#linuxcnc | Logs for 2013-07-22

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[18:55:57] <fbx90> as far as new motors, probably looking at something like this
[18:55:59] <fbx90> http://www.homeshopcnc.com/index.php?page=shop.product_details&flypage=gk_flypage.tpl&product_id=26&category_id=4&option=com_virtuemart&Itemid=1
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[18:57:54] <archivist> with proper servos some mesa cards then :)
[18:58:39] <fbx90> i'm going to have a 5i25 for my steppers in a few days. some other folks here recommended some mesa daughter cards... but i've been having a hard time telling the difference between them
[18:59:07] <fbx90> and whether i need pwm output or +/-10V output
[18:59:27] <fbx90> and which mesa cards have which
[19:02:23] <andypugh> fbx90: For the 5i25 you can use a 7i76 for steppers or 7i77 for servos.
[19:05:08] <fbx90> andypugh: it seems like the 7i77 supplies +/-10V output...
[19:05:22] <andypugh> Yeah, that's for servo drives.
[19:05:52] <fbx90> something that's been confusing me is whether all the servo drives i find which are labeled as PWM servo drives, accept PWM input, or are simply PWM'ing their output...
[19:06:17] <fbx90> like all the AMC servo drives
[19:07:02] <andypugh> They all PWM their output, but some also want a PWM input.
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[19:09:26] <fbx90> if i could get away with a much smaller servo, would i be able to dangle a 3c20 off the 5i25 and connect it directly to the servo?
[19:11:52] <andypugh> I am fairly sure that the 3C20 doesn't work with LinuxCNC, but you ought to ask PCW. For the DC servos you listed I think you would be looking at the 7i29
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[19:13:45] <andypugh> But, (and this is important) the 7i29 is intended for the other type of Mesa FPGA card, with the 50-pin header rather than the D-plug.
[19:14:13] <fbx90> what's the operative difference between the 7i29 and 7i77 which makes it more suitable for the motors i listed?
[19:14:38] <andypugh> The 7i29 is a drive, the 7i77 is a daughter card.
[19:15:22] <fbx90> oh i see
[19:18:56] <andypugh> If you already have the 5i25 coming, then I suggest seeing how you get on with steppers.
[19:19:22] <andypugh> Maybe keeping an eye out for cheap +/-10V controlled drives.
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[19:22:15] <fbx90> yeah, i need the 5i25 anyway because i'll still have 2 axes with steppers
[19:22:40] <fbx90> and maybe when the 5i25 gets here, and i can run with smaller microsteps, i'll be able to do without a servo on the axis in question
[19:22:47] <fbx90> good call there
[19:24:23] <fbx90> this is for a piece of weird optical machinery we developed in-house
[19:24:41] <fbx90> and that axis needs to be extra smooth
[19:25:55] <t12> andypugh: I read you've worked with an 8i20 + ac servomotor?
[19:26:14] <andypugh> Yes, my milling machine runs 8i20s.
[19:26:25] <t12> what kind of angular resolution can you get out of it?
[19:26:40] <andypugh> I am not sure.
[19:27:03] <t12> i've been thinking of setting one up for direct drive lathe spindle
[19:27:29] <andypugh> Given that the resolver interface has 24 bits of resolution, it ought to be possible to get pretty spectacular resolution.
[19:28:05] <fbx90> hmm, that's something i'm dealing with on another of our weird-ass machines...
[19:28:38] <fbx90> trying to get <.04 degrees on one axis
[19:29:07] <andypugh> Should be possible with a multi-pole resolver, I think.
[19:29:44] <andypugh> I was going to experiment with an 8i20 and a washing machine motor, but I accidentally bought a Rivett 608 and that moved the washing machine motor down the list.
[19:30:30] <t12> for high accuracy are resolves superior to optical encoders?
[19:30:32] <fbx90> heh
[19:30:33] <t12> resolvers
[19:30:59] <andypugh> t12: Yes.
[19:31:08] <andypugh> Washing-machine motor: http://www.youtube.com/watch?v=_P027KQ8ZHo&feature=share&list=UUexvgsGz_QFvOublovDYoTQ
[19:32:08] <fbx90> the inside of that is pretty cool looking
[19:33:14] <andypugh> t12: because Resolvers are analogue devices you can get much better accuracy.
[19:34:01] <t12> i see these mitsubishi servos that say they have 2^17 count encoders?
[19:34:30] <fbx90> jesus
[19:34:40] <t12> or maybe i'm misinterperting
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[19:35:03] <fbx90> i'm looking at 2500count optical encoders which can give me 10k counts in quadrature
[19:35:19] <t12> let me see if i can find a datasheet
[19:36:10] <fbx90> i've seen 5k and 10k, which translate to 20k and 40k respectively, but everything higher that i've seen hasn't been in an actual product
[19:36:43] <t12> http://www.mrostop.com/pdfs/mr-j3.pdf
[19:36:51] <t12> mr-j3
[19:37:41] <andypugh> t12: The Mesa resolver card gives 2^24 bits of resolution (probably 16 bits of accuracy, in real terms).
