Gyros 101: Make your model fly better

Model Airplane News, Oct 2000 by Edberg, Don

After a few years, piezoelectric materials were reintroduced into gyros-and with great results. Now, most of the major RC system manufacturers sell piezo gyros that offer great performance at a reasonable cost. Improvements in electronics have allowed these gyros to be made even smaller than the mechanical units. They also have much less current drain, since a motor is no longer needed to spin the flywheel. Because they don't use much battery power, you can get by with smaller battery packs and so reduce your model's overall weight. Sensitivity to motion is enhanced because there are no rotating parts with bearings to wear out. The piezo gyros are the way to go.

Wing gyros. These are intended for fixed-wing airplanes; they smooth things out in the roll axis. They're simply rate gyros that have two servo outputs rather than one and are intended for aircraft that have two independent aileron servos. These are mainly used to stabilize the motion of scale models and any model that has to land in wind when the wings might bounce back and forth. I've also used a wing gyro in a competition glider to smooth flight performance during landings.

Heading-hold (HH) gyros. The newest gyros provide not only the damping control discussed earlier but also the "stiffness" needed to keep an aircraft at a certain attitude; in the case of a helicopter, they keep the fuselage pointing in a constant direction.

The analogy of the HH gyro is to sit on a pivoting chair and to tie a spring to the ground. The spring causes the chair to always return to the same heading: the stronger the spring, the quicker it returns to that heading. They also provide damping like conventional rate gyros to prevent your heli from "overshooting" the desired position and oscillating back and forth.

HH gyros are very popular with heli pilots, as they essentially allow them to ignore the tail rotor while hovering. More experienced pilots like the way the HH gyro holds a particular heading both in hover and when doing aerobatics in crosswinds, backward flight and in 3D flying.

HH gyros are more expensive than other types, but their performance makes them worth the extra cost. In the RC heli world, they are fast becoming the norm, both with beginners and master 3D fliers.

INSTALLATION AND SETUP

To help ensure that your gyro is not subjected to excessive vibration, you should plan its installation carefully. I make a balsa box and line it with foam rubber so that the gyro case fits snugly inside. This helps to protect it from the engine "noise" and vibration that can cause performance problems. If you have a gyro with more than one piece, the sensing portion needs the most protection. The other parts can be mounted more firmly, perhaps with double-sided adhesive foam tape.

The gyro's sense axis is usually marked on its case with a circular arrow (see Figure 1). If it isn't marked, it's generally perpendicular to any circular parts of the sensor case. Double-check to ensure you installed the gyro as you want it, or you'll see some strange aircraft behavior!