#robotics Logs

May 11 2013

02:39 R0b0t1` I have been looking for articles on motor control beyond "sensorless" BEMF detection, anyone got anything?
02:39 R0b0t1` Or keywords.
02:40 R0b0t1` TI had something which used the induction of the motor as a parameter for some calculation, which is kind of what I was envisioning,
02:40 R0b0t1` but is rather mute on implementation, as expected.
02:42 theBear i suppose current tells you how fast it is already moving/how much torque you applying
02:42 theBear as far as movement only back emf makes sense, to measure induction yer gonna be effecting things slightly
02:42 theBear err, inductiveness
02:42 theBear inductance !
02:42 GargantuaSauce inductation
02:42 theBear :)
02:45 theBear back emf works well for multi coil motors, it's easy to implement with minimal components, it's good
02:46 theBear pretty sure there's a atmel/avr appnote that covers it, name has something to do with bldc control i think, or 3phase pc fan, something like that
02:47 theBear and of course bldc is just a stepper with VERY few steps
02:52 GargantuaSauce i think that might be an oversimplification :V
02:53 R0b0t1` theBear: I was thinking monitoring the phases with ADC as opposed to comparator, knowing the inductance of a coil should tell you how far along the formation of the field is
02:53 R0b0t1` if you know the voltage
02:53 R0b0t1` you could use this to tweak commutation more precisely
02:53 R0b0t1` For example using a stroboscope I notice periodic disturbances on a motor with a on-chip solution
02:53 R0b0t1` and with a hobby ESC module
02:54 R0b0t1` Quite honestly it probably does not matter, but I still kind of wonder why it happens.
02:54 R0b0t1` Interrupt/processing/code quirks, I guess.
02:56 R0b0t1` If they use brushless motors for line drives there might be work on tighter control, but typically I thought they just used induction motors
02:57 theBear GargantuaSauce, it really isn't
02:58 theBear R0b0t1`, i suppose, but in the same way if you a-d instead of comparating, you got a VERY good idea where the motor is
02:58 theBear yeah, probly problems with the controller, in reality it's a VERY accurate way to measure what a motor is doing
02:59 theBear for example, if you got a motor/drive setup (dumb/no feedback) run it steady and scope the coils while you do
03:00 theBear inductance makes me uneasy, feels like to pulse hard enough for a decent reading you'd be effecting the movement too much
03:00 GargantuaSauce couldn't you use the response to the pwm you're doing anyway?
03:00 theBear hmm, i suppose if you 'read' inductance of the coil you were driving
03:00 theBear GargantuaSauce, heh, great minds eh :)
03:01 theBear so i suppose that's what, current sense... little shunt maybe, lowside, adc on a low ref, wonder if you could get enough resolution without dropping too much on the shunt
03:01 theBear with bigger stuff you could use halls for non-contact sensing, but small stuff they aren't a lot of use
03:02 theBear and you wouldn't wanna run more than 1 'turn' thru a hall, or you add so much inductance your measurements will be silly
03:02 GargantuaSauce i imagine we're already talking about using two amplifiers
03:02 GargantuaSauce per channel i mean
03:02 theBear two ? why two ?
03:03 GargantuaSauce becaue it's 5 am and i'm getting fuzzy
03:03 theBear hehe
03:21 R0b0t1` theBear: Yeah you measure motor response to the PWM signal
03:21 R0b0t1` that drives it
03:21 R0b0t1` see how the motor attenuates it
03:21 R0b0t1` either way, probably moot point
03:22 R0b0t1` I must sleep. Good night.
03:22 theBear have a good sleep :)
03:22 theBear interesting... i wanna measure or see some graphs now... i woulda thought the driving inductance was much more affected by torque/load than position
03:24 R0b0t1` Indeed, I think it was to help better compensate for load
03:26 theBear for position the back emf is good 'cos it should be completely independant of load
03:53 Jak_o_Shadows Hukka: no, i got hte original
03:53 Jak_o_Shadows also, just measured current draw of a motor similar to one i'm using. 5A startup, 2A continous, 15A stall
03:55 Jak_o_Shadows which is rather a lot all said
04:00 theBear sure is
04:16 Jak_o_Shadows My H-bridge might be able to go to 6A, but I'm betting closer to 1A CTS.
04:17 theBear how fancy is your bridge ? can you (hard) limit it ?
04:18 Jak_o_Shadows I can, but I wasn't going to, it's a decent chunk of additional circuitry
04:18 theBear so how yer gonna deal with the gaint motors ? just avoid stall conditions ? <grin>
04:19 theBear spose if you don't expect them a fuse should cover it
04:19 Jak_o_Shadows pretty much. Also the motor i'm going to use is a tad smaller
04:19 theBear hooray
05:38 orlok goddamn it, i didnt follow rues instruction #1
05:39 orlok now i cannot find the two cables i handmade, because i DIDNT PUT EVERYTHING IN A BOX!