[19:38:15] <andypugh> But you can also get high pole-count resolvers, so can multiply the two numbers together.
[19:38:41] <t12> then its sort of like
[19:38:48] <t12> however many a/d bits per pole section
[19:38:56] <t12> and the resets to zero, and you just track poles?
[19:39:20] <andypugh> Yeah, sort-of :-)
[19:39:27] <fbx90> yeah, if i understand what you're saying :)
[19:39:42] <CaptHindsight> nice, when did washing machines start using brushless motors?
[19:39:59] <fbx90> when did they stop using hand cranks? :D
[19:40:21] <fbx90> you guys and your futuristic washing machines
[19:40:22] <CaptHindsight> hand crank and hand operated bush
[19:40:23] <andypugh> CaptHindsight: I think it's been about 5 years, maybe more.
[19:40:25] <archivist> do they still use a rock in the river!
[19:40:27] <CaptHindsight> brush
[19:40:50] <fbx90> heh
[19:41:20] <CaptHindsight> the transmissions were usually what would wear out along with the relays
[19:41:51] <fbx90> http://www.ebay.com/itm/KOLLMORGEN-AKM41H-BKCNR-00-SERVOMOTOR-NEW-OLD-STOCK-/290945281457?pt=LH_DefaultDomain_0&hash=item43bdb0adb1
[19:42:10] <CaptHindsight> they must have figured out how to make a motor for less and how to undersize it just right to last the warranty + few months
[19:42:46] <jdh> my washer uses a plain old almost-framed induction motor
[19:45:55] <t12> maybe i can make my description more vague!
[19:46:03] <t12> heh
[19:50:28] <andypugh> fbx90: A nice motor, but only one of it.
[19:51:06] <CaptHindsight> I've been using Parker servo drives for while now. Usually ~$100 on ebay unless they have some factory bus everyone wants, then they sell for 4X or more
[19:51:17] <andypugh> I have been watching this set, but have avoided buying it. http://www.ebay.com/itm/261144227546?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
[19:51:45] <fbx90> andypugh: yeah, luckily i only need one :)
[19:52:27] <fbx90> andypugh: what application do you have in mind for those?
[19:52:56] <andypugh> I was looking at a lathe conversion (X, Z and toolchanger)
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[19:54:25] <CaptHindsight> http://www.ebay.com/itm/SANYO-DENKI-QS1E03AA-01-AC-SERVO-DRIVE-0-163-VAC-3-PHASE-NEW-/290947032283?pt=LH_DefaultDomain_0&hash=item43bdcb64db
[19:54:49] <CaptHindsight> only 163V, but a steal if they sell for <$50 New
[19:55:41] <andypugh> CaptHindsight: A steal indeed but for brushless rather than the brushed ones he was looking at.
[19:55:52] <andypugh> (Just thought I would point that out)
[19:57:54] <CaptHindsight> thanks, read that wrong
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[19:59:17] <CaptHindsight> I have some extra DC servo drives that came with that Matsuura
[20:00:05] <CaptHindsight> what voltage and current?
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[20:11:38] * JT-Shop wonders how you get the powder to go into the hole your hanging the part from when powder coating
[20:13:48] <Jymmm> long tube, fill from bottom up.
[20:17:38] <JT-Shop> http://imagebin.org/265285
[20:18:07] <JT-Shop> I hang it by the center hole when powder coating and most don't have any coating inside the center hole :(
[20:18:54] <Jymmm> Yeah, I've always wondered about that.... how do you powder coat the point you are hanging from?
[20:19:09] <Loetmichel> you dont
[20:19:16] <Jymmm> same with annodize.
[20:19:22] <Loetmichel> ise a hol which gets a thread anyways
[20:19:29] <Loetmichel> use
[20:19:34] <Loetmichel> hole
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[20:25:16] <JT-Shop> no threaded holes in this part
[20:25:28] <JT-Shop> guess I'll just have to touch it up with paint
[20:26:47] <Jymmm> JT-Shop: what are you baking it in?
[20:27:15] <JT-Shop> a kiln
[20:27:29] <Jymmm> can you do two runs in the kiln?
[20:28:05] <JT-Shop> I can fit several parts in the kiln
[20:28:29] <Jymmm> I mean run it twice in the kiln
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[20:33:01] <t12> i guess with resolvers error wouldn't be additive either?
[20:35:48] <jdh> nice use of shipping tubes
[20:39:07] <jdh> anyone have an opinion on using a 1HP DC treadmill motor for a 9x20 spindle?
[20:44:39] <andypugh> I think Gene has done exactly that?
