#robotics Logs

May 09 2015

00:55 al-caveman as far as i know such motors have 6 phases, and one locator? or is the locator for old models only?
01:15 rue_house locator?
01:15 rue_house 3 phase
01:38 al-caveman rue_house: you mean 6 phase not needed?
01:39 al-caveman rue_house: also by locator i mean the thing that identifies the position of the propeller to decide how to send signals to the brushless dc motor to rotate that in the direction needed
04:27 al-caveman i kinda don't get why robotics can't walk normal
04:29 deshipu al-caveman: define normal
04:29 al-caveman like humans or animals
04:29 al-caveman all robots seem to walk like retards
04:30 deshipu they are getting better
04:30 al-caveman i think i can make a perfect one
04:30 deshipu good luck
04:31 joga http://i.imgur.com/Gg6wa3S.gifv
04:31 deshipu I think Spot is pretty good already
04:32 al-caveman joga: lol
04:32 deshipu joga: I wonder how well you would do, if you had no sense of touch, gravity or the position of your limbs, and only saw through a small hole
04:32 deshipu joga: my guess is that would look very similar
04:32 joga deshipu, badly probably
04:33 joga but painless too!
04:34 deshipu sensors is one important thing, integrating the sensor data and motion planning is second, and actuators that are strong and fast enough is third of the main problems
04:35 deshipu al-caveman: there was a marvelous online course on MIT about the topic last year
04:35 deshipu al-caveman: "underactuated robotics", highly recommended
04:36 deshipu al-caveman: https://www.youtube.com/watch?v=Z8oMbOj9IWM&list=PL72571A26386CB446
04:37 al-caveman 2009 is last year?
04:37 al-caveman i know about underactuation i forgot where i heard about it
04:37 al-caveman omg the instructor is PERFECT. beard + fat + blue genese + said the word 'hardcore'
04:37 al-caveman bbl watching
04:38 deshipu al-caveman: it's every year, that video I found is from one of the earlier editions
04:38 deshipu al-caveman: you can probably find newer video
04:39 deshipu al-caveman: wlaking starts at lecture 11
04:39 deshipu walking*
04:53 deshipu by the way, you could put that alarm() in a start() funtion that you would run manually from a console -- then if anything is wrong, you can simply restart it
04:54 deshipu argh, wrong channel
04:54 deshipu sorry
05:02 LiohAu deshipu: here?
05:02 deshipu where?
05:02 LiohAu i meant awake xD
05:03 LiohAu well about the stewart platform, I'm looking in depth at how it works, and I only see designs that requires 6 servos
05:03 LiohAu but it's possible to achieve the same thing with only 3, right?
05:04 deshipu well, not exactly the same
05:04 deshipu you will only have 3 axes, not 6
05:05 LiohAu and how do you control it, are there well known formulas?
05:05 deshipu basically a platform on a ball bearing, and three servos in 120° distances
05:05 deshipu well, it's easy to calculate with basic trigonometry
05:06 LiohAu do you think that the Jibo robot head works like that?
05:06 LiohAu (talking about this robot : http://www.thatsreallypossible.com/wp-content/uploads/2014/11/JIBO-positions.png )
05:06 deshipu no, it just has two motors
05:07 LiohAu you think it does not rotate on Y ?
05:08 LiohAu (Y = roll)
05:08 deshipu yeah
05:08 deshipu or if it does, that's linked with other motions
05:13 LiohAu deshipu: so something like that : https://www.youtube.com/watch?v=Ozrp0oxKDNQ&spfreload=10
05:13 LiohAu but I have to do this, with servos instead of these bigs actuators ^^
05:15 LiohAu is there something to know about the spring used in the middle?
