#robotics Logs

Aug 03 2017

12:48 AM Sol is now known as Guest83728
05:07 AM theBear: hehe, for a second there i thought grafana was a fancy name for ground pencil lead in a jar
05:28 AM veverak: :D
05:49 AM Guest83728 is now known as Solgriffin
09:22 AM rue_more: you would think its an overcast day, but its just smoke from all the forrest fires...
09:51 AM orlock: hey, rue
09:51 AM orlock: i got a pot i'm using as a trigger stlye throttle, due to the mechanical setup i'm only getting maybe 30% of the available movement
09:52 AM orlock: its a 10k pot so i'm missing out on a chunk of resolution from the adc
10:25 AM Snert: parallel a 10K resistor.
10:26 AM Snert: that would make a 5k pot.... with a crappy taper most likely...but still much closer.
10:27 AM orlock: there's software to deal with the details
10:27 AM orlock: cheers
10:27 AM orlock: i put in a log pot stupidly, i see a whole 5 different values over the travel range
10:28 AM orlock: the 3d printed quadrature encoder using a pair of optical end sensors from a printer work
10:29 AM orlock: which is really awesome for the differential steering this bot has
10:29 AM Snert: software can correct for the wrong value pot that produces a dead zone?
10:29 AM orlock: just simple 2 motorskid steering, rotary encoder for left/right control, pot for throttle
10:30 AM orlock: Snert: i could probably get away with 2 speeds
10:30 AM Snert: so no I guess.
10:31 AM orlock: the tricky bit is handling the rotary encoder
10:31 AM orlock: not tricky
10:31 AM orlock: fun
10:31 AM orlock: interesting
10:32 AM orlock: i'll be measuring time between impulses to get some sort of velocity reading for whetherthe steering wheel is turning left or right
10:33 AM orlock: and the shorter the time between impulses, the harder the turn
01:31 PM Solifugus: How can I calculate the DC motor I need to push up to 57 kg at up to 6,500 cm per second? (I can gear it.. but what are the motor characteristics I need? bi-direction DC)
01:39 PM Solifugus: It seems like there should be a calculator somewhere to figure this out... with best efficiency.
01:40 PM Solifugus: To simplify, I could round down safely to 56 kg and 6 m/s
02:09 PM Solifugus: 12 HP motors.. I probably miscalculated.
02:12 PM mrdata: Solifugus, is the load on wheels?
02:13 PM mrdata: 65 m/s is 234 km/h ; rolling resistance will be in the calculation
02:15 PM mrdata: wait, you rounded 6500 cm/s down to 6 m/s? oh are you using , in the european way, so you mean 6.5 cm/s?
02:16 PM mrdata: how fast do you want to accelerate?
02:18 PM mrdata: you will find motor use torque-speed curves
02:18 PM mrdata: so calculate the torque you want from a standing stop
02:19 PM mrdata: and compare that to motor datasheet
02:48 PM peepsalot: what should you do if you are worried you might create the precursor to the robot apocalypse when the robots decide they have better uses for earth's resources than humans?
03:08 PM codepython777: Has anyone used a bridge rectifier on their ground robots ?
03:10 PM robopal: how
03:15 PM robopal: really, how do you mean?
03:17 PM codepython777: robopal: was that for me?
03:18 PM robopal: yes sir
03:18 PM robopal: I mean a bridge rectifier goes between AC <-> DC right?
03:19 PM robopal: where is it needed?
03:22 PM mumptai: many PSU fed with AC
03:24 PM codepython777: robopal: I'm trying to use a ac generator to charge my battery on a ground robot. It's a 36V, 350W BLDC 3-phase motor that is rotating -> Bridge rectifier -> I would like to feed that to the Lipo on board - but...
03:24 PM mumptai: sounds like an application for a 3-ph rectifier
03:26 PM codepython777: The problem is how do i use the rectifier output to charge the lipo
03:26 PM codepython777: Lead acid was good :)
03:35 PM jhylands_ is now known as jhylands
03:49 PM mumptai: codepython777, lipo? hemm.
03:49 PM mumptai: the typical cc/cv operation needs an amount of power defined by battery and charger
03:50 PM mumptai: i guess that a voltage and current limit are still usefull
03:51 PM codepython777: mumptai: how does one use the output from a bridge rectifier to charge a lipo on load?
03:52 PM mumptai: put some capacitors across the dc side
03:52 PM mumptai: but this might actually be tricky as the frequency and voltage will vary
03:53 PM mumptai: anyway the next step would be some type of regulator
03:53 PM mumptai: most lieky likely some switch-mode type
03:54 PM mumptai: but linear, and shunt regulators might also be an option .. but those will get hot in most cases
03:55 PM mumptai: actually, this would be similar to a MPPT in a photovoltagic system
04:04 PM mumptai: there are some lifepo starter battery replacements, maybe those can stand the float charging operation better
09:13 PM rue_bed: how can they still charge so much for mppt?