#robotics Logs

Mar 24 2013

00:14 dioxide if i wanted to turn a fingerprint into a hash, would i use opencv?
00:14 dioxide a picture of a fingerprint
00:15 dioxide ive been trying to find a starting point for fingerprint recognition for 6 months and i keep coming up empty
00:40 Jak_o_Shadows That steriotypic image of an ultrasonic sensor, with the two round black things, is that stereo? If so, can I get a measurement from one side and one from the other?
00:41 RifRaf no
00:41 Jak_o_Shadows is one the reciever and the other the tranceisever?
00:41 RifRaf one side pings and one side recieves the echo
00:42 RifRaf but you can easily use 2 units for what you want
00:42 Jak_o_Shadows That's what I thought. So i'll have to do some maths and stuff to detect a straight edge, If i put it at an angle
00:54 Triffid_Hunter Jak_o_Shadows: yep. if you want to have multiple sensors firing at the same time you have to be careful of echos. http://www-personal.umich.edu/~johannb/eeruf.htm discusses a method to do it sensibly
00:55 Triffid_Hunter basically it uses statistical analysis to sort out each sensors own ping replies vs other sensors by randomising the firing pattern
00:56 Triffid_Hunter for detecting lines, I vaguely recall RANSAC being an algorithm to use.. it might be for detecting planes in 3d but should work with lines in 2d as well I think
01:01 Jak_o_Shadows Normally i'd just drive over the edge with the sensor pointing straight down, but I can't do that in this case.
01:49 BlueTree Is there a channel for discussing servo motors or is it this one?
01:56 Jak_o_Shadows this might do I suppose
02:01 BlueTree I'm trying to look for cheap 27kg*cm^3 torque servo motors, a lot of the websites have lots of servos and no way to sort them by specifications, what are your websites you buy from?
02:02 Jak_o_Shadows I've only bought stuff (not servos) from ebay, but surely some of the big hobby stores would let you?
02:03 BlueTree they sort by price and name :(
02:04 BlueTree there's a lot of <1kg*cm^3 servos
02:05 BlueTree This seems to be unusually cheap with high torque, I can't find it any other website except manufacter's: http://www.hobbyking.com/hobbyking/store/__18742__Vigor_VSD_11AYMB_MG_HV_Extra_Large_360_Degree_Winch_Servo_0_75sec_50kg_150g.html
02:05 Hukka Er, what is kg*cm^3?
02:05 BlueTree Is there a catch with this?
02:05 BlueTree It's stall torque
02:05 BlueTree there's oz*in^3
02:06 Hukka Where do you get that ^3?
02:06 BlueTree The equivalent of 27kg*cm^3 is 380oz*cm^3 I think
02:06 BlueTree not sure, it's the length?
02:07 Hukka cm^3 is a unit of volume...
02:07 Hukka Perhaps you just meant 27kg*cm
02:08 Hukka Anyway, if you really need to lift 27kg in a distance of one cm, you need more
02:09 Hukka The stall torques are often inflated numbers, and more so it's truly the stall torque; the servo cannot move at all with that load
02:10 BlueTree Yes, the minimum torque I wanted is 13, so I think 27 is a good limit
02:12 Hukka I was going to recommend Pololu's website, as they have a real good interface. You can sort by different values etc.
02:12 Hukka But it doesn't make much sense to order stuff from the states to China...
02:12 Hukka Of course that's assuming I'm getting your ip right
02:13 BlueTree Australia, actually
02:13 Hukka Oh, that's weird then
02:21 summersault is there any application of geometric calculus and geometric algebra in robotics?
02:22 RifRaf pretty sure there is
02:22 summersault is that application important?
02:23 summersault i am looking for real math background because hamiltonian math is painfull
02:23 RifRaf for control theory and such applications yes
02:23 summersault RifRaf, do you recommend any book?
02:23 RifRaf well you are not lookin for me
02:24 RifRaf nope i am only just starting to learn, but i will recommend some videos on the subject
02:24 summersault RifRaf, starting to learn robotics or real math?
