Catapult?

[Taylor]

I haven't seen any discussion on anybody using a catapult design - is anybody going this route? Has anybody tested this? If so, is it accurate and effective? I imagine this design would be very difficult to defend (aside from breaking the arm off). Just curious....

[sciencenerd]

I can't speak for everybody, but team 1318 dismissed the catapult idea early in our first brainstorming meeting as hard to reload, hard to make accurate, hard to shield, and hard to make as powerful as necessary. I will be very impressed with any team that pulls this off successfully.

And I'm not sure what you mean by "hard to defend". I don't see how it would be harder to defend against a catapult design than any other type. And of course, breaking the arm off would be against the rules, so that isn't a legitimate strategy.

[Alan Anderson]

I think a well-constructed catapult is likely to be more consistent in its aim than a wheel-driven shooter. I also think it's pretty obvious that a catapult will be slower than a wheel-driven shooter.

Any teams designing a catapult will have to be careful not to run afoul of the very first rule.

<S01>
...An example of an unsafe design is a shooter mechanism that has a large mass that is stopped abruptly at the end of travel and is at risk of breaking off the ROBOT and becoming a projectile.

[Leav]

Originally Posted by Alan Anderson

I think a well-constructed catapult is likely to be more consistent in its aim than a wheel-driven shooter. I also think it's pretty obvious that a catapult will be slower than a wheel-driven shooter.

Any teams designing a catapult will have to be careful not to run afoul of the very first rule.

A trebuchet would potentialy work (especially a Floating Arm Trebuchet) and would still be considered safe by <S01> regarding the large mass being stopped abrubptly, however, a large arm, and a large mass would be required for a good trebuchet, both of which would be difficult to acheive with the game limitations...

-Leav

[Dorienne]

I don't think a catapult is a good idea. If any team can build a successful one, then by all means, go ahead and try...but it will indeed be difficult to work with..Unless it can scoop and shoot.

[KenWittlief]

I dont know, a catapult for this application would not have to be very big - maybe a 10 or 12" throw

esp when it can be actuated with a pnuematic cylinder that can provide up to 180 lbs of force (2" diameter cylinder charged with 60psi)

[sciguy125]

Actually, my spring tensioning cam was stolen from a catapult of sorts. I don't know the name and thus can't google it, but it was designed to throw basketballs. It's a little hard to explain the exact mechanism, but effectively, it was a lever with springs on one side of the fulcrum and a ball holder on the other. The thrower has super heavy duty springs (possibly garage door springs) so that it has a short throwing arm.

With the basketballs, it was able to throw about 30' and hit the same spot within a 1' radius. Personally, I think a similar device would be much more repeatable than most other ball throwers that are being discussed in the forums. For one thing, nothing is moving just before firing. This ensures that you have the same conditions every time.

[Leo 1529]

i also dont think that a catapult is a good idea. it may be accurate but it takes even more to get 1 ball to fall into the catapult at once, unless you want to shoot more than one at a time

[Ikeyballz]

Originally Posted by Leo 1529

i also dont think that a catapult is a good idea. it may be accurate but it takes even more to get 1 ball to fall into the catapult at once, unless you want to shoot more than one at a time

Not to toot my own horn, but two or three years ago, when we had the last non-autonomous period, we had a game based on soccerballs. We built a catapult powered by constant force springs (the springs made of coiled sheet metal) using 6 5lb springs, we got our robot to shoot soccer balls 99% effectively. The good thing about this was that our robot did not shoot at different velocities because of the change in our battery level.

[Bruce Mather]

Our first design was a modified trebuchet.
But it was 1500 kg and was over 8 meters tall.

Next we built a giant rabbit...and we crawled inside it waiting for the right moment after autonomous mode...

[kmcclary]

Now I'd *love* to see how someone designs a Trebuchet "repeater".
Resetting it to make the SECOND shot (esp autonomously) is
NOT a trivial robotic design problem.

But even if you *could* solve that one, it'd have to be a TINY
Trebuchet to comply with this year's build shooter sizing rules.
IMO, your biggest problem is getting it into the original volume,
to comply with shooter sizing rule <S03>:

> <S03> Shooter Mechanism must remain inside the ROBOT
> - Any mechanism used to throw balls must be contained within
> the original 28” x 38” x 60”starting envelope of the ROBOT [...]

Hmmm... How would a catapult shooter deal with this rule?

- Keith

[KenWittlief]

how much 'throw' do you think a catapult will need to launch the nerfball at 25mph?

we are not talking about launching a car 2,000 yards through the air here :^)

[Alekat]

Originally Posted by Ikeyballz

The good thing about this was that our robot did not shoot at different velocities because of the change in our battery level.

Consistency is very beneficial. But the same consistency can be accomplished with the right sensors. Of course this is only in theory for my team, seeing as how this is the first time we've incorporated a sensor into regular game play.

[waialua359]

Originally Posted by Ikeyballz

Not to toot my own horn, but two or three years ago, when we had the last non-autonomous period, we had a game based on soccerballs. We built a catapult powered by constant force springs (the springs made of coiled sheet metal) using 6 5lb springs, we got our robot to shoot soccer balls 99% effectively. The good thing about this was that our robot did not shoot at different velocities because of the change in our battery level.

Boy was that impressive!! I remember that one.

[Tim Arnold]

Our shooter was just rapid fired for the first time yesterday and I am proud to present a video of our bot firing. Please let us know what you think (leave a comment here)!


Shooting.wmv (19.6 MB)