These two sets of five clues each leads to five words that only differ by one vowel (the vowel is a, e, i, o or u, but not necessarily in that order). What are the words?

Small robot.
Small part.
On the contrary.
Nocturnal mammal.
Wager.

Struck.
Heated (archaic British).
Straw dwelling.
A head warmer.
Not cold.