05:16 deshipu LiohAu: except you want rotation instead of up/down motion
05:16 deshipu LiohAu: so you want a ball bearing in the middle instead of that spring
05:16 deshipu and you want those actuators to be a little twisted
05:17 deshipu of course that's not the only way to do it
05:17 LiohAu "little twisted" => not sure to follow for that part
05:18 deshipu so that if they all expand equally, it rotates
05:19 deshipu ok, imagine a platform on a ball bearing, with 3 rubber bands tied between it and the base in equal distances
05:19 deshipu than imagine you are moving and rotating the platform
05:19 deshipu imagine what happens with the rubber bands
05:20 deshipu now just replace those rubber bands with servos with pushrods
05:21 deshipu I think it's the same algorithm as for swash plates for helicopters
05:22 LiohAu ok so basically, if I understand correctly what you describe, I need 3 servos, 3 mount on the servos to fix the pushrods (don't know how you call it), 3 links (the pushrods), 1 platform, and 3 eyelet to fix the pushrods on the platform.
05:22 LiohAu and 1 ball bearing
05:23 LiohAu but with that, I can only think about tilt / roll movements, I don't see how it can pan.
05:23 deshipu yes, that's one possible way of doing it, not necessarily the simplest
05:24 LiohAu except if I have a 4rd servo
05:24 deshipu it can pan, because the height is fixed
05:24 deshipu so when all 3 servos expand
05:24 deshipu it can't go up
05:24 deshipu so it will twist
05:25 deshipu imagine the rubber bands
05:25 deshipu what happens to them when you pan the platform
05:25 LiohAu they extend
05:26 deshipu all at once
05:26 LiohAu yes
05:26 LiohAu the pan is dependant of the servo arm size, no?
05:26 deshipu all of those ranges are
05:27 deshipu on the travel of the pushrod, to be precise
05:27 deshipu and on the radius of the platform
05:28 deshipu if the platform has small radius, you get large but weak movements
05:31 deshipu LiohAu: you can look at how rc helicopters are made for an idea on how to arrange the servos
05:34 deshipu http://tamir-asbabbazi.com/uploadimage/b-1623-esky-king-3-rc-helicopter-ali-swash-plate.jpg
05:36 deshipu LiohAu: by the way, before you buy all this stuff, I would make a model out of papaer and paperclips
05:43 deshipu ah, and I didn't mean ball bearing, but ball mount
05:43 deshipu something like http://nanoflash.net/yahoo_site_admin/assets/images/nebtek_ball_mount.8161328_std.jpg
05:59 LiohAu deshipu: ball joint
06:17 deshipu LiohAu: right
06:19 LiohAu deshipu: the hardest thing is to find where to buy these items..
06:19 LiohAu for the servos I was planning to buy dynamixel AX-12
06:19 LiohAu 3 of them.
06:20 deshipu you can probably get a ball joint cheaply in a photographic store
06:20 deshipu or one with furniture parts, maybe
06:21 deshipu the pushrods you can make yourself out of wire
06:21 deshipu or buy them with pins and mounts in a hobby store
06:21 deshipu http://www.hobbyking.com/hobbyking/store/RC_PRODUCT_SEARCH.asp?strSearch=pushrod
06:22 deshipu you could even buy a whole swashplate
06:22 deshipu http://www.hobbyking.com/hobbyking/store/__10599__TZ_V2_50_Size_Swashplate_Assembly_Metal_.html
06:22 deshipu not sure if it's strong enough
16:44 xp_prg2 hi all, I have a tunigy speed controller, trying to connect to my brushless motor, not sure what wires connect to what
16:44 xp_prg2 can anyone help me please?
16:53 SpeedEvil All of them
16:53 SpeedEvil The three motor output wires connect in any order. If the motor goes backwards, swap two
17:32 deshipu https://youtu.be/-Vg-BdXps50
17:32 deshipu this is proper humanoid walk!
17:41 wolfmanjm that is pretty impressive
17:43 deshipu the other videos of that robot are amazing too
17:43 deshipu the one where it carries tangerines
17:46 deshipu I wonder how much of it is hardwired