#robotics Logs

Dec 01 2014

03:09 DarthMachinist lol, how does a motor controller even control a generator
03:10 DarthMachinist I'd assume bldc motors work on the inductance of the windings converting square wave into a sine wave
03:11 DarthMachinist so can I expect that same property to keep a voltage up when the output is pwm
09:36 rue_more I think I'm confused about what your doing
10:32 cnnx the bigger the radius of a wheel the stronger the dc motor has to be?
11:52 darsie Is the brain in a humanoid robot usually in the head or in the torso?
11:53 deshipu doesn't matter
11:54 deshipu whatever is more convenient in the particular design
11:54 deshipu may also be strewn around
11:55 darsie Hmm, k. I thought it might rather be in the torso, cause there's more space. But decapitated cyborgs often see/speak with their head in movies.
11:55 darsie Well, hmm, the torso doesn't have cameras/speakers ...
11:56 deshipu it often does, actually
11:56 darsie ahh, ok.
11:56 deshipu look at the darpa robot challenge this year -- most of the robots have sensors all over their bodies
11:57 darsie I've seen humanoid soccer bots with cameras on their head.
11:59 deshipu there are all sorts of designs, really -- it's very specific to what the robot is actually supposed to do, how large it is and what materials you have available
12:27 darsie Very interesting, the darpa robot challenge.
12:27 darsie http://www.youtube.com/watch?v=hzmMVHGNXvI
12:27 darsie Robot highlight footage from DARPA's Robot Challenge 2013
12:38 deshipu darsie: that's basically where we are with humanoid robots at the moment
12:39 deshipu darsie: that is: expensive, slow, failure-prone and ugly :P
12:39 darsie yeah, I thought so.
12:41 deshipu on the other hand, hexapods... https://www.youtube.com/watch?v=nHvaqpcGI1c#t=76
12:41 darsie Heh, someone said, they'd like to beat humans at soccer in 50 years, similar to beating humans at chess :).
12:43 deshipu well, they can beat humans at soccer right, now, just not humainod
12:44 deshipu you design a robot for the particular job
12:44 deshipu for instance, a quadcopter with a ball holder
12:44 deshipu try to beat that
12:45 darsie Will do when the quad copter soccer bots exist ;).
12:45 darsie I don't play soccer, but I'd do then ;).
12:46 deshipu well, technically the rules of soccer are bady phrased for anything non-humanoid
12:46 darsie Grabbing the ball is illegal.
12:47 deshipu darsie: there are no soccer quadcopters precisely because it would be so easy that it doesn't make any sense
12:47 deshipu darsie: you can grab it with your legs, though
12:47 deshipu darsie: besides, using a net or basket would not be grabbing
12:48 darsie That quadpod is impressive, too. http://www.youtube.com/watch?v=aUotR1-Bt88 I've seen earlier versions before.
12:50 deshipu would be more impressive if it actually moved like an animal, not like a bouncing ball
12:51 deshipu but I guess you can't have everything
12:55 darsie Yay, that rolling bot is cool, too. http://www.youtube.com/watch?feature=player_detailpage&v=VpUhDSwkFgM#t=130
12:56 darsie Like those rolling bots from Star Wars :).
12:58 deshipu they claim it's "running"
13:01 darsie Why are those cameras rotating? Or is it (infrared?) lasers?
13:01 darsie On the humanoid bots.
13:01 deshipu another point where human definitions don't make sense in case of robots
13:01 deshipu darsie: those are lidars, most likely
13:01 deshipu or some hybrid device doing several ways of scanning at the same time
14:10 cnnx if a 12vdc pump says it self primes at 2 feet in the specs does that mean you need 2 feet of tubing for it to suck the air out or does it mean something else?
14:14 darsie cnnx: It can pull water through an air filled hose up to two feet.
14:15 cnnx darsie: so the distance between the pump and the water being pulled should be less than two feet?
14:15 darsie Up to two feed vertically.
14:15 cnnx yeah it says height
14:15 darsie feet
14:15 darsie Can be less.
14:16 cnnx so its kind of the "suction power" it has?
14:16 cnnx if the water is below and the pump is above
14:16 darsie Yeah. IMHO, though.
14:16 darsie I haven't actually had such a pump.
14:17 cnnx ok thanks
14:17 darsie Ohh, and assuming normal atmospheric pressure (at sea level).
