So we had alomst the same design. What we changed to make it accurate was put a piece of tread across the bottom two wheels (ours were 6in). We also are only spinning the bottom wheels for a shot from the key. The top wheels are not moving at all. The bottom wheels are at full power, giving it the back spin. We are also using a 775 motor on a 4:1 reduction. Maybe make some of these changes and see how it works?!
Our shooter was really consistent, we went undefeated this week and won our first regional
! Good luck with your shooter