Blog re-activate!

I've never been an especially social person, and that is apparent in my use of social media. I've tried a couple times to get involved in the whole social media thing, but it's never lasted more than a few weeks.

I'm going to make another go at this and see if I can keep it up a little longer this time. I think that some of the projects that I choose to undertake would be of interest to other people. So perhaps if I make the effort to post some of the thing I'm doing, I'll get a few followers, and that will encourage me to keep up with the posting. We'll see if it works out this time.

I have three social media sites that I'll be using at this time:
1) This blog. Used to share things that are likely to interest other people. Longer posts taking some effort to compose will go here.
2) Google+ page. For quick things and things that are not as likely to be of interest to the world at large.
3) Youtube channel for videos. I'm a little conflicted about this one because much of the time I'd rather read a text post than watch a video. However, I've found that some Youtube channels with the right type of host are fun to watch. So I'll try posting a few videos and see what comes of it.

I'm also expanding the scope of the blog slightly. It was previously intended to be a project log for things like programming, electronics, physical things I built, etc. I'd like to now include some less concrete topics that I've developed an interest in.

Most of the topics that I've developed an interest in over the last few years are all different aspects of self reliance:
  • Home improvement and construction, including:
    • Alternate construction methods like earthbag building.
    • Water capture and reuse, graywater use and treatment.
    • Solar heating, solar power.
  • Gardening and aquaponics.
  • Financial independence (reference Mr Money Mustache, Early Retirement Extreme.)
I plan to have posts about these types of things, in addition to the technical projects that the blog originally covered.


Quick status update

I see I haven't posted anything here in almost two years. It's not that I haven't worked on any interesting projects; I'm just really bad about taking the time to write about what I have done.

Since my last post here I've moved from New York to Arizona, bought an old car that has required far too much repair work, and bought a house which has also required a lot of work. Much of my time has been consumed in moving across the country, car repairs, and house repairs.

I did take some vacation time this year to go first to the Maker Faire in San Mateo, and later to Burning Man. It's the first time I've been to either of those events, and I think they're both very inspiring for people who like to build and create stuff for themselves.

My largest project that I've completed lately is to build a recumbent tadpole trike based on plans from Atomic Zombie. I've never done any kind of bicycle work before, so I'm pleased that I managed to create a working contraption. I plan to write a more complete post about that, but I have one picture here:

I just created a Google+ account (https://plus.google.com/102429887004109052348), but I may be as bad at updating that as I am at posting to the blog here.


Playing with servo motors

I bought some cheap mini servos from DealExtreme to play with.  They're less than $4 each (in quantities of 3 or more.)

I designed a few little plastic parts to hold the servos together into a structure that can do something.  The assembly is meant to resemble a single leg from a hexapod robot, but the current design is much too weak to support any weight.  It works fine for playing with motor control software, though.

I designed the motor mounts by playing with SketchUp for a few hours.  The first thing I did was grab a pair of calipers and model one of the mini servos.  Then I just pushed the motor models around in SketchUp, and draw parts to connect them.  This is what I came up with:

I exported these parts to STL and printed them out using my MakerBot Cupcake 3D printer:

I'm still working on tweaking the printer.  After a bit of cleanup with a knife and a file, the parts work fine:


I like this 3D printer.  It's so easy to go from a rough idea to an actual part!

I did have a lot of trouble getting from SketchUp to an STL file.  In fact, the parts I printed out are actually mirrored compared to the design.  They work fine that way, though.  I've since discovered that getting an STL out of SketchUp is easy if you know the trick to making the STL export plugin work: the part to export has to be exploded for the plugin to find it.

The next step was to try control the arm (or leg, whatever it is.)  I hooked the servos up to an Arduino, which has an extremely easy to use servo library.  It took no time at all to get the servos responding to a simple test program.