14:18 applepi Hi all!
14:18 monkers o/
14:18 darsie cnnx: Which one are you looking at? URL?
14:19 cnnx darsie: http://www.trossenrobotics.com/large-liquid-pump
14:19 applepi So, a question... I've started mentoring a high school kids robotics team the past couple of years, and I'm discovering that I'm absolutely going to have to have some tangible stuff at the beginning of the year to teach them with because they're already reading and doing homework for six to eight classes and just flat out aren't going to read what I give them.
14:21 cnnx darsie: the pump is 24.95$ and the cheapest shipping is 38$
14:21 cnnx from IL.. i dont get it
14:21 darsie cnnx: Beware, PVC may contain harmful plasticiser.
14:22 cnnx darsie: look at this one, http://www.adafruit.com/products/1150
14:22 cnnx darsie: is it better?
14:22 cnnx darsie: its smaller.. only 100ml/min
14:22 applepi Can anyone suggest some relatively good and cheap robotics building materials that I could use to get the basic ideas across? I'm considering Lego because of how cheap it is, but the lego motors are so painfully weak it'll be hard to make a useful demo.
14:23 cnnx applepi: i built my own robot from scratch.. wood platform, 20$ motors .. linux computers etc
14:23 cnnx applepi: no need to buy legos
14:23 cnnx applepi: now i'm adding a pump to the robot
14:24 applepi cnnx: yeah, I've considered just thrown together stuff as well.
14:24 darsie cnnx: Are both peristaltic?
14:24 cnnx darsie: no.. just the second one
14:25 cnnx darsie: i think anyways
14:25 darsie peristaltic may have superior priming height and precise flow rate.
14:25 applepi A kit would be nice though as it would be easy to throw together a ton of simple examples
14:25 applepi Which is what I think I'm going to need at the start of the next year
14:25 cnnx applepi: whatever you feel more comfortable with
14:26 cnnx applepi: look at sites like robotshop.com and pololu.com
14:27 applepi Lots of little "here's an example of gearing up / gearing down / idler gears / lift systems"
14:27 cnnx darsie: you think its a good pump?
14:27 applepi Most of them have little to no mechanical experience and I need stuff I can throw together and change rapidly for teaching, which was the appeal of the kit.
14:28 applepi cnnx: I'll take a look at that, thanks. :)
14:28 darsie cnnx: dunno.
14:28 darsie I guess it'll work as advertised.
15:22 cnnx if you look at this board http://www.embeddedarm.com/products/board-pictures.php?product=TS-8100 is the serial looking port a regular rs-232 serial port?
15:23 cnnx specs says 1 RS-232 / Console Port (Selectable)
15:23 cnnx does that mean i can connect to it from another computer using rs-232 cable?
17:25 ardor What is a good stepper motor driver that works off of an 5 volt rail?
18:13 GuShH rue_more: ok the saddle is off, one solid cast iron piece (vewy heavy) it never had any sort of half nut in there, from what I can see. Also the dovetail point was so sharp I nearly cut my fingers, it went through the rag like a knife.
18:14 GuShH I need to pull out a wedge they used to lock the wheel in place, I don't have an inertia hammer (could probably make one) so I'm out of ideas
18:15 GuShH gave it a quick slap-up of primer anyway. I need to decide whether I want to remove the headstock or not, I'm assuming it is already properly aligned... wouldn't want to waste time aligning it again
18:29 GuShH I also worked out that if the legs survived what we did to them when we pushed the lathe sideways, they must be able to cope just fine with the casters to move it from point A to point B carefully if I strap the lower portion to keep it from flexing
19:39 rue_more the thing I'd wory about is them tearing off sideways
19:40 Tom_itx rue_more, i got the compile done
19:41 rue_more good show
22:00 rue_shop2 hat to refit my pulley with a steel centre, it'd worked loose and opened up its shaft hole
23:11 rue_more silly alumuinum
23:12 GuShH ?
23:12 GuShH rue_more: refit which pulley?
23:14 rue_more the new one I made for the boiler
23:14 rue_more did I post that pics of that?
