Using a Plunger System to Launch Balls
 

Our team was thinking of using a plunger system to launch balls. The balls would be loaded into a barrel, which is open at one end and has a plunger-type device on the other. Then, a motor pulls the spring-loaded plunger to a specific distance depending on how far we want to shoot the ball (think of a pinball machine). Anybody else thinking of going this route? We would use linear encoders or an ultrasonic sensor to sense how far back the plunger is pulled.

Re: Using a Plunger System to Launch Balls
 

It would be improbable. First you would have a mechanism to load the barrel, then aim, and finally shoot. There are too many moving parts. Keep it simple.

Good luck on whatever design you decide upon. :yikes:

Re: Using a Plunger System to Launch Balls
 

I wouldn't rule it out completely, it would be difficult to do, but if you pulled it off right it would function pretty well.

Re: Using a Plunger System to Launch Balls
 

I can see it as possible. Breech-load from the top (balls just fall into place). Re-cocking the mechanism can't take to much time though - a second is a long time.

Whatever powers the slingshot needs to be highly repeatable - if you pull back X inches, the trajectory needs to be exactly the same, time after time, even if you have to replace whatever it is between matches because it broke or something. That's not an easy problem.

It appears that you are considering being able to "shoot from anywhere" - perhaps you might want to optimize the shot from one or two spots (distances) only. Otherwise this becomes a serious technical challenge - the mechanism must be built very precisely to have that capability.

Re: Using a Plunger System to Launch Balls
 

Really... I can think of a couple of mechanisms from 2008 that could be modified to do it well, that are quite simple. Say, Winnovation's punch from that year modified to allow it to latch in any position desired and supplied with a barrel. Then you have to deal with the loading problem, which could be much simpler.

Re: Using a Plunger System to Launch Balls
 

A double CAM with two separate draw distances is one possibility for a two-distance shooter, though you'd have to time the breech load properly.

Re: Using a Plunger System to Launch Balls
 

Actually 1114 had a not entirely dissimilar mechanism when they won the world championships in 2008.

Different game, different ball, different target... but devastatingly effective in the right application.

Jason

Re: Using a Plunger System to Launch Balls
 

Our team actually used a similar mechanism for Breakaway to kick the ball. Our biggest challenge was latching that much force in a spring. We ended up using 2x 2in dia, .5in throw cylinders to do it. That being said we were drunk with power with the fact that we could kick the whole field that we completely forgot to design a decent aiming mechanism.:yikes:

Lesson for this year for us? Don't focus only on power.. Balance that with a good way of aiming.

Re: Using a Plunger System to Launch Balls
 

Were you ever on RAGE? They went through a stretch where it seemed like they had plungers on their robot all the time.

Seriously though what you're looking for is the RAGE (173) 2009 robot.

Re: Using a Plunger System to Launch Balls
 

Whatever you wind up doing I would incorporate a way to induce a controlled amount of spin. I think the last thing you'd want is a knuckling flight path.

Re: Using a Plunger System to Launch Balls
 

We're considering using a straight up system almost like a paintball marker. The loader would be simple-a laundry basket with a hole in the bottom that has a sliding door attached. The inbounders for our team will pitch or place the basketballs into the basket. the breech would be a 90 degree angled piece of 12" diameter pvc tubing. The "barrel" would be a length of 12" pvc or heavy duty cardboardtubing. We would use a Medium sized Bimba pneumatic piston with the acutating arm moving through a piece of pvc drilled and glued into the center in the 90 degree piece.Inside, the piston end would have a small piece of ply or pine covered in bumper fabric to keep it from ripping the game basketballs. We will use the adjustable inlets to regulate pressures between matches The trigger would be acutated via button on controller or via programming in hybrid. The piston would be moved back into the ready position by a second button/refilled with air. As the arm moved back into place, a line would pull the "shutter" open to load another ball into the breech almost like a paintball marker uses vertical feed. The barrel itself will be raised and lowered by a second pneumatic piston. This is rough...very rough at this point. The other option is a baseball thrower. We're deciding how much time we really want to spend on shooting versus getting to the ramps, staying on the ramps, blocking and getting coop points. Which is more important and will help us advance to the alliance phase? All good questions, we're kicking them around as we build and program the other components of the bot.