05:39 orlok having said that, i have my software all sorted, controller handset 90% done, both motors responding correctly
05:40 orlok drilled hole in the bottom of baby telescope and JB weld'd a 1/4" nut to the inside for secure fastening to a tripod type thread
05:40 orlok just need to put everything back in enclosures, and find the damn cables to connect the motors to the controllers
05:40 Jak_o_Shadows I found out today that all my drillbits are useless, and that I cannot fabricate anything to save my life
05:41 orlok i'm also finding drillbits everywhere i look it seems
05:41 orlok i need to put some shelves up
05:41 orlok and then some more
05:41 orlok and some more
05:42 orlok still sorting out the garage/workshop too
05:42 orlok GF's stuff takes up the double garage, workshop is mine
07:33 fRaf stumbles in drunk as p
07:33 RifRaf what did we make today? i made sweet fa, but did tidy up
07:34 orlok i made a mess of my finger!
07:34 orlok and some working code
07:35 RifRaf sounds juicy, rip the knuckle off or just a slice?
07:35 orlok and i glued a nut to the inside of a telescope
07:35 orlok we have this flimsy plastic 60cmx70cmx120xm black plastic "garden storage chest"
07:35 RifRaf cool, i gave up on telescopes fora bit, too hard to follow stars, they move too fast
07:35 orlok went outside in dark, sidestepped something else, fell into the chest
07:35 RifRaf need cnc control
07:35 orlok just took a chunk out of the middle finger on right hand
07:36 orlok RifRaf: thats the code i just finished
07:36 orlok for the CNC control feedback loop
07:36 RifRaf nice one, you have any footage coming up?
07:36 RifRaf would be so cool if you could track what you are trying to see
07:37 orlok nah, didnt follow rue's rule #1, cant find the cables i made 2 years ago to conenct steppers to the control box
07:37 orlok RifRaf: tracking thats actually trivial, but it depends on your mount
07:37 orlok know the difference between equatorial and alt-az?
07:37 RifRaf solder up some new ones, often faster than finding the cables you lost
07:37 orlok yeah, its the cable ends that are tricky
07:37 orlok 8 pin mini DIN
07:38 RifRaf i don't know yet no, but if you make a nice working platform would be interested
07:38 orlok RifRaf: alt-az you have to move in 2 axis to follow a star, thats you basic standard canon/camera/etc tripod
07:38 Jak_o_Shadows I have enough trouble soldering fine wire to .1" headers
07:38 orlok left/right/up/down
07:38 RifRaf orlok, yep that makes sence
07:39 orlok RifRaf: equatorial, you adjust it to your latitude.. so if its pointing "straight ahead" its actually pointing up at 30 (or whatever) degrees
07:39 RifRaf Jak_o_Shadows, maybe you need goggles as well, i cannot work without a decent magnifier and lights
07:40 orlok RifRaf: then you just move it in one direction, and it follows the stars
07:40 orlok well, you are actually compensating for the earths rotation
07:40 orlok which is why you have to set it to your latitude
07:40 RifRaf orlok, nice, will have to try again once this reprap is made, its consuming my time and i don't even have parts yet
07:40 Jak_o_Shadows Hmm, I dont know. I just dont think the wire i'm using is ideal.
07:40 Jak_o_Shadows also, enough web dev for today
07:41 orlok RifRaf: so to track the stars like that, you just need a single motor turning at the correct rate
07:41 RifRaf you make it sound easy, and from the deals on ebay etc maybe it is not that hard
07:41 orlok RifRaf: if you have looked at pictures of star trails, then think of what would happen of the camera was rotating as well, it should make sense?
07:42 RifRaf computer control seems almost the norm for a decent scope now
07:42 orlok RifRaf: its actually quite minor, the mechanical quality of the mount is more important
07:42 RifRaf orlok, yep have done a few stars trails with bulb mode on tripod
07:43 orlok RifRaf: so you know how they all rotate around the southern celestial pole?
07:43 RifRaf and yep, if you could follow that path it could be done with a single motor in the correct plane easy i guess
07:43 orlok RifRaf: anyway - i have a small telescope, webcam hooked up instead of the eyepeice. software uses images from that taken every half a second
07:43 RifRaf its the north here i think
07:44 orlok figures out how much stars are drifting up/down/left/right
07:44 orlok no, we are down under
07:44 orlok south!
