Fine Tuning your Mechanical T/R Setup

Many times we are in a hurry to get our heading hold gyros installed just to see how well they work. When it doesn't work quite as well as we would like, we blame the gyro. Often times the only thing that's needed is a little tune up.

The first thing to check is the length of the tail rotor control rod and the position of the servo arm when the model is in a hover. If it is too long or too short, the tail rotor will not be able to react the way it should. This shows up as " the tail keeps letting go". Normally, if you'll notice, it always goes the same direction when it lets go. This is a classic symptom of a poor setup. It is caused by two bad things working with each other, differential and biased control. Of course there are other factors, such as the size of the t/r blades, headspeed, gyro gain and the smoothness of the control system and engine. However, unless the rod is the right length, it won't work regardless.

In order to get the rod the right length, you must be sure the servo arm is exactly 90 degrees to the control rod when the model is hovering. This is easiest to accomplish in normal/rate mode. If your gyro is switchable, put it in normal mode and observe the servo arm. Do whatever it takes to get it 90 degrees to the rod. The preferred method is to find a servo arm position that works. If you're using a JR Heavy Duty long arm, there are only two choices. Pick the one that's closest. Or, you can also use a Heavy Duty wheel and drill a hole in the exact position.

Now hover the model. If the nose goes left, shorten the control rod. If it goes right, lengthen the control rod. Check it with the nose into the wind and tail into the wind. Once it will hover without yawing one way consistently, verify the control arm is still 90 degrees. Have a friend observe the t/r servo while you hover to be sure.

Remember, since you have rev-mix turned off, in normal mode the model will react to changes in torque. Any time you add power the nose will want to go left and any time you reduce power, it will want to go right. Make your adjustments based on how it reacts in a solid hover.

This alone might improve the performance of your gyro dramatically. Also check these things:

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