#robotics Logs

Jan 13 2012

00:42 ackerdacker don't poke me!
00:42 katsmeow umm, rue?
00:43 ackerdacker [23:18] <rue_house> the date is jan 12 2012, I'm on #robotics of irc.freenode.net come back in time and talk with me about it, use the nickname "ackerdacker" so I can tell its you
00:43 tsmeow co
00:43 katsmeow i sense a causality bug
00:44 ackerdacker oh, it won't happen till i read the logs again, and find out i shouldn't have come back now
00:44 katsmeow right, cause you should know rue isn't here now
00:45 ackerdacker but only because no one called to me till i got here from my now
00:45 katsmeow err, true
00:45 katsmeow so you'll be back later?
00:45 ackerdacker yeas
00:46 ackerdacker this is eating more energy that you can imagine
00:46 katsmeow ok bye
02:09 Burninate My question: How would you design a guitar tuner
02:12 Burninate I'm trying to put together a way to make active telescope optics affordable, and it involves precisely tensioning stretchy wires in much the same manner. I'm trying to work out the optimal device to pull a wire at between 0 and 100N of force, and adjust that force several times per second.
02:13 Burninate I'm pretty unfamiliar with mechanical actuators though, and wondering what type I need... a servo? a stepper motor? something with a feedback of the force I'm dealing with?
02:14 Burninate the overall control loop involves a big interferometer on the mirror surface, which is standard
02:15 Burninate Resolution between 0 and 100N has to be pretty high, maybe 1N steps
03:14 Triffid_Hunter Burninate: I'd suggest doing a manual pre-tension then using something with a lot of gears for final adjustment
03:15 Triffid_Hunter Burninate: using the frequency is a great idea for precise tensioning :)
03:16 Burninate Thinking maybe this: http://parts.digikey.com/1/parts/2013472-motor-geared-stepper-15mm-15v-bi-pg15s-d20-hhb9.html
03:16 Triffid_Hunter maybe a big stepper with a good gearbox on it, 100N isn't hard with proper gearing and even relatively small servos
03:16 Burninate but I don't know how to translate torque to force really... it should break down as you get to very small spindle diameters
03:17 Burninate Can you recommend a vendor?
03:18 Triffid_Hunter Burninate: http://zonalandeducation.com/mstm/physics/mechanics/forces/torque/introductionToTorque.html
03:18 Burninate The guitar tuner is really just an analogy for a telescope active optics system, btw
03:18 Triffid_Hunter Burninate: vendor? for what? motors?
03:18 Burninate I mean I know the equation for torque, but the lateral stress on the spindle has got to have some maximum unrelated to torque
03:19 Triffid_Hunter Burninate: also if you want to convert between newtons (force) and mass to better understand the force, just remember F=MA, 100N of force is approximately equal to the force that a 10kg mass exerts under earth gravity
03:19 Burninate for stepper motors I guess
03:19 Burninate robotics gear in general
03:19 Triffid_Hunter Burninate: don't hook it direct to the stepper, use some 608 skateboard bearings
03:20 Triffid_Hunter mount a shaft, connect to stepper with a big gear
03:20 Triffid_Hunter heh now you have me wondering if my 3d printer could make a gear strong enough to transmit 5kg.cm of torque
03:21 Burninate Put it this way
03:21 Burninate Could a geared stepper motor of compact size (1" cube), anchored to a steel plate, hold 10kg on its knob, without applying any torque?
03:22 Burninate or would it crunch
03:22 Triffid_Hunter Burninate: hm 25mm is pretty small to carry that amount of force just in terms of internal bearings and mounting
03:23 Burninate Is there a numerical specification I'm likely to find related to that problem?
03:23 Triffid_Hunter dunno, I never had any formal training, I've learnt my engineering from experience and curiosity
03:24 Triffid_Hunter and I think if you put a 100N force on anything with a 25mm mounting plate it wouldn't last long unless it was rather expensive
03:24 Triffid_Hunter now once you start getting towards nema17 (42mm) / nema23 (~60mm) territory you'll be fine
03:25 Burninate much appreciated
03:26 Burninate Would you like a peek at the actual project?
03:26 Burninate Telescope mirrors are traditionally mounted on whiffletrees, a recursive set of levers that balances out the forces and prevents any one support point from supporting too much of the weight
03:27 Triffid_Hunter Burninate: ah, like windscreen wipers on cars?
