caterpillar into ayesha!

Hi guys anyone having problems with their caterpillars? I cannot for the life of me get caterpillar right. I know that you need a very strong caterpillar to get inrush your ayesha. When I invert my right leg is at the front and the left leg behind, I then split my grip with my left hand at the bottom (head height) and right at the middle (belly button height) I have also tried reversing the grip ie right hand at the bottom and left hand at belly button. I cannot seem to push my bum up then re-grip. I seem to lose my grip as soon as i push out then my legs give way and I end up on the floor! What am I doing wrong? Is it the grip? Or is the hands positioning? My legs? Any advice would be much appreciated. I want to master this and get into my ayesha. Thanks in advance! X