Yup, only need to train abs like every other muscle group. 1 maybe 2 times per week. I do mine with bi's currently. I just grab on a pull up station and do leg ligts, and do crunches. I will say tho the old school ab rocker roller thing... the purple thing sits on the floor. Its good for when you want to hit abs. It makes sure you dont stress your neck. To do crunches without using your neck, also try staring at the ceiling and put your tongue against the roof of your mouth.
Another good core exercise is to take a small straight bar, but a 10lb plate in the middle, basic ab roller. be careful tho, it will work your abs, but can hurt your lower back

or take a 5 gallon lid, plactic lid, and put it in the floor. get on all 4's, feet on the lid and do a jack. same thing as using a ball, but a little more stable.

but abs wont really be seen until you get to a lower BF%.