03:27 Burninate Something like that
03:27 Burninate https://www.google.com/search?q=whiffletree%20mirror%20cell&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=APcPT9WPGofg0QGd87WMAw&biw=967&bih=577&sei=BPcPT62uFMyx0QH-j-DPAw
03:28 Burninate They use arrangements of triangle levers, but the principle is the same as the device that was invented to balance workhorses
03:28 Burninate Now, telescope price is about proportional to the weight of the primary mirror
03:29 Burninate so the temptation is to use very thin mirrors
03:29 Burninate The problem is, a telescope mirror needs a *VERY* exactly figure
03:29 Burninate standard specification is 1/4 wave, or about 100 nanometers
03:29 Triffid_Hunter yep so your thin mirrors bend too much
03:29 Burninate RMS peak to valley
03:29 Burninate yeah
03:30 Burninate they also bend differentially, exhibiting astigmatism, when the mirror is pointed at anything other than zenith
03:30 Burninate it's also very difficult to figure them accurately, given how floppy the glass is
03:31 Burninate we can smooth them out well, but the overall shape of the surface varies according to the supporting system
03:31 Triffid_Hunter so would be useful to set them in something very light but also fairly stiff?
03:31 Burninate not just stiff, but reasonably balanced. It's very difficult to move anything with 100 nanometer precision
03:32 Burninate it begins to take engineering-grade gear
03:32 Burninate My idea was what if we just used the existing whiffletree, and added tension
03:33 Burninate Active optics is where you actively control the shape of the mirror as it changes in response to orientation and support, but not fast enough to compensate for atmospheric distortion (100hz)
03:34 Burninate Most of the weight could be supported on the existing structure, and some tension would be able to subtly cause bumps or valleys to appear in the mirror surface
03:34 Burninate existing whiffletree on top, my design on bottom: http://i39.tinypic.com/2po730x.gif
03:34 Burninate cheap / simple / lightweight is the goal
03:35 Triffid_Hunter ah neat
03:35 Triffid_Hunter well I would check out hobby servos if I were you. they probably won't give you quite 100N but should certainly give enough force to check the validity of your hypothesis
03:36 Burninate thanks
03:36 Triffid_Hunter esp if you use a slightly stretchy cord so their coarse positioning and dead zone aren't much of an issue
03:36 Burninate yeah
03:36 Burninate I do need decent resolution
03:36 Burninate but the amount of play necessary to achieve the force, and the spring constant of the wires, is up in the air
03:37 Triffid_Hunter Burninate: geared steppers then, and for 100N you'll need about 3kg.cm of torque assuming a 5mm diameter shaft
03:38 Triffid_Hunter and you'll need to work out a feedback scheme so you know what tension you've achieved
03:38 Burninate the eventual control loop will involve an interferometer / wavefront sensor measuring the telescope surface
03:38 Burninate but tension...
03:39 Burninate I do need to know when I've 'bottomed out' my actuator control
03:39 Burninate whether that is determined by maximum torque or the wire snapping
03:40 Burninate just for safety purposes
03:41 Burninate is there a compact version of the newton tension scales we used back in school?
03:42 Burninate (an electronic version)
03:42 Triffid_Hunter no idea, I'd hook up a guitar pickup, ping the wire and see what frequency it resonates at, I really like your idea there
03:43 Burninate thanks, that may be practical after all :)
03:43 Burninate any idea how to ping the wire automatically?
03:43 Triffid_Hunter Burninate: yeah fire a voltage pulse into the pickup coil!
03:45 rninate reads up on gui
09:06 rue_house I need a name for a library that has delay and tone functions
09:06 rue_house I'd call it time, but I dont want to imply keeping real time
09:39 dunz0r rue_house: Tonetime?
16:57 zhanx_ we got snow
20:37 rue_shop hmm
20:42 rue_house zhanx, break a leg
20:42 rue_house no! wait! dont!