02:25 RifRaf real math
02:25 RifRaf http://www.youtube.com/watch?v=aSwCMK96NOw
02:25 RifRaf if you follow that through it goes into the maths
02:26 RifRaf anyway, i am soo happy
02:26 RifRaf got my project ported to a mega2560, every sensor and adc working as it should, and 80% free space and lots of i/o left over
02:28 summersault i am at that course... but i am not attending to it. Have no time.
02:28 summersault What is your project about?
02:28 RifRaf colour and light sensing
02:28 summersault nice
02:28 RifRaf verses power and distance, logged to sdcard
02:29 RifRaf and can use lcd now that i have space, and rs232, this is wonderful
02:29 summersault you measure color, and light, and the distance of the lights?
02:30 RifRaf yes, and the power and voltage driving the lights
02:30 summersault nice
02:30 summersault any recommended book for the real math?
02:31 RifRaf nope, i am on C for dummies right now
02:31 RifRaf if you hang around i know there are people that could help
03:10 ocei3ko Dont read the dummies books
03:10 ocei3ko ffs
03:11 RifRaf well it was in hard copy, so was easy to lay down and read
03:12 RifRaf have been mainly getting this new mega2560 working, and very happy with it
03:29 Hukka summersault: Perhaps "Fetter-Walecka: Theoretical Mechanics of Particles and Continua" would be what you are looking for
03:29 Hukka But I haven't compared it to other works about continuum mechanics
04:16 summersault Hukka, is that a good book?
04:17 summersault Hukka, do you think is useful to learn that kind of math for robotics?
09:12 gmag Hi, any idea why they (the seller) states that an external impedance is needed? http://tinyurl.com/c6f3tnf This is what he says exacly: "Need external inductance only in antenna matching place"
09:12 gmag this one http://tinyurl.com/cytwwq3 does not mention anything about needing an inductance
09:12 gmag but the first one is cheaper
09:12 gmag Im not sure if I should be concerned about that. I think I should be able to plug and play
09:12 gmag right?
09:12 gmag I mean no need for external components I would assume
09:12 Triffid_Hunter gmag: heh it's hard to derive exactly what they mean from that engrish
09:12 gmag hehe :)
09:13 gmag chinenglish
09:13 gmag Triffid_Hunter, I assume you never used one of those
09:14 gmag those seem a very nice solution for simple short range/bandwidth wireless applications
09:15 gmag but if I have to buy additional components (specially inductors...) I dont thing I'll give it a try
09:15 Triffid_Hunter gmag: I suspect they're trying to say you'll need an inductor if you add an external antenna so as not to upset the impedance of the onboard one
09:19 gmag Triffid_Hunter, I think you're right
09:19 gmag that makes sense
09:20 gmag I think I'll buy it
09:21 gmag :)
09:21 gmag I'm also thinking about buying a rasp-pi or a something similar. I think this one is the cheapest. Any other boards you would like to share.
10:19 ocei3ko Is it better to get a BeagleBoard than Arduino?
10:23 ocei3ko nvm
14:03 Celelibi Do you know a website where I could learn how to build the physical structure of a robot?
14:04 ace4016 you mean just the frame?
14:05 ace4016 they might have some info here: http://www.seattlerobotics.org/
14:05 ace4016 really, there's no standard way to build a robot
14:05 ace4016 not unless you're building a kit robot
14:05 Celelibi Well. I know nothing about that.
14:07 Hukka It's a problem/question that's not very well defined, so there's no single or easy answer
14:07 ace4016 robots will closely resemble machine creating as they have moveable parts and such that have certain dynamic stress requirements
14:08 Hukka Rover, walker? 4wd, 2wd? Big, small? etc etc
14:08 ace4016 so you won't build them like you build houses...
