Friday, August 12, 2011

Helicopters: Gyro Setup

By Lood Birk

Ermelo Radio Flyers

Gyros have really come a long way since the first mechanical gyro till where it is today with the new MEMS gyros. Through the years, gyro setup has indeed become easier, but there is still some setup involved in the gyro.

Firstly, as with the rotor head, your tail setup has to be mechanically correct. On the tail rotor control rods, the same 90deg rule applies to the servos horns and control rods. The following bit is for those that missed my heli setup videos.

The above picture was taken from a typical heli setup manual. This picture tells you exactly how the mechanical setup should be. Have a closer look at the servo and the servo horn. As with the servos on the cyclic of your heli, you have to find a horn that is closest to 90deg while the servo is in the fully center position. Once you get a servo horn that is close to the 90deg mark, use your transmitter’s sub trim to make it fully 90deg. Beware though that if you use too much sub trim it is then better to rather reposition the horn, or get a different horn.

Once you got the mechanical setup correct, it is time to set up the tail servo direction. For this you will have to connect your servo (NOT through the gyro) directly to the receiver. Setting the servo direction is actually not so difficult. Rotate the tail rotor to the bottom of the rotation circle. Look at the tail rotor pointing down. If you give left rudder stick, the leading edge of the blade must move to the right. If the leading edge moves to the left, the servo needs to be reversed.

At this point, you are ready to mount and connect your gyro. Please pay close attention to the mounting orientation and mounting method of the gyro. This is especially so in the case of MEMS gyros. MEMS gyros are more susceptible to vibrations and electrical interference. Below is a typical picture of the mounting instructions of a gyro.

These pictures are just examples. Please consult your particular gyro’s manual.

Once the gyro has been mounted you need to connect the leads. Most gyros today are all heading lock gyros. Now heading lock gyros connection differs from normal rate mode gyros by the fact that heading lock gyros have a tail servo lead, a rudder signal lead and a gain signal lead. Rate gyros does not have a gain signal lead. The tail servo lead plugs into the tail servo. The rudder signal lead goes into the rudder channel of your radio and the gain signal lead goes into a spare channel set aside for gyro gain. That info you will have to get from your transmitter’s manual. For those that don’t know, the gain channel allows you to set the sensitivity of your gyro during flight.

There are a couple of things you have to set now. You have to set the gyro direction and the endpoints.

The gyro direction is the most important to set as the wrong direction will make your heli spin out of control. To set the direction connect your receiver and make sure the transmitter can talk to the receiver. Wait for your gyro to initialize. The direction test is easiest to do when the gain on your radio is set to 100%. Turn the rotor so that one tail rotor blade points downwards. Now move the tail to the left. The leading edge of the bottom tail rotor should move to the right. If it moves to the left, you have to reverse the gyro direction.

Next, you have to set the endpoints. I am not talking about the endpoint adjustments on the radio, but the endpoint setting done on the Gyro. The endpoints sets the limit to which the gyro will allow the servo to move as to prevent tail pitch assembly from pressing against the tail rotor hub or on the other side of the shaft where the bearing is. To do this, move your stick fully left or right and set the endpoint down till the servo stops buzzing. Most new gyros you can set the left and right endpoint. If your gyro only has a general endpoint setting, you set it till both left and right are clear.

At this point you thing you are done. But you are not. Next you have to spin up your chopper while your gyro is set to rate mode (gain set to 40% or below). The reason for this is that different main rotors will have different influences to the center position of your tail rotor. What you have to do now is see which way the tail moves when you hover. If the tail moves to the left, move the servo mount backwards a bit. And I do mean a bit. It will take a while to get it right. If you are not a good flyer, ask an experienced pilot to help as a gyro makes the heli more difficult to fly. After you got the servo position in that sweet spot, check the endpoints again.

Now it’s time to fly and check the gain on the gyro. I normally find that on about 85% gain is a good starting point. If the tail wags fast from side to side with out any input, the gain is normally too much. If the tail has difficulty stopping after control input was given, the gain has to be set up a bit. It takes a bit of time, but once done it is normally set.

I really hope this helps those who struggles with the gyro setups.

Happy Landings.

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