Introduction: Industrial Strength POGO STICK

If you want to bounce 200 pounds three feet in the air, you're going to need some serious power. And, if you're like me, you're going to want that power for as cheap as possible.  The traditional way to get that power is through a metal spring, and if you go to Walmart for a pogo stick, that's what you will see.  You will also see a label that says "Maximum Weight Capacity: 80 lbs". 

It turns out that metal springs aren't all that effective for doing what a pogo stick needs to do (more detail in the theory section).  People have tried other methods to get the big bounce, from compressible air (as in the $369 "Vurtego") to bow-and-arrow-ish bending sheets (as in the "Bowgo" developed at Carnegie Mellon).  But the simplest and cheapest way (and the way that the very popular $349 Flybar uses) is to use rubber bands.

But why pay $349 for a Flybar, when you can do one better for less than $90? Big, powerful rubber bands are actually pretty cheap. You can get the two you need for this project for less than $20 at McMaster Carr, who sells them for keeping pallets together while shipping. With a few other parts from McMaster Carr, a trip to the scrap metal yard, and a little bit of time welding and machining, you can have a pogo stick that will send you flying. 

Step 1: Theory (For Interest Only: Completely Skippable)

Why not just get the biggest metal spring you can find? One reason is that metal springs are heavy and expensive, but the second (and more important) reason requires a little bit of theory.

The purpose of a pogo stick is to jump as high as possible... without breaking your legs in the process. This means that your pogo stick needs to do two things:
  1. Store as much energy as possible
  2. Do so without imparting too much force to your legs
How much energy do you need? That depends on how much you weigh and how high you want to jump. In fact, the equation is pretty easy:

Energy You Need = (Height You Want to Jump) x (Your Weight) 

So if you weigh 200 lbs and you want to jump three feet (36 inches), you need 36 x 200 = 7,200 inch-pounds of energy.

How much energy does a spring give you? That depends on the stiffness of the spring (in pounds per inch) and the maximum deflection of the spring (how much the spring can be squished or stretched, in inches). The equation is also pretty easy:

Energy a Spring Gives You = (0.5) x (Stiffness) x (Max Deflection)2

So let's say you buy a big spring (like this spring-tempered steel jumbo compression spring, which is 12" long and almost 5" around and costs $31.21). The spring is rated for 875 pounds, so it looks promising.  But let's do the calculation.  The spring rate (i.e. stiffness) is 127 pounds per inch.  The maximum deflection is 6.9 inches. That means that the spring can store 0.5 x 127 x 6.92 inch pounds, or 3,023 inch pounds of energy.  That's only enough to bounce you 15 inches high, and it's going to be putting 875 pounds of hurt on your feet when it does so.

What's the problem here? How can we get more energy without putting even more force on our feet?  The key is in the equation for energy. Notice that the maximum deflection is squared. That means that the maximum deflection, NOT the strength of the spring, is the most important factor to look at. 

Say you have two springs. Spring A is twice as stiff as Spring B, but Spring B has twice the maximum deflection of Spring A.  Which will store more energy? The answer is that Spring B will store TWICE as much energy. Go ahead, do the math: Energy A = 0.5 x 2 x 12 = 1 ; Energy B = 0.5 x 1 x 22 = 2. This isn't a math trick, it's the way energy storage works, and it's why a rubber band (with low stiffness but massive deflection) will bounce you much higher than a metal spring, and it will do it with much less force.

QUALIFYING NOTE 1: You can actually jump much higher than the spring on your pogo stick bounces you. This is because you're jumping: you're adding the energy in your muscles to the energy in the spring. The height calculated in the equation is the height that your pogo stick could bounce a rock. You, being a person with muscles, will be able to bounce even higher. 

QUALIFYING NOTE 2: Rubber bands don't follow the spring equation perfectly, because as they stretch, their stiffness actually changes. But I did quite a few experiments (involving hanging weights off my balcony), and the stiffness doesn't change too much. You can still use the energy storage equation to get pretty close.

Step 2: Gather Your Materials

The total cost of your materials will be about $90. 

