How do the Shooters work?

[Akash Rastogi]

Since I'm still a mechanical noob and I will be one of the main mechanical people on the team next year, could the teams who have implemented a shooter or something like a shooter please post how it works and what you used to build it. Pictures or CAD of your robot or the specific end effector would be awesome. Thanks a lot in advance.


-noob

[lukevanoort]

Ours is very different from most you'll see around here. It operates on a similar principle to the classic "there's no replacement for displacement." Ours operates off of pure power - to the tune of 2 Chiaphuas and 2 FPs, for a combined total of over 1000 watts in the shoulder. As to how well it works... lets just say you should make sure your pot mounting is really rigid when using them on parts that accelerate really fast. A little flex that caused our pot's gear to disengage from the one on the shoulder under sudden acceleration turned the PID tuning from a 15-20mn job into a takes-the-entire-regional-and-still-isn't-completely-done job.

[s_forbes]

There are several ways to do it; team 1726 took the approach of using pneumatics to launch the ball. The cylinders were set up in such a way that they could build up pressure while the ball was on top of the catapult and then launch it over quickly after the pressure overcame the weight of the ball. (pictures here)

39 also used a pneumatic launcher, but it works much better in our opinion. Instead of letting the cylinders build pressure, they just increased the airflow to the (single) cylinder to make it fire quicker. They had three valves running into it, allowing for a very simple and effective launcher (the best one I've seen so far).

The other main launching method I've seen involves using latex tubing to make a slingshot/catapult apparatus. 118 is noted for posting the design first, and many other teams have a similar set up.

[kaszeta]

Originally Posted by s_forbes

There are several ways to do it; team 1726 took the approach of using pneumatics to launch the ball. The cylinders were set up in such a way that they could build up pressure while the ball was on top of the catapult and then launch it over quickly after the pressure overcame the weight of the ball. (pictures here)

39 also used a pneumatic launcher, but it works much better in our opinion. Instead of letting the cylinders build pressure, they just increased the airflow to the (single) cylinder to make it fire quicker. They had three valves running into it, allowing for a very simple and effective launcher (the best one I've seen so far).

Team 95's robot Zog used pneumatics as well, with a two-stage pneumatic cylinder arrangment and six valves to get all the flow we needed. I'll see if I can get a good pic of it. We liked it, since Zog can hurdle the ball from floor level while driving.

[Akash Rastogi]

Wow, some of these look sick. 125's got air for sure. Thanks a lot for the posts so far, its cool for someone learning in FIRST to see such creative designs.

Keep 'em coming

[HighLife]

We use two 150lb garage door springs and surgical tubing. The springs and tubing are pulled down by two globe motors and released with the small kit pneumatic.

Here's a few pictures:
http://www.adambots.com/images/6/65/F08C-GL-084.jpg
http://www.adambots.com/images/1/10/F08B-218-09.jpg
http://www.adambots.com/images/1/14/F08C-GL-012.jpg

Here's is some video of it at Great Lakes Regional:
http://vimeo.com/850287
(Please excuse the poor Hybrid on this match )

[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

[martin417]

Originally Posted by Sam N.

Pneumatic pistons by themselves (directly pushing a ball) are not enough to get the ball over the overpass when firing from the ground.

Hold on a minute! Here is a quote you should heed:

Originally Posted by Arther C Clarke

When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.

I don't know how many time I heard on this very forum all through January and February that "so-and-so will never work" or "This mechanism cannot do that".

Two examples I heard over and over involve the use of vacuum to acquire and hold the ball, and pneumatic cylinders (thats the proper term, the piston is the part inside the cylinder that moves) used to shoot. I read numerous posts that said things like "you can't pick up a ball with vacuum", "the cover is too porous", "you can't develop enough holding force" as well as comments like the one you just posted.

