How to do a backhand spring?

I have wanted to do one for years now but Im afraid to do it. Ive done it on the tramp a few times but then my arms started to crumble so I stopped. I want to do it on the ground now more than anything but I dont and cant go to tumbling cles or anything. I even if a had a spotter (which Ive tryed before) Ill be so ready to do it then ill just stop when im ablout to swing back and I cant seem to get it or get over my fear. HELP!