#robotics Logs

Apr 17 2014

00:00 orlock also, long time no see
00:10 rue_more :)
00:10 rue_more the servos center is not at 1.5ms
00:10 orlock basing it on 180deg or 90deg?
00:13 rue_more }:] I can get 180 out of these
00:13 rue_more I CAN
00:13 rue_more but the pulses run the 0.5 to 2ms
00:14 rue_more with the assumed centre at 1.5
00:14 orlock i think i did something with a compass/protractor
00:14 rue_more I wont fix it right now, the robot moves just fine
00:14 orlock yeah, you can spend a lot of time dicking around for very little gain
00:14 rue_more I have pot->pwm code that proves the range is there
00:14 rue_more I just need to adjust the numbers
00:15 rue_more tho, there are 3 different types of servos on the same robot
00:15 orlock 2ms max? not 4.5ms?
00:15 rue_more haha, yea
00:15 orlock i thought it was a 4000ms range, starting at 500 - so 500 to 4500
00:16 orlock i think i lowered my pulses until it "buzzed" against the stops, then backed off till it stopped
00:16 rue_more I can control the actual pulse width in the software level per servo , but the avr code limits it to the .5 to 2ms range
00:16 orlock set that as 0
00:16 orlock ahh
00:16 rue_more its tuning
00:17 rue_more I'm really happy to have it playing 6d points from a text file
00:17 orlock i got a rasberry pi
00:17 rue_more no comment :)
00:17 orlock heh - GF couldent think of what to get me for birthday
00:17 orlock (and she's been wanting a media player box for ages now)
00:18 orlock so she got me the rasberry pi with a set of xbmc accessories, and she's now used it more than me
00:18 orlock laser cut case, 2A PSU, usb wifi dongle, USB IR remote dongle, 16GB mini sd card
00:19 rue_more ah cool
00:20 orlock though - as soon as i plugged in the PSU (no load attached) BANG
00:20 orlock tripped breaker, and there was a decent chunk of the prong vaporised
00:20 rue_more hmm
00:21 rue_more not enough turns on the primary side
00:21 orlock i havent probed it or opened it yet
00:21 orlock they gave a free replacement, but the TV usb port seems to power it ok
00:21 orlock and it mounts everythign via nfs anyway, so its fine if it turns on with the tv
00:22 rue_more nfs4 is evil
00:22 rue_more I have one machine, and if you dont mount properly, files are delted when you save them
00:23 rue_more well, truncated to 0 bytes
00:29 orlock Oh - the place we got the rasberry pi from also sells CNC gear
00:29 orlock http://stores.ebay.com.au/learcnc
00:57 GargantuaSauce https://www.youtube.com/watch?v=uL6e3co4Qqc
00:59 rue_more hmm real or fake
01:12 rue_more https://www.youtube.com/watch?v=sjMhJxS96Lk
01:12 rue_more made my own video :P
01:13 rue_more the base is a bit chattery on the gears
01:15 rue_more I'll fix that later
01:20 orlock nice!
01:21 rue_more :) thanks
01:26 rue_more I think this robot will be verry handy as a workpeice holder at the soldering station
01:27 rue_more 'hold' 'flip' 'flip' 'flip' 'put in done bin'
01:40 Hyratel has good repeatability, though the ridigdity looks like it leaves somewhat to be desired
01:41 rue_more yea!
01:41 rue_more I'm going to work on tightening it up
01:41 rue_more I have to cut that shaft too
01:45 rue_more https://www.youtube.com/watch?v=v2jpnyKPH64
01:45 rue_more wins my "most annoying video ever"
01:49 rue_more gnight
02:09 rue_bed https://www.youtube.com/watch?v=6Yppdszg8vc
02:09 rue_bed insane
02:09 rue_bed carrier gears tho
07:00 GuShH_ https://www.youtube.com/watch?v=WXzSZVgQwts
07:14 Jak_o_Shadows So, cams
07:20 GuShH_ Jak_o_Shadows: you ungrateful bastard! that's a work of art, not just cams
07:20 GuShH_ speaking of bastard, this guy claims the iron for the flywheel came from a dumbbell http://home.comcast.net/~webster_engines/Breakdown.JPG but as far as I know dumbbells are white iron, almost impossible to machine and they're full of crap
07:21 Jak_o_Shadows Sorry.
07:21 Jak_o_Shadows I appreciate cams.
07:21 GuShH_ You must, or else.
07:21 Jak_o_Shadows Oh, trust me, I do.
07:21 GuShH_ Notice the cylinder oiler?
07:21 Jak_o_Shadows Yeah.
07:22 GuShH_ The piston also has a tube which allows oil to pass into the piston to lubricate the conrod bearing
07:22 GuShH_ quite interesting, these "open" designs
07:23 Jak_o_Shadows White iron: Can't machine because it has too large amount of the brittle phase?
07:23 GuShH_ well it would also lube the wrist pin etc. I reckon the wrist pin in fact is hollow and with pilot holes inside
07:24 GuShH_ but maybe not, never actually seen one apart.
