you've all seen one. you know what they are. the little ball of exploding joy. i had one of these as a child, the small ones. i always eyed the big ones with envy as a lil boy. but they where super expensive. no way i could convince The Parentsâ„˘ to buy one! so, like many makers-to-be, my first response was to 'make one'. i never did, because out of what? how? but it's been on my mind ever since.

now, i'm an adult, and i could go buy one if i wanted. but where's the fun in that? let's MAKE one! and i even have access to a 3d printer, i could totally make one of these things.. time to dig in!

for this project you'll need:

a copy of Fusion360.

a 3d printer.

a wood burner or soldering iron.

LOTS of time...

**Edit: I've discovered some flaws in my math and method. i'm reworking this. untill this message goes away, dont download the parts and print this on your own! i have uploaded new, updated parts, but i have yet to test them. **

## Step 1: Using Fusion 360 to Calculate Measurements.

So, when i did this project, i discovered that my math was off, twice, AFTER i'd printed several hours worth of parts to test them. the first time because i eyeballed it and hoped it would work, and the second time because i'd made a mistake in my calculations. because it's so vital to the success of the project, i'm going to show you how to get the correct measurements using fusion 360

so, what we need to achieve is a complete circle using 8 sets of 'arms' and 16 connectors. to do this we need to know a few details first. the very first choice that needs to be made is the length of each arm. i started with, and intend to finish with 6 inch arms. the next detail we need to know is how thick our arms will be. just for stability, i recomend no less than 1/8 inch.

with this second measurement we can figure out detail 3. how wide our joint pieces are. this is largely a measure of how thick the walls need to be to hold an pin without cracking. originally i tried to have a thickness of .125 before the holes are added, but this prooved too thin, so i added a 1/16th, which has worked pretty good so far. so to create the joint width, we need the thickness of the arm, .125, plus the thickness of the 'wall', which is .1875, which is .3125 (as it just so happens this is exactly how tall the joint is too!) and then double it to represent the mirror half of the joint, .625. (see the picture for help.)

suposing that you do not make your arm thinner, this is pretty much the smallest you can make the joint before it cracks (with PLA. other plastics might work out better at smaller sizes.)

alright drawing time.

so, the first thing we're going to do is create an edge polygon with a side length of .625 and 8 sides. this achieves two things. first, it gives us the edges of the individual joints that form the inside of the circle, as close as they can get together. next, it gives us a common centerpoint to rotate everything around.

next we are going to draw in one of the joints, in a simplified fashion. draw a box on one of the edges that is as long as the edge and .3125 wide. now, draw a line from one of the top corners towards the midpoint, make it .09375 long. now make another from the endpoint of that line, going down the same distance. this will give us the centerpoint of the arm that attaches to it. do the same thing for the other top corner

it's not strictly necessary to do this next step but it helps visualize. use the circular pattern tool and select the new geometry you've just made. the box and the two vertical lines. click the center of the octagon for the center of the pattern, and then tell it to make 8 copies. you can now see how the joints will come together, barely touching.

next we will add some centerlines to constrain things to. start a line from the center of the octagon, extended about 9 inches, and at an angle of 22.5. now use circular pattern to make 8 of them.

now we have to do something that is going to sound a little strange, but, we need to draw a line that starts from the end of those tiny lines we drew earlier, and make it go straight up about 9 inches. mirror it over like we did with the small lines, and revolve this as well, for 8 copies.

your screen should look like an utter mess. brilliant! perfect. i know it's not the nicest thing out there but this is the quickest way to get what we need. if you'd like to clean things up, all we REALLY need is one joint, a vertical line connected to it, and a diagonal from touching the corner on the same side as the vertical line. everything else is mirror and radial symetry. (see image.)

now, use the fix constraint to make it so those lines will not move. it's important that they are locked in place. you can actualy do this with EVERYTHING you've made so far. anything Fixed will be green.