21:22 rue_house DETALE: nao eh 100% garantido pois count+size_send pode estorar 255 e ficar < MS */
21:23 katsmeow no
21:23 rue_house I think it says to be carefull cause there is no garuntee about something
21:23 rue_house maybe be about buffer rollover
21:25 katsmeow it's portugese, i duno
21:25 rue_house oh
21:25 rue_house I thought it was spanish
21:27 rue_house teclado.c
21:27 rue_house wonder what that is
21:28 katsmeow i shult my brian of erlyer to tak two centurytel, sory
21:28 rue_house Converte um dado lido do teclado para o char hexadecimal correspondente
21:29 rue_house convert
21:29 rue_house data lid to technical paramiter of character hexidecimal
21:29 rue_house I think it converts something to hex
21:37 katsmeow i dunno at thins time, sorry
21:38 katsmeow remembering why i got confused as heck for years at some 1950's country song , the woman singing she was going to meet her bf at the alter, and i never could figure what was being altered
21:39 rue_house the rest of her life
21:39 katsmeow i guess
21:39 rue_house I'v been thinking about it, and I honestly cant think of ONE thing the female benifits from by having an offspring
21:40 katsmeow but since she was obviously saying "alter" on purpose, what was her intent in misleading me?
21:41 katsmeow there's a few benefits, altho several of which involve believing in fairey tales
21:41 rue_house mhm
21:41 rue_house being able to read the exhausst temp of the boiler is great
21:41 rue_house I can tell how the fire is doing
21:42 katsmeow "grab your partner" ... "no no, by the hand, grab their hand"
21:42 rue_house tee hee hee
21:43 rue_house modulation of the blower mnotors isn't going well, I need to change the voltage steps for the motors I'm using
21:43 katsmeow dc motors?
21:43 Tom_itx rue_house did you fix that blown out motor? or was it determined it was ok
21:44 katsmeow it was ok as a properly burned up motor, but not as a functional motor
21:46 rue_house it wasn't ok when I was done with it
21:47 rue_house between the sawsall, the angle grinder, and the hammer it came out a little damaged
21:47 rue_house the important bit that it came out
21:48 katsmeow cause it's odd it did not take the sawsall, the angle grinder, and the hammer to install it
21:49 rue_house the tools were required to get around the grub screw that was frozen in
21:49 rue_house after drilling a 3/8" hole thru the shaft, the grub screw just kinda let go
21:50 rue_house GetExh
21:50 rue_house ExhaustTemp 112.7
21:50 rue_house over 100 is good
21:51 katsmeow shame you cannot get that 112c intothe house where you need the warmth
21:51 rue_house yea
21:51 rue_house air/air would be awesome
21:51 katsmeow ruefing tin?
21:52 rue_house about $8/sq foot
21:52 katsmeow nono, like flashing, or 5v or corregated
21:52 katsmeow 29awg
21:52 katsmeow galvanised
21:52 rue_house yea
21:52 rue_house the corrigated might be cheaper didnt check that
21:53 katsmeow it's < $10 for 8ftx2ft here
21:53 rue_house a 3' section of 5" duct is about $20
21:53 katsmeow sheesh, they don't want you to improve anything, do thay?
21:53 rue_house thats why I'm havin trouble with the sheetmetal stuffs
21:54 rue_house hwt cases are pretty attractive
21:54 rue_house nice flat metal with only 2 holes
21:54 katsmeow be cheaper to drive down to usa one day to raid a homedepot or Lowes or soemthing
21:54 rue_house prolly
21:54 rue_house maybe somewhere in florida
21:55 rue_house I know a place I might be able to crash for the night
21:55 katsmeow no, Fla is high on some stuff too, and they won't let scrap yards here sell tome either
21:55 rue_house so start a scrap yard
21:55 rue_house offer people a better deal
21:55 rue_house take what you want
21:56 katsmeow it's a dirty business, and the county would crack down on me eventually too
21:56 katsmeow my shoulders and back are messed up, my legs are not good, i couldn't do it as a full time business
21:57 katsmeow there is a guy down the road that parks his scrap trailer where i can get at it, i gave him $10 for the aluminum frame of a bimini boat topper
21:58 katsmeow he has two nukeboxes in it, but a) i am full up on big transformers to rewind, and 2) he prollay wants money for them
21:59 katsmeow has a dead clothes washer in it too, i wonder if i need a open frame motor
22:21 katsmeow <song lyrics> you had those big green eyes ...
22:21 katsmeow <me> wait, what? "had" ??
