Updated table design and progress

Cherry boards glued together.

I’ve finally made some more progress with the table. I changed the design a bit. All of the table-top boards will be perpendicular to the long dimension of the table.

I’ve updated the Sketchup model to reflect these changes:
[iframe src=”http://sketchup.google.com/3dwarehouse/mini?mid=72c8fb162c90a716dc6d75c6559b82a2&etyp=im&width=400&height=300″ frameborder=”0″ marginwidth=”0″ marginheight=”0″ scrolling=”no” width=”400″ height=”300″][/iframe] (click on the model to access)

I also detailed how the legs will be built:

[iframe src=”http://sketchup.google.com/3dwarehouse/mini?mid=9649970961fee260dc6d75c6559b82a2&etyp=im&width=400&height=300″ frameborder=”0″ scrolling=”no” marginheight=”0″ marginwidth=”0″ width=”400″ height=”300″][/iframe]

You might wonder why I’m building the legs out of four individual pieces. That’s a lot of extra work!

For a few reasons:

Hardwood is expensive. Cherry isn’t terrible expensive compared to walnut or other more exotic varieties, but making the leg hollow means I need less wood, so it’ll be cheaper.

Hardwood is heavy – I’m just guessing, but I believe the table top will be around 75 pounds. That’s heavy. The legs are 2.5″ square. They will be very heavy if made of solid cherry.

It’s just not possible. Finding solid heartwood cherry that is at least 2.5 inches thick will be nearly impossible, and incredibly expensive.

Instead of doing this I will buy 1″ cherry boards then plane, rip, join, glue, clamp, cut.

So there you have it.


Multiple web cams in Linux

The machine has two cameras currently:

One camera looks up, the other looks down.
It won’t always be held by rubber bands.


Yesterday I set out to see both cameras at the same time. Simple – they’re USB, I’ll just fire up two instances of VLC:

cvlc v4l2c:///dev/video0 :v4l2-width=640 :v4l2-height=480 :v4l2-fps=4&
cvlc v4l2c:///dev/video1 :v4l2-width=640 :v4l2-height=480 :v4l2-fps=4&

Well, one shows up. The other cvlc instance crashes. It turns out that some webcams claim the whole available USB bandwidth in isochronous mode. Being smarter than it needs to be, the computer decides that I wouldn’t be happy with choppy video, and the result is that I’m not allowed to see both video feeds at once.

Some web searches indicate that I might want to try changing to a compressed video mode such as MJPG. It would take up less bandwidth than whatever uncompressed mode it defaults to – so I tried changing the video mode to MJPG, using v4l2-ctl:

v4l2-ctl --set-fmt-video=width=640,height=480,pixelformat=MJPG -d /dev/video1
v4l2-ctl --set-fmt-video=width=640,height=480,pixelformat=MJPG -d /dev/video0

There’s also an option to set MJPG when invoking vlc itself, however I can’t remember it at the moment, and it doesn’t matter because it didn’t work. It’s likely I will settle for taking individual snapshots with vlc and bringing them into OpenCV. I’m not quite at that point yet, but I’ll update when I am.

3 Axis Movement

Here are a couple pictures of progress made

I’ve managed to get all 3 axes running. The second picture is the machine drawing a sample picture with a marker.

As you might notice, I have some serious hacks going on in my “design” thus far.

I plan on fixing these issues as I go along. I was so excited to get the machine running that I couldn’t wait to get the proper materials for motor brackets.

It does move on it’s own. The cheapo 3 axis stepper driver I bought from a Chinese vendor on eBay runs from a parallel port interface. I don’t have a working parallel port on my newer desktop PC so I’m using my old Thinkpad T43 which happens to have a parallel port.

The software that comes with the board will probably be useless for pick & place operations, but it is interesting to think of the possibilities that this machine might have for possibly routing parts from delrin. I’m sure it doesn’t have the rigidity to mill any metals.