23:14 GuShH no
23:14 GuShH haven't seen them
23:15 rue_more damn
23:19 rue_more http://ruemohr.org/~ircjunk/projects/heatplant/p1060868.jpg
23:19 rue_more http://ruemohr.org/~ircjunk/projects/heatplant/p1060874.jpg
23:19 rue_more http://ruemohr.org/~ircjunk/projects/heatplant/p1060888.jpg
23:19 rue_more the forward pulley has a sinch ring made of steel pipe around it
23:20 rue_more http://ruemohr.org/~ircjunk/projects/heatplant/p1060889.jpg
23:20 rue_more seen more clearly
23:20 GuShH first pic looks like it was a bit cold and didn't flux/degass
23:20 GuShH did it machine like iron?
23:20 rue_more (I completely deny anything about the welding bottle being taped to the led of a tent)
23:20 GuShH like dusty tiny chips
23:20 rue_more sure
23:21 rue_more cast aluminum always machines brittle...
23:21 rue_more http://ruemohr.org/~ircjunk/projects/heatplant/p1060890.jpg
23:21 GuShH depends on the alloying elements though
23:21 rue_more http://ruemohr.org/~ircjunk/projects/heatplant/p1060892.jpg
23:21 rue_more its alloyed with crap
23:21 rue_more :)
23:21 GuShH :D
23:21 rue_more anything that would melt went in
23:21 rue_more -- thats all my images --
23:21 GuShH I don't have much scrap aluminum at all :(
23:21 rue_more latley, I been throwing in brass
23:22 rue_more I dont know why, but a guy on youtube who seemed to know what he was doing did it
23:22 rue_more I also have no temp probe, so I'm prolly all over the plate
23:22 rue_more place
23:22 GuShH maybe a bit on the cold side
23:23 rue_more what temp should I pour at ya think?
23:23 rue_more 800c?
23:23 rue_more er
23:23 GuShH can't measure what's the point
23:23 rue_more I'm working on it
23:23 GuShH I've heard about adding copper to get alu-bronze
23:23 GuShH I never actually machined this alloy
23:24 rue_more it takes it a while to eat copper
23:24 RifRaf 1200c?
23:24 rue_more it eats up brass quick
23:25 rue_more RifRaf, that was going to be my other answer
23:25 GuShH but with brass you kinda end up burning the zinc
23:25 RifRaf i juast thought it was 1200 - 1300C for aluminium?
23:25 GuShH both nasty to breathe in and... you lose the zinc :p
23:25 GuShH it can certainly melt at much lower temp
23:25 GuShH but it has to be hot enough to flow properly
23:25 rue_more yea, zink must be about 400cish
23:26 rue_more soemwhere I have the basics for a thermal probe, but I need to go to the highschool and calibrate with theirs
23:26 GuShH I'm glad you got to cast all of those at once even if they had a few inclusions, it doesn't matter
23:26 rue_more the IR ones dont seem to go high enough
23:26 GuShH just spit into it and see how high the molten aluminum jumps
23:27 GuShH then measure that height
23:27 ShH g
23:27 rue_more the first one I wrecked when my 1/2" bit decided to bore and not drill
23:27 rue_more interestingly enough, I'v not had any moisture problems with the aluminum
23:27 GuShH what are you using for the crucible
23:27 GuShH stainless pot?
23:27 rue_more and I'm told that untill your casting steel, having it jump out of the mold isn't an issue
23:28 rue_more yea :(
23:28 rue_more the alloys eat it
23:28 GuShH well... graphite ain't cheap
23:28 rue_more BADLY
23:28 GuShH you should try mild steel, doesn't last at all
23:28 rue_more std steel would last better
23:28 rue_more er?
23:28 GuShH not on thin cross sections like that
23:28 e_more checks what side of the fence he'
23:29 rue_more I can get 1/2" water mains pipe
23:29 rue_more 1/2" thick
23:29 GuShH that will last
23:29 rue_more little while
23:29 GuShH a bunch of pours, but say something thin like the pot
23:29 GuShH it won't
23:29 GuShH the cheap low carbon steel will rust, delaminate and crumble (tried it)
23:29 rue_more http://ruemohr.org/~ircjunk/projects/smelter/p1040233.jpg
23:30 GuShH then you get a gravity pour, onto the furnace heh
23:30 rue_more I understand that aluminum + iron oxide = danger
23:30 rue_more "vigorous reaction"
23:30 rue_more yea, see the pan around it?
23:30 rue_more I'v had leaks before...
