#robotics Logs

Jun 13 2018

12:00 AM CBloom: I see
12:03 AM CBloom: I pretty much just want a servo motor without an IC in it, so I can use my own IC
12:05 AM rue_mohr: buy SG90 and take the servo baord out
12:05 AM rue_mohr: an SG90 is about $1.50
12:05 AM rue_mohr: an SG90 without the servo board can be obtained for about $20
12:05 AM rue_mohr: and no, I'm not missing any dots
12:06 AM rue_mohr: the S3003 is the large one
12:06 AM CBloom: sorry, what do you mean about missing dots?
12:08 AM rue_mohr: <rue_mohr> an SG90 is about $1.50
12:08 AM rue_mohr: <rue_mohr> an SG90 without the servo board can be obtained for about $20
12:08 AM rue_mohr: SG90 whole -> $1.50
12:08 AM CBloom: oh, thanks
12:08 AM rue_mohr: SG90, no controller baord -> $20.00
12:08 AM rue_mohr: _ea_
12:08 AM CBloom: I see. I was hoping to use a large powerful motor
12:09 AM rue_mohr: a window winder or winshield wiper motor?
12:11 AM CBloom: I'm not sure, haven't looked into those. I just want to look at large brushless dc motors that have built in position encoders so I can see which one meets my needs
12:12 AM rue_mohr: your looking at $300 or more ea
12:12 AM orlock: any idea on what sort of positional accuracy?
12:12 AM CBloom: At least 1024. I'd be happy with 1024 positions
12:13 AM rue_mohr: you need roomf or errror
12:13 AM rue_mohr: so, if you have 10 counts for error, you need 10240
12:13 AM CBloom: I see
12:13 AM CBloom: It would be good if it could apply at least 2 N m of torque.
12:14 AM rue_mohr: ok, what max speed?
12:14 AM orlock: https://www.portescap.com/resources/motor-selection
12:15 AM CBloom: I'm not sure, depends on how much speed decreases with torque. I'd like it to spin at around 200 RPM while clost to half torque
12:15 AM CBloom: Would the error be less of an issue if it used an absolute encoder?
12:16 AM rue_mohr: no
12:17 AM CBloom: I see, so when servos say they have 1024 position accuracy, does it really mean they are only reliable to ~10% of this?
12:17 AM rue_mohr: good question
12:24 AM CBloom: the motion compass website isn't giving me any results when I give reasonable torque values
12:42 AM rue_mohr: need to work out how far to space the rings
12:42 AM rue_mohr: hmmm
12:43 AM rue_mohr: I'm thinking about 6"
12:43 AM rue_mohr: 150mm, hmm
12:43 AM rue_mohr: need to find a pipe that I can use as a pin
12:48 AM * z64555 wonders what the outside compression ratings on pipe are
12:49 AM rue_mohr: its a truss structure, so... not sure
12:51 AM rue_mohr: I wonder is square spacers would be sufficient
12:51 AM rue_mohr: 1/8" plate
12:57 AM rue_mohr: http://ruemohr.org/~ircjunk/robots/arm6/p1070897.jpg this guy needs more work
01:02 AM rue_mohr: hmm, I need force feedback servos
01:03 AM rue_mohr: I need a high speed optical link, I suppose I should start seeing what kinda data rates I can push thru leds
01:04 AM rue_mohr: I wonder what the turn-off time is of those lasers
01:04 AM rue_mohr: the capacitance of the reciever is prolyl the limit
01:16 AM z64555: sounds reasonable
01:51 AM rue_mohr: best slew is 4v/10us
01:52 AM rue_mohr: so limit is ~20Khz
01:52 AM rue_mohr: thats not the data link I'm looking for
01:54 AM rue_mohr: not even close to spdif even
01:55 AM rue_mohr: er, toslink
01:55 AM rue_mohr: up to 125MB/sec
03:01 AM Jak_o_Shadows: hmm, do you have any all plastic arms? Apart from the motors?
05:57 AM Jak_o_Shadows: My laser time of flight sensor arrived today!
05:57 AM veverak: rue_mohr: use optocouples?
05:58 AM veverak: rue_mohr: I suppose that could have faster rate?
