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an incoherent world 002, gimp + bamboo cth460

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I suppose I ought to make note of the silliness in these pages. 
SLAM = simultaneous location and mapping. at the end of 2.737 mechatronics we each talked a bit about projects we’d worked on, and my classmate will vega-brown is in the robust robotics group @ CSAIL and is working with quadrotors. I think the video he showed is is still hidden (awaiting publication or something).
panel 3: they really do make tiny functional robots! 
I watched this video when the prof from the UC berkeley biomimetic millisystems lab came and gave a talk. I guess if I had planned life out more thoroughly or if I was more ambitious, I might have applied there for grad school. The more options the better, and right now I only applied to one place x.x oh well. WHATEVER. life will fall out as it will. also inspired by the bugs in 9 and this creepy and kind of depressing comic I read while bored.
oftentimes, though, with these tiny robots they don’t process their data onboard and send it via radio to a computer that gives them an estimate of where they are and where to go next.

panel 4:
555 footrest (turned nightstand in this instance?)
jordan dropped her quadrotor and one end was bent at approximately the angle of the quadcopter in the mobile, but something about trimming the propellers and her quadrotor still flew perfectly fine.

oh and that thing to the very right is a ballcopter (well, the kit ones upstairs of MITERS are white plastic so they must come from somewhere else), popular thanks to this video.
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hrm and pg 1:

pg 1
cruft = discarded junk. crufting = the art of hunting for such junk to reuse in projects.
and… idk what that is. tesla coils on hexapods. hexlas. because why not?
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Oh yes, about GIMP and bamboo CTH-460 on windows 7: works fine.
Initially it didn’t work : / even after installing the bamboo drivers and restarting, this is what I would get:
I ended up uninstalling the drivers via the control panel and reinstalling, and this time when I started GIMP the tablet I borrowed works fine.

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punt punt punt

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punt punt punt
…
a few days ago on the facelolz i said that

It’s now conclusive that I do not ask enough questions when I get stuck on things, and that this is unacceptable as it will impact my work performance. (I theorize that this ask-questions problem is why I am so mediocre at school).
Therefore, my goal for the next two weeks is to ask at least five dumb but coherent questions a day, and as proof of that I will write the answers up on my blog.
(I am still thinking a bit as to whether this casual-question-asking will actually translate to me asking more questions when I feel like people expect me to know more than I actually do).

So! then i asked questions. turns out most of the questions were so silly they don’t even merit writing down and/or I’ve completely forgotten them. But here today I’m writing down some notes on controls courtesy of Shane with mock-quadcopter demos by Charles (not duplicated here).

some of those questions were silly questions like how do i do controls in real life, as opposed to in labview on a $10,000 national instruments card.
then my brain went “speaking of things i want[ed] to do consistently to improve on skills…”

src files. wacome graphire4 4×6, inkscape, gimp. crashlanding, caeldera, digitalstrip2 fonts from blambot. ~4.

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the theory behind both is the same, ignore current incompetence (flaunt it? sorry, internet, for adding to the general scuz of atrocious material) and focus on learning learning learning to get to where i want to go…
(credit to MITERS folks for creative inspiration, including conversations with Dane about post-apocalypticc robot boxcar somethings.).

hmm. Right. controls.
Say I have a quadrotor. How would I go around implementing controls for it?
e.g. in 2.737 mechatronics class, we use a digital signal analyzer to characterize the plant. But no one tries to do that to their quadrotor. One possible way: mount quadrotor on stick, rotate it along one axis at a time. But, in real life:
Generally PD controllers.
If you didn’t know that, you could model it as a mass and damper (really simple model). Small number for damping (only comes from moving through air, minimal), e.g. damping coefficient of 0.1. Don’t know distribution of mass along quadrotor axis, so just model as evenly distributed — really does not matter since will end up tuning gains empirically anyway.
Proportional controller is like a torsional spring. Bigger error, bigger control effort.
Derivative controller is like additional damping. Otherwise, with proportional controller will correct for error but then due to lack of damping will oscillate.
Start out with too little gain, because then it will fly but drift off to the side. With too much gain, it will oscillate and flip over. Then slowly increase P gain.
Converging on the gains — a common method is Zieger-nichols. General idea is to up the P gain until it just begins to oscillate. Now up the damping (D gain) until compensate for oscillation, use some magical constants, … that sort of thing.
PD fine for flying indoors. But outdoors, wind will cause constant offset. Need I[ntegral] term. Also helpful if one motor is weaker than others, other sources of constant error.
Bandwidth and sampling frequency.
Limitation: how fast can control code loop run on microcontroller (mcu). Mcu has system clock (16Mhz for atmega’s). Rule of thumb, +-* each operation 1 clock cycle. Dividing integers four clock cycles. Floating point, tens of cycles. More margin because processor will need to respond to interrupts. This is upper bound on sampling frequency.
Lower bound, well, only need to respond to user input, and human reaction time perhaps 0.5 secs, 20 Hz. But also want to reject higher frequency noise e.g. from wind.
If calculate these and not overlap, need more efficient code or more powerful processor.
Tuning gains — actually pilot dependent. Some people like higher gain despite closer to instability because will respond quicker to sudden turns. While people shooting video will want higher damping so that footage is smooth, okay to more slowly respond to errors in position. 
Segging things are like quadrotors but with one axis instead of two.
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misc. ubuntu things

I was always a bit disappointed that bash history saves  to disk only the session that is closed last.
Turns out there is a way to fix that:

vi ~/.bashrc
export PROMPT_COMMAND='history -a; history -r'

(http://northernmost.org/blog/flush-bash_history-after-each-command/)

I have a vmware ubuntu 11.04 (natty narwhal) setup.
things I investigated today:

  • screenlets and digitalclock (“dark clean” theme)
    • digitalclock appears glitchy — artifact of vmware?
    • themes for the cairo-clock
      • http://gnome-look.org/index.php?xsortmode=high&page=0&xcontentmode=1861
        • http://gnome-look.org/content/show.php/Japanese+Theme+Cairo-clock?content=91147
  • equinox set of themes
  • elegant-gnome theme (was not able to get this to install) http://gnome-look.org/content/show.php/Elegant+Gnome+Pack?content=127826
  • wallpaper-clocks http://www.vladstudio.com/wallpaperclocks/browse.php
    • http://www.vladstudio.com/wallpaperclock/?northern_lights
    • http://www.vladstudio.com/wallpaperclock/?robots_in_love
  • orta theme http://mygeekopinions.blogspot.com/2011/06/how-to-install-orta-theme-pack-in.html

Currently settled at Dusk with transparent menubars