It's a matter of both SP and how much you vote, right now looking at your SP it is still very low so it doesn't take too many upvotes to drain it to zero, you can check the value of your votes at steemnow.com also there's a calculator (top mid right) which tells you what your vote is worth at each percentage
I got a bellyRub and this comment has received a 12.01 % upvote from @bellyrub thanks to: @wilx.