#robotics Logs

Feb 04 2013

03:52 Tom_itx nope
04:00 Rif seems to be a linrary issue maybe, but need to fix it
04:00 moriarty linrary?
04:00 Rif yes a library :/
04:01 moriarty lol
04:02 Rif look its the way i can get stuff done for now, i'll learn in time
04:03 Rif have put 3 standard servos in base now and the whole arm is better
04:03 Rif and works wicked as a hanging arm
04:04 Rif moriarty have you heard of webbotlibs for avr?
04:05 moriarty Rif, nope whaddat?
04:06 Rif its pretty cool dude, allows you to setup the hardware part easy and focus on doing other stuff
04:06 Rif this is the only help i have http://webbot.org.uk/WebbotLibDocs/object.jsp?id=41437
04:08 moriarty haha nice, i remember making my own hardware out of polyutherane boards etc
04:09 Rif it says to add this line G8_RUNNER gait = MAKE_G8_RUNNER(all,animations); if i add it as G8_RUNNER gait = MAKE_G8_RUNNER(all, 0); as i readthe instructions to say it compiles but nothing happens, if left at G8_RUNNER gait = MAKE_G8_RUNNER(all,animations); won't compile with above error
04:09 Rif moriarty did you see me arm?
04:09 moriarty Rif, nice arm
04:10 Rif its better now with stronger servos, but must make it work detached from pc
04:11 Rif can reach anywhere in about a 500mm radius
04:11 moriarty sweet deal
04:11 moriarty what are you building it for?
04:11 Rif cause i want to make a big full size arm
04:11 Rif and need to learn
04:11 moriarty ah
04:12 Rif the first arm was to prove that micro servos could do the load
04:12 Rif but while i have not burnt one out they get rather hot
04:13 Rif hence replacing 3 of them
04:13 Rif want to use more powerful dc geared motors with encoders for the bigger version
07:19 MrTrick Rif: have any pictures?
07:34 MrTrick I built two servo-based robot arms, but I'm finding them too inaccurate... so I'm looking at geared steppers.
08:05 Triffid_Hunter MrTrick: you want to ditch the servo's feedback loop and implement a better one.. that or use a digital servo
08:05 MrTrick I did use digital servos.
08:05 Triffid_Hunter MrTrick: one technique that's popular is to pull the feedback pot out of the servo and fix it to the arm itself
08:06 Triffid_Hunter if the joint has a limited range of motion, try to organise the linkages so that the pot still sees full travel, that'll improve the precision
08:07 Triffid_Hunter also, most servos are optimised for R/C usage where a wide dead zone and loose tolerances are acceptable
08:07 MrTrick Thanks Triffid_Hunter
08:07 Triffid_Hunter there's a reason you can get servos from hobbyking for $10, yet folk still pay the $200 or so for dynamixel and similar servos designed for robotics
08:07 MrTrick The three insurmountable issues I had were; backlash. non-linearity of the positioning, and SPEED - the things were too damn fast.
08:08 MrTrick even the mega expensive dynamixel servos are tough to make do what is a stepper's bread-and-butter; At t0, be at x,y. At t1, be at x2,y2.
08:11 Triffid_Hunter pretty sure the mega expensive dynamixel servos have no trouble with that stuff at all as long as you operate within their ratings
08:12 MrTrick not synchronising.
08:12 Triffid_Hunter no way you can do a decent walking gait without that stuff being very solidly sorted
08:12 MrTrick You can specify max speed...
08:12 MrTrick but then you've got to figure that all out in your controller, and configure the servo before each movement.
08:13 MrTrick I've been in communication with robotis about this. ;-)
12:55 NightRavenXS guys, anyone worked with Pandaboard
12:55 NightRavenXS ?
12:55 NightRavenXS what power source does it require?
13:13 Rif MrTrick pictures of the arm? http://imagebin.org/245098 http://imagebin.org/245167
13:14 Rif have upgraded servos as required, the bottom 3 are now standard size and was able to give the arm longer reach with the bigger servos
14:21 Rif //boolean gaitRunnerIsPlaying(const G8_RUNNER* runner)
14:21 Rif //Return TRUE if an animation is still playing or FALSE if it has stopped.
