Team 888's 2nd prototype
Do you have trouble with that aggressive tread shredding Poof balls? That’s what happened when we spun treaded wheels at 2,500 RPM…
With our two wheel shooter you could watch the foam fly off the ball as it left shooter.
When we tried another tire design without tread, it did not perform as well. However with this design, the balls are only momentarily contacting the tread and little shreading occurs.
Yes I agree with professor coldabert as we call him. The shearding that occurs is very small nothing noticable.
While I agree with the prof and Dewber that slight shredding occurs, if you mount the launcher to a table and shoot off five or six balls the table becomes covered with little chunks of foam.
With all this talk of shredding balls, I would look into a redesign mostly because FIRST won’t be to happy about that.
See the post here http://forums.usfirst.org/showthread.php?t=288&highlight=ball about ball damage.
It IS possibile to build a one wheeled shooter that won’t damage the balls and still achieve the 12m/s that is allowed (or close to it.)
We originally used the 9"x2" Skyway pneumatic wheel pictured at the beginning of this thread. It worked GREAT… but left, as mentioned, little pieces of foam and skin lying on the table where we had the mock-up mounted. We tried machining off the tread, but it still “visibly abraded the surface”. So I posted the “Ball Damage - Follow Up” question mentioned above to the Q&A forum.
We have since revised our design, using two 8" Skyway kit wheels mounted a couple inches apart on the same shaft (it is still, essentially a single wheeled shooter), and adjusted for the decreased radius by bringing in the “wall” that compresses the ball by about an inch.
If you do the math… the 8" wheel is 20cm in diameter, or about 60cm in circumfurence. Spin it at 3000 rpm and you get 1,800 m/minute (30 m/s) linear velocity. Assume the ball will be travelling at 1/2 the linear velocity, and you will have all the speed that you are allowed… along with a comfortable margin to account for ball slippage, etc.
We’ve fired brand new poof balls from this set up dozens of times with NO visible damage. None.
FIRST does not mess around with its rules. If it is in the Q and A… it is in the rules. Shred balls at your own risk.