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....
Step 2: Day 2 Design and Prep
-Stuff from last day
-Rolls of paper, pencils
-Grinder, files, vices, saws... usual metal shop stuff
Once the kids have figured out materials they can move on. The trick with a pogo-stick is that the design is such that the rider is holding on to and standing on a single piece of material. The first one i built had the foot pegs attached to the spring and the handle independent of the pegs. I jumped on and was promptly tossed onto the ground as my legs shot into my chest. I sprawled on the ground while the kids crowded around. I'd like to say they were concerned for my safety but really, they were laughing so hard no-one thought to call the school first aid. :-)
Whats so great about this project is that it is a problem that KIDS solve really intuitively. I put them into groups and using big sheets of paper they drew ideas out until a design was reached. What i did was supply the groups with the materials from the first day so the kids could manipulate the materials and figure it all out.
The end result is the design you see here. I fine tuned the designs by offering suggestions but in the end it was a student design we went for.
We found that 3 springs was perfect. The original design was WAY too high to use so the kids decided that the springs could extend out of the main tube. If you look at the photos you'll see that the springs are almost the length of the main tube and that the inside tube would always stay inside of the main tube at least by a few inches.
The foot pegs are about 6-7" long and the bars are about 16-18" long.
I than taught the kids to safely use an angle grinder. Really, i think this tool is seriously dangerous so i go over the top on safety. The kids must wear a full face shield, leather apron and gloves and must be behind the welding curtain.
You can do basically the same job with a hacksaw and files and some kids will prefer this so i present it as an option.
What i wanted the kids to get was a well prepped surface to weld. Insist that the surfaces are all clean and shiny and that the gaps are as small as possible. I usually end up tweaking a few things or filling in gaps when it comes time to weld, but that's all part of the process.
Step 3: Day 3/4 Building
-Drill press with 5/16' bit
-5/16" bolt... long enough to go through the big tube...
-5/16" nut and washer.
Welding the Springs
It is really important that the springs are aligned. When they compress they must line up so that they will fit inside the main tube. To solve this problem I taught the kids to do a small tack on each side of the spring joint with the small tube in place. Once the springs were lined up i got them to do a nice solid weld all the way around. The weld must not be so big that it hits the main tube when they compress inside.
Now the kids can weld the small tube to the bottom of the spring... We left about 3" poking out so that the steel tube would hit the ground... not the spring.
Drilling the Adjuster
I found that the springs could be set for kids with different weights and heights by drilling a number of 5/16" holes going through the main tube spaced about 2-3" apart. Basically all this does is changes the starting position for the height of the springs. It changes whether the springs will bottom out BUT the trade-off is that the foot pegs will be higher from the ground which makes starting tricky. Be sure to trim as much of the bolt off as possible so that the bolt doesn't scratch the rider.
Welding on the Pegs and Bars.
Just be sure that the pegs are a low as possible on the main tube and welded REALLY securely. Weld the bars along the top of the tube... I did this because it was logical but as an added bonus it stops the springs from exploding out of the tube and attacking the rider if the adjusting bolt fails. Make sure that the kids weld the pegs and bar flat and in alignment. If they are out of alignment the pogo is still ridable but will keep turning as you bounce.
Step 4: Day 4 Finishing and PLAYING
-Pipe clamp for small tube
-a Piece of old bike tire
The kids can now sand the pogo and paint. I don't use spray paint because it can be nasty and really messy. Its strange how more paint ends up around the material rather than ON it.
Use a piece of tire folded around the bottom tube and held in place with a pipe clamp. This stops the pogo from sliding on concrete and minimizes the HUGE core samples created.
I realized after taking the first group of pictures that a helmet is an absolute must. You may well be saying duh at this point. I understand.
To ride the pogo just put one foot on a peg, compress the spring, slide on the other foot and start jumping. Keep the pogo close to your body at first to get balance than gradually move it away and start jumping harder. Bonus for the pogo stick is that it is an excellent workout! Throw away the video games everyone! join the outside revolution!!
Thanks for reading...Try it out and let me know how it goes. Send me pics and I will add them to the Instructable!