14:21 Rif if (gaitRunnerIsPlaying(const G8_RUNNER* runner = FALSE))
14:22 Rif please how would i write the if statement properly
15:20 Tom_itx if (gaitRunnerIsPlaying(const G8_RUNNER* runner = FALSE)1,0)
15:20 Tom_itx something like that
15:20 Tom_itx check immediate if
15:20 Tom_itx syntax
15:21 Tom_itx RifRaf
15:22 Tom_itx if (gaitRunnerIsPlaying(const G8_RUNNER* runner = FALSE))
15:22 Tom_itx {return 1}
15:22 Tom_itx else
15:22 Tom_itx {return 0}
15:22 Tom_itx or something like that
15:55 RifRaf Tom_itx thanks, will try when i get home, so frustated at wasying a night
15:56 RifRaf wasting*, am gonna give up robots and study c++ for a week, can someone please recommend a giude or book that will help me with acvr
15:56 RifRaf avr and c++ *
16:08 MrTrick RifRaf: looks good!
16:08 MrTrick Your own desing?
16:12 MrTrick How much strain is there on the elbow servo? Have you considered a counter-spring? (Kind of hard to see, but like http://www.robotshop.com/Images/xbig/en/lynxmotion-al5a-4-degrees-freedom-robotic-arm-combo-kit-B.jpg )
16:17 RifRaf MrTrick yes all my design, have changed a few servos, is stronger and more balanced now
16:17 RifRaf and still redesigning each day
16:18 RifRaf till i get the lightest but strong enough arm
16:22 GargantuaSauce http://www.youtube.com/watch?v=1HPVbuaONO4
16:22 GargantuaSauce finished my terrible servo controller
16:43 MrTrick GargantuaSauce: looks nifty! What's so terrible? Or Terrible like T-rex?
16:43 RifRaf GargantuaSauce looks great, well done
16:44 GargantuaSauce well the software driving it is kind of awful, and i should have added a slave avr or something instead of just driving it with spi
16:45 GargantuaSauce but whatever it gets the job done i guess
17:14 MrTrick GargantuaSauce: With the pulses that get sent out - does every channel's pulse start at the same time?
17:15 GargantuaSauce yes
17:15 MrTrick ah, excellent.
17:16 MrTrick I was getting rather irritated at the micro maestro servo controller, because it'd stagger the channels over the time domain. (Which if you wanted multiple servos to move together was very irritating!)
17:18 GargantuaSauce i almost bought something along those lines to save me the trouble
17:19 GargantuaSauce but i suspect they are all similarly terrible
17:21 MrTrick A fun thing I realised the other day; A decent servo has specs like 0.10 seconds / 60 degrees.
17:22 GargantuaSauce i think those specs are a little misleading
17:22 MrTrick And the standard servo pulse rate is 20 ms. So it can have moved TWELVE degrees by the time you send the next position.
17:23 MrTrick Depends on the servo. I bought two of these: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=13809 and they're blindingly quick!
17:23 GargantuaSauce oh yeah ok, REAL servos are less overblown like that
17:23 GargantuaSauce i am using chinese knockoff-of-knockoffs and they are uh
17:23 GargantuaSauce not the best
17:23 MrTrick The shoulder servo will move my robot arm through ~180deg in less than a second.
17:24 MrTrick sure.
17:25 GargantuaSauce but at <$6 each i can hardly complain
17:26 GargantuaSauce they're allegedly .13s/60deg
17:26 GargantuaSauce mmm maybe that's not too far off, there's a little discontinuity in the sequence i'm running them through now and they jerk over pretty damn fast
17:27 GargantuaSauce but the 12kg/cm is definitely bullshit
17:28 MrTrick It also depends whether they're analog or digital.
17:28 MrTrick Typically analog servos just have a proportional response - apply a voltage proportional to the error.
17:28 MrTrick Which has to be dialled low, so as to avoid jittering too much.
17:29 MrTrick So for small distances, they don't have a lot of torque.
17:29 GargantuaSauce ah that explains a bit
17:30 GargantuaSauce i was originally planning on using analogue ones for the hips because they were cheaper but i've seen the error of my ways since
17:30 GargantuaSauce gonna be straight mg996r's as soon as the new ones arrive
17:30 GargantuaSauce the digital ones tolerate faster pulse repetition without freaking the hell out too
17:31 MrTrick yes, I tried running my digital servos on 8ms-spaced pulses.
17:32 MrTrick Unfortunately, I think I killed an analog micro servo.
17:32 MrTrick Is the MG996R digital, though?
17:32 GargantuaSauce allegedly
17:33 GargantuaSauce it at least performs much more sensibly than the mg995 and i think they share motors and drive trains
17:34 MrTrick hmm, there's nothing on the page to suggest it.
17:34 MrTrick Digital servo search results: http://tinyurl.com/a8ptgb8
17:34 RifRaf got a few of those mg996 last night
17:38 GargantuaSauce http://www.hobbyking.com/hobbyking/store/__6221__Towerpro_MG996R_10kg_Servo_55g_10kg_20sec.html
17:38 GargantuaSauce bit of contention in the comments as to whether they are or not
17:38 GargantuaSauce i dunno i'll tear one apart eventually
17:44 MrTrick I wish openservo would actually sell servos.
