Step on edges of large pedal (7)
I believe the answer is:
treadle
'pedal' is the definition.
(I know that pedal can be written as treadle)
'step on edges of large' is the wordplay.
'step' becomes 'tread' (tread is a kind of step).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'edges of' says to hollow out the word (remove centre letters).
'large' with its centre taken out is 'le'.
'tread'+'le'='TREADLE'
(Other definitions for treadle that I've seen before include "Rocking lever operated by foot" , "Bit of machine" , "Foot-pedal" , "(Machine's) foot-control" , "Foot lever that works a machine" .)