Using a Plunger System to Launch Balls

[HFCHS-NASA]

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.

[EricH]

Originally Posted by HFCHS-NASA

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.

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.

[pfreivald]

Originally Posted by HFCHS-NASA

How does a spring and cam system work? That sounds what we want to do.

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.

[Brandon Zalinsky]

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!

[DavisDad]

Originally Posted by HFCHS-NASA

Our team was thinking of 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.

[DavisDad]

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.

[pfreivald]

Originally Posted by DavisDad

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.

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

[DavisDad]

Originally Posted by pfreivald

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

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.

[pfreivald]

Originally Posted by DavisDad

Recoil isn't really the right term.

"Shimmy"?

[DavisDad]

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