07:25 GuShH_ Jak_o_Shadows: it's quenched almost immediately, and dumbbells are made out of pretty much swarf or the remainings of the crucible from some other process, I don't think they use good iron and allow it to cool properly for such thing.
07:26 GuShH_ when I was cleaning up my set to repaint them I noticed sand inclusions and lots of tiny porosities.
07:26 Jak_o_Shadows So you've got a pretty iffy carbon concentration, and by quenching them you increase the size of the brittle phase too much
07:27 GuShH_ Given the amount of red rust some of these gather, you can't really tell what alloy they are, it's just meant to have a specific amount of mass and be durable enough that's all. so I don't think you can machine this type of iron at all, at least not with conventional tooling.
07:28 Jak_o_Shadows If you heat treated it fully, but then what's the point of that?
07:28 GuShH_ Some model engine plans call for cast iron bar stock, which is pretty hard to obtain in most countries
07:28 GuShH_ I'm not entirely sure why they use cast iron pistons, could it be due to expansion coefficients and the fact that they have no rings, thus a very close tolerance fit is required
07:29 GuShH_ cylinders are often steel, so you'd want dissimilarity to begin with
07:30 GuShH_ other than that, a heavy piston is often detrimental to efficiency... so there has to be a good explanation.
07:30 Tom_itx so then why do they use aluminum which has a high expansion coefficient?
07:30 GuShH_ Tom_itx: on bigger displacement engines? they do have rings to seal the deal though
07:31 Jak_o_Shadows Aluminium is light, so you waste less energy due to the inertia of it.
07:31 GuShH_ at least one ring... and are they not often iron? (now adays they have fancier metals to work with)
07:31 GuShH_ Jak_o_Shadows: I'm still questioning why they use iron pistons on tiny model IC engines it has to be the expansion
07:32 GuShH_ you lap the piston to the cylinder so it's a slide fit, with no binding
07:32 GuShH_ and that's all you have to seal
07:32 GuShH_ plus the oil.
07:33 Jak_o_Shadows Don't a lot of engines have a little groove to make an oil seal?
07:33 Jak_o_Shadows How do you do that in cast iron if you can't machine it well?
07:33 GuShH_ grey and other irons machine fine
07:34 GuShH_ from what little experience I have with iron, it turns to dust it doesn't chip
07:34 GuShH_ there ought to be as many iron grades as there are for brass
07:36 GuShH_ Tom_itx: so I can only imagine solid iron pistons are used because manufacturing tiny piston rings at home would not be a simple task, or you just can't fit them since they would break, unless you used spring steel, but then wouldn't the cylinder have to be plated or made out of a stronger material?
07:36 GuShH_ again, not a model engine builder... but I want to start my first one of these days.
07:38 GuShH_ I've only found one site where the guy made his own rings for a portable honda genset (I think it was a Honda) because he couldn't source them or they were too expensive, however those were rather massive compared to a 2cc model engine size
07:39 GuShH_ a slitting saw was used, he then breaks it apart using a vise and pliers, not sure how he cleans the edge... most rings I've seen are either slanted or grooved (2 stroke for the locating pint)
07:39 GuShH_ must be he started with a rather bigger OD
07:45 GuShH_ Jak_o_Shadows: not sure about the groove, you mean for the ring?, I don't think any modern engine uses anything but aluminum!
07:45 GuShH_ plus they have multiple rings, specially 4 stroke you need oil rings, seal rings, etc.
07:46 Jak_o_Shadows Yeah, simplifying because I know little about engines
07:46 GuShH_ the oil rings carry the oil with them to keep the cylinders lubed
07:46 GuShH_ on 2 stroke you don't need that since the fuel contains the lubricating oil
07:47 ShH_ is not an expert at
07:48 GuShH_ hrmm I do know the more rings you have, the less efficient the piston becomes due to the added drag, but I don't know where you draw the line between being able to seal at higher pressures and loosing efficiency due to the added drag. <shrug>
07:48 KongfuPanda GuShH_, hi
07:49 Jak_o_Shadows I think that would be an empirical thing, or possibly you could model it.
07:50 KongfuPanda What do you guys think about lithium-air batteries ?
07:54 Jak_o_Shadows Engine design seems a very complicated thing.
07:54 Jak_o_Shadows Scratch that, design seems very complicated.
07:55 GuShH_ Jak_o_Shadows: it is, timing is what melts my brain.
07:55 GuShH_ specially on multiple cylinder engines
07:56 GuShH_ working out the offsets for the camshaft and actually machining them... no thanks, I could never get it right.
07:56 GuShH_ let a multiple axis cnc machine do the hard work I say, dammit.
07:57 Jak_o_Shadows I think the offsets is doable enough
07:57 Jak_o_Shadows Machining is far from my area, but I presume there would be tools to help
08:02 ShH_ stares at a grenade holster on ebay.... JUST WHAT I NEE
08:04 KongfuPanda GuShH_: hello
08:04 Jak_o_Shadows Anyway, petrol engines are a little annoying to model.
08:08 GuShH_ Jak_o_Shadows: I would consider the tiny ignition-less model engines to be 2 stroke diesels
08:08 GuShH_ but it's not diesel right out of the station, you have to make your own mixture.
