design build.

http://www.globalspec.com/

You will be able to find a wide variety of springs using the link above.

I hope that your design will be more creative than a simple slingshot that any five year old could make.

Springs......Ha..Small fry! Now, if it were my project, I'd use compressed air and launch that tennis ball into kingdom come!

Bungee cord is probably best as it was better force extension characteristic than a coil or leaf spring.
Alternatively build a trebuchet.

(Trust me ...springy thingys are one of my specialities)
Del

I like mixing the mechanics.

Say, a pendulum that cranks a gear that complresses a spring that fills a pressure vessle that pneumatically fires a ball. And, a laser targeting device, solar powered of course, as coup de gras.

http://www.pitching-machine-superstore.com/p/louisville-slugger-ultimate-pitching-machine

GA

That's the right way to fire tennis balls, vary the speed for distance, accuracy top!!

what is that? your foreigner really can play.

CATAPAULT!! on a small scale, much more energy than other technologies, and whole bunch more fun--good track record of success, also! (Think ---Romans!) (they do them with pumpkins, watermelons, and dwarfs(at least in Australia) )--Just have fun with whatever design you come up with--make sure it is out of the box------C-MAC

Hardware stores or home centers have extension springs. The ultimate pitcher is based on an 8" of this type. Here is link to get a better idea of it's design.http://www.sluggerupm.com/downloads/UPM45QuickReference.pdf

Steam catapult! If it's good enough for the Navy, its good enough for me.

Whatever happened to academic integrity? Can we get some of your credits when you graduate? With Google, the student at least has to pose a reasonable question for a useful search. I hope that the professor or adviser for your project does a simple Google search for "tennis ball" and "spring." Finds this thread and flunks anyone who uses a spring for the stored energy.

I can't believe no one brought up a Polish cannon. I don't know if there is a politically correct name but they are cool and we made them as kids out of soup cans and duct tape. Butane or white gas now called unleaded was ignited with a quantity of air behind a tennis ball in the soup can cannon tube. Even fired Foot balls(US) out of a coffee can cannon. Touch hole size is important. So is clearing out the used gasses for the next shot. Also a small jet comes out the touch hole so don't burn yourself.

Be careful because gas fumes have a lot of power. We also have launched Gerry cans 50 foot into the air with gas fumes and they have a 3 inch hole.

Brad

Living so close to Idaho you should know that you are talking about making a "Spud Pistal" which is the cousin of the "Spud Cannon" which is part of the greater "Spud Gun" family.

...and there are several (scary!) YouTube videos showing them firing potatoes hundreds of meters.......using such cannons......OUCH!!!

Never shot spuds, we ate them. Tennis balls were free because we didn't care if they were a little flat. Rarely did we fire them as a gun or pistol. More like a mortar.

Never fired them to hit someone either. We could shoot them over twice as far as they could be hit with a racket. At a range where it would be accurate I'm sure it would knock you off your feet. At just over 4 foot the back pressure started deforming the breach. Air fuel ratios are a bit tricky too get exact.

I have some Shelby Tubing I bet wouldn't have that problem but I would hate to lift it much.

this thread has gone around the corner. when i first posted the question i only wanted to know where a novice like myself could get information on springs and their purchase.

we have design limits, we have budget limits, etc.

some replies have been helpfull or at least entertaining. some, however, have been turse or even rude. I am sorry if my freshman community college design build seems ameture, IT IS. I am an ameture. that is why i am in school.

Don't get your tail in a twist When asking for information realize your question is open for interpretation from many perspectives.

What you are learning is how to discern and developing your personal system to do so. A below average IQ researcher with a good discernment system will be able to get more out of the classical mess than a brilliant researcher with a poor discernment system.

In in other words a good BS filter, goal and planning system can take you there faster then wandering without direction. Learn to find what you need fast by asking the right questions.

I like to start at my goal and work backwards. This gives me direction. If I don't know my goal then I at least have an area of interest and I become familiar with it. A point will come when I start being able to discern the dynamics and can make reasonable deductions to find my goal then see if resources are available and worth while. Now you have the foundation to plan.

Develop a systematic approach to problem solving and refine it continuously.

This is the short and simple version. It took me a while to even discern the need. Even longer to systematize it.

CR4 is a very dynamic (lots of variables) group. Many will not answer you because of the guest dogma of other guests actions. I pick and choose guest by their actions.

I rarely ask questions of CR4 because I don't get the understanding to go with the answers. I'll start researching my question for them and usually find the answer in developing the knowledgeable question.

Brad

GA... would love to hear the long version of this if you get time, and I'm sure all of CR4 would benefit! or where do I buy the book?

Chris

Still in development (the system that is).

A nuclear engineer friend of mine explained the teaching system the navy developed to keep from losing it's high tech systems to greenhorns. Systematic Approach to Training.

We should be using it in our schools but that is another issue. After we had many long discussions about it we lost contact with each other and I have tried to find out more and found very little. Go figure. This was several years ago so more may be available now.

Anyway along time ago a very astute man Bruce Lee (yes 'The' ) said "if it works use it if it don't throw it away" He was referring to the classical mess/dogmas of martial arts but I realized it was a short cut through the classical messes.

The pearls of wisdom come from many places. One of my favorites is The Art of Wealth by Thomas Cleary. Based on writings from a man in India 275 years BCE.

Japan has taken Constant Improvement as their national motto.

Systematic Constant Improvement should be the world's. Who knows I may have to write the book just to finish systematizing it for myself.

Can you tell I take many directions for the discernment process? Then again if I would have had the book at a younger age and had comprehended its use, it would be a revision.

Brad

I look forward to it! let me know when it comes out. In the meantime, thanks for the link. I'll try and chase that one down, and look into any navy docs I'm able to find.

Wisdom, another universal language.

Chris.