Quote:
Originally Posted by Sam N.
Most shooters took inspiration from the team that released their design rather early in the build period. Our team planned to build a shooter all along, and endeavored to make several prototypes before the real thing. This is what we learned.
Pneumatic pistons by themselves (directly pushing a ball) are not enough to get the ball over the overpass when firing from the ground. This comes from the fact that the pistons extend too slowly (the inherent problem of filling large chambers with small air tubes). While the pistons did provide enough force to move the ball, but they did not deliver that force quickly enough.
The question we were faced with is: what can deliver the same amount of force on the ball over a shorter period of time? To us the answer was clear: springs.
Huge springs, two of them. 240lbs of force combined. We used two 2in bore pneumatic pistons to extend these monster springs, and a small .5in bore piston to operate a latch that would release all this potential energy when retracted.
That's the concept. The actual construction was more complicated. We were faced with more problems such as: how can we extend the springs with the pistons, and then disengage the pistons from the springs when we wanted to fire. Keeping the pistons connected to the springs would lead to an unwanted decrease in firing speed.
I will post some pictures of our spring-loaded catapult later if I have time. Any questions are welcome.
Sam
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Perhaps I seemed close-minded when I commented about using pneumatics to fire the ball over the overpass. Let me be more clear about our prototyping endeavors.
We found out that using two 1.5in bore pneumatics (directly pushing on the ball) only fired it around 6.5 feet high. That not being enough, we sought out other ways to shoot the ball higher.
So I was wrong when I said that using pneumatics to directly push on the ball wasn't enough to hurdle. I should have said that using two 1.5in bore pneumatics (directly pushing on the ball) wasn't enough to hurdle.
So I stand corrected because my original statement was vague. You certainly may use cylinders to push the ball directly if you have enough energy to do so. Many of the shooters (including ours) used compressed air for a reason, it was not my intention to discourage its use. (I'm also sorry if I ticked anyone off, everyone is proud of their own designs - for good reason too!)
Attached is a picture of our catapult in construction (left side of picture). Two pneumatics (as shown) are used to extend two springs of that size (only one was on the robot when the picture was taken). A small pneumatic controls a latch that releases the potential energy at operator command.
The 2in bore pneumatics are connected to the rotating structure that the latch cylinder is mounted to. When the large cylinders retract, the latch will hook on to the catapult structure. When the large cylinders extend, the latch will pull on the catapult until the springs are extended about 8 inches. When the latch disengages, the catapult will fire as the springs release their energy. The entire reloading process is automated.
It consistently shoots the ball 12 feet high.
Once again, sorry for coming off as close-minded,
Sam