#robotics Logs

Jul 31 2019

06:37 PM logb0t_ is now known as logb0t
08:34 PM alesan: hello wanted to try my first stepper motor... I was about to buy a NEMA23 one but I also liked to get a gearbox
08:34 PM alesan: this is supposed to be an antenna rotator
08:35 PM orlock: nice
08:35 PM orlock: Why geared?
08:35 PM orlock: for torque or increased resolution?
08:35 PM alesan: I think both - again this is my first experience but
08:36 PM alesan: antenna(s) might be a couple of VHF yagi
08:36 PM orlock: and you just want direction, not elevation changes?
08:36 PM alesan: light stuff and not too big
08:36 PM alesan: well yeah itr will be both but I'm starting with one
08:36 PM alesan: I just have no experience with the motors
08:36 PM orlock: unless they are really tiny, you probably don't want to try attaching them directly to the steppers
08:36 PM orlock: Got a driver?
08:37 PM orlock: also, there's two main flavours of stepper - remembering, NEMA17 / 23 etc are mounting standards more than anything
08:37 PM alesan: I have one in my amazon cart :D
08:37 PM orlock: most steppers these days are bipolar
08:37 PM alesan: bipolar is good or bad?
08:37 PM orlock: you can get carrier boards for arduino's with space to fit a few steppers
08:37 PM alesan: the other flavour is...?
08:38 PM alesan: carrier board? wait let me look up what is
08:38 PM orlock: Just dirrefent - Unipolar you can drive just with a set of transistors, bipolar the driver circuirty is a bit more complicated, but you can easily get driver chips that will integrate nicely with an arduino
08:39 PM alesan: wait I was thinking about something like this: https://www.amazon.com/gp/product/B074TBMC7N
08:39 PM orlock: https://www.reprap.me/3-axis-usb-cnc-arduino-nano-controller-a4988-stepper-motor-driver-board.html
08:39 PM alesan: I thought that is sufficient with an arduino like (I'm going to use a ESP32 but that is irrelevant now)
08:40 PM alesan: is that not too small?
08:40 PM orlock: https://initeq.info/product/arduino-nano-cnc-shield-3-axis-drv8825-stepper-driver-board-complete-package-kit
08:41 PM alesan: the one I linked is not good in your opinion?
08:42 PM orlock: It all depends on your stepper..
08:42 PM alesan: I had randomly chosen this one https://www.amazon.com/gp/product/B00PNEPW4C
08:42 PM orlock: but those little driver chips are what are used on all the 3d printers, etc etc
08:43 PM alesan: yeah but I am to rotate a 2m long antenna, even if balanced, I think it needs more ... torque?
08:44 PM orlock: Maybe - do you have them mounted and the mast rotation all worked out?
08:45 PM alesan: I will have to figure everything out
08:45 PM orlock: I'm moving this, with mine (with appropriate gearing...)
08:45 PM orlock: https://somepicturesof.space/IMG_3273.jpg
08:45 PM alesan: nice
08:45 PM orlock: i replaced the factory controller with one of those little 3 axis CNC boards
08:45 PM alesan: you have much higher precision requirements
08:45 PM alesan: my precision is ~1degree
08:46 PM alesan: so I do not need extreme ratios, also becvause some sdatellites are quite fast and I need some speed
08:46 PM orlock: ah
08:46 PM orlock: yeah, you will then
08:47 PM orlock: it's funny when the satellites show up in images
08:47 PM orlock: you can see what sort by the trails
08:47 PM alesan: you use that for terrestrial subjects or astronomy?
08:48 PM orlock: geosync leave a trail, but it's kind of an inverse of the star trails
08:48 PM orlock: as the telescope moves while the geosync stays in place, making a trail
08:48 PM orlock: while the rest of them are so fast they just make a line
08:48 PM orlock: only astronomy really, terrestrial only when testing
08:49 PM alesan: what exposure times are we talking about here?
08:49 PM orlock: i've only just gotten that telescope on that mount, previuously i used DSLR
08:49 PM orlock: rouchly 60 seconds per image, maybe 30 maybe 120, depends on the target and conditions/alignment/etc
08:50 PM alesan: I used to be into astronomy image capture and processing
08:50 PM alesan: had access to a 32"
08:51 PM orlock: nice
08:51 PM orlock: https://somepicturesof.space/
08:51 PM orlock: those are mine
08:51 PM alesan: mounted on the top of a building so not that stable :D
08:51 PM orlock: most of those are taken with a 200mm FL F/4 telephoto lense, '70's vintage
08:51 PM orlock: ahh, university then?
08:52 PM alesan: not bad at all
08:52 PM orlock: i wrote my oan arduino code to emulate a subset of the the Meade LX200 commands
08:52 PM orlock: so combined with webcam it can do guiding
08:53 PM orlock: https://somepicturesof.space/IMG_2202.jpg
08:53 PM alesan: yeah, but then a couple of friends (that work in great telescopes (BLT, etc) design) build their own observatory
08:54 PM alesan: so you have a "regular" camera as a finder scope and
08:55 PM alesan: the main lenses in what looks like some sort of polymer mount?
08:55 PM orlock: nope, two different imaging setups
08:55 PM orlock: the big newtonian is new, i havent hooked up a bracket for a guider yet
08:55 PM orlock: the Pentax + DSLR is the main imager, and there's a finder with a webcam attached to the back for guiding
08:56 PM alesan: OK
08:56 PM orlock: and yeah, all mounted in a combination dovetail + ring setup i designed and printed in PLA
08:57 PM orlock: with a lit of hollow threaded spaces to insert those threaded rods
08:57 PM alesan: is PLA rigid enough?
08:57 PM orlock: lense caps are on to take darks! :)
08:57 PM alesan: yeah
08:57 PM orlock: Crap weather, so i havent done much meaningfull testing with that setup
08:58 PM alesan: oh australia
08:58 PM alesan: my friend the one that made the observatory collaborated with some australian dudes
08:58 PM orlock: most of those images on my page were taken with an EQ3
08:58 PM alesan: so they could "share" each othwer's observatory
08:58 PM orlock: so much slop it was impossible to align nicely
08:59 PM orlock: But i'm still quite proud of the results you see in the first three images
08:59 PM orlock: my homebrew controller's timing was way off, but with autoguiding enabled it managed to guide out most of the timing errors
08:59 PM orlock: and you can see compared to the factory firmware it also eliminated a lot of the PE
09:00 PM alesan: nice
09:00 PM alesan: listen I need to fix dinner now
09:00 PM alesan: thanks for the duiscussion! I'll be back :D
09:00 PM orlock: 1st image guided with homebrew controller, 2nd image unguided with homewbre controller, 3rd image is with the factory controller (which has no capability of guiding)
09:00 PM orlock: NP
09:11 PM rue_mohr: hi
09:11 PM orlock: hi
10:55 PM alesan: orlock, at the end... what gear reduction did you use on the scope?
11:36 PM sinned6915: rue_mohr: you about?
11:37 PM sinned6915: i could use a little guidance
11:37 PM sinned6915: trying to verify that an oled module works, i am trying to use an example sketch
11:38 PM sinned6915: and even though i know its questionable, an example online