One big thing that I see a lot of teams forget is that the mechanism needs to work on the field in the heat of competition, not just in the shop under perfect conditions. Just because your intake picks up a ball that’s sitting right in front of it doesn’t mean it can get one rolling away from it, off-center, slightly over/under-sized, etc. Test your mechanisms in the worst conditions you expect, then test them again in conditions worse than that. Don’t be satisfied until it meets your expectations in worse than the worst conditions.
For that matter, set requirements before you start prototyping. For example: “our intake needs to be able to pick up a 12-14 inch ball within 5 inches from its centerline within one second”. That way when you’re testing your prototypes you know whether they meet your specs or not. If you find that you’re unable to design a mechanism that meets those specs, you can adjust them but that may mess with your match strategy.