22:24 Tom_itx katsmeow
22:24 Tom_itx did you move?
22:24 Tom_itx are you moving?
22:24 Tom_itx where are you?
22:24 katsmeow Tom, why do you ask me that same question every day?
22:25 tsmeow looks clue
22:25 Tom_itx didn't realize i asked that and got any reply
22:25 katsmeow i answered yesterday or the day before, i forget
22:25 Tom_itx guess i missed it then
22:25 katsmeow i am in process of moving, i am waiting on the barn to get built, to put things into
22:26 katsmeow only this week could i start getting mail here
22:26 Tom_itx you're moving into a barn?
22:26 katsmeow i did not count myself as one of the things i am moving
22:27 rue_house katsmeow, "do what your best, hire the rest"
22:27 rue_house they wouldn't be in scrap metal if it didn't make money
22:28 katsmeow hire with what money?
22:28 rue_house wel l you havce to get creative on that one till your started
22:28 rue_house starting a business is like starting a fire
22:28 rue_house paper, kindling
22:29 rue_house ..
22:49 tsmeow always thought "one way ==>" signs were just the gov wasting money, as turning either way at the intersection is obv
22:53 katsmeow i have always wanted to put up another sign giving equal time to the other way
22:54 katsmeow one way ==>
22:54 katsmeow <== the other way
22:59 katsmeow <song lyrics> "your lips, your eyes, your cheeks, you have two of each"
23:16 rue_house 'scarry ned had arms on his head, but they weren't his..."
23:17 katsmeow "the cop put his hands on the prisoner's shoulders, because the cop was also a part time surgeon"
23:17 rue_house http://www.lyricsbox.com/arrogant-worms-lyrics-scary-ned-pbfxr44.html
23:20 katsmeow i was done reading it with wget and textpad before I even showed the page
23:20 katsmeow err
23:20 katsmeow i was done reading it with wget and textpad before IE even showed the page
23:20 rue_house I tried to find one with the least flash/javascript
23:23 tsmeow
23:24 katsmeow there's some sites it's just best to visit with an url miner first, and put every offsite url in the hosts file, redirected to the neutral zone
23:25 katsmeow sadly, some sites are using https, which doesn't help, you haveto proxy the internet and re-write the page before the browser sees it, deleting the offsites
23:26 katsmeow which i do too, but it's still a pain
23:34 katsmeow Researchers have successfully stored a single data bit in only 12 atoms.
23:34 katsmeow Currently it takes about a million atoms to store a bit on a modern hard-disk, the researchers from IBM say.
23:39 katsmeow Web addicts have brain changes similar to those hooked on drugs or alcohol, preliminary research suggests.
23:40 tsmeow puts down her joint and martini to write a long diatribe in pro
23:42 zhanx__ web connection sucks
23:42 zhanx__ and kat make sure you use a feather pen to write that
23:44 tsmeow gets onto her highest horse, grabs a quill pen, and tilts at the windm
23:45 zhanx__ careful now thats a high horse
23:46 tsmeow has a safety har
23:47 katsmeow overhead bridge cranes are sooooo wonderful
23:49 zhanx__ i needs one
23:53 katsmeow i should goto bed
23:53 zhanx__ sleep is good, on duty so none for me tonight
23:54 katsmeow going to draw dirty pics of your spider-ess?
23:55 zhanx__ no my laptop is in my room and its still icy and snowing out with my knee i am not risking it
23:55 katsmeow i was on phone the other day, and he asked why i was moaning and groaning, i said i was crawling around under Tiggr
23:55 katsmeow he said that was too much info and didn't wanna know, i said it wasn't dirty this time, i was just pluggin in cables, etc
23:56 zhanx__ lol
23:57 katsmeow i often refer to schematics as dirty pics, just because of the pencil/pen graphite/ink stains on hands and bits of eraser all over
23:57 zhanx__ thats the old school way
23:58 katsmeow and oftent he fastest to prototype
23:58 katsmeow remember, iw as schematicing decades ago, well before a home puter could have enough ram to hold a decent app or a schematic
23:58 zhanx__ true
23:58 zhanx__ i use a dry erase board
23:59 katsmeow dry erase tends to get accidently erased
23:59 zhanx__ yep
23:59 katsmeow i use different color pens, and once sure of a line, i ink it in the same color