## Step 2: Blueprinting Pt 2, the Hard Part

so, now that we have our framework in place, we can start throwing in data and let the program start filling in the blanks for us. let's start with the back of the first arm. we decided that we would use a six inch arm. first we need to know what that means. all of the critical dimensions on the arms actually relate to the placement of the holes for the hinges. so a six inch arm is a measure from hole to hole. in reality your arms will be a little longer than this. so keep that in mind if you want an arm that is exactly 4 inches long, or something like that.

so! the first step is to use the line tool to place a line starting from the endpoint of the tiny line we created before, specifically for this purpose. (see image.) drag it out at a diagonal, snapping the point to the diagonal line. now dimension it at 6 inches long. chances are very good that your line is not actually coincident, and it is vitally important that it is. even if it IS, i recommend breaking out the Coincident constraint tool, and enforcing it.

we've just defined two of the three holes for the arm. now we need to define the position of the third one. and it's this hole that is the crux of the difficulties suffered by my attempts to make this piece. start by making a line along the length of the six inch line. do not make it constrained to an endpoint nor midpoint nor any other snap point it might prompt you to, except the line itself. the length of this line also does not matter, so long as the end point is unconstrained.

now we're going to add in some more constraints to represent the data we know. this line should be perpendicular to the six inch line. that's easy enough. it should also be 1/3 of the length from the end (this is, i believe, arbitrary, though it can never be more than half. it must always be closer to the far end, or at most dead center. i'd also try not to go to far to the end either.), also easy. add a dimension for 2 inches from the base point of the line and the endpoint of the six inch line.

now we get to the more complicated part where we have less data. we need to make another six inch line starting from the diagonal line to the vertical line. like the first, we must make sure the ends are coincident with the lines.

like before, we'll make a new line somewhere along the length of the new six inch line, and then make it perpendicular. it will also need to be 2 inches away from an end, but this time the lower end instead of the upper.

this is where the real magic happens. first, we need to make the two shorter lines constrained to be Equal. then we will make the two endpoints coincident. if you now measure either of the short lines, you will have the dimensions of the arm.

that's it, we've done it. for our purposes, the critical dimension we needed is .5327

## Step 3: The First Part

alright! we've got our relevant dimentions, and a hopeful belief that it's going to work this time! let's get cracking and prove we can remake this toy!

start with a six inch line, then two inches in make a perpendicular line .5327 inches long. (sounding familar?)

now, at the three points, make a circle that is 1.9mm wide, and another that is 4.3mm wide this should give you a donut with a wall thickness of 1.2 mm. i chose this number specifically because MOST 3d printers have a nozzil size of .4 mm, so this wall thickness SHOULD alllow you to print 3 full walls for strength.

next start drawing the outline of the shape using tangent lines from circle to circle. then, because i like the flare and it probably reduces weight and plastic usage without harmiing structure, add an arc to the bottom and trim out the lfat line.

extrude everything except the holes (as seen in the picture) 1/16.

now sketch on the surface, and draw lines tangent to the holes in the piece. then add the 4.3 circles back in. select the new stuff and extrude it 1/16. i had trouble with this spot, so i ended up having to add the holes into the sketch to prevent it from filling them in. always check your parts over to make sure the operation did what you thought it would!

last step, we need to create a mirror image of the whole part. you can do this in fusion 360 or your slicing software, but we will need two opposites.

## Step 4: The Joints

the joints themselves are a simple device. basically one is a four way connection, and the other is a 3 way connection, with little flat covers to blunt the corners. so let's start with the square.

this part is relatively easy to make, but the numbers are all over the place. i've remade this part a couple times to get it to be sturdy enough not to crack when i use it, so unfortunately the numbers arnt very even. first, draw a square .625 inch wide, and extrude it 1/8th up. then draw on it's surface, and add a pattern of squares .1875 tall by .3125 long. (look at the pictures). select and extrude these squares .1875 inches.

next we're going to add a center line. click two opposite faces and then under Construct, add a midplane. do the same thing for the other two opposite faces, so that you have an ex going through your part. then use construct, axis from two planes, and select these new planes. you should now have a centerline going vertically through your part!

select the front face and sketch. add a circle .09375th from the top left corner vertically and horizontally. the circle should be 1.9mm. extrude cut the circle .45inch deep

now use a circular pattern to create for more of these holes, using the centerline we set up.

and that's it. this part is done.

## Step 5: The Triangle

now, this part is a bit of a pain, in my opinion. on the original toy it ws the smaller of the two joints. but frankly, i cant figure out how to make it smaller without weakening the joints, so this bit is going to be larger, much to my annoyance. we'll start with an edge polygon, .625 inches long, and 3 sides. then we'll make a cube starting at a corner that is .1875 wide and .3125 long.

next make another cube connected to the other corner of the same line that is .1875 by .1875. this should leave a space between the two cubes that is .125 wide.

use a circular pattern to make three of these sets of cubes.

select everything except the center triangle, and extrude .1875.

now sketch on the surface and connect all the corners so that you have a large triangle with beveled corners. select and extrude .125

as before we're going to select two sides of the triangle, and create a midplane, then do it again with two more. only, this time we don't have opposite faces, because it's a triangle. so instead, just be sure to click two different 'sides' of the triangle. it doesn't matter which, so long as they belong to the same triangle.

create an axis through two planes, and there you go. now for the hole. select a side view, and sketch on the side of one of the small boxes. make a circle in the center of it that is 1.9mm wide.

like the box, extrude cut this circle .45 in, and use a circular pattern to add it to the other two sides. i had trouble getting this to make a pattern, so you may have to redraw and cut it manually on each one.

extrude this up .125, and it's done.

