Gyros 101: Make your model fly better

Model Airplane News, Oct 2000 by Edberg, Don

Gyros sense rotation, so it isn't too important where we mount them, as long as the sense axis is pointed the right way. Remember that when a body rotates, every part of that body rotates the same amount. In a helicopter, we could mount the gyro at the very front of the cockpit, in the rear near the rotor shaft, or even in the back of the fuselage near the tail rotor! The only things to worry about are ensuring the proper temperature, sense-axis direction, adequate mounting space and low vibration levels.

Having installed the gyro system, just plug the servo into it, and connect the gyro to the receiver. Depending on the brand and type of gyro, you'll have one or two connectors to plug into your receiver. If there's a second connector, it will be used to remotely control gyro sensitivity or gain from the transmitter. Wing gyros have a third connector for the second servo. Rudder gyros, often used to smooth takeoffs in tail-dragger and scale airplanes, will not have this third connector.

OPERATIONAL CHECK

After you've connected the gyro to your airborne gear, you must check some very important things:

Power up both the transmitter and the airborne system.

Allow the gyro about 5 to 10 seconds to warm up and settle into its normal operating mode.

I'll assume that you installed the gyro to damp out vertical rotations (yaw or rudder direction). When you quickly move the tail to the right (the nose moves left), the gyro should command the rudder/tail-rotor servo to move in a way that makes the tail move left. If you damp wing roll, you should check for aileron servo motion opposing the roll you input by rotating the wings.

Depending on how the radio is installed, it is possible to have gyro response reversed, and if you do, you'll have to reverse the gyro's polarity by flipping a switch on its case. If your gyro does not have a polarity-reversing switch, you'll need to rotate it so that the sense axis is 180 degrees from where it was before. Note that you cannot reverse the servo's direction to get the proper response you want.

Gyros and fixed-wing aircraft. Scale models, in particular, can benefit from having a wing and/or rudder gyro, especially when the model is not very stable or is very sensitive. You can put a rate gyro in a model to better manage rudder input, and it will let you take off without needing as much yaw correction as you usually need.

As previously noted, you can also install a wing gyro with its sense axis along the fuselage centerline so that it will damp rolling motion and will give opposing aileron input whenever a wingtip drops. This is a nice feature, but it isn't very helpful if you're trying to do snap rolls!

If you fly competitively, before you install a gyro in your model, be sure it's allowed. Some scale events allow gyros only on rudder.

Gyro sensitivity. Once you've verified that the gyro's polarity is correct, you need to set its gain, or sensitivity. Some gyros have one or two trimmer potentiometers that can be adjusted with a small screwdriver. How much gain you have is important: too much gain and the model will start wagging, or "hunting,"-not a good thing. A gain that's set too low is like not having a gyro at all. It's best to start with low gain, increase it until the model starts to wag back and forth, and then back off the gain a little. If you have a gyro with two gain settings, set one to be nearly off so that you can use it if you've set the other setting too high!