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Tricopter Rear Servo Oscillation

kah00na

Senior Member
#1
As soon as I get my tricopter up in the air and the rear servo starts oscillating slightly back and forth. It is real easy to see when it is hovering out in front of me. Because of the oscillation it starts to do small jerky movements into one direction and I have to yaw it in the opposite direction to compensate for it. When I fly quickly in one direction it has a slight "pull" to the one side because of it. Any idea how to reduce it?
 
#3
I found not all metal gear servos are created equal. Some have more torque (control authority) and some find and hold center better than others. The first servo I used wouldn't find center very well under load from the gyro spinning against its plane of control. The second servo which had more torque handled this issue much better and centered well.

Here is the one I used in the second attempt: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=33316
 

kah00na

Senior Member
#5
I found not all metal gear servos are created equal. Some have more torque (control authority) and some find and hold center better than others. The first servo I used wouldn't find center very well under load from the gyro spinning against its plane of control. The second servo which had more torque handled this issue much better and centered well.

Here is the one I used in the second attempt: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=33316
I was originally using a HS-80 or HS-81 (I can't remember which one) with metal gears. I crashed it and burned out the motor so I got a HS-81 or HS-82 (same as the first but with plastic gears). It did fine till another crash and I stripped out the gears. I still had the metal gears so I moved over to the new servo and that is what I'm using now. The gears were identical other than plastic-versus-metal.

Even on the ground, as soon as the motor starts up the servo starts oscillating. It is so annoying when I'm flying.
 

vk2dxn

Senior Member
#7
I had the same problem with my KK2, as it turned out the servo was good and my oscillation was caused by vibration. You can prove it by arming the board and on low throt wiggle the tricopter and you will notice the gyro manipulating the servo movement. In my case I could not fix it. I tried every pi gain setting and even played with stick scaling. In the end I just ran a y cable and drove the servo directly from the RX and the other end of the Y cable plugged into the kk2 for arming
 
#8
you could try upping your servo filter in the misc settings. ive got a 70$ servo in the tail of my tri and it was glitching real bad till i changed the servo filter settings.
 

kah00na

Senior Member
#9
Well I figured it out. There were a couple of teeth on the servo gears that were broken off. I replaced the analog plastic gear servo with a smaller digital metal gear servo (MG90D) and flies great now. I'd read that digital servos are more precise with the controls they receive from the transmitter. I am a believer now. This is my first digital servo and I'd rather not go back to analog ones.
 

vk2dxn

Senior Member
#10
Well I figured it out. There were a couple of teeth on the servo gears that were broken off. I replaced the analog plastic gear servo with a smaller digital metal gear servo (MG90D) and flies great now. I'd read that digital servos are more precise with the controls they receive from the transmitter. I am a believer now. This is my first digital servo and I'd rather not go back to analog ones.
Good to see that you sorted it out