You'll need a few types of steel.  You can get it online, but I recommend going to a local shop to avoid some hefty shipping charges.
  • 11.5 ft of 1" OD steel tubing with 1/16" wall.  If you can get chromoly steel (which is used in bike frames), it will be a little stronger, but I ended up using SAE 1018 (sortof a generic carbon steel), which according to my stress calculations and some pretty rough use of the pogo stick is plenty strong enough.
  • 2 ft of 1"x2" rectangular tubing with 1/16" wall.
  • 2 inches of 7/8" OD steel bar (or thick-walled tubing)
  • A scrap of 1/16" thick sheet steel (about 5 x 5 inches will be plenty)
The parts you need can be bought from McMaster Carr and shipped next day. The links are below, and the part numbers are included in the bill of materials above.
You will also need one screw and nut, but unless you want a pack of 100, you might want to get these at your local hardware store. The screw should be 1-1/4" long with 8-32 thread, and the nut should fit it (a lock nut is preferable).

Step 3: Cut Rectangular Tubing to Length: One 14" Piece and One 4-1/4" Piece

Use a bandsaw. If your perfectionist bone is strong, face off the ends with a mill. Just make sure you end up with one piece that's 14" long and another that's 4-1/4" long. These will become the step and the brace.

While you're at it, cut four 1-inch by 2-inch rectangles out of your 1/16-inch sheet metal. These will be caps for the rectangular pieces.

Step 4: Cut Holes in the Rectangular Pieces

Each rectangular piece will have two 1" holes (for the frame tubes) and one 1.25" hole (for the flanged sleeve bearings).  The dimensions are shown in the drawings below. 

If you don't have such a big end-mill or drill-bit, you can use a boring bar to make the holes big enough.

Alternatively, you could drill a small hole, run the blade of a coping saw or thin band-saw through the hole, and then cut out the holes by hand. 

Step 5: Check Your Fits

The 1" tubing should fit into the 1" holes. If not, make the hole a little bigger.

The sleeve bearing should fit into the 1-1/4" hole. If not, make the hole a little bigger.

Step 6: Turn a Groove Into Each Flanged Bearing and Install Retaining Rings

In order to get the bearings to stay in place, you'll be using an external retaining ring. This ring sits in a groove and keeps the bearing from sliding out of place.

Chuck the bearing in a lathe and machine the groove as shown in the drawing: 1" from the flange, 0.056" wide, and 0.037" deep (to a 1.176" diameter). 

When you're done, check your fit by installing the bearings in their holes and clipping an external retaining ring into the groove. There's a special tool made for installing these rings (called, creatively, retaining ring pliers), but you can use a sharp pair of needle-nosed pliers too.

Step 7: Cut Three 36-inch Pieces of Round Tubing and Machine "fish-mouth"s Into Them

Use a bandsaw to cut three lengths of tubing to 36".

Then use a 1" end mill (or a band saw, or a cutting torch) to make a round "fish-mouth" on one end of each piece of tubing. The nicer you make this cutout, the easier your welding will be later on. 

Step 8: Drill a Hole in the Fish-mouth of One Piece (the Shaft)

The central shaft will have a hole in the fish-mouth to secure another piece with. The hole is 3/16" diameter and is placed 3/16" from the fish-mouth tip. 

Step 9: Cut and Slot Two 5-inch Pieces of Round Tubing

Use a bandsaw to cut two 5-inch lengths of the round tubing you have left. Machine or cut out a slot (2 inches wide, 1/2 inch deep) in the center of each piece, and check to make sure that the rectangular tubing fits snugly into the slot. 

These pieces will hold the rubber bands on the step.

Step 10: Cut Two 1-1/2 Inch Pieces and Two Ovals for the Top of the Shaft

Use a band-saw to cut a 1-1/2-inch piece of the 1" tubing.

Use a band-saw to cut a 1-1/2-inch piece of the 7/8" bar, and use a 1-inch end mill to fish-mouth the bar.

Use a band-saw to cut two ovals (1 x 1-1/2 inch) from the sheet steel.  While you're at it, cut four more for the bottom pieces (so six ovals total).

Make sure these four pieces fit together well. They will hold the rubber bands to the top of the central shaft.

Step 11: Cut a 14-inch Piece of the Round Tubing for the Handle

Use a band-saw to cut a 14-inch piece of the round tubing for the handle. Cut two 1-inch circles from your sheet metal to cap the ends if you like.

The cutting is now finished!  Get ready for some welding.

Step 12: Assemble the Frame

Put it all together. Make sure everything fits.

You don't have to put on all the end-caps yet, but make sure you have them all at hand.

Step 13: Prepare the Frame for Welding

Assemble the frame and get everything lined up. 

