Short story about a soldier's reaction to finding out his sergeant is a robot

Question

I'm trying to find a classic science fiction story, maybe 70s era. There is a soldier going through boot camp under a very harsh and demanding sergeant. Later in the story the soldier discovers the sergeant is a robot. He finds this out when he happens upon the sergeant "going to sleep" which involves the sergeant folding up his limbs in an inhuman way. The soldier reacts by killing/dismantling the sergeant. An officer, remarking on these events, says that the soldier only did what any average human would do. I believe the title of the story has something to do with "balance" but I don't quite recall the word used (it was a different word from "balance," some sort of medical term).

Answer 1

I found it: Vestibular Man by Felix C. Gotschalk.

Summary:

Derek has been conscripted for military service in 2800 AD. He tries to dominate his drill instructor but quickly learns that the DI is bionic and that it can disable him simply by grabbing Derek's elbow. Derek mostly follows orders but maintains a sharp eye out for weaknesses in the bionic DI. He eventually finds one.