#robotics Logs

Jan 03 2019

06:35 AM SleepyTurtle: When sing a diff drive robot you get minimum needed turning clearance when starting the turn when the center of the diff drive is level with the instant centre of rotation right? Vel vector perpendicular to the vector from the ICR to the middle of the diff drive
06:39 AM SleepyTurtle: using*
08:39 AM SoCo_cpp_: rue_mohr I put a knob on the servero and verified 50Hz 0.4 to 2.0 ms On duty, and adjusting the duty cycle by hand, I couldn't get it to do anything but spin one way continuously or buzz. I think I'm just going to chuck the servo and get a better kind.
08:44 AM SoCo_cpp_: It was good practice for whipping up a variac + voltage divider and making some ADC input sampling code on the micro, if nothing else.
08:48 AM rue_mohr: SoCo_cpp_, I think it was worked out you have a continious rotation servo, which isn't what you apparently want
08:48 AM SoCo_cpp_: It seems so.
08:48 AM rue_mohr: can you post a picture with the back off?
08:50 AM SoCo_cpp_: I could in a few hours. It had a little board, with no adjustable/moving parts, and no visible sensors. Just two wires going to the motor.
08:50 AM SoCo_cpp_: So no sensor unless it was hidden in the motor and communicated on the same two wires.
08:57 AM rue_mohr: its usually beside the motor
08:58 AM rue_mohr: http://ruemohr.org/~ircjunk/tutorials/elex/hobbyservo/servo101.html
09:00 AM SoCo_cpp_: It didn't have anything like that. I really don't think it has a sensor of any kind.
09:00 AM rue_mohr: the board might have two fixed resistors that lock it into continious rotation
09:01 AM rue_mohr: I'd have to see a picture of its circuit board
09:01 AM rue_mohr: so, where did you get the servos?
09:02 AM SoCo_cpp_: some random ebay seller
09:02 AM SoCo_cpp_: about 4 hours I'll be back from lunch. I'll try to snap a good pic with the digital microsope thing my brother got me for xmas :)
09:05 AM rue_mohr: hmm its possible they didn't even know
09:07 AM SoCo_cpp_: it seemed to have really nice metal gears for being a misrepresented device.
09:08 AM rue_mohr: it could just be a nice continious rotation servo
09:08 AM rue_mohr: people use them for driving the wheels on robots
09:08 AM SoCo_cpp_: that seems most likely.
09:17 AM rue_mohr: is the seller still up?
09:17 AM rue_mohr: did thy list anything else?
09:18 AM SoCo_cpp_: the listing had very little info. so it would be my mix up
09:18 AM rue_mohr: oh
09:18 AM SoCo_cpp_: the stickered model number does point to specifics that don't line up with how it acts though.
09:19 AM SoCo_cpp_: but info on that number is pretty light even.
09:19 AM rue_mohr: well,, you got the way to drive them now!
11:05 AM weyland|yutani_ is now known as weyland|yutani
01:14 PM SoCo_cpp_: Took the best pictures I could of that servo insides. The board was too big for the digi microscope thing to work well. https://imgur.com/a/8vE1X8U
03:04 PM prasket: anyone around to chat about power supplies? I am working on the InMoov project and have my finger-starter ready but not enough power with my Uno kit. Per Gael's direction's need to get the full power going but all the links and such are out of date so not really sure what to do about it all.
03:50 PM polprog: you should get a lab psu
03:51 PM polprog: afaik standard USB ports provide only 500mA
03:51 PM polprog: what exactly are you making
03:52 PM zhanx: polprog, looks like prasket is making this http://inmoov.fr/finger-starter/
03:53 PM prasket: @polprog funny you say that I was just looking at them. Might not be a bad idea for playing and testing before i have it all together.
03:54 PM prasket: yes @zhanx is correct on link. Starting with that and then the whole project hopefully
03:54 PM zhanx: i am over like why is this the first time i have seen this
03:55 PM polprog: thats quite cool :D
03:56 PM prasket: :D
03:56 PM prasket: thats what I thought when I stumbled on to it from Thingiverse after getting my 3D printer
03:56 PM polprog: i suppose that only needs +5V
03:56 PM prasket: the project head says 6v is better to make the servo's move a little quicker
03:57 PM polprog: hmm
03:57 PM prasket: also saw that servo's take around 2 amps each. 21 total in the whole project, just 1 for finger, and 6 for hand/wrist/forearm.