23:30 GuShH :p
23:31 rue_more http://ruemohr.org/~ircjunk/projects/smelter/p1040231.jpg
23:31 GuShH rue_more: talking with some local guys doing backyard foundry work... they've even tried dirt instead of refractory cement and they've had great success
23:31 GuShH but usually 3-4 times thicker than yours
23:31 rue_more the diesel blower died, I'm using a tiger torch now
23:31 rue_more that refractory is just vermiculite, cement, and sand
23:31 rue_more its like 5 years old now,
23:31 GuShH yeah but it turns out regular dirt (in most places) works fine
23:32 rue_more http://ruemohr.org/~ircjunk/projects/smelter/p1010997.jpg
23:32 GuShH depends on the clay content
23:32 rue_more that was almost new, and you can see I'v not really lost that much
23:32 GuShH but what was the total cost for your pour
23:32 rue_more its just getting latley that I cant hold my hand on the side after its been running
23:32 GuShH vs buying the ingot from a second hand source heh
23:33 rue_more ?
23:33 GuShH err the billet
23:33 rue_more cost on fuel or aluminum?
23:33 GuShH total cost
23:33 GuShH alu was probably "free"
23:33 rue_more aluminum is free
23:33 rue_more and for about $5 in diesel I could get 2-3 pours (at about 3L ea)
23:33 GuShH I think I can get offcuts from extrusions (window shops) but that's usually a shitty alloy
23:33 rue_more I havn't used the propane enough to know
23:34 rue_more http://ruemohr.org/~ircjunk/projects/smelter/p1020001.jpg
23:34 GuShH I don't have the diesel burner from my heater furnace :( whenever they converted to natural gas they took the old burner out
23:34 rue_more anyone have an IR thermometer and can tell me what the temp of that is?
23:34 GuShH lol
23:34 rue_more I'm using a propane tiger torch now
23:35 GuShH you don't cap it?
23:35 rue_more I was thinking of switching a while ago, and then something jammed in the blower
23:35 rue_more http://ruemohr.org/~ircjunk/projects/smelter/p1010996.jpg
23:35 rue_more I do
23:35 rue_more I have to make a freaking insulated cap tho
23:35 GuShH that is about the size of a big paint can... I really wanted a 200L drum to make mine
23:35 rue_more http://ruemohr.org/~ircjunk/projects/smelter/p1020013.jpg
23:35 rue_more this is a great way to ruin a perfectly good plastic bucket
23:36 GuShH oh the drums come in steel or plastic
23:36 GuShH oil drums are usually steel
23:36 GuShH they turn them into garbage bins here!
23:36 rue_more http://ruemohr.org/~ircjunk/projects/smelter/p1020016.jpg
23:36 rue_more yanno, my firrst pour wasn't much better than my first 3d print
23:36 GuShH like the bbq grills, but for trash.
23:37 GuShH rue_more: I've only cast a couple tiny billets, nothing complex 'til I get more serious
23:37 GuShH plus a failed cast is not too costly, you do lose some aluminum but you can still remelt it
23:38 GuShH that was just too cold
23:38 GuShH the guy I bought those lathes from does lost-wax casting and all sorts of fancy stuff
23:38 GuShH but I didn't want to annoy him with questions
23:39 GuShH we spoke for two hours about finishing processes and I thought that was enough
23:40 GuShH reminds me... I need to figure out if I'll have to make my own collet holder for the other turret lathe (it currently has a 3 jaw chuck with missing jaws) or .. source new jaws
23:40 rue_more aren't jaws pretty specific?
23:40 GuShH yes
23:40 GuShH the number on them is the model
23:41 GuShH at least, how you identify the set
23:41 rue_more mine weren't marked
23:41 GuShH for older non china chucks, you can find used sets
23:41 rue_more it took forever to work out who went in which slot
23:41 GuShH mine are on the chinky, 223 or something like that
23:41 GuShH and they are marked 1, 2, 3 (except the 2 you can barely see it)
23:41 rue_more mine weren't
23:41 GuShH the jaws are tiny compared to the jaws on shorty lathe
23:42 GuShH as is the standard 3 jaw they give us on chinky lathes
23:42 GuShH so tiny
23:42 rue_more I tried to stamp them, they ARE hardened properly, think I nearly flattened my number 1
23:43 GuShH yeah but my compound isn't hardened. the corner is now round, the jaws are fine of course.