I did have a occasional problem with the stepper motors, where all the motors would just start spasming.  It looked like the arm was having a seizure.  This turned out to be caused by my powering the 3 mini servos from a 1.5A regulated power supply, which was apparently insufficient.  I hooked the servos up to 4 AA batteries instead, and the problem went away.

After demonstrating that servo control with Arduino was a trivial task, I wanted to control the servos from a computer program.  To do this, I threw together a quick and dirty program in C#.

A side note here: I use Linux more often than Windows, and I like programming in Python.  However, I've found that when I just want to get something with a GUI working quickly, Visual Studio and C# are hard to beat.

I modified the Arduino program to watch the serial port for commands which set the position of each servo motor, and threw 3 sliders onto a form as the UI.  This worked as expected, and made it easy to set the angle of each servo.  However, even with only 3 degrees of freedom, it's rather difficult to position a robotic arm by specifying the angle of each joint.

So, next part: inverse kinematics.  Inverse kinematics is something I've found interesting for a while, but never tried to do anything with.  Luckily, it turns out that the inverse kinematics equations for this particular configuration are relatively simple.  It still took me quite a few hours to get everything working, though.  This is the page I used as a reference: http://www.learnaboutrobots.com/inverseKinematics.htm

I ended up with a picture box which can be clicked on to set the XY position of the end of the arm, while the mouse wheel sets the Z position.  It works well, and it's really neat to see all 3 motors moving in tandem to get to the designated position.  I also used forward kinematics equations to draw the current estimated configuration of the robotic arm in the background of the picture box.  Even without the physical thing hooked up, it's interesting to see the drawn arm and all the sliders move around as the picture box is clicked.

Here's a video showing the inverse kinematics in action:

This is the first time I've tried uploading an HD video.  I was going to use Vimeo, but it's not accepting uploads as I write this.  I guess I get to try YouTube.

This whole project took maybe 3 days.  About 1 day of messing around with SketchUp and printing parts, 1 day to get the Arduino code and basic sliders working, and 1 final day to get all the inverse kinematics stuff working. 


3D printer: now working better

I've been getting a little frustrated with the 3D printer.  The past couple days, it has continually been failing to get through a printed object.  It starts out well, but after a few layers the extruder starts slipping on the filament.  It digs a nice little notch in the side of the filament instead of extruding it.

I tried extruding hotter and colder, tried with the idler wheel tighter and with it looser.  I even tried taking the insulation off of the heater barrel in case the filament was melting too far up into the barrel.  Some changes made it work worse, but none made it work better.  I've been seeing a lot of this:

These are supposed to be dodecahedrons.

I did finally figure out the problem late tonight.  I completely disassembled the extruder barrel assembly.  It turns out that the PTFE thermal barrier was too tight towards the bottom, and greatly restricting movement of the filament.  I cleaned it out using a 1/8" drill bit (held by hand, not in a drill) until the filament could move through it with no resistance.  I had to remove some more material from the inside of the thermal barrier after screwing it back in to the heater barrel.  Now it works quite a bit better:

See that in the back?  It's a complete dodecahedron!  Here's a closeup:

The one on the right is sitting on top of a green laser pointer.  It glows nicely.

It was exciting to see this part completed.  I was surprised at how well bridging the top material over the hollow inside of the shape worked.

I just realized that I don't have any pictures of the completed 3D printer up here yet, so here are a couple.  The wire routing still needs some work!


More printed objects

I tried printing a couple more objects today.

I managed to get a complete MakerBot coin printed.  It looks pretty good.  After that, I tried to print a dodecahedron.  Unfortunately, the machine stopped extruding part way through the print each time I tried.

I think the extruder motor keeps going, but the pulley digs a notch into the filament instead of moving it.  I might try tightening the idler wheel a bit, but I'm wary of breaking it.  Maybe I should check that the extruder is still hot when it stops extruding; if for some reason it's cooling off, that would certainly make the filament too hard to extrude.

Here's the completed MakerBot coin, and a partial dodecahedron: