#robotics Logs

May 22 2015

00:22 rue_house the direction is working tho
02:33 LiohAu SpeedEvil, veverak: can you tell me more ?
02:34 LiohAu when you say "people usually power servos externally", what do you mean exactly?
02:52 rue_bed well, seeing as servos can consume about 1A ea
02:52 rue_bed and a controller board usually cant take more than a few amps
02:53 rue_bed it generally reduces to having seperate controller and servo power supplies
02:53 rue_bed LiohAu,
02:53 LiohAu rue_bed: so I only connect the signal wire of the servos to the controller?
02:55 LiohAu and I let the 2 other pins provided by the servo controller unconnected ? or I use a board that provides only PWM pins for the signal?
03:09 rue_bed nope
03:09 rue_bed the grounds of all systems have to be connected togethor
03:09 rue_bed howmany servosdo you want to run?
03:13 deshipu most controllers will let you connect separate power for the servos
03:14 deshipu LiohAu_: how about this one? https://www.pololu.com/product/1357
03:14 deshipu LiohAu_: I used a 18-channel version of that for my hexapod
03:15 deshipu you talk to it over serial using a weird protocol, and it has a separate line for power
03:32 LiohAu rue_bed: around 25
03:33 LiohAu deshipu: I was thinking to use this one : http://www.lynxmotion.com/p-1032-ssc-32u-usb-servo-controller.aspx
03:34 LiohAu or this one : http://phi-education.com/store/sync32
03:35 deshipu I've never used those, but they look good
03:35 deshipu there is also that adafruit one 12 channel one, which is chainable, so you can use two
03:59 SpeedEvil LiohAu: the grounds of the servos connect to a high current 5/6V power supply ground. The positive connection connects to the positive one.
03:59 SpeedEvil LiohAu: The pwm leads connect to your control boards, and you connect the ground of the control board to the power supply ground
04:18 LiohAu SpeedEvil: "a high current 5/6V power supply" => this means I can connect the servos directly to a 7.2v nimh battery ? (sry for delay in my answers)
04:19 LiohAu (the servos I use accept 8.4v iirc)
04:20 LiohAu Or do I need the voltage step down/up board in the middle?
04:24 LiohAu looks like you're fighting with your irc client :P
04:26 SpeedEvil sigh
04:26 SpeedEvil It should be fixedish now
04:28 LiohAu =)
04:43 LiohAu SpeedEvil: as a result, I dont know if you saw my last question :)
04:44 LiohAu the servos I'll use are rated for 6v and 8.4v, so I guess that I can use 7.2v nimh battery. But should I connect the battery wires directly to the servo? or should I use a step down/up board between ?
05:15 SpeedEvil 7.2V is nominal
05:16 SpeedEvil When fresh off charge, the cells can hit ~1.55V.
05:16 SpeedEvil This is for 6 cells >8.4
05:16 deshipu should still be fine
05:16 SpeedEvil yes, but it's over spec
05:17 SpeedEvil 8.4 is clearly inteded for 2 lithium cells
05:17 SpeedEvil 7.2-
05:17 LiohAu anyway the easiest is to put some voltage regulator between the battery and the servos right? else each time I change my battery I'll have to think about this problem
05:18 deshipu I can't help but smile when I see "single cell *battery*" written anywhere -- English is so silly
05:18 deshipu LiohAu: a voltage regulator will have a drop
05:18 Jak_o_Shadows haha
05:18 deshipu LiohAu: also, make sure it's not linear
05:20 deshipu LiohAu: as those simply burn the excess energy
05:21 deshipu LiohAu: and then it has to hanle the amount of power that you need, which is quite large
05:28 SpeedEvil LiohAu: you're looking for a 32A regulator
05:28 SpeedEvil err
05:28 SpeedEvil 40
05:28 SpeedEvil it's way easier just to use appropriate batteries.
05:41 LiohAu deshipu: my mobile robot base uses 24v motors
05:41 LiohAu so eitheir I step up the voltage for them, or I step down the voltage for the servos
05:42 LiohAu Or I step-up and step-down :D
05:45 SpeedEvil (and yes, it's very likely that the servos if specced for 8.4 would be OK with the short-term ~9.5 or so max you'll get from a nimh pack fresh off charge
09:37 rue_house LiohAu, how would you like a controller that can run 8 servos and costs just $2.50?
09:37 rue_house and has 22000 counts of postion per servo
09:39 rue_house its serial
09:41 rue_house oh 31000 counts
09:41 LiohAu you're building it?
09:42 LiohAu I need around 25 servos
09:42 rue_house I already have
09:43 rue_house I was just looking at the code, I didn't put it in, but it CAN be set up to have 4 controllers on the same serial bus, for 32 servos total
09:44 rue_house and again, its a provision, but you can cache all the new postions and have them all move at the same time
09:45 rue_house https://www.youtube.com/watch?v=qZF9WJ1Ueew
09:45 rue_house I used it on there
09:45 rue_house its fit for a different avr now
09:45 LiohAu rue_house: tapsterbot on github should be interesting for you :)
09:47 rue_house http://www.ebay.com/itm/281382960721
09:48 rue_house thats the controller I'm currently using for it
09:48 rue_house http://ruemohr.org/~ircjunk/robots/arm8/p1060720.jpg
09:49 rue_house http://ruemohr.org/~ircjunk/robots/arm8/p1060649.jpg
09:55 rue_house http://ruemohr.org/~ircjunk/robots/arm8/slide.htm
10:25 LiohAu rue_house: this is the controller only, not the power supply right?
11:07 Jinxit I'm trying to implement an extended kalman filter for position estimation. If I have a (world-space) velocity sensor, and the state of the filter is {position, velocity}, how do I determine the jacobians F and H?
14:52 MrCurious rue_house: looking nice!
17:13 rue_bed Jinxit, how does a kalman filter work
17:13 Jinxit if I knew I wouldn't be asking lol
17:13 Jinxit the use is to fuse different sensor readings, and get rid of noise
17:15 MrCurious http://bilgin.esme.org/BitsBytes/KalmanFilterforDummies.aspx
19:15 zumba_addict hey guys, i would like to buy a device like raspberry pi and then hook it up to my serial device so I can send a command to it. However, I'm not sure if raspberry is ok or if there are other better ones that are also affordable
19:19 MrCurious s it just to control things, or will there be significant THINKING happening on the board
19:20 MrCurious if its just to turn lights on and off, ore read a sensor or two, then esp8266 for $3 is a good answer
19:57 Loshki Jinxit: check out https://www.openslam.org/. Tons of code to rape and pillage there.
20:04 Loshki Jinxit: also, there's a particularly easy to follow TA session for CS141 on slam implementation. I had to fix the audio, so let me know if you want a fixed copy.
20:29 MrCurious 2 questions, 2 answers, no ty's....
23:49 zhanx Evening
23:50 Jak_o_Shadows yo