17:45 GargantuaSauce ya i'd love actual digitally controlled servos for a non-ridiculous price
17:46 GargantuaSauce digitally controlled and with position feedback
17:46 GargantuaSauce now THAT i'd tolerate the i2c bus for
17:51 MrTrick Do hobbyking have any servos that aren't POT-based? Like a rotary or magnetic encoder?
17:53 GargantuaSauce well constant-rotation ones definitely must be
17:53 GargantuaSauce and perhaps the wide range ones used for sail pulleys and that sort of thing
17:54 MrTrick ah, this one does; http://www.hobbyking.com/hobbyking/store/__14832__Mi_Digital_High_Torque_Metal_Gear_Servo_JR_Hitec_11_8kg_0_07_61g.html
18:29 MrTrick I wonder... in designing for manufacturability, you tend not to use 3d-printed parts because they take a comparatively long time to fabricate.
18:30 MrTrick However, if you're manufacturing 3d printers - why not have the burn-in test be to build a set of printer parts?
18:30 GargantuaSauce you just invented the reprap project
18:31 MrTrick Well yeah I know - I was thinking more for the companies that ship assembled printers..
18:36 Tom_itx RifRaf, i learned by looking at others' code
18:37 Tom_itx i'd suggest reading all Dean's articles off my main menu: http://tom-itx.dyndns.org:81/~webpage/abcminiuser/articles/avr_timers_index.php
18:37 Tom_itx he's got code snips etc for avr
18:39 Tom_itx http://www.lysator.liu.se/c/bwk-tutor.html
18:39 Tom_itx more general c tutorial
18:39 Tom_itx http://www.physics.drexel.edu/courses/Comp_Phys/General/C_basics/c_tutorial.html
18:39 Tom_itx and another one
19:57 RifRaf Tom_itx the problem is i cannot find any code, seems like not too many opeople are using it yet
19:57 RifRaf all examples online are there due to an issue with code
20:06 GargantuaSauce learn the fundaments
20:07 GargantuaSauce and start with c not c++
20:12 RifRaf GargantuaSauce ok then, what is the best place to learn?
20:12 RifRaf will try for a week rather than make stuff
20:14 Tom_itx what code are you looking for?
20:15 GargantuaSauce take a look at The C Programming Language, Kernighan & Ritchie
20:15 GargantuaSauce there are more pragmatic ways to learn but i firmly believe you need a strong handle on the basics to get anywhere
20:16 Tom_itx i'd bet nearly every c programmer has that book
20:26 GargantuaSauce also in my experience things like web tutorials are often counterproductive
20:26 DagoRed That's like... the only good book for C.
20:32 RifRaf ok will get a copy and start with some basics
20:32 rue_house RifRaf, you want to do some C now?
20:32 DagoRed C is fun!
20:32 RifRaf am at work on lunch, no time
20:32 rue_house ok
20:32 DagoRed RifRaf, I think I have a copy if you want it.
20:32 RifRaf 3.5hours rue?
20:32 goRed e-books are
20:33 rue_house nope, I'm to bed at 9:45
20:33 rue_house !time
20:33 tobbor My watch says its 06:25PM Mon Feb 04 2013
20:33 RifRaf DagoRed ok will try find first
20:34 RifRaf got the attention of the dude that wrote webbotlibs, so hopefully will get these issues ironed out soon
20:36 DagoRed yay!
22:55 rue_house which issues?
22:56 theBear think there was a compile error errm, section type conflict caused by <libname>
22:58 home hey guys
22:58 home hey rue_house ..
22:58 home I actually am starting to get some tool skills :/
22:58 RifRaf yep thanks theBear, on 45min of work left
22:59 RifRaf only*
22:59 theBear heh, i'm an experienced tool by this stage in life <grin> i even got a shirt, got a stick figure holding a spanner up and big TOOL underneath :)
23:00 home cool
23:00 home I still don;t know how to use a lathe though..
23:00 home and a bunch of other things XD
23:02 theBear i'm pretty good with a woodlathe these days, i THINK i could still use a metal one 'manually', probly take a bunch of looking and headscratching to do threads or that kinda thing... i'd hope you can still see enough on a modern one to 'work it out' visually :)
23:02 theBear i haven't done stuff like that since i was 'a kid'
23:07 home I never did
23:07 home lucky you XD
23:12 rue_house home, cool
23:43 RifRaf ok time to go home and learn C