14:08 Celelibi I can build complex software architecture, but I've never done anything about something beeing physical. :)
14:08 ace4016 Celelibi, best I can tell you is to experiment
14:08 ace4016 and be creative
14:08 ace4016 being creative means you can use cheaper material :P
14:08 Celelibi ok :)
14:09 Hukka I'd say that you first get an idea, hopefully a pretty detailed one, about what you want, and then just start doing it. And getting information how to do it
14:10 ace4016 instead of having parts welded and machined, you can just get some PVC or some light flexible wood and build main structures out of that. robots don't have standard parts, so a guide to robot building will be limited in its usefulness
14:10 ace4016 it's like asking the question: how do I build a vehicle
14:11 ace4016 land based? air based? water (under or on top)? space based? what does it do? how much weight should it carry? etc. etc.
14:14 RifRaf this might be a start also http://www.societyofrobots.com/step_by_step_robot.shtml
14:25 Celelibi well, my robot won't really have dynamic stress. I (still) plan to build an inverted pendulum.
14:25 Celelibi 2 wheels.
14:25 Celelibi It basically just have to handle its own mass.
14:27 Hukka For that you could use Lego :)
14:28 Celelibi I know. :)
14:28 Celelibi I've seen a couple of lego robots like this.
14:28 Hukka Would you like me to paste a link to a website that has instructions for that, then :?
14:29 Celelibi Well, I'm not interested in doing the same robot as someone else. ^^
14:29 Celelibi I would like to use free parts mostly.
14:29 Hukka No such thing as free
14:29 Celelibi I mean, free as in freedom.
14:29 Hukka But if you have a cache of some material, sure, use that
14:30 Celelibi Opensource and stuff.
14:30 Hukka Well, for an inverted pendulum you only need to saw a few pieces of wood
14:30 Celelibi Like, using an arduino for the controlling part.
14:31 Hukka Unless you have access to a laser cutter or 3d-printer, then plastic probably isn't worth the trouble at this point
14:31 Celelibi I have access to a 3D printer.
14:31 Hukka Arduino, or launchpad, or stamp or something like that
14:31 Celelibi Not a very precise one.
14:31 Hukka Arduino would be actually pretty big for an inverted pendulum
14:32 Celelibi The fablab in my town is not open yet, then no laser cutter currently.
14:33 Hukka If you have an easy supply of aluminum, you could just cut and drill that too
14:33 Hukka Learning to weld would be a bit extreme at this point
14:45 rue_house oo who's making a balancing robot!?
14:45 Celelibi Almost everyone ? :p
14:45 rue_house you making one?
14:46 Hukka I'm making one as soon as I get a robot
14:46 Hukka I'm thinking tomorrow
14:46 rue_house oh
14:46 rue_house whats the robot?
14:46 rue_house eeek, lunchtime
14:46 Hukka Tomorrow I'm getting a robobuilder
14:46 Celelibi rue_house: I'm planning to make one, yes.
14:46 Hukka And sometime later a bioloid, but it hasn't been even shipped yet (my friend who has it is sick)
15:19 RifRaf hrm i have a platform i want to make balancing as well, ima join the club
15:20 RifRaf got buttons working this morn, can change modes and variables :)
15:30 DagoRed what are you making now RifRaf?
17:24 dryc-x Hi
17:24 dryc-x Any humans/robots in here?
17:30 dryc-x ??
17:32 dryc-x Any active Robotics channel?
17:35 RifRaf make it active, make something
17:36 yahweh I'm in here
17:38 dryc-x Hi
17:38 dryc-x Finally a living human here :)
17:39 dryc-x I like robotics but I don't know how to improve my humble skills
17:50 dryc-x Let's all sleep in this channel!
18:04 dryc-x <b> This should be bold </b>
18:05 yahweh Sorry, I'm not human.
18:05 yahweh I'm something much worse.
18:07 RifRaf dryc-x wat have you made so far?
18:09 dryc-x A simple stupid floor cleaner
18:21 dryc-x Tha't all I could make, a floor sweeper robot
19:44 RifRaf http://www.societyofrobots.com/member_tutorials/node/185
19:46 rue_more ok I got a few more printers stripped donw
19:46 rue_more only 3 more of the large lasers to do
19:46 orlok eurgh.. nothing quite like waking up to vomit stained blankie twice in a row.. poor bub
19:47 orlok though she seems ok, and she didnt start crying during the night
19:47 orlok i still have a laser and two inkjets to strip down
19:59 summersault is anyone alive here?