07:51 AM SpeedEvil is now known as Guest943
09:08 AM BitEvil is now known as SpeedEvil
09:28 AM rue_mohr: the reason I need an optical link is cause the joint rotates
09:29 AM rue_mohr: Jak_o_Shadows, plastic arms?
04:26 PM veverak: https://scontent-frt3-2.xx.fbcdn.net/v/t1.15752-9/s2048x2048/35265849_1989562084388500_7923643413289762816_n.jpg?_nc_cat=0&oh=3c1ced09c37f5c42cee8828a5545019b&oe=5B7A3701
04:26 PM veverak: hydropony
04:26 PM veverak: with automatic watering, ver 1.
05:46 PM slim_jim_johnny is now known as durrf
07:54 PM rue_mohr: iiinteresting, chromium loads a LOT faster after its cache has been deleted
09:45 PM rue_bed: I neeed to make force feedback servos
09:54 PM rue_bed: it needs to be a variable bipolar current source
09:54 PM rue_bed: if thats switching, I need it to be filtered properly
10:18 PM rue_bed: https://threeneurons.files.wordpress.com/2011/09/s_led_drv1.gif
10:19 PM rue_bed: hmm, making a bipolar swtiching current source might be a trick
10:19 PM rue_bed: maybe this is a call for tompwm
10:21 PM rue_bed: if I use a single supply, I can play with an H bridge, maybe
10:24 PM rue_bed: https://i.stack.imgur.com/2oIzg.jpg
10:30 PM DIRT: i was thinking about making a hybrid quad copter
10:31 PM DIRT: but i bet the vibrations are going to mess with the sensors
10:32 PM DIRT: what i might do is just have a gas powered prop to directly carry most of the weight. seems more efficient than running a generator, charging batteries, then running a motor
10:38 PM rue_bed: huh
10:54 PM Tom_L: gas motor will vibrate just as much
10:54 PM Tom_L: either way you need shock mounts
10:55 PM Tom_L: it's not easy finding a suitable spindle motor improvement
10:56 PM rue_mohr: hmm
11:02 PM Tom_L: https://www.aliexpress.com/item/750W-1HP-Spindle-Head-Unit-ER20-Chuck-60mm-Power-Head-5000-6000rpm-5pcs-Bearings-CNC-Milling/32834245955.html?spm=2114.search0302.3.56.7b526c91ENVLZN&ws_ab_test=searchweb0_0,searchweb201602_0_10130_10152_10151_10618_10059_10696_10084_100031_10083_10547_10624_10546_10623_10307_10548_10341_10065_10340_10068_10343_10342_10103_10620_10344_10325_10545_10622_10324_10621,searchweb201603_0,ppcSwitch_0&algo_pvid=e43f9ef0-9857-
11:02 PM Tom_L: doesn't say much about how it's powered
11:02 PM Tom_L: maybe that's just the spindle no motor
11:15 PM Tom_L: https://www.aliexpress.com/item/9KW-380V-ATC-Spindle-Motor-6-4Nm-22A-Long-Head-ISO30-BT30-12000-24000rpm-replace-Italy/32834801153.html?spm=2114.search0104.3.9.7cfa7d9da4TAdf&ws_ab_test=searchweb0_0,searchweb201602_2_10152_10151_10065_10344_10068_10130_5722815_10324_10342_10547_10325_10343_10546_10340_5722915_10548_10341_10545_5722615_10696_10084_10083_10618_10307_5722715_10059_100031_10103_10624_10623_10622_5722515_10621_10620,searchweb201603_11,pp
11:15 PM Tom_L: that one might be a little big
11:21 PM rue_mohr: oof
11:22 PM Tom_L: that one is 30 taper, we ran 40 & 50 taper on the big machines
11:22 PM Tom_L: pretty hefty still
11:22 PM Tom_L: it's next to impossible to find a spindle motor
11:25 PM Tom_L: https://www.alibaba.com/product-detail/High-Speed-Bldc-Brushless-Motor-Spindle_1905913371.html?spm=a2700.7724857.main07.144.44a7f52bv4KL8E
11:25 PM Tom_L: possible contender