HXT-900 servos can jitter when used with a heavier servo, maybe on the elevator. This shows the effect and a solution. It will vary with each installation due to wire length and equipment used, but the theory is the same. I use small metal gear digital servos on the elevator as it's most important and I've broken a few plastic gear servos on landing.
![](https://i.ytimg.com/vi/sEp4VT6NL6o/maxresdefault.jpg)