## Step 6: Math

now's the second hard part. figuring out how many of these blasted parts you need. let's start with the joints, because there is less of them.

each sphere is made up of three rings of squares, and triangular corner pieces that round off the build. there are a total of 18 cubes, and 8 triangles. (i've included a very basic diagram of how this works. but you'll just have to trust me or go count yourself :P) but wait! there's more! :D each joint is actually TWO joints. top and bottom. so you need 36 cubes, and 16 triangles.

there are 48 connections, and each connection is made up of 4 arms, 2 of the normal and 2 of the mirrored variety. 48*4. 192, half of them arm a, half arm b. this'll take awhile!

i'm not sure if i can get all the pieces printed by the end of the In Motion contest, so i am publishing it now to get it out there while i start printing. :P

## Step 7: Files

here's the files while i work on phase two

i recommend printing these solid, as it is a mechanical part with thin walls.

added updated files for thicker arm

## Step 8: Combining Things!

After you've printed off your 244 parts (yeesh) you can start putting things together, we'll be using short snips of 1.75mm filament to act as axles for the project, so this is an excellent time to bust out that roll that has only a tiny bit left! :D heat up the wood burner/soldering iron and let's get cracking (i actually recommend working AS you print. waiting for all the parts to print before you start is just wasteful of time :P)

let's start by mating pairs of arms. **make sure to pick two mirrors**. first, pick up two arms, and place the ribless sides together, with the short ends on the same side. now, feed some filament through the hole in the middle of each arm. if the holes are tight or messy, you can use a tooth pick to stretch them out and try to make them round.

now, carefully melt down the end of the filament so it makes a mushroom to stop up against. you can actually weld the filament to one of the arms, but be careful. after you've got the filament mushroomed or welded on, fip it over, and snip the rest so it's just enough to mushroom down. be very careful not to weld the plastic to the second arm this time, as it will ruin the set!

__i highly recommend if you decided to weld parts together, that you keep all your welds on the same arm. that way if you mess up you can snip all the lines and save the rest of the parts. it's not hard to just mushroom the tops though, and in my opinion this should be the preferred method. __

are the pieces connected? do they still move? congrats! time to do that 192 more times! grab another set and go until you run out of pairs.

tired of this yet? heh. you've only just started. pick up two pairs, and line up the short ends smooth side to smooth side. weld one set, and then the other so that all four arms are connected, and still move. set this one aside and repeat until all of your arm pairs are now sets of four.

as you can see from the pictures i would do each step in lots instead of by the piece. this saves time, though it does make things very tedious. put on some music or something :P

NOW you're done!... psyche. you should be pretty good at this by now though. now it's time to move on to the joints. and mercifully, these should be easier since we only have to melt one mushroom per arm. as long as you don't go crazy with the heat, you should be able to put these together easily.

## Step 9: The Real Hard Work

to start the next step, first grab four cube joints. weld one to each of the long ends of an arm chain. now grab another arm chain, and attach it to the cube joints of the first arm chain, so that you make a line. (or a curve, rather, but i digress)

continue like this until you have 8 arm chains attached to 8 sets (16) cubes, that makes a perfect(ish...) circle. i'd honestly connect the start and the end together.

from here you can start attaching arm chains to the open connections of the cubes from the ring.

congrats, you're about 15% done. :P

connect cubes to every other arm on either side of the line, and fill the rest with triangles. (see diagram) this SHOULD use up all the rest of your triangles. you're about half way done now.

.now attach arm chains from open cubes to open triangles.

you should now have most of a ball! congrats. now all that's left is to attack the last 8 arm chains to the remaining openings on the ball, and then attach THOSE to the last four cubes.

## Step 10: Reserved for the Finished Product.

here's hoping i can finish before the end of the contest. but if not, keep an eye out, i'll be posting this thing reguardless.

in the mean time, PLEASE, comment, ask questions, tell me how i can make this better for you! :D