The gyro is an essential component in many rc helicopters. Gyros in rc helicopters are most commonly used to control unwanted movement on the yaw axis. When an rc helicopter rotates on its yaw axis, the direction the nose points (the heading) changes. The yaw gyro’s job is to sense any undesired rotation around the yaw axis (clockwise or counterclockwise rotation when viewed from above), and to automatically correct the orientation of the rc helicopter. Without a yaw gyro, even if the rc helicopter was trimmed out to fly straight initially, it would eventually begin to drift and rotate right or left. Normal maneuvering of the rc helicopter and external forces can result in undesired yaw rotation. When this occurs, the gyroscope senses this change in yaw and corrects it by controlling the thrust generated by the tail rotor to compensate for the rotation. This results in stable flight for the rc helicopter and no undesired changes in yaw.
Old rc helicopter gyros operated by using the inertia of a spinning weighted wheel. The wheel would resist changes in orientation, due to it’s angular momentum. A sensor would monitor the orientation of the spinning wheel and use it as a reference to compare to the rest of the rc helicopter. However, these gyros were heavy and consumed energy to keep the wheel spinning. As technology improved new rc helicopter gyros were developed. The solid state gyro has no moving parts, consumes less electricity than its mechanical counterpart, and is more crash resistant.
There are two important types of rc helicopter gyro. The rate gyro senses changes in yaw, and applies corrective action. When the motion stops, the gyro stops correcting. There are two disadvantages to this type: first, although this gyro stops the motion of the rc helicopter, it does not return it to it’s original heading. In other words, if a force were applied to an rc helicopter in level flight, it would turn and then the gyro would stop this motion. The end result would be that the rc helicopter has been turned to a new heading. A second disadvantage is that since the gyro only corrects after the motion has been detected, and the corrective action is always a little late.
The heading hold gyro operates in the same way as the rate gyro, with the exception being that after yaw movement has been corrected it returns the nose of the rc helicopter to it’s original position. This type of gyro does not stop giving commands to the tail rotor when motion stops, but will continue giving these commands to hold the nose of the rc helcopter in a certain orientation. Even more advanced gyros of this type will interpret the yaw requests that the pilot is sending through the radio control system, and will make whatever corrections are necessary to cause the rc helicopter to yaw at the desired rate. With this type of gyro, an rc helicopter will turn equally even in a crosswind.
Even though the heading hold gyro has many advantages, it places several demands on the rest of the rc helicopter system. It will require a very fast tail rotor servo, and a powerful battery to supply the servo, which will be required to make very fast corrections. This can strain the servo, and consume more power. The rc helicopter battery will need to supply the gyro and servos, so a higher capacity battery is better. However, the larger the battery, the larger the weight. An rc helicopter with a heading hold gyro and fast servos can use significantly more power than a less aggressive rc helicopter with a rate gyro.
Clearly, there are many choices of gyros for the rc helicopter pilot, each with it’s own advantages and disadvantages. When choosing a gyro system for your rc helicopter, be sure to consider battery capacity and weight, how you will be flying, and the type of servos with your radio system.
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Posted in Gyro Stabilization for RC Helicopters