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[20:45:11] <andypugh> (Or is gene78 's lathe smaller than that?)
[20:46:57] <jdh> or somethign like this: http://dealerselectric.com/item.asp?cID=0&PID=6900
[20:47:42] <andypugh> My 9x40 runs with a VFD and 1kW motor.
[20:48:20] <jdh> I was pretty enthused about ripping the lathe apart to convert, but after cleaning it up, refitting all the moving parts, it moves pretty well and seemed to cut OK on steel.
[20:48:45] <jdh> but, turning steel by hand seems to be ungodly boring.
[20:55:34] <andypugh> Yes, but if you sink money into CNC-converting a Chinese 9x20 you still have a Chinese 9x20.
[20:56:14] <andypugh> (Speaking from experience)
[20:57:41] <Loetmichel> hmm, invest in some new bearings and a scraping class and go for it ;-)=
[20:59:07] <andypugh> You still have no back-gears, no adequate lubrication for the spindle bearings and flimsy dovetails
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[21:00:35] <Loetmichel> andypugh: right
[21:00:49] <Loetmichel> was more of a joke.
[21:01:13] <Loetmichel> wit a bit of "better than no lathe" in it
[21:01:20] <Loetmichel> i know what i am taling about
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[21:02:21] <Loetmichel> i had to "work" wit that for not so short time: http://www.cyrom.org/palbum/main.php?g2_itemId=6100&g2_imageViewsIndex=1
[21:02:33] <Loetmichel> http://www.cyrom.org/palbum/main.php?g2_itemId=520&g2_imageViewsIndex=1
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[21:02:54] <Loetmichel> ANY lathe is better than that, but even this one is better than NO lathe ;-)
[21:03:31] <andypugh> I had one of those.
[21:05:23] <andypugh> Then upgraded to: https://picasaweb.google.com/lh/photo/aD3U7TVt-SvekGIitO20B9MTjNZETYmyPJy0liipFm0?feat=directlink
[21:06:14] <andypugh> And now I am playing with: https://plus.google.com/photos/108164504656404380542/albums/5889085582650378897
[21:07:57] <Loetmichel> have a "new" one here. about a year. still have to get a new motor, didt found the time. got a VFD lately, tough... -> http://www.cyrom.org/palbum/main.php?g2_itemId=11462&g2_imageViewsIndex=1
[21:11:50] <andypugh> Looks rather ordinary, if I may say so.
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[21:24:58] <pimperle> hi
[21:25:30] <pimperle> is there a way or even an example how to write a kinematics module as a .comp file?
[21:25:43] <pimperle> or are functions with arguments supported only in .c files?
[21:26:05] <pimperle> (it's my first linuxcnc project and my first robot and thus my first kinematics module)
[21:29:09] <DJ9DJ> gn8
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[21:35:31] <andypugh> pimperle: You can't write a kins in .comp. But you can compile and install the module with comp
[21:36:23] <andypugh> I would suggest starting with trivkins and just modify the maths that defines the forward and reverse transformations.
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[21:44:26] <jdh> The 9x20 was cheap. I have motors and drives. If I use the stock screws the conversion will be mostly 'free'
[21:45:08] <jdh> or $150ish for chinese ball screws and bearing mounts
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[21:48:21] <jdh> If I had some tiny steppers, I'd do my Clisby lathe.
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[21:49:24] <pimperle> andypugh: thanks. I already had a look at trivkins and will go that way. I also saw that comp can compile .c as well but thought using .comp files might make it easier/more concise. thanks for clarifying. :)
[21:50:45] <andypugh> As you guessed, .comp only exports one function, with no arguments.
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[22:36:36] <Tom_itx> JT-Shop, use smaller stiff wire and might flow around it
[22:37:27] <JT-Shop> yea, I'll try that next time... I just used the hooks provided by the powder coating kit
[22:38:41] <Tom_itx> i used to use stiff piano wire for stuff like that
[22:38:45] <andypugh> jdh: If you have access to a mill you can make custom mounts
[22:39:52] <Tom_itx> another plane down
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[22:41:22] <Tom_itx> laguardia
[22:41:37] <JT-Shop> what's going on?
[22:41:45] <andypugh> jdh: The X slide is not all that easy to convert, there isn't much room. However an 8mm ballscrew does seem to be adequate. http://www.cnczone.com/forums/mini_lathe/63621-mini_lathe_cross_slide_ballscrew_solutions-2.html#post509784
[22:45:31] <andypugh> Sounds like more of an expensive landing than a crash.
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[23:32:23] <JT-Shop> http://imagebin.org/265300
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[23:44:15] <jdh> cool. What are they?
[23:45:23] <jdh> andypugh: do you have any pics of your Z motor mounting?
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[23:53:42] <JT-Shop> gizmos for a production line
[23:59:59] <JT-Shop> we have to make 800 units