Re: Using a Plunger System to Launch Balls
 

If I understand you correctly you're using a piston to directly launch the ball? If you want to go this route I would strongly suggest using either multiple small-diameter cylinders with one solenoid valve per piston, or multiple solenoid valves per piston if they are larger. These are the only way to get enough air flow for an effective pneumatic shooter that I know of

Re: Using a Plunger System to Launch Balls
 

If a punch-launcher is what you're after, you might want to consider other activation methods as well (like a spring with a cam) as pneumatics.

Re: Using a Plunger System to Launch Balls
 

<R78> The outputs from multiple valves may not be plumbed together into the same input on a pneumatic cylinder.

Correct me if I'm wrong, but I think this precludes your second alternative. You are correct though, with the CVs we're allowed, large pneumatic cylinders are quite slow for this application. Small ones likely are too, depending on the range you're looking at. I won't say it's impossible, and there are ways to speed things up. Any team looking at this should do the math and test thoroughly, or you may be sorely disappointed painfully late in the season.

In the past, teams have used pneumatics (and cams, and countless other systems) to [edit]arm[/edit] such linear punches, but used springs/surgical tubing/etc to transfer the actual force, as they're so much faster.

Re: Using a Plunger System to Launch Balls
 

Good catch on the rule. IIRC it was legal up through 2010 when I last looked. Always pays to double check :o

Re: Using a Plunger System to Launch Balls
 

We are trying to avoid pneumatics because we want to have the precise control of electric motors. How does a spring and cam system work? That sounds what we want to do.

Re: Using a Plunger System to Launch Balls
 

http://www.chiefdelphi.com/media/photos/31538
http://www.chiefdelphi.com/media/photos/31539

That should get you started on some things of that nature.

Re: Using a Plunger System to Launch Balls
 

A cam is just a plate or something of the sort with an irregular shape. You attach it to an output shaft (geared up/down as necessary) and use it to stretch a spring or other elastic material (surgical tubing, for example). As it goes around, the object slips off of the cam and slams to equilibrium position. You can stop the cam each revolution using a sensor of some kind, so it doesn't fire continuously.

This video, http://www.youtube.com/watch?v=_hTyXQUgYLE at 1:49 shows a cam-powered kicker running.

Re: Using a Plunger System to Launch Balls
 

we messed with a pneumatic/spring plunger mechanism and we couldn't figure out how to make the ball fly farther than 10 feet without dumping our entire tank. If you find a way to do it well, please share!

Re: Using a Plunger System to Launch Balls
 

After some brainstorming, I think this is a solid approach. I was thinking that the plunger end would be cupped, holds the ball and not require contact cylinder walls.

Most of the launch systems I've seen use apposed spinning disks like:
http://www.youtube.com/watch?v=l8U9u2iqMEs While this works, I think getting good accuracy will be technically challenging. Note the "slice" behavior (Magnus effect) of the ball in some of the shots. Variable control of launch velocity and symmetric launching will be much more technically challenging than simply pushing the ball in a straight line. The pro/cons for plunger are:

PROS:

• Inherently shoots straight
• Simple mechanism for guiding the plunger
• Velocity control simplified by displacement based adjustment of spring loading

CONS:

• Ball load mechanism is more complex
• Cocking (spring pre-load) and trigger mechanism more complex
• Cycle time for each ball much greater than disk design

Given how short each tournament is and the game design, I think that shooting from midcourt with a high shot percentage will be key to high scoring.

Re: Using a Plunger System to Launch Balls
 

I made a prototype to see how the spring loaded shooter would work. Pretty much a big pinball machine design. I used a heavy duty door closer spring. Pulling back about 40 lb force, I launched the ball a whopping 8 feet.

If the goal is to shoot from behind the mid court line, ~ 25 feet, it'd take "cocking" the spring to more than 160 lb. Too scary for me. The recoil at 40 lb was pretty violent.

Also, my son says springs are verboten on his team.

Re: Using a Plunger System to Launch Balls
 

That kind of recoil wouldn't exactly produce the level of accuracy you'd be looking for on a half-court shot, either!

Re: Using a Plunger System to Launch Balls
 

Recoil isn't really the right term. The ball is gone when the rod and spring reach the end of their travel. There's a lot of inertia in the mechanism when it slams into the end-stop.

Re: Using a Plunger System to Launch Balls
 

"Shimmy"?

Re: Using a Plunger System to Launch Balls
 

Found this: http://www.youtube.com/watch?v=j6Jzsv2OKAY
http://www.youtube.com/watch?v=l8iqG...eature=related