Looking for a design app

For years I was Android until I got an iPhone, and for the last four years I’ve been (mostly) happy. I recently got an Android tablet for design projects but am at a loss. I don’t mind paying for an app as long as 1) price is reasonable and 2)not monthly/subscription/AI (since that goes to the monthly/subscription fees) I am looking for an app that I can design a pulley system. Doesn’t have to be fancy or elaborate; just something I can sketch my ideas out. Is there anything out there that might work for me?