I had the idea to build a double pendulum fidget spinner quite a few month ago, when fidget spinners first started to become popular. Thanks to the fidget spinner contest on instructables I finally took the time to make one.
I find it extremely addicting to play with and I hope you are feeling the same way. In contrast to other designs this spinner looks rather simple and doesn't spin as well as others. In fact the true fun starts once it is going slower.
The special thing about this fidget spinner is that its movement is completely chaotic and therefore different every time you spin it.
A double pendulum simply consists of one pendulum attached to another. Ever since I was introduced to them in school a few years back they fascinated me. Please check out this link should you be interested to find out more about them.
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Step 1: The Design
During the design process my main concern was to make the spinner small enough so it could be held in a hand. I also wanted to keep the it very simple, but pleasing to look at. You can of course go crazy with it.
I started out with 608 (8 x 22 x 7 mm - inner diameter x outer diameter x thickness) bearings (these are the ones used in skateboard wheels and most fidget spinners), but quickly had to realise that they were to big. So I decided to go with 626 2RS (6 x 19 x 6 mm) bearings. The next thing I realised was that using three bearings would make it too big as well. Therefore for my first try I used a screw head as a counter weight which later got replaced with a piece of a steel rod. To save some time I ended up designing a version I could laser cut first and later used Fusion 360 to make a 3D printable version.
You might have to adapt the design to your finger length, since mine are quite long. I uploaded the Fusion files to this step. Simply adjust the length in the sketches named "Bottom01" and "InsidePendulum".
Once I was done I decided to do some research and found out that the idea wasn't as new as I thought. Thingiverse user videohead118 has published two double pendulum fidget spinners here and here. He used 1 x 608 and 2 x 624 (4 x 13 x 5-millimeter) bearings. So the bearings he used for the second pendulum are way smaller than the one I used. It is obviously your choice which design you would like to go with, but bear in mind that due to the bigger bearing (production tolerance need to be higher in smaller bearings) and better weight distribution my second pendulum should spin better. In my opinion the spin of the middle bearing is not quite as important since most of the movement results from the second pendulum. The advantage of his design is that you won't have to cut a steel rod. Even before that Rotablade started selling a pendulum fidget spinner here. The price point with about $175 is pretty steep though. Please tell me should you know other designs. I would like to check them out.
For the final version I designed you will need:
- two 626 2RS bearings (e.g. here)
- filament of your choice + access to a 3D printer
- a 6 mm piece of a 10 mm steel rod
- brake cleaner (to remove grease from the bearings)
- something sharp e.g. a box cutter knife (to remove the protective cover of the bearings)
- a small glass jar
- hammer (to assemble the pieces)
You can take a look, download and edit my design here:
Step 2: Degreasing the Bearings
One of the most crucial things when building your own fidget spinner is to degrease the bearings. If you ever wondered why the cheap spinners you bought turn way better than your self-made ones, the reason is usually that most of the store bought bearings are greased. While the grease is necessary for many applications it hinders the movement of your spinner.
Carefully get rid of the protective covers by lifting it off with something sharp. It is easier to do so by starting from the middle.
I found brake cleaner to be the perfect choice to get rid of the grease. Simply place the bearings in a glass and cover them with the cleaner. Let them sit in it for about 20 minutes and carefully shake them from time to time. Take them out and check how well they turn. Depending on how much grease was on them you might have to repeat the process with a new batch of cleaner.
Step 3: 3D Printing + Assembly
Before 3D printing the pieces you will have to make sure that the tolerances match your printer and the nozzle size you use. In order to get a tight fit I used a 0.1 mm ofset, but you might have to use a different one.
In order to get a high stability I used 100% infill.
The assembly is quite simple, but you might need a hammer. Start by assembling the middle. Afterwards push the other bearing into the bottom piece and the middle piece opposite to it. Now glue the top part to the bottom part. Be very careful not to get any glue into the bearing. All that is left to do is to glue the bottom turner to the top turner. Depending on how well your fit is you won't need any glue.
Congratulations you are done. Enjoy your fun new toy!
In my experience the best way to play with it, is to hold it at a slight angle and and to slowly move your fingers from side to side, like I am doing in the title step.