03:57 PM polprog: oh. thats beefy
03:58 PM prasket: yeah its a pretty impressive project. They are using these for chilren in Europe who cannot go out side. They wear vr headsets and let them go out and interact
03:58 PM polprog: ive got a small power brick, industrial power supply that gives like 5.5A on its 5V bus
03:59 PM prasket: for your lab PS?
03:59 PM polprog: for the mech part you defintely wanna a separate ps
03:59 PM polprog: no, its just one of many ive collevted over time
03:59 PM prasket: ahh OK
03:59 PM prasket: I am new to robotics and electronics so all this is new to me trying to figure it out :D
03:59 PM polprog: my lab ps is korad ka-3005 p
04:00 PM polprog: you should look for popular ones as chineese lab ps quality ranges from excellent to "-30V spike on terminals when you switch it on" type
04:01 PM polprog: before that i was using another industrial, older unit, 4A 5V, fitter a 400mA polyfuse when a short in an atmega melted my breadboard a little!
04:01 PM polprog: fitted*
04:02 PM prasket: so that one only has 5amp out, that wont do for me then will it since I need at least 12 for the hand/arm/forearm (if I say 2amp per servo)
04:02 PM polprog: you can use many
04:02 PM prasket: Oh like hook up multiple Ps?
04:02 PM polprog: you wanna use a separate lower power one for the arduino, or some other conteoller to keep the noise away
04:03 PM polprog: yeah, one for each 4 servos or something
04:03 PM polprog: or make a smart program that only moves one at a time :)
04:03 PM prasket: Gael (project lead) is currently using something like this to power the full robot when plugged in vs batter. https://www.ebay.ca/itm/New-6V-Power-Supply-300W-6V-50A-Switching-Power-Supply-WITH-CE-/173713444627?hash=item287220cf13
04:04 PM prasket: I am in US so that link wont work for me, also that seems a little too much for me at the time until I get further along
04:04 PM prasket: wont work to buy I mean
04:04 PM polprog: that is a beast indeed
04:04 PM polprog: but if you are doing small stuff for starters a lab psu will suffice
04:05 PM prasket: OK let me see if I can find one on Amazon :D
04:05 PM polprog: plus, its adjustable. a lab ps allow you to precisely set a voltage and a current limit
04:05 PM polprog: they usually go up to 30V
04:05 PM polprog: thats enough for most stuff
04:06 PM polprog: once you build something particular, get a right ps for that thing
04:07 PM prasket: is TekPower a good brand?
04:07 PM polprog: also ATX power supplies can be handy. they are easy to use and have good +12 and +5 busses
04:07 PM polprog: never heard.
04:07 PM prasket: specifically https://www.amazon.com/Tekpower-TP3005T-Variable-Linear-Alligator/dp/B00ZBCLJSY
04:08 PM prasket: I did see someone mention they use an ATX PS, but nothing more on that.
04:09 PM polprog: basically on the big connector you short the green cable to ground and ot turns on. older units should not be ran unloaded bevause they overvolt and break
04:09 PM polprog: but newer ones are pretty okay
04:10 PM polprog: it turns*
04:11 PM polprog: cat is walking around meowing
04:11 PM polprog: it wants to go to sleep but the lights are on
04:11 PM polprog: goodnight ;)
04:11 PM polprog: hang around here, someone might help
04:11 PM zhanx: prasket, funny thing, i am printing the gear boxes for its legs
04:12 PM prasket: :D
04:12 PM polprog: people just leave irc open in background
04:12 PM zhanx: I was using them as part of my arm shoulder
04:12 PM prasket: good night, thanks for input @polprog
04:12 PM zhanx: my PSU is 90A
04:22 PM prasket: care to link it?
04:24 PM zhanx: prasket, its a HP server PSU
04:24 PM zhanx: 24 , 12, 5 , 3 v outputs
04:29 PM prasket: Ahh gotcha
10:10 PM rue_mohr: SoCo_cpp__, do you have a pic of the other side of the circuit board?
11:36 PM rue_mohr: polprog, you still out there?