction.

Rate gyros will simply control your RC heliecopter’s tail servo so as to resist rotation in the direction they measure. In other words, it “dampens” the tail movement.

Because a rate gyro “slips” when trying to counteract the main rotor’s thrust, it can’t effectively counteract the main rotor’s thrust on it’s own.

The amount of thrsust provided by the tail is set by the revo mixing function on your radio transmitter.
Revo mixing allows you to set the tail rotor thrust to match the throttle curve so that it exactly counters the main rotor’s thrust. There’s no formula for setting the values – they must be set by experience and trial and error.

Heading Hold Gyros

Heading hold or heading lock gyros are a conceptually simple extension of rate gyros.

In a heading hold gyro, a built microprocessor that keeps track of and remembers how far the helicopter has turned from its set position. Based on the deflection from the set position, the gyro will control the rudder servo such that the gyro returns the helicopter to the set position.

Therefore, as you increate the throttle or headspeed of your heli, the holding hold gyro will counter the main rotors thrust automatically keeping your heli’s tail in its original position.

Heading hold gyros are very popular and pretty much standard amoung RC helicopter pilots for that very reason - they’ll hold your tail in a constant position no matter what you’re doing as long as you don’t input a rudder command, even if you’re doing 3D aerobatics or flying in a strong wind.

With a heading hold gyro, the rudder signal from your transmitter no longer directly controls the tail – it simply tells the gyro how many degrees to turn per second. It will also reset the gyros stored position to the new position you move your heli to. Revo mixing on your radio must be disabled when using heading hold gyros.

In conclusion, unless you’re going scale, and are looking for the more real characterstics often associated with scale RC helicopter flight, you’ll want to purchase a heading hold gyro, preferrably of the piezoelectric or MEMS variety unless.