Drew these a bit ago, with ink.
These are amazing for 30s! The amount and correctness of detail you can achieve is very impressive.
My advice is to move in one of two directions, either increase the time or change your approach (ex. gestural or blind drawing) either will test different techniques.
Great job, i'd like to see more line of action strong poses, long strong lines of strokes. I suggest this book "drawing with force" by michael Mattessi