under one's own steam
Independently, without help, as in For two years I published the quarterly newsletter under my own steam. This expression uses steam in the sense of “driving power,” as in a steam engine. [Early 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.