GET EVERYTHING LINED UP.  Install the bearings and make sure the shaft slides well without binding. Use a square, or a level. Make sure everything is nice and steady so that when you start tack welding, you don't throw off the alignment.

And make sure the fish-mouths on the top are lined up. They should be parallel so that the handle fits into them nicely. You'll be kicking yourself if you weld the frame only to realize these nicely-machined beauties are cock-eyed. (But if they are, you can always throw the frame back on the mill and correct them... as I did.)

Step 14: Begin Tack Welding

It's ok to leave the bearings in to make sure the shaft is well lined-up for the first couple tack welds, but you'll want to take them out soon. If you're using oil-impregnated bearings, as I did, the heat will cause them to leak oil everywhere.

Excuse the quality of my welds; I'm a newb.

Step 15: Remove the Bearings and Continue Welding

Step 16: Weld on the Bottom Rubber Band Holders

Use as little heat as possible on this step. Too much heat will tend to bend the tubes and the step. If this happens to you (as it did to me), you may end up having to file the hole a little bit to make the bearing fit back in again.

Step 17: Weld on the Handle

Here's your chance to shine. If the fish-mouths are machined and aligned properly, this step will be a breeze. If not... it will not.

Step 18: Weld on the Rectangular Caps

These are the candy of welding: external corners, which even I found that I could weld tolerably.

Step 19: Weld on the Circular Caps and Flanges on the Bottom Rubber Band Holders

Step 20: Assemble and Weld the Topper for the Central Shaft

You could arguably weld this onto the central shaft instead of making it removable, as I did. I chose to make it removable so that if the central shaft bent, I could easily replace it. 

Unless you're a much better welder than I am (which is more than likely), you'll have to do quite a bit of grinding to make the topper fit into the shaft. But that's ok. Once it does, drill a hole in the topper so that the screw fits through.

Step 21: Grind

Use a belt-sander and/or a bench grinder (or a file if you want to be really manly) and clean up all your bad welds. Just don't go too deep, or you'll weaken the joints.  

Step 22: Sand, or Sand-Blast

Ok, you can try it out now. Make sure everything fits and works, and that you can jump as high as you'd ever dreamed.  But then get back to the shop and sand this thing. You've gotten this far; you might as well finish it.

Step 23: Paint or Powder-coat

There are some good resources out there for painting bike frames. The same principles would apply here. Unfortunately, I was nearing the end of the semester, and people in class were getting a group together to send parts out for powder coating, so I gave in, forked over about $60, and had a local shop do the powder-coating for me. It turned out really nice, but I bet you'd get a lot more satisfaction from painting it (or powder-coating it) yourself.

Step 24: Install the Bearings

Install the linear bearings and snap on the external retaining rings. You're close, now. Smell the cumulonimbus.

Step 25: Install Two Rubber Bands, Two Rubber Handles, and a Rubber End-cap

Each rubber band will start at the bottom step, wrap over the top, down to the bottom step again, over the top again, and back down to where it started.

That means each rubber band will be quadrupled. 

Divide the length of the rubber band into fourths and make a mark at each fourth. When you install the rubber band, try to make each mark line up with one of the bends, so that the tension is even.

You can also cut one of the extra rubber feet into a bumper to absorb some of the shock of the top piece (see assembly drawing in step 2).

If you're still confused, watch the video at the end of this instructable.

Step 26: Jump

If you've never jumped on a pogo-stick before, start slow. This one is quite powerful. Put one foot on the step, then stand up and balance for a second. Once you've got the feel of that, start taking little hops. You should probably wear a helmet if you're prone to landing on your head.

Since this pogo stick is so powerful, it may be difficult to bounce if you're really light. If that's the case, remove a rubber band, or wrap them fewer times.

If you're heavier, or want to bounce even higher, you can always add more rubber bands; just be careful, because with too much force that shaft will bend. But that just means another trip to the shop.

Step 27: Gallery

I did this project at the Stanford Product Realization Lab (PRL) as part of my masters coursework. It was a blast, and I was fortunate to have access to the tools and expertise at that facility. 

Here is a brief video highlighting the design and building process.  You'll notice quite a few prototypes, from chopstick pogo-sticks to one made out of 2x4s (which worked!) to the final product. This is part of Stanford's design mantra; prototyping early and often leads to better designs.

