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.

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.

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.

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.

Particle-Surface Interactions Pendulum

My new boss, Hugh Smyth, has given me the green light to do open notebook science on some of the projects I’m working on in the lab. The project I’ll discuss below is especially cool since it is simple and relatively straight forward to accomplish. Plus, the fact that Hugh is excited about open notebook science makes it all the more fun.

What I designed is a very simple pendulum that has the capability to whack the heck out of something. Figure 1 is a SketchUp image of the pendulum showing the basic design.

Figure 1: Particle-Surface Pendulum. Thorlabs parts were used as the structure. There is a double sealed ball bearing that allows the stainless steel ball to swing freely. The item to be whacked is placed in the optics holder. The SS ball came from Precision Balls and all other items came from McMaster-Carr.

It works surprisingly well and I’m happy about its design. There are a few issues with it that I will discuss when I post real images of the build. Till then, here is a parts list for, what I’m calling the “Pendulum 5000″.

Parts List

Thorlabs

• MB4 – 4″ x 6″ Aluminum Breadboard.
• BE1 – Pedestal Base Adapter.
• CF125 – Small Clamping Fork.
• PH2 – 2″ Post Holder.
• TR2E – 2″ Optical Post.
• LH1 – Adjustable Lens Mount.
• PH4 – 4″ Post Holder.
• TR4 – 4″ Optical Post.
• TR6 – 6″ Optical Post.
• RA90 – Right Angle Post Clamp.
• LMR15 – Lens Mount for Ø15 mm Optics.
• ER2 – 2″ Cage Assembly Rod.
• ER3 – 3″ Cage Assembly Rod.
• MSCB1 – Tapped Mini-Series Construction Cube.
• MSA25 – Thread Adapter 1/4″-20 to 4-40

McMaster-Carr

• 92311A535 – 1/4″-20 Set Screws.
• 7804K143 – Flanged Double Shielded Ball Bearing.
• 92185A535 – SS 1/4″-20 Socket head cap screw 3/8″.
• 8517A58 – Stainless Steel Protractor.

Precision Balls

• 100-B-T – Ø1″ 1/4″-20 Threaded SS ball.

As a final note, getting Figure 1 to display properly was a heck of a feat due to my lack of HTML skills. So, I’m going to post the code for it below. The reason why I didn’t use the built-in WordPress figure + caption gui is that it wouldn’t allow me to bold or italicize words in the caption. So, I had to build a table to stick the figure in. Even posting the below code was a pain since the symbols < and > are rendered as HTML tags and need to be escaped with their ASCII equivalents.

<div id="image" style="width: 330; margin:0 auto; background: lightgray;">
 <table class="image">
  <tbody>
   <tr>
    <td align="center"><a href="http://image"><img class="size-medium wp-image-20" title="" src="http://image" alt="" width="300" height="200" /></a></td>
   </tr>
   <tr>
    <td class="caption" align="left"><strong>Figure 1:</strong> <em>Title</em>. Caption</td>
   </tr>
  </tbody>
 </table>
</div>