19:59 ace4016 yup
20:00 rue_more mmm
20:00 rue_more ...brains....
20:11 summersault anyone of the alives, knows what is the most important topic of advanced math for building robots?
20:12 rue_more well, lots of people dont know how to work out motor torque for makeing a robot of Xkg drive forward
20:12 rue_more so I choose that
20:13 summersault you mean brushless motor controller?
20:14 rue_more there are lots of 3d forward and reverse kinematic stuff, and lots of algorythms for working out vision etc, but knowing how to size a motor to make a wheeled robot drive seems to be the most frequent question
20:15 summersault but about forward and inverse kinematics, what book do you recommend?
20:15 rue_more knowing simple trig
20:16 rue_more know how to calculate the distance between two 3d point
20:16 rue_more s
20:17 rue_more and know how to work out the angle required to make the endpoints of segments on a common elbow a set distance apart
20:17 rue_more V
20:17 rue_more >V<---d
20:17 rue_more >v<---d
20:17 rue_more ^ theta
20:20 ace4016 summersault, control theory (which involves linear algebra, trigonometry, anaylitcal geometry and calculus), basic mechanics (algebra, geometry, trigonometry, calculus), statics and dynamics (more of the same math), etc,
20:21 ace4016 books...i can't recommend too many
20:21 ace4016 also, depending on the robot, there are other specific topics to know
20:21 ace4016 it's a pretty open ended field :P
21:05 RifRaf how are the balancing robots going?
22:28 rue_more ok I stripped down another printer,
22:28 rue_more I'm eating and going to bed
22:28 rue_more ... kitty litter too
22:34 MrCurious man i love stripping printers
22:34 rue_more I should unleash you on my pile
22:35 MrCurious pro note. if they are ink jet, do it outside unless you are into psychodelic carpet
22:35 rue_more I'm trying to recover my deck
22:35 MrCurious i love harvesting linear rods, bearings steppers belts encoders, ...
22:35 rue_more yea, and for lasers, carefully remove and bag the toner cart. first
22:35 MrCurious yeah, my hobby room (a bedroom) has a desk and is so full you may enter and sit, and thats all
22:36 rue_more you want to balance the stuff yo uhave with the room you have to work
22:36 MrCurious i have synthetic blood on my walls from a full red tube in a ink jet
22:36 rue_more never save anything for a 'special project'
22:36 MrCurious hard lesson. that ink seems permenent
22:36 MrCurious nope
22:36 rue_more I have to make supper and go to speel
22:36 MrCurious harvest it, catalog it, then pick from it for the project at hand
22:37 MrCurious later
22:37 MrCurious i did nothing but harvest a pair of laptop lid cameras
22:43 rue_more I'm always amazed how only 1/10 or so of things by volume are usefull parts
22:44 rue_more maybe tommroow I'll break down the server and test the lcd screens
22:44 rue_more its a 200lb server, 4 redundant power supplies, 1.2Ghz processor, 512M of ram, raid 5 arrays of 1G and 2.3G
22:45 rue_more did I mention it weighs about 200lbs?
22:45 MrCurious sounds ancient
22:45 MrCurious melt it down for gold!
22:45 rue_more maybe they used really thick steel for the case
22:45 rue_more maybe its got backup batteries in it I didn't notice...
22:46 MrCurious power supply is salvagable, fans, heat sync's numper cables, usb connectors
22:47 rue_more mosfets :)
22:48 rue_more I can rewind the cores for custom smps too
22:48 MrCurious sounds like work
22:48 MrCurious second camera soldered to a usb connector and hot glued
22:49 rue_more ... are they usb cameras!?
22:49 MrCurious yeah
22:49 MrCurious from laptop lids
22:49 rue_more 8-|
22:49 rue_more they are USB!?