I'm also including several pictures of the prototypes and a few iterations of the final pogo-stick that I ended up abandoning.
Thanks for reading! If you liked what you saw, and you can bear to move your mouse six more inches, I would appreciate your vote in the "I Could Make That" contest.

Good luck!

Comments

author
Julie S.S (author)2017-06-16

Very cool and excellent presentation about pogo stick

Thanks.

author
solobo (author)Julie S.S2017-06-17

thanks!

author
almostran (author)2015-12-21

An excellent presentation. A+

author
almostran (author)2015-12-21

An excellent presentation. A+

author
chris.gray.31521 (author)2014-09-22

Hi. Have you tried it with bicycle inner tubes in place of the rubber bands? Thanks. Chris.

author
solobo (author)chris.gray.315212015-01-06

No, I haven't. It'd be worth a try, but inner tubes feel less stretchy/springy than those rubber bands do.

author
victor.smeets (author)2015-01-01

How do you change your rubber bands?

author
solobo (author)victor.smeets2015-01-06

Just by hand. I'd loop one end of a rubber band over one of the bottom pieces, over the top piece, around the opposite bottom piece, back over the top piece, and down to the original bottom piece. Sometimes I would mark lines at 1/4, 1/2, and 3/4 of the length of the rubber band so I could make sure those lines corresponded to the bottom and top pieces and the tension on the rubber band was even.

author
Stan1y (author)2013-12-31

have you tried replacing the bands with windings of12mm (1/2") shock cord my local diy store sells it by the metre often used for securing the sheets on bulk trailers. I've used it in the past as a get me home replacement on a light aircraft undercarriage the real item being a custom made loop about 50mm(2") thick

author
solobo (author)Stan1y2013-12-31

no, I haven't tried that... sounds promising though.

author
kyle brinkerhoff (author)2013-12-09

ever thought about switching to a compressed air piston? they are a little pricey but thats how people get crazy air on pogosticks

author
solobo (author)kyle brinkerhoff2013-12-10

I looked into it a little bit, but the rubber bands seemed a lot simpler/cheaper for what I wanted. I'm not even sure where to get a compressed air piston... do you know of a good place?

author
kyle brinkerhoff (author)solobo2013-12-10

http://www.ebay.com/itm/like/370513354437?lpid=82 or custom order http://www.bimba.com/Products-and-Cad/Actuators/Inch/Round-Line/Non-Repairable/Original-Line-Cylinder/ these guys are awsome, i used one for my spud gun

101_0743.JPG
author
solobo (author)kyle brinkerhoff2013-12-11

Very cool, I'll keep that in mind. Thanks.

author
dangeroustomtom (author)2013-10-10

are you some sort of physics teacher or just a genius this has helped me do my homework

author
solobo (author)dangeroustomtom2013-10-10

ha neither... but I'm glad it helped!

author
24Eng (author)2013-10-03

Amazing build. Where did you get the idea for using rubber bands? It's really kind of genius. This inspired me to take the idea of elastics and try to make jumping stilts on the same premise.

Showing the evolution of your designs with the chop stick models was really helpful to see your thought process and develop my own line of reasoning.

The only problem I have; where is your helmet?!

author
solobo (author)24Eng2013-10-03

Thanks! Well, partly from the calculations that said more deflection and less strength was better, and partly because there's a pogo stick called the Flybar that uses them. Nice on the jumping stilts; that'd be awesome.

author
Wazzupdoc (author)2013-09-29

Just beautiful!

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solobo (author)Wazzupdoc2013-09-29

Thanks!

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padbravo (author)2013-09-26

Wait a second, pls!
on the step 12, you put an animated sequence of assembly...

Wold you mind to tell me what software did you used to got that result?... The common sense is that you used the same software to do all the drawings too, and use those drawings for the animation...

author
dfield (author)padbravo2013-09-26

looks like Solidworks

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padbravo (author)dfield2013-09-28

tks

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solobo (author)padbravo2013-09-26

Yep, SolidWorks. If you make an assembly and do an exploded view, you can animate the exploded view. I saved this as a video, then used Photoshop to turn it into an animated gif.

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padbravo (author)solobo2013-09-26

Thanks!... I have in mind some designs that I wold like to present that way: make the drawings (for the actual -make-) and use an animation to present the idea (before actually construct the thing!)

