double pendulum (various lengths)

Watch the video first and enjoy.... https://youtu.be/rK5wfl6OZg8

This is a double pendulum constructed with the simplest possible materials.
The double pendulum is often used as a model of chaos, but it's also interesting to watch　
unexpected behavior.

I also made a base (base.stl) so that you can attach this thing to the edge of desk or something with clamps or screws.

The force that the base receives from the pendulum is greater than expected, and the base must counter this. Therefore, in order for the pendulum to move for a long time, it is important to fix the base to something as heavy and solid as possible.

[size]
I have prepared 5 different lengths of bars, so print your favorite 2 lengths of bars.
You can enjoy the fun of double pendulum movement even with the combination of the two smallest bars.
bar_175 : 200 x 30 x 7 mm (axis to axis =170mm)
bar_135 : 165 x 30 x 7 mm (axis to axis =135mm)
bar_100 : 130 x 30 x 7 mm (axis to axis =100mm)
bar_65 : 95 x 30 x 7 mm (axis to axis =65mm)
bar_35 : 60 x 30 x 7 mm (axis to axis =30mm)

[materials]
3D printed things (2 bars and base)
M8 bolt 80mm x 1
M8 bolt 25mm x 1
M8 nut x3
M8 washer x8
608 bearing x2 (id=8mm, od=22mm, t=7mm, open type recommended, I used "NSK SS608")

[post printing - Inserting the bearing]
Insert the bearings into the A and B bars using a vise or the like.
The thickness of the bearing and the bar are the same, so you don't have to worry about the position of the bearing, just clamp it firmly in a vise and you're good to go.

[post printing - assembly]
There is no difference in shape between the front and back of the bar. The side with the stamp can be the front or the back.
Please prepare the necessary materials and assemble it referring to the photo. If the two bars touch during rotation, increase the number of washers.

[bearing removal]
If you want to remove the bearing and reuse it, I recommend using the bearing eject jig (bearing_eject_jig.stl) that I designed. You can easily remove the bearing without damaging it.

[print conditions]
-printing type: FDM
-printer: Original Prusa i3 MKS
-filament: PETG
-support: no
-brim: no
-raft: doesn't matter
-infill: 20%
-shell: 5 --- This is recommended to ensure strength against bearing insertion.
-nozzle diameter: 0.4mm
-layer height: 0.2mm
-print directions: Please refer to the photo.

[update]
2023/05/12
Since two files with the same name were created, I changed the file name and uploaded them again.

2023/04/22
Increased the types of bar length to 5 types.
Please choose your favorite two types and print them.

2023/03/23
-I made a jig to remove the bearings. (bearing_eject_jig.stl)
This allows the bearing to be removed without damage and reused.
-I made the bearing hole slightly larger (0.1mm) because it was a little tight to insert the bearing.