I believe that, while well intentioned, these comments discourage innovation, and prevent people from trying new approaches. Just because you haven't figured out how to make something work doesn't mean it's impossible. If you read my earlier post in this thread, and visit the links there, you will see that not only can pneumatics alone "get the ball over the overpass", they can do it very well.

I think this point is so important, I should start a new thread.

Here is a true story that illustrates what people can do if you don't tell them it's impossible.

A young college student was working hard in an upper-level math course, for fear that he would be unable to pass. On the night before the final, he studied so long that he overslept the morning of the test. When he ran into the classroom several minutes late, he found three equations written on the blackboard. The first two went rather easily, but the third one seemed impossible. He worked frantically on it until, just ten minutes short of the deadline, he found a method that worked, and he finished the problems just as time was called. The student turned in his test paper and left. That evening he received a phone call from his professor. "Do you realize what you did on the test today?" he shouted at the student. "Oh, no," thought the student. I must not have gotten the problems right after all. "You were only supposed to do the first two problems," the professor explained. "That last one was an example of an equation that mathematicians since Einstein have been trying to solve without success. I discussed it with the class before starting the test. And you just solved it!"

http://www.snopes.com/college/homework/unsolvable.asp

[kaszeta]

Originally Posted by Sam N.

Pneumatic pistons by themselves (directly pushing a ball) are not enough to get the ball over the overpass when firing from the ground.

I always love reading quotes like this, since Team 95's robot does exactly this, with quite a bit of margin:



Yes, we use six cylinders in a two-stage arrangement, and it took more than a little tweaking, but we are "directly pushing on the ball" with nothing but pneumatic pistons. We could get even better performance if we triggered the two stages separately at staggered intervals, but we called this setup good enough.

[cwood]

team 1629 uses two cylinders and two springs to fire the ball.

First the cylinders are charged to extend the springs and lower the scoop (fancy curved catapult) it is then latched with 1 small cylinder. At this point the only force is the springs but as we begin the firing sequence the opposite side of the cylinders is charged (applying force in the same direction as the extended springs) and when the latch is released up the scoop, and what ever may be on it, go. This arrangement gives us gives us the ability to hurdle from ranges back to the end of the lane dividers, as well as the ability to launch diagonally from one homestretch to the other.

Its was a tricky arrangement to control until we discovered that it was much easier to let the programming do the timing required to be efficient.

if you have any other questions you can message me or stop by our pits in atlanta

[ttldomination]

We do nothing too complicated. We have a fork lift which take the ball in. and then we use surgical tubing and tie our shooter to a bar on the robot. Then we use a wench to pull the shooting platform back...and bam.

[Sam N.]

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

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

[martin417]

Originally Posted by Sam N.

(I'm also sorry if I ticked anyone off, everyone is proud of their own designs - for good reason too!)

Nothing to apologize for, I don't think you ticked anyone off. Your comments just brought to mind something that had been bothering me for some time, and I decided to address it. As I said this type of comment is generally well-intentioned, (trying to prevent a team from wasting time on an approach that is destined for failure?) but if not done very carefully, can stifle creativity. I think it is OK to say that a specific design wont work (if you are absolutely sure, and completely understand the design) as long as you can point out alternatives. But making blanket statements about the unworkability of concepts should be avoided.

My 2 cents. (again)

[PizzmasterP27]

You guys (MORT 11) are going to the champoinship. Feel free to come by the pits of team rush 27 and ask any of our members how the catapult works. A brief description is that we use an andymark gearbox as our winch and we pull back our catapult arm which has 400 lbs of surgical force. This force is distributed to 8 cartridges of 50 lbs each. more detail on motors, sensors and such can be provided in our pits.

As i said, feel free to come and ask any member. We are trying to get everymember involved in answering questions for people too.

[Akash Rastogi]

Originally Posted by PizzmasterP27

As i said, feel free to come and ask any member. We are trying to get everymember involved in answering questions for people too.

Yup, I'll be dropping by a couple pits to scout anyway. I'll make sure I'm the one scouting your robot