Projectile Launcher Project Problems

[jbartlettjr]

We are attempting to build the project found on this page, but are having huge problems because the parts that are to be used are not sufficiently identified:

http://www.sciencebuddies.com/science-f ... M&from=TSW

Specifically, I do not have size or "where to buy" information on the following parts:

Wooden dowel (need diameter)

Spring (what size and other info sufficient to identify/buy the right spring?)

"Copper Sleeve" (I do not even know what this is, much less where to buy one and what size to buy)

"Plastic Sleeve" (I do not even know what this is, much less where to buy one and what size to buy)

The credit for the article is Andrew Olson. I could really use some guidance for this project.

Thanks.

Jim

[deleted-71487]

Hmmm... I agree that that's not very well specified. Partly that might because it's hard to specify exact dimensions because different things will be available in different areas.

Judging from the instructions, it appears that the hardest thing to find is likely to be the spring. A little searching online seems to indicate that suspension springs for remote control trucks, etc., might be the easiest to find. (for example, http://www3.towerhobbies.com/cgi-bin/wt ... XHFW7&P=FR) You'll want to measure the spring's force (or ask the shop) to be about 20 N (~4.5 pounds), according to the small amount of information in the instructions. I don't think it matters *that* much exactly what the spring constant is, though... as long as it provides enough force to launch your projectile a reasonable distance.

You won't know what size dowel to get until you find your spring. It should fit loosely and be a bit smaller than the inside diameter of the spring.

As for the sleeves, I'm at a loss for what that might mean. There are compression fittings that are used to join together PVC pipes, and one of the parts of them is called a "sleeve", so that might be a good place to start. The main goal of the sleeves appears to be just to make the pipes and dowel fit better together so they don't bounce around so much.

Sorry not to be more help.

[kgudger]

Hello and welcome to the forums!

I see what you mean about finding out the specifics for the parts needed for this experiment However, I guess I pass the geek test, because I have all these materials in my garage ...

The experiment says that you don't have to use the external PVC sleeve. The "copper sleeve" is just to make the inner sleeve tight in the outer sleeve. I think that some copper sheeting would work for this (or just don't use the outer 1.2" PVC sleeve.)

The 1" PVC pipe has an inside diameter of about 1". That means you need a washer that fits inside 1" - I have washers that are 7/8" O.D. (outside diameter) and 3/8" I.D. (inside diameter). This size would work fine. A 3/8" or 5/16" or 1/4" dowel would then fit inside the washer. You then want a spring that fits around whichever size dowel you choose, but fits inside the pipe.

I see "plastic sleeve" mentioned twice. I think this is a piece of PVC pipe that will fit inside your 1" PVC. I tried 3/4" PVC, and it was too tight a fit, so probably 1/2" PVC pipe would work best.

I think the project assumes you have access to a good hardware store. Go to the hardware store, find the washer first, pick the dowel to fit in the washer next, and then find a spring to go around the dowel.

The project probably does not mention these values because you may not be able to find exact matches at every hardware store, but with a little looking, you can probably find materials that match and will work.

Let us know if you have any more questions.

Keith

[deleted-71360]

Welcome to the divide between science and engineering. Science tells you the theory and reasons while engineering tells you how to design it, build it, and make it work. Also, this project is not a Lego toy that was engineered by a toy designer, you need to design it yourself from what you have available and what you have the skill to do. (Take a look at en.wikipedia.org/wiki/MacGyver.)

Regarding specifics, copper is a metal that is easy to work with and does not rust. Consider alternatives, such as plastic, cardboard, or other metals. Springs are a good hardware store item and they usually have them in numerous sizes, ranging from garage door to watch. Go through the hardware store, home improvement store, and the stores that cater to the arts and crafts hobby group.

Think outside the box, there is more freedom out there.

[jbartlettjr]

Ray/Keith - thanks for your replies, they were very helpful.

Jim

~ post edited by Science Buddies administrator, December 30, 2010

[amyC]

Hi Jim - I hope you've been able to identify what you need to move forward with the project based on Keith and Ray's input. We will be making updates to this project to help alleviate this problem.

Please keep in mind that our volunteer Experts are exactly that -- dedicated professionals who volunteer their time and experience here at Ask an Expert to help students (and their families) when they run into problems with science projects.

Amy Cowen
Science Buddies