#robotics Logs

Aug 19 2017

01:59 AM rue_house: i2c over 2wire?
02:02 AM rue_house: no, 3 wire
02:02 AM rue_house: i2c over 3 wire
02:02 AM rue_house: there isn't a 3d printable kitchan bug trap yet
02:02 AM rue_house: so I'm making one
02:02 AM rue_house: uv tray thing
02:02 AM rue_house: keep the flies from dieing on the stove
04:43 AM Jak_o_Shadows: i2c is gnd, clock, data
04:44 AM Jak_o_Shadows: so yeah, 3
04:45 AM Jak_o_Shadows: I admittedly am having some troubler on the actually talking side
04:45 AM Jak_o_Shadows: I can see it sending the address byte, but I don't get much further thna that
04:59 AM Jak_o_Shadows: Nope. I'm out for tonight
04:59 AM Jak_o_Shadows: Never fun when you have to debug 3 things at once
05:13 AM Jak_o_Shadows: a) Your own code
05:13 AM Jak_o_Shadows: b) Your test equipment
05:14 AM Jak_o_Shadows: c) The external module you're trying to talk to
01:17 PM rue_house: yup, baby steps
01:18 PM rue_house: sometimes using large complex proven buiilding blocks, but, baby steps
01:44 PM peepsalot: are there commonly available adapter shafts that taper to between different diameters, for example going from 4mm to 5mm, or are female-female couplers the main solution for that sort of thing
01:44 PM peepsalot: without having to turn my own
01:46 PM rue_shop3: if you have extra money, there will always be people to help you get rid of it
02:27 PM SpeedEvil: peepsalot: taper doesn't really work well
02:27 PM SpeedEvil: peepsalot: you can do moderate accuracy by simply drilling a 4mm hole, and then enlarging it to 5mm.
02:34 PM peepsalot: i mean just transitioning a rod from one diameter to another, not a taper press fit
02:35 PM peepsalot: actually i guess stepped would be fine too, just not as pretty :P
02:36 PM peepsalot: so on each end there would be some length of constant diameter, and it would transition somewhere in between
02:42 PM SpeedEvil: I do wish CNC scaled better.
02:44 PM SpeedEvil: A CNC lathe with autochanger and ... that could do steel parts in the range (say) 100mm long to 25mm diameter, and be easily portable would be so nice.
02:44 PM peepsalot: heh, yeah
02:44 PM SpeedEvil: (scaled in cost too of course, if it costs $80K, it's way less fun)
02:45 PM peepsalot: of course
02:46 PM peepsalot: for most machines I consider purchasing, I like to stay in target range of $2k or less
02:48 PM peepsalot: i have a mini lathe (not cnc) i'm just being lazy i guess, hoping they were more common, and maybe i just didn't know the term for it
03:02 PM peepsalot: on unrelated note, I'm fascinated by the power density and value of modern electric RC hobby stuff. i've been thinking it could be interesting to take a high power EDF,motor,esc and see how good of a DIY appliance like leafblower, or shopvac/dust collector could be made
03:04 PM peepsalot: i'm wondering if there is a particular scale of hobby motors and speed controllers that provide the best power / cost
03:09 PM peepsalot: for example this $80 motor peak watts translates to 3hp, which seems pretty amazing to me? https://hobbyking.com/en_us/turnigy-aerodrive-sk3-6374-149kv-brushless-outrunner-motor.html
03:22 PM SpeedEvil: peepsalot: neglecting stuff, mass of motor is proportional only to torque, not RPM, for a given design of motor.
03:23 PM SpeedEvil: and cost goes with mass moderately strongly
03:25 PM peepsalot: huh? doesn't kv rating(can be different for a given mass) affect torque?
03:25 PM SpeedEvil: Do be careful assuming peak watts is very usable
03:26 PM peepsalot: SpeedEvil, are you saying that small high rpm motors are cheaper per power output?
03:27 PM SpeedEvil: often, yes
03:28 PM SpeedEvil: That is likely to be ~1kW/kg or so long-term capable.
03:29 PM SpeedEvil: MAybe a little more
03:32 PM SpeedEvil: https://hobbyking.com/en_us/turnigy-c580l-870kv-brushless-inrunner-edf-motor-for-120mm-fan-5000w.html - for example - 5kW (peak), a thirdish of the weight, three timesish the RPM
03:32 PM peepsalot: i want a AWD gokart with these https://www.aliexpress.com/item/4pcs-set-RW-RC-8318-100KV-120KV-Aerial-Plant-Protection-UAV-Brushless-Motor-6-12S-ZEO/32786192036.html
03:35 PM SpeedEvil: I would as a starting point assume that more like 2kW is a sane running number, at most.
03:35 PM SpeedEvil: without careful checking of thermal properties
03:36 PM SpeedEvil: Also, how do you plan on going from 5000RPM to 50-100 or whatever.
03:40 PM SpeedEvil: And consider what happens when a motor dies in 6 months, and you can't get a replacement
03:45 PM peepsalot: say the gokart has 8" wheels, and 35mph top speed, that's 36960 inches per minute. divide that by 25 inches per rev (8" * PI) and you get 1470 RPM. would need gear ratio in the single digits, which isn't too bad
03:48 PM SpeedEvil: Oh - gokart.
03:48 PM SpeedEvil: I misread 'ATV'
03:48 PM SpeedEvil: nvm
10:48 PM synja is now known as synaj
10:48 PM synaj is now known as synja
10:56 PM Jak_o_Shadows: ok, the pca9685 is working on the arduino
10:56 PM Jak_o_Shadows: it's at 100khz, so lets match that and all the rest for the stm32
11:00 PM Jak_o_Shadows: (The PCA9685 is for servos in the short term, lights int he long term - so I wan tit owrking regardless)
11:45 PM rue_shop3: your much better off using a4017 and a timer