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solobo (author)padbravo2013-09-26

Sounds good, good luck!

author
dcms4 (author)2013-09-26

you mention above "the same tubing used in bike frames", so could one lower the cost by recycling a bike? Would there be any specifics on what to look for that would indicate that a bike is constructed with the tubing that's needed or up to the job?

author
solobo (author)dcms42013-09-26

Good idea. Yes, I think you could use an old bike frame. I would look for a steel frame rather than aluminum (just because aluminum is harder to weld). As far as types of steel, anything used on a bike frame should be fine. I tried to design the dimensions so that everything would be strong enough even with low strength steels (this is hard to be sure of, though, because the loading from a person jumping at different angles and heights is hard to predict. i used fairly low strength steel and had no problems, and I weigh around 200 lb, so that gives some test data to confirm though).

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dcms4 (author)solobo2013-09-27

Thanks for the reply. I would assume one could use magnets to determine if the frame was aluminum or steel?

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solobo (author)dcms42013-09-27

Yes indeed, unless it's stainless steel (which isn't magnetic). But you might want to shy away from stainless steel anyway; it's harder to machine and (I think) harder to weld.

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alcurb (author)2013-09-27

Beautiful work! I love seeing the improvement iterations of your project. Nicely done!!

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solobo (author)alcurb2013-09-27

Thanks!

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husamwadi (author)2013-09-26

I favorited and voted. Totally legit man!

My question is, it seems as though there is more of a lag between the time you bounce and when the pogo drops (due to the elasticity).

Does that REALLY give you a workout since the bounce delay is so long? It seems as though you need to put 2x effort on the way up, which isn't necessarily a bad thing! That would make one awesome workout!

author
solobo (author)husamwadi2013-09-26

Thanks!

I'm trying to understand what you mean on the delay: when you jump on it, it definitely doesn't feel like there's a delay. It's kindof like jumping on a trampoline: as you fall, the force on your feet increases and you slow down, and at the bottom you jump and it feels like something is pushing you and helping you jump much higher.

Does that answer your question? Sorry, I'm not quite understanding it. It definitely is a workout though.

author
husamwadi (author)solobo2013-09-27

I was wondering if it feels the same as a spring loaded pogo stick, but you answered the question!

Still awesome bro!

author
harold Paine (author)2013-09-27

This one of the best explainations on how to build an Instructable Project I've had the pleasure to look at.

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solobo (author)harold Paine2013-09-27

Wow, thanks.

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harold Paine (author)solobo2013-09-27

No thanks needed Praise where Praise is due is my motto

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Reiff (author)2013-09-26

Hey, that's great, but couldn't you buy one for cheaper?

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solobo (author)Reiff2013-09-26

I don't know; the only places I've been able to find that sell "adult-sized" pogo sticks sell them for about $350; this one only cost about $90 (plus paint/powder coat as desired). If you know of a cheaper place, let me know; I'd love to check it out.

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Reiff (author)solobo2013-09-27

Okay, $350, well I guess your right. No I don't know anything much about pogo sticks, I just thought that you could have bought one cheaper.

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rallekralle (author)2013-09-27

u just got another vote

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solobo (author)rallekralle2013-09-27

sweetness

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snoopindaweb (author)2013-09-26

I recall when AMF took over Harley Davidson in the 70's and made some fuel powered Pogo Sticks that were impossible to ride - "Out in front of the H/D Shop - Everyone Drunk".. Yup.

author
glorybe (author)2013-09-26

If a band snaps will it strike the user in the groin? Will a band breakage result in a hard landing and crash situation? The idea has some merit but it does strike me as a bit hazardous. Your display of the math and science of the unit deserves special recognition as so few do that sort of thing these days.

author
solobo (author)glorybe2013-09-26

I think it's possible; when my band snapped (slipped off of a bolt in a prototype), I landed a little harder but wasn't snapped or hurt in any way, but I could definitely see situations where it could have gone worse. Thanks; I like understanding the math and science behind things, and I'm glad others do too.

author
stumitch (author)2013-09-26

I posted an 'ible called "the pogostick of insanity" awhile back but i think your design is way better. steel springs are kinda sketchy and a giant rubber band has a kind of panache to it. :-) well done!!

author
solobo (author)stumitch2013-09-26

Yes, I think I saw your instructable. That's cool that you taught it to kids in your machine shop class.

author
Captain Robert (author)2013-09-26

Excellent design and build and phenomenal set of instructions!

author
solobo (author)Captain Robert2013-09-26

Thanks! And thanks for the patch.

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