Saturday, December 2, 2017

Double Pendulum

A double pendulum is a pendulum with another pendulum attached. The motion of the pendulums is governed by a pair of coupled differential equations and is chaotic.

This will be an easy build using mostly woodworking skills.  Subscribe to my Channel to learn how to make more woodworking projects. 


                                         Double pendulum


The pendulum will be made of wood so it must have a heavy base to keep it from moving around. In order to do this lead weights will be added.

The base (4"x8") is made of three pieces of 1/2"plywood. 
They will all be glued together but first one of the three pieces -the middle one- has to have a section   cut away, this will be for some weights.


A forstner bit is used to drill four holes in the centre piece, this will make it easy for a jigsaw to fit in to remove the marked section. 


Here the piece is cut, it does not have to be a perfect cut since it will be the middle part of the base and will not be seen. Notice the protrusion, that lines up with the post and will add support for the screws for the post.


I found some lead weights in my shop and placed them on the bottom of the base. They can be loose since the middle piece will keep them secure. Any weights will be fine, you can try a hobby store or use some fishing weights.  


 The bottom of the base will have two holes, they are drilled and countersunk, this will be for two 3" screws for the post. 


A 3/8" hole is drilled in the post for a bolt which will hold the bearing. A carriage bolt will work fine for this project. It has a round head and square neck, when the bolt is hammered into post it will be secure. 


So far the base, post and bearing bolt is made. It has a good weight and good height. The post is 14" high and with this information we can move on to the arms. 

For the arms a rough design was marked with pencil and cut with the bandsaw. Then they were  further shaped and cleaned up with belt sander.

A 1" Forstner bit is used for the hole for the bearing. I tested the bearings and my bits and got lucky with a tight fit.

 Two holes in the large arm, one for the bearing and one for the 3/8 bolt to attach the smaller arm. 

 The bearings are ready to be put in the arms. I used my vise and squeezed them in giving them a tight pressure fit. My  vise jaw liners were used so the bearings and the wood would not be marked. 

I gave the pendulum some stain and then bolted it together.  

Small lights can be added to the arms. After the shop lights were dimmed I gave it a spin and played with it for some time. This is a fun toy for any age. I am sure I will be making some more.

See Also

               Levitating Dowel                                  Spring Gun




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  2. Where did you get those bearing?

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