1310 had this issue all the way up until after the first match at champs. That was the only qual we lost, as we jammed at about the 1:40 mark, and ended up loosing by 2 points. Had it not been for that jam, we would have had #1 seed on curie, and things on that field would have been totally different.
http://www.youtube.com/watch?v=rfqeoMx0GeI
4814 pushes us into an upside down disk, then the wall. we normally cant pick up upside down ones, but with the walls help it went in at 1:36. it has difficulty going through the pickup, but makes it out the top from 1:36-1:39. we fire the 2 disks we picked up before that, then we jam for the rest of the match. If you cant tell, i have watched this match in detail multiple times to see exactly how it happened.
First a little background.
Our hammer (the part that pushed the Frisbee into the wheel) engages the outer edge of the Frisbee, and is powered by a spring out, air in piston. our hammer is a bent piece of 1.5" wide, 1/16th aluminium. The bend on the top was just enough to lift an upside down Frisbee, as it impacts right at the curve. this would cause our robot to be a glorified "dishwasher" as our students called it. We came up with the solution before champs, but reluctant to change things, we didn't implement it, as it had only happened once or twice all season. It was such a simple fix, and i bet it would work for any team with this issue and an external hammer.
The solution? A self tapping screw at the right height through our hammer. It is sharp enough to catch the rounded edge of the Frisbee, and eject it. the first time we tried it, it was magic. consistent ejection of upside down Frisbee's at a minimal weight gain. The screw needs to be for wood, as the tip is sharper.