Robot men reassembled brass instrument (8)
I believe the answer is:
trombone
'brass instrument' is the definition.
(I've seen this before)
'robot men reassembled' is the wordplay.
'reassembled' indicates anagramming the letters.
'robot'+'men'='robotmen'
'robotmen' anagrammed gives 'TROMBONE'.
(Other definitions for trombone that I've seen before include "play this" , "Bfrass wind instrument with slide" , "Blow me!" , "Brass musical instrument with slide" , "Musical instrument with long slide" .)