You might be thinking to yourself: 'Another fidget spinner? WHEN WILL THIS CRAZE END!?' But just give this instructable a chance, because this fidget spinner is not like any you have seen before.

At first glance you might be thinking this is the worst fidget spinner ever, but it works just as well a 'normal' one and manages to look completely useless at the same time. I got the inspiration for this instructable from a 'theory of machines' concept that i did in class last semester. The concept is fairly simple, have a bunch of unequal weights at some random angles and distances from a center of rotation and balance the system with a single compensating weight.

I made this from a bearing i salvaged from an old 'wheelies' shoe wheel, a toilet float rod, an old paint brush and some scrap pieces of wood. With some maths, physics and some patience on your side, you can also make your own unique looking fidget spinner.

Step 1: Gather What You'll Need

Stationary:

Pen
Paper
Protractor
Ruler
Calculator

Tools:

A saw (Hacksaw, bandsaw or whatever you like)
Files and/or a belt sander
A drill
Something grippy (a bench vice or clamps)
An accurate kitchen scale

Materials and expendables

Wood
Some sort of heavy material to use as weights
Epoxy or superglue
A small bearing
Sanding paper
Linseed oil, paint or whichever material you would like for finishing

Step 2: A Little Bit of Preparation

This step might seem useless at this time, but just take a moment to visually get to grips with the scale of your project. With this I mean it is a good idea to decide on the size of your weights and the lengths of the arms.

I found that 20 to 40 mm arms are ideal (I went over and it worked, but smaller would be more comfortable).

For my weights i used an old brass toilet float rod that i cut up. This is perfect for this project, because most of the mass will be concentrated in a small area when looking from above. And to change the weight, you only have to shorten the rod. I cut a short piece of rod that i thought looked like a reasonable length (the middle size). I weighed it to get an idea of the weights I will be working with, it came out as 6g (How accurate this is, I don't know).

Step 3: Doing the Math and Planning

The heart of this instructable is a simple balancing operation. There are a couple of methods and scenarios for machine balancing, but we will work with one of the simpler cases: weights rotating around a single point on an axis; essentially a fidget spinner.

To start off with, we will choose 3 weights, lengths of arms and angles (we will find one weight to compensate for these random weights and therefore balance the system). I used a 'Randbetween' function in Excel to find my random values. Take care when choosing the angles, having 2 angles very close to each other might be difficult to make. I worked with weights between 2g and 10g (use the first weight you prepared as a size reference to establish your boundaries), lengths of 20 to 45 mm and of course angles between 0 and 360 degrees.

Now, with your 3 arms fully defined, we will find the 4th arm's values with the balancing procedure. You can choose to have more arms and find the last, but more arms will be a difficult build.

In a table, as shown in the picture above, number your 3 weights, write down their weights, distance from the centre and the angles (a) you chose. Multiply the weights (M) with their respective radiuses (r). To find the x and y components of each mass's force, just multiply (M x r) with the cos and sin of the angles.

Now just sum the x and y components and find the resultant force needed to balance the spinner. You can do this by taking the square root of the sum of the squares of the resultant x and y components. And for the angle you can just take the inverse tan of the y over x components. This value will probably given as an acute angle, so to make your life easier when figuring out in which quadrant this mass should be, draw a vector polygon. Just draw the three 'Mr' forces at their respective angles on end, then close the polygon with a straight line to the origin. You can just measure or equate the angle and size of the vector.

Your angle is fixed, but you can play around with the radius and weight by just dividing the size of the vector you found by a weight within your parameters and then you'll have your radius. If you find that your radius will be too long or weight too big to balance your spinner, just choose different beginning values and see if you'll get a better result.

Calculation Table.xlsx
Download

Step 4: Preparing the Weights

Using your first weight as a size reference, guess the length of the 3 other weights and cut them to size. Use the scale to weigh the cut pieces. Luckily all mine were just about a gram heavier than what they should have been.

The difficult part is to match the weights to your calculated values, my scale does not go into decimal places, this is not ideal. Just go slow and grind/file or if you are brave, cut the weights shorter and keep weighing until they are where they should be. Don't give up, this step needs to be accurate.

Step 5: Making the Frame

If you have a 3D printer, this step will be a piece of cake, but i managed fine without one.

Just draw the design directly onto the piece of wood or material you are using. Using your protractor draw the angles as accurate as possible. The arm lengths will be to the center of your mass.

I marked the positions of my masses and drilled 8mm diameter holes for my rods to fit into as well as a 19mm hole for my bearing.

Using a bandsaw and hacksaw i cut off most of the excess wood. I used a belt sander to grind the wood back, closer to the lines i drew earlier. I finished off the profile with a Dremel, sanding bit and for the tight spaces (between my first and second weight) I touched up the profile with my needle files.

I used 120 grit sanding paper to take off the roughness from the surface, the wood was already flat. And finally painting some linseed oil onto the wood will not only prevent it from cracking, it also brings out the grain.

Step 6: Glue Time

This step takes no skill, but BE PARANOID with every move you make.

Just keep your calculations close and match the weights to the holes on the profile you made. I glued profile to the middle of the rods. The spinner will be completely wack if you mix up your weights so correct your mistakes before the glue dries. Let the epoxy or superglue dry.

Slide your bearing into its hole and give it a spin, if you are not happy with your bearing's performance (like me), you have 3 options:

Ignore the fact that the bearing is stiff and doesn't spin well
Get another bearing
A salvaged bearing can clogged with old, dirty grease that is slowing it down. You can clean up the bearing by taking the shields off and washing the grease out, I used engine cleaner. This might be a very bad idea if you have a bearing with a plastic separator (for keeping the balls in place). Then finally just lube up the bearing again with some WD-40. I am not guaranteeing that this will work or even that your bearing will survive, so be careful.

With your bearing ready, just press it in or glue it in place. Needless to say, don't get glue in the bearing.

Step 7: Making Caps to Hold Onto

If you are happy with the performance and if you can hold it comfortably, you can skip this step.

I used a hole saw to cut 2 disks of the same wood as the frame. Then i simply reclaimed an old paint brush's slightly tapered handle to make the shaft connecting the two disks. The ends of the little shaft was just ground down to fit in the 6mm center hole the hole saw made.

Now just glue the 'fat' end of the taper pin into one of the disks. Get some glue on the inside of the bearing and force the pin into the whole till it fits snugly. Leave this assembly to dry. And finish it off with gluing the other disk to the shaft.

You can now just sand down the ends do that the shaft is flush with the disk surfaces and give it a coat of linseed oil.

Why are my caps so long? Well, that is the only way my fidget spinner is comfortable. My longest arm has the biggest weight, meaning it will catch my finger if the caps are flat. Stick to the 20-40 mm arm lengths and you'll be fine.

Step 8: Finishing Up

And there you have it, a balanced weird looking fidget spinner.

If you feel a jerking motion while spinning, one of your weights are probably a bit too heavy. Your scale is also probably not perfect and the length of your arms could be slightly off. Try to pinpoint the weight that is giving you trouble by letting it spin freely on a table or try to 'feel the weights jerking. One of my weights (the first one) was a bit heavy so i just touched it on the belt grinder and it was balanced (don't get dirt in your bearing while doing this).

In the end this was a fun way to physically see the math and theory we learn in action and to be honest, it works much better than what i could have hoped for. I am looking forward to the strange arrangements that you will come up with.