D.K.
Every child is different and motivated differently. Stop trying so hard and he will do it when he is ready and probably when you least expect it. My daughter didn't crawl until almost 11 mos, didn't walk until 14 mos and I remember being so worried. Then my son came along and was completely different and started crawling at 6 mos and walked at 11 mos. My daughter used to roll herself to get a toy, hee hee. Then one day it happened, then the walking shortly followed by running and the rest is history! Hang in there and just be patient!