If you spend about 4 seconds searching youtube you'll find this..
This is good inspiration for the kids although it has one small typed vernacular at the top of the comments... welcome to youtube... they still haven't managed the good-natured kindness and sensibility of Instructables.
I started this project because a student suggested it. He showed me a few clips on the web which inspired me to try it. This project is SO basic that it is really quite deceptive in its trickiness so i'll go over a few stumbling blocks I encountered and the ways to get around them.
The best part of this project is that it encourages kids to THINK about how a project will fit together and work. The end result is a project that is REALLY FUN. Students were lining up to try the prototype. Once the first student built one he was helping his friends in my class design and build others.
-Students will learn to apply basic design to solve a problem
-Basic measurement of spring compression to discover spring rate will be learned and applied in the project
-Students will learn to Measure, Cut, Grind and Weld steel to create an interesting project.
Tools and Materials:
-I usually offer alternatives in my Instructables to some of the big and expensive tools but in this project you really will need a good welder. I use a MIG with the kids.
-Angle grinder with basic grinding disc
-Hack saw or good horizontal metal band-saw
-Files and finishing tools
-Drill press with assorted drills, centerpunches and clamps.
Materials depend on what you have on hand...
-A whole bunch of big springs (i have ideas for you to get them free or cheap...)
-Steel tubing that matches the springs.
-Steel tubing for bars and foot pegs.
-5/16 bolt about 3" long, nut and washer
Take a quick look over the instructable and try it!
I think it would be an excellent addition to any curriculum.
Step 1: Day 1 Figuring Out Supplies
-2 jigs... one for figuring out spring rate, one for figuring out spring number...see the text...
There are so many springs available that i'm thinking this project will only get better as people submit ideas so fire away everyone! I used Motorcycle springs because it seemed logical. I stopped by a local bike shop (thanks Bent Bike!!) and the owner set me up with a box of about 50 springs from the back of motorcycles... The kind that attach the rear swingarm to the frame where you sit. I figured that since the springs are designed to support the weight of a bouncing adult that it would work for a kid on a pogo stick. These springs are found at most used motorcycle places and are usually sold by the weight to scrap metal places. The money is very little so most shops are more than happy to give them to kids.
I scrounged around the shop until i found 2 tubes. The big tube fit around the springs (which slide inside) and a small tube that fit inside the spring. They were all about 3-4 feet long. You'll also need to find 1" round tube for the bar and foot pegs. The material i ended up with was pretty thick... about 1/8" wall which i think is WAY too thick. i'm going thinner next time. I'm not worried so much about strength when they get thicker but rather the process of MIG welding thin tubing. Right now they are pretty heavy! I'm going to pay my local scrap metal place a visit and see what they have. Most metal they have is all bent up but thats okay because we only need 3-4' long pieces.
Once the kids have figured out what is available we measure spring rate. I set up a jig in a press. I found a scale at a garage sale for 5 bucks. Check out the photos.
The idea with spring rate is that it takes a certain amount of force to compress a spring one inch. All we did was stick the spring on top of the scale and slowly pumped the handle on the press until the spring compressed one inch. It would be easy to build a small portable press as well using a small car jack.
I asked the kids to compress the spring one inch than write down the weight. They would compress it 2 more times and write the numbers again to see if the spring rate was progressive or not. Thick spring coils meant a much stiffer spring rate. We talked about WHY some springs are progressive in spring rate and what it all means. It took about 4 minutes for the kids to realize that a motorcycle meant for super high impact would have a progressive rate so as to prevent bottoming out. Seemed logical to me.
We also found out that 1 spring wasn't nearly enough. These kids wanted serious height and to get that they would need springs that would compress a great deal but not bottom out. What you do to figure this out is to make a tester pogo... basically just a set of tubes that fit most springs... We set up a couple of different tubes inside the large one so that we could try any number of springs. Check out the photo.
The kids would than jump on the pogo, try different springs and generally fool around until they found a combo that worked well. What we found was that a heavy kid needed a higher spring rate... clearly :-) Too high of a spring rate meant a pogo that was really stiff and hard to get any height at all.
Figuring out the steel tubes was easy... all we did was measure knee to chest for the kid than use that measurement as the length of the long tube. The inside tube was determined by sliding it inside the springs until it reached just over 1/2 way inside the springs.
Well that was an exciting first day. Lets move onto the design and prep for welding....