Puncher Shooter

[cmwilson13]

we used it on our 2008 ball and its what we are using this year.
link from my old teams 2008 bot
http://www.youtube.com/watch?v=QeQSGmFnKAE

[J.Warsoff]

Our team tested both a puncher and catapult design (when I was home for break). Last time I checked, I believe that we found the catapult was more accurate and consistent (Someone from my team correct me if I am wrong, as I haven't been at the shop since last Saturday.)

From what I can tell, a puncher has a smaller area of contact than the catapult during the actual shooting process. Since it is applying a lot of force to a small area, it causes much more deformation in the ball than the catapult, which can lead to inconsistency in the shooting (due to even the smallest factors like amount of air in the ball, location of point of contact, etc.) Once again, someone correct me if my observations are wrong.

[Qbot2640]

I think our's fits into the description you are calling a "puncher," but we discovered that "punching" was not as effective as "pushing."*

http://youtu.be/UK2f9lvskcQ

This is three 3/4" cylinders with 12" stroke through some fairly high performance solenoids (.75 M^3/s flow) and the return ports left open to allow quick venting. We need to turn the pressure down to about 42 psi to avoid breaking things. (And we'll need to attach some kind of spring to bring the plunger back to the firing position.)

*The difference: we found it most effective to have the ball rest on the plunger of the cylinders before launch (push) rather than have a separation and have the ball struck by an already moving plunger (punch).

[nuclearnerd]

I'm not sure if this is a "puncher", but we were able to get an air cylinder to push the ball for a ~15 ft shot during our "proof-of-concept" stage. It took more work than you're expecting though:

1) You need a big cylinder. We used a 2" bore, 15" stroke
2) You can't deliver enough power through the FRC legal solenoid valves. Instead, treat the cylinder like a gas spring and pre-charge it.
3) Because you can't exhaust air through the solenoid valves fast enough either, you can't use the same cylinder to retract. Instead, you need a separate cylinder (or winch), and a release mechanism (basically all of the things you would need if you were working with surgical tube instead of a cylinder)
4) The cylinder should have a tank of at least equal volume attached directly to the port with hard pipe (preferably 1/4") *not* tubing. The extra volume of the tank will keep the pressure in the cylinder from dropping to nothing when it expands, but the flow restriction through the port puts an upper limit on power.

So in summary - doable, not much easier than a surgical tube slingshot, although it does let you vary force.

Check out this thread from a few years ago: http://www.chiefdelphi.com/forums/sh...ad.php?t=79952

[nuclearnerd]

Aw hell, I just re-read the manual after seeing a couple of successful pneumatic catapult. I thought the solenoid valve restriction was 1/8" orifice diameter (another way to limit CV). Turns out it's 1/8" NPT Port Diameter. You can get solenoid valves with 1/8 npt ports and CV's above 1.0 each - more than enough!

/that moment when you realize you've made a wrong assumption, and its too late to change course

[RRLedford]

Surgical tubing puncher with pneumatic retraction:
http://www.chiefdelphi.com/forums/sh...highlight=rail



It is all about hitting a good peak ram velocity while it remains in contact with the ball. Having pneumatics pre-pressurized and surgical tubing prestretched with ram in retracted position is important. Rapid acceleration is what is needed, so a low mass ram with high initial force is best,

-Dick Ledford

[Trey178]

Originally Posted by RRLedford

Surgical tubing puncher with pneumatic retraction:
http://www.chiefdelphi.com/forums/sh...highlight=rail

My advice to you and the rest of your team is never have your face anywhere near this beast when pulled back. I still get flashbacks to 2006 when we tested a similar method for launching foam basketballs.

[Jibri Wright]

Originally Posted by Trey178

My advice to you and the rest of your team is never have your face anywhere near this beast when pulled back. I still get flashbacks to 2006 when we tested a similar method for launching foam basketballs.

I don't mean to call you out, but I don't think 2006 had basketballs. I believe the balls were foam though.

[orangemoore]

Originally Posted by Trey178

My advice to you and the rest of your team is never have your face anywhere near this beast when pulled back. I still get flashbacks to 2006 when we tested a similar method for launching foam basketballs.

It it is a little scary standing next to it while it is loaded. Luckily we don't have to do that during the competition.