How can i workout my abs at home without a machine?

i workout my abs a lot but since im kinda skinny my abs are small even thought its cut, since i have the cut look now, i just have to make em bigger.

Problem is i need weight machine, cuz isnt that the only way to make your abs bigger? More weight less reps, More reps less weight. Big, Cut…Righte??

so what should i do?