Debugging the particle-surface pendulum

The bearing I purchased from McMaster-Carr had way too much slack in it. This caused the weight to acquire a tilt to it when it was at rest, see Figure 1.

Image of the pendulum with the bearing from McMaster-Carr.
Figure 2: Ball bearing slack. The above image shows the slack in the ball bearing that was purchased from McMaster-Carr. The red lines are there to help guide the viewer.

To alleviate this, I opened up an old hard drive lying around the lab and salvaged the voice-coil hard drive head-reader, see Figure 2.

Culled hard drive voice-coil.
Figure 1: Culled hard drive voice-coil. The bearing in the center of the voice-coil is what I needed. Luckily it was being held in place with a screw, otherwise I would have had to press it out in a drill press.

Of course, the new bearing doesn’t fit into the holder I got for the original bearing. This isn’t a problem as I found a nut that Sarah epoxied onto the bearing. The epoxy takes 3 days to cure so we will know if it will work on Monday. I did use some 5 min epoxy on it to show that it will work. 5 min epoxy is not good enough for the parts unfortunately. The retaining ring is a bit more difficult to get into place but, that will just have to be the way it is.

The next issue is to try and get the pendulum to be held in one place and release without issues. One thing I noticed when both Sarah and I were attempting to release the weight, we both gave it a little upward kick without realizing it. This is an issue that needs to be resolved. In Figure 3, I have setup a simple mockup behind what we would like to do. It doesn’t work that great but it does remove me or another user from giving the weight an upward motion before release.

A method for clamping ahold of the pendulum.
Figure 3: Pendulum holder. A simple (and bad) way for holding the pendulum in place. There has to be a better way.

I have Sarah right now investigating different materials that we could use in order to make a better holder. She is right now looking at different materials we can use that would fit better on the base. Things such as flexible coolant hoses, third hands, etc.

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  1. #1 by Anthony Salvagno on December 2, 2011 - 6:38 pm

    Ya know, for something like this a video would be really handy. From the pictures I can’t tell exactly what you are referring to. What does it matter if you give it an extra upward kick?

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