22:49 MrCurious 1 is really fast and clear in good light
22:49 rue_more damn
22:50 rue_more I got rid of a few
22:50 MrCurious yes, camera's in laptops are usb
22:50 rue_more thats halarious
22:50 MrCurious they are also very tiny :D
22:51 MrCurious perfect for itty bitty raspberry pi bots
22:58 summersault ace4016, but all that you said is school level math, i am saying more advanced topics.
22:59 summersault hey i need to build an absolut encoder, any tips for diy ?
22:59 summersault or a cheap one, (probably it does not exist).
23:05 Triffid_Hunter summersault: sure, smt photodiodes and IR leds, print a greycode wheel onto a transparency with your laser printer
23:06 rue_more practical robots only need school level math
23:06 rue_more if you want to design robots that will never be made and are purely speculative, you can put any kinda math in you want
23:08 GargantuaSauce__ lol
23:14 MrCurious i prefer using a pair of magnets and 1 or 2 hall effect sensors reading a gear wheel early in teh geared motors drive
23:14 MrCurious hall effect are cheap, and not light averse
23:14 MrCurious DISCLAIMER, not saying its best, just saying what i use
23:15 Triffid_Hunter MrCurious: like the AS5040 hall-based rotary absolute encoder, or incremental encoder style?
23:15 rue_more MrCurious, could you take a pic or draw that setup?
23:15 MrCurious 785-SS411P
23:15 MrCurious Honeywell Board Mount Hall Effect
23:16 MrCurious you put a magnet facing N on one side, S on the other
23:16 MrCurious as it spins over teh sensor, it will toggle it back and fourth once per rev
23:16 MrCurious you can use 2 sensors to do quadrature encoding
23:17 MrCurious http://www.anaheimautomation.com/manuals/forms/magnetic-encoder-guide.php
23:17 MrCurious my use case is teh OWI robot arm. it has 4 gear wheels driven by a hobby motor with a worm screw
23:17 Triffid_Hunter MrCurious: ah, sounds similar. the AS5040 takes it to the next level though, gives 1024 counts per rev with both incremental quadrature and absolute output
23:17 MrCurious i broke a rare earth magnet in half, and hot glued it to a plastic gear
23:17 rue_more but your using it against a gear eh?
23:17 MrCurious yeah
23:18 MrCurious so i am catching it on the feed end of the gears, so should get 400 ticks per rev i expect
23:18 rue_more ah
23:18 Triffid_Hunter those robotis dynamixel servos use something similar to the AS5040 with a cortex-m0 micro to drive the motor
23:18 rue_more the halls from fans are nice, they latch
23:18 MrCurious only have one fitted, and i have only tested it pulses. havent tested accuracy yet or ticks per rev
23:18 MrCurious rue: this one latches
23:19 MrCurious so you have to have 2 poles
23:19 MrCurious if it didnt latch, one magnet would be enough
23:19 MrCurious unless of cource i mounted the magnet on its side, so it leads with north and trails with south DOH!
23:20 MrCurious there is a nice encoder chip that listens to a magnet spinning on the axis of spin, and gives more accurate readings
23:21 MrCurious i think its this one that Triffid_Hunter mentioned http://reprap.org/wiki/Magnetic_Rotary_Encoder_1.0
23:21 MrCurious saw it for sale on boards for 10 or 20$
23:21 MrCurious was debating attaching a magnet to the motor shaft out the back side, and using it to make it possitionally accurate
23:29 rue_more aha, if you make a robot spaceship you will need rocketscience grade math
23:32 MrCurious if you make a robot space ship, learn fron nasa, and never mix unit styles (metric/english)
23:32 MrCurious whats that expression about hitting broad side of a barn
23:32 MrCurious rue_more: did you forget to sleep?
