We have a single axis shooter that doesn't have a consistent compression. Basically the ball enters the shooter at the 0 degree mark with no compression. At 90 degrees it has 1" and at 180 degrees it puts 2" on the ball. There is an extra strait (tangent) 2" after the half circle that holds the ball on track while it is decompressing and it definitely helps accuracy. We've never had any ball go left or right (I'm not saying anything about a vertical accuracy because we had some sensor issues). Anyway, the ball auto centers in the rails before being grabbed by the wheels. The wheels are basically polished and that really helped us not tear up balls (at 5200 rpm having a grippy wheel will tear up any ball) and they worked because of the compression.
All this being said, the amount of back spin we achieved was amazing and we could hit the very top of the backboard and still make it. During prototyping we tested from beyond the co-op bridge and made it, with about a 25% accuracy
In the end it comes down to having had experience with designs you make during prototyping.
We wanted to keep our center of gravity as low as possible. So we ended up with it about 10" of the ground. Very helpful when balancing. I've seen too many teams flip their bot in the last seconds trying to balance. With that low of ground clearance you'll never flip. To show off we tested ours to about 70 degrees before tippage
