Mechanical crib too unstable (7)
I believe the answer is:
robotic
'mechanical' is the definition.
(I've seen this before)
'crib too unstable' is the wordplay.
'unstable' indicates an anagram.
'crib'+'too'='cribtoo'
'cribtoo' anagrammed gives 'ROBOTIC'.
(Other definitions for robotic that I've seen before include "Man made" , "Stiff and emotionless" , "Mechanical; unemotional" , "Mechanistic" , "Like automatic device" .)