08:08 GuShH_ usually ether and synthetic oils or similar
08:08 GuShH_ (compression ignition)
08:09 GuShH_ hi KongfuPanda
08:09 Jak_o_Shadows Diesel's are a tad easier, because CI
08:09 Jak_o_Shadows I have little practical experience.
08:10 GuShH_ It's a bit problematic getting ahold of the accelerant for the fuel mix though
08:11 GuShH_ amyl nitrate and the ether is diethyl ether, then they use kerosene with castor oil (typically)
08:11 GuShH_ I annotated the details but if I'm not able to source the chemicals, might as well not build it.
08:11 Jak_o_Shadows Steam engine instead?
08:11 GuShH_ boring
08:12 GuShH_ I'm sick of steam in general.
08:12 GuShH_ that's what I used to work with every single day.
08:12 Jak_o_Shadows Stirling then. Takes a little more tolerances I think.
08:12 ShH_ considers stirling useless but intrig
08:13 Jak_o_Shadows well, yeah. Possibly a good demonstration of thermodynamics though
08:13 GuShH_ a wobbler steam engine is one of the simplest to build, but I want IC.
08:15 GuShH_ wonder if those diesel magic cocktails they sell contain ignition improvers
08:16 GuShH_ (the goal is to lower the ignition temperature?)
08:16 GuShH_ (otherwise higher compression would be required)
08:16 Jak_o_Shadows Makes sense.
08:39 KongfuPanda GuShH_: have you heard about lithium-air batteries?
09:41 austintrigue morning/afternoon/evening
12:39 SlaveToTheSauce https://www.youtube.com/watch?v=g9exlSW3HK0
14:52 MrCurious this goes out to robustra... https://www.youtube.com/watch?v=oRIsC764Nn4
21:52 zhanx Evening
21:53 Jak_o_Shadows yo
21:55 zhanx Rue
21:56 GargantuaSauce you will rue the day!
21:57 zhanx nope
22:27 zhanx Ok who is smart
22:27 Jak_o_Shadows What is your problem
22:27 zhanx Or can give input
22:28 zhanx Working on my 4' biped robot
22:28 zhanx Using 3 dof weight transfer yo help balance it
22:28 zhanx To*
22:29 Jak_o_Shadows ooh, fun.
22:29 Jak_o_Shadows especially if you start moving those weights around fast
22:29 zhanx Yep. To aid in IK EVEN more fin
22:29 zhanx Gun
22:30 zhanx Damn tablet
22:32 Jak_o_Shadows Yeah, especially if you have to start really considering inertia in the weights
22:33 zhanx Yea since my knee is fubar again not an issue. Scaling is my issue
22:34 zhanx Test bed is small
22:35 zhanx Real thing not so much
22:35 zhanx I killed all other projects to do this
22:36 MrCurious where is robo-strata
22:37 zhanx ?
22:39 MrCurious robostrua
22:39 Jak_o_Shadows But yeah, I could possibly help with the maths for that? Maybe
23:05 Jak_o_Shadows MrCurious: How did you do that camera overlay thing for your hexapod?
23:06 MrCurious well
23:06 MrCurious that was easy
23:06 MrCurious first i put on my GargantuaSauce costume
23:06 zhanx Opencv?
23:06 MrCurious then i broke into his house and pretended to be him
23:06 Jak_o_Shadows righto, sorry.
23:06 MrCurious the rest is just technical
23:06 MrCurious :)
23:06 Jak_o_Shadows GargantuaSauce: How did you do that camera overlay thing for your hexapod
23:06 MrCurious sorry, could not resist
23:06 Jak_o_Shadows Sorry!
23:06 GargantuaSauce i recorded the video streams using vlc
23:07 GargantuaSauce and then composited them into one video using a shitty video editor that made me rage
23:07 Jak_o_Shadows That video editor part is the thing i want to know
23:07 GargantuaSauce kdenlive
23:08 zhanx MrCurious just use opencv
23:08 MrCurious how did i get involved in this :)
23:08 GargantuaSauce opencv is a pretty shitty video capture library
23:08 MrCurious could prototype in simplecv...
23:08 GargantuaSauce it's nice for processing but its interface to windows' uvc interface and v4l2 is garbage
23:09 MrCurious as much as i lothe python, it is nice for fast taping shit together
23:09 GargantuaSauce i just used vlc for the streaming too
23:10 zhanx I just use it as a input
23:16 Jak_o_Shadows https://www.youtube.com/watch?v=rBHjx4dYxjA is cool
23:17 GargantuaSauce pretty late to the punch but yes it is damn cool
23:17 GargantuaSauce read the paper too
23:18 GargantuaSauce http://www.cs.ubc.ca/~van/papers/2013-TOG-MuscleBasedBipeds/index.html
23:20 Jak_o_Shadows The kangaroo is pretty cool
23:20 Jak_o_Shadows Festo should have looked at this more.
23:20 GargantuaSauce festo's kangaroo is made using actuators that actually exist.
23:20 Jak_o_Shadows Festo's kangaroo doesn't have a tail that does anything.