23:43 rue_more so I scuffed them with my worst punch
23:43 GuShH one of my first "near" crashes
23:43 rue_more heh, not crashed mine yet
23:43 rue_more I watch carefully for that
23:43 GuShH I don't know if crash means total stall and breakage
23:43 rue_more I stalled it today
23:44 rue_more I was cutting off, and the peice slipped and dug in
23:44 GuShH my jaws touched the side of the compound, it went "tuk tuk tuk tuk", moved the slide to the right, stopped... and the corner was round.
23:44 GuShH that's how you learn
23:45 GuShH now I let the tools hang a little more.
23:45 GuShH since I'm using bigger bits
23:45 GuShH 5/8 is nice, sadly too expensive
23:46 GuShH most are 1/2 or so, but I'm always using HSS with aluminum.
23:48 rue_more you use a fluid with alum?
23:48 GuShH rue_more: I've had the blade dig in during cutoff, I just contribute it to the compound mount being too weak
23:48 GuShH I do
23:49 rue_more kerosene?
23:49 GuShH I've yet to finish my 4 point mounting plate for the compound... I was getting so much chatter I only faced one side and stopped
23:49 rue_more either?
23:49 rue_more propane?
23:49 GuShH kerosene and atf works fine
23:49 rue_more atf!
23:49 rue_more ok
23:49 GuShH tiny bit of atf
23:50 GuShH I can't stand the smell of kero though
23:50 rue_more oph, a mix?
23:50 GuShH yes, say 90% kero, 10% atf
23:50 rue_more oh
23:50 GuShH brush that in, works fine
23:51 GuShH my coolant system is on hold... I might go for a plastic tray and a smaller setup
23:51 GuShH now that I'm missing several coolant pumps, I need to figure out a cheap way of doing it
23:51 rue_more the challange is to see how many toxic, flamable bottles one can put beside a metal shaper
23:51 GuShH LOL
23:51 GuShH I've been using alcohol lately
23:52 orlock bottled therapy?
23:52 rue_more 20-test?
23:52 GuShH with atf, can't say the oil mixes properly and it doesn't work as good as kerosene, but at least it doesn't smell terrible... but I bet you could get drunk eventually
23:52 rue_more 74 a good year?
23:52 GuShH rubbing alcohol
23:53 GuShH there's a mil spec where they tell you to use alcohol as a lubricant for some fluid lines during installation, to leave no contamination behind.
23:53 GuShH back in the day screw machines used some heavy sulphur based oil as coolant, terrible smell
23:53 GuShH it was also almost black
23:53 rue_more huh
23:54 GuShH (but it worked fine for steels)
23:54 GuShH I don't think I can source proper oil+water coolant on a small amount
23:54 GuShH 20 liters or 200 liters only
23:54 rue_more do you think I could weld togethor a dovetail? (to make one)
23:55 GuShH out of bar stock?
23:55 rue_more brake fluid is hydroscopic
23:55 rue_more yea
23:55 GuShH you could try
23:56 GuShH too bad that homemade lathe video is in spanish...
23:56 rue_more toxic tho
23:56 rue_more gingery
23:56 GuShH he didn't use dovetails, but that machine cuts nicely
23:56 GuShH nope
23:56 GuShH his own design
23:56 GuShH no castings
23:56 rue_more huh
23:56 rue_more heavy built?
23:56 GuShH started with a round spindle using regular bearings, then used that as a mill to mill out the pockets for the taper bearings on a square headstock design
23:57 GuShH yeah for what it is, much better than the chinky
23:57 LoRez GuShH: the 5gal bucket probably won't actually last that long. That stuff gets nasty.
23:57 LoRez things grow in it.
23:57 GuShH LoRez: sure does, again... the smells.
23:57 rue_more my brake fluid + water mix turned red
23:57 rue_more after 2 weeks
23:57 GuShH I don't want to use brake fluid for anything really
23:57 LoRez I couldn't use atf for very long. that stuff is nasty smelling.
23:58 rue_more ooh, right the brake fluid was taking paint off
23:58 GuShH kerosene is nastier
23:58 rue_more forgot about that
23:58 GuShH and every homemade coolant I've tried will rust your surfaces
23:58 GuShH in no time.
23:58 rue_more I was noticing
23:58 GuShH that's how my drill press got a black spot on the table
23:59 GuShH after I got rid of the flash rust, that's the reminder it left me.
23:59 GuShH rue_more: the guy made his own 4 jaw chuck from scratch also, no milling machine.