Here’s a summary of my coffee table project that many of you have seen me work on (or struggle with) over for the last several months.
I like furniture that can flex or modify it’s position to address different needs. I’ve seen coffee tables that raise to eating height before, but I wanted to design one that really expresses the mechanism and plays up the physics behind it. Back in October I made a 1/2 scale mock up of the design to understand the motion.
Then it was back to designing a full size mock-up.
I realized it wasn’t going to be stable enough with just one set of arms, so I decided two sets would still look good. Everything was designed in Autodesk Revit. The software allows you to figure out volume, then with a given density of materials I could get weights from the various parts. This allowed me to determine the balance. I didn’t want it to be perfectly balanced with the counter-weight, but have enough weight to assist the movement.
First I started making the frame out of aluminum. It’s fastened using a pneumatic riveter.
Painting the steel arms.
CNC cutting the concrete forms out of pink foam
Creating the concrete counter-weight form
Failed attempt to CNC cut aluminum for brackets. I’ll skip the rest of these struggles…
Casting the concrete base
Casting the counterweight (nice and sloppy)
The base assembled.
Frame is attached.
There were many tweaks after testing it. There was some wiggling around the axles, so I widened the holes in the steel arms to put nylon sleeve bearings in for a tighter smoother fit. There was still some shifting after putting some weight on the front, so I designed a locking mechanism with a latch.
Lots of struggle with this latch at the top of the photo. (FYI, learn the cold metals milling machine if you need a part like this)
Thanks to all who showed up on Monday night (Feb 18th, 2013) for the signal processing class. It was a lot of material to cover in one night, but I hope everyone at least learned (and retained) something. I was asked by several people to post my lecture notes online so people can review them. It took me awhile to go through my notes and clear them up (somewhat) for someone besides me reading through them. Also, I had to erase and rewrite a bunch of stuff because they were too close to the edges and were being cut off by my scanner. So that’s why it took so long. Anyway, here are the notes, the notes for the pre-class Math Review, and the 8-page info packet that I passed out during class:
Now that the class is over, the next thing to do is figure out what class to teach next. I noticed that many of the attendees enjoyed the filter design example we went over. Perhaps we could do a short class on some practical Analog Filter Synthesis? Some people have “thumbsed-up” the idea for doing a class on learning how to use LTSpice to build schematics & simulate circuits. Recently, I’ve been reverse-engineering schematics from double-sided printed circuit boards in older consumer electronics. I could demonstrate some techniques on how to do that. Another idea is moving directly past the Analog Signal Processing class and going right into Digital Signal Processing. All the same topics from analog appear in digital such as convolution, impulse response, frequency response, & transfer functions. Except most of the integrals become discrete summations when in the digital domain. There are neat topics specific to digital such as FIR filters and sample rate conversion, which I think are the most interesting. Actually, the website Coursera just started a DSP class this week. If you were at Monday’s class, the Coursera course should be much easier since most of the topics are similar, like I described above. Check it out.
If you have any feedback on Monday’s class, ideas for other electronics classes, or any other comment, then please let us know. If you see me at Pumping Station: One and remember what I look like, then feel free to talk to me in person.