23:33 rue_more yes
23:33 Triffid_Hunter MrCurious: http://en.wikipedia.org/wiki/Barn_%28unit%29
23:33 rue_more I hav to do kitty litter
23:33 rue_more You have: 1 lightyear2
23:33 rue_more You want: barn
23:33 rue_more * 8.9505421e+59
23:34 home :o
23:34 Triffid_Hunter I love the bit where it says "eventually, the word became a standard unit in particle physics"
23:34 rue_more hh
23:34 rue_more ah
23:34 MrCurious hah! its an unit of area
23:35 Triffid_Hunter apparently 1 mm^2 = 10^22 barns
23:36 rue_more You have: 1mm2
23:36 rue_more You want: barn
23:36 rue_more * 1e+22
23:36 MrCurious i am really becoming a fan of hot glue...
23:36 rue_more he means it literally
23:36 home Eoe
23:36 home Wow
23:36 home I never knew that
23:36 rue_more blow harder, its still tackey
23:37 Triffid_Hunter MrCurious: you have no idea how awesome hot glue is until you ditch the hot glue gun and use SMD rework hot air instead
23:37 rue_more OOOOOooooooooooooooo
23:37 MrCurious hah! hot air reworking hot glue :)
23:38 Triffid_Hunter completely loses that tacky look and starts looking like it was injection molded when you get the hang of pushing it around with the jet
23:39 MrCurious i use electrical tape to damn it and confine it. then just inject, wrap, and mold
23:39 MrCurious (then swear until fingers stop hurting)
23:42 summersault MrCurious, hall sensors is more precise than light sensors right?
23:42 summersault are*
23:42 summersault omg i need to sleep
23:42 Triffid_Hunter MrCurious, rue_more: http://triffid-hunter.no-ip.info/101_0053.JPG <-- hot glue + hot air
23:42 MrCurious dont know precise is the right word
23:43 MrCurious just tolerant to light vs magnetic fields
23:43 Triffid_Hunter summersault: no, light is more precise because it's easier to constrain than magnetic fields
23:43 MrCurious you may need to shroud optical encoders in full sunlight to avoid the sun drowning it out
23:43 summersault because if i put a lot of magnets i will make a mess with the hall sensor.
23:43 orlok that does look nice!
23:43 rue_more hahah I'm not the only one to use hot glue for wire reliefs!
23:44 MrCurious nice
23:44 Triffid_Hunter rue_more: nope, it's got a great balance of flexibility and strength for that usage
23:44 summersault Triffid_Hunter, but magnet force decreases ^3 with the distance, and light will decrease ^2 , theoretically .
23:44 Triffid_Hunter summersault: sure, but it's a shitload easier to make a narrow slit with a bit of film than mumetal or similar
23:44 MrCurious address risks of envirmental light :D
23:45 summersault temperature is IR light, right?
23:46 summersault i never played with those kind of sensors... maybe i should try.
23:47 Triffid_Hunter summersault: blackbody radiation starts down at microwave levels, goes all the way up past UV.. IR is generally the most useful range for temperature sensing though
23:47 MrCurious that glue tip will be enough to make me get a hot air station within a year
23:48 Triffid_Hunter MrCurious: I paid $66 delivered for my iron + hot air smd rework station
23:48 MrCurious hmmm
23:48 MrCurious ebay?
23:49 Triffid_Hunter MrCurious: nope, sureelectronics. they had a special, friend got a bulk order
23:49 Triffid_Hunter should still be under $100 now though if they still have them
23:49 Triffid_Hunter MrCurious: http://www.sureelectronics.net/goods.php?id=1593
23:50 MrCurious i dont think my wife is going to want to be your friend Triffid_Hunter
23:51 summersault just another question, how about a absolut encoder, because in the links they seem to be only relative.
23:51 MrCurious just ordered a new toy tablet. will have to let things calm before getting this
23:51 MrCurious does what your encoding use gears?
23:52 MrCurious or is it a servo
23:52 MrCurious and what rpm range is it likely to have
23:53 Triffid_Hunter summersault: http://www.scienceprog.com/using-gray-code-for-rotary-encoders/
23:54 MrCurious with all i have spent to make a robot and learn robotics, i think it would have been cheaper to just buy a robot for 2k, and cut directly to the programming cake
23:58 summersault Triffid_Hunter, yeah graycode is the way to go, if you use just binary, you will get far ambiguous positions when reading between marks.