07:44 RifRaf yep cool, have a few webcams i have saved for the tadsk in future
07:44 RifRaf oh oh south :)
07:44 orlok and then sends commands in a standard format to tell the motors to correct for it
07:45 orlok using a serial format from one of the big telescope companies
07:45 RifRaf yep nice, can't wait to see wat you do with it
07:45 orlok been trying to get this shit working ion some way for years
07:45 orlok but house and baby, etc in the way
07:45 RifRaf i'd just like to get nice moon images with dslr, and it even needs to move a bit for long exposures
07:45 orlok i have it set up so i have one arduino controlling the two stepper motors
07:46 orlok and also checking the state of 5 gpio's
07:46 orlok which are north/south/east/west and track
07:46 orlok track meaning "just rotate to compensate for the earth spinning"
07:46 RifRaf yep
07:47 orlok and another arduino thats using somebody elses code thats emulating one of the big expensive telescope mounts
07:47 orlok and then toggling 5 outputs
07:47 orlok so i can either have a dumb handset p[lugged in and position it manually
07:48 RifRaf yep joystick control would be good too
07:48 orlok or plug in the telescope mount emulator, and have the computer control it for the whole webcam feedback loop
07:48 orlok currently my images usually turn to shit after about a 30 second exposure due to mechanical and calibration errors
07:48 orlok this should let me stretch that much longer
07:49 orlok i'm only using a telephoto lense on a canon dslr
07:49 orlok not an actual telescope - too much weight for my little mount
07:50 orlok also, i spent half an hour siphoning petrol out of a torana today so it wouldent go stale in the tank
07:50 RifRaf yep i have got some nice shots with just the dslat olympus and zoom lens,
07:50 orlok now i have half a tank in the brumby, yay!
07:50 orlok i hate zoom lenses
07:50 RifRaf most attemps at connecting it to a scope have failed so far
07:51 RifRaf it 600mm, but blurry at full zoom a bit
07:51 orlok for decent astro stuff, you need to take a few different types of calibration images
07:51 orlok and with a zoom lense, its impossible to keep your zoom and focus the same to take them
07:52 RifRaf did get some good images using the fujifilm into good binoculars though
07:52 orlok so i use 1960's pentax telephoto lenses
07:52 orlok big metal things
07:52 orlok 200mm F4
07:53 RifRaf yep have some big old school lens that i hope i cn use for something one day, garage sale stuff, but several kg each 300mm +
07:55 RifRaf i found most of the parts to make 1/2 a reprap today, like bearing smooth rods and threaded rod, but not enough of anything to really make it yet
07:56 RifRaf i have a question though, found these lead screw things, wondering if they would be of any use instead of threaded rod
07:56 RifRaf http://imagebin.org/257307
07:59 Triffid_Hunter RifRaf: what's the pitch?
07:59 Triffid_Hunter RifRaf: you don't want more than about 2mm pitch for Z, and you don't want less than 25mm pitch for XY
08:00 RifRaf ok well seems to be 5mm per gap, and there are 3 spines, so maybe 1.5cm per rev
08:00 RifRaf i dunno how to measure these things yet sorry]
08:01 RifRaf far too much by the sounds of it, i just assumed that maybe there were many steps and it might be able to use them
08:01 RifRaf the have no backlash and are so smooth even after sitting outside for years
08:02 Triffid_Hunter 3 start? you sure? looks like 4 or 5 in the pic to my eye
08:02 RifRaf will check with glasses on, brb
08:02 Triffid_Hunter RifRaf: easiest way probably to look at the end of the screw
08:02 Triffid_Hunter or wind the block off and look at that
08:03 RifRaf wow you are good Triffid_Hunter, was 5
08:03 Triffid_Hunter block is delrin btw, a commonly used thermoplastic for bushings
08:03 RifRaf yep i love delrin
08:03 Triffid_Hunter RifRaf: right well 5 start 5mm gap is 25mm pitch, those are usable for XY if you don't mind taking a bit of a speed hit
08:03 RifRaf have found many rods i can make parts from today while scrouncing around
08:03 RifRaf need to get lathe setup
08:04 Triffid_Hunter RifRaf: now you just need a 3d printer so you can print matching parts to use those for your 3d printer :P
08:04 RifRaf ok cool, well will put them aside for the next machine then :)
08:04 RifRaf i want to make a bigger one Triffid_Hunter
08:05 RifRaf with 2 or more beds, am i silly thinking that?
08:05 Triffid_Hunter RifRaf: start with normal size first, get it dialed in and get some experience under your belt
08:05 Triffid_Hunter RifRaf: big ones come with many more issues
08:05 RifRaf yep for sure, this project will be all standard
08:05 RifRaf ok :(
08:06 RifRaf but am happy with this new frame
08:06 RifRaf but till i make the rest i still dunno if its any good
08:06 Triffid_Hunter it's harder to get the axes moving smoothly and not binding while keeping your repeatability
08:06 Triffid_Hunter also large parts are _far_ more prone to warping unless designed very carefully
08:06 RifRaf yep so is alot more than just the cad design
08:07 Triffid_Hunter yep
08:07 RifRaf i have been playing with slic3r and a few things, i see you have a big part in teacup
08:08 RifRaf does the avr board come preprogrammed?
08:08 Triffid_Hunter heh I wrote teacup from scratch, then handed it over a year or two ago when I moved on to other projects
08:08 Triffid_Hunter RifRaf: it should do but you'll probably end up flashing new firmware at some point
08:08 RifRaf yep i want an lcd and sd card
08:09 RifRaf just because they seem handy for other things i am makin, can't wait to make some parts though
08:11 RifRaf Triffid_Hunter, will be another week or so before i get parts, do you have an i3 or want to try a frame for one?
08:11 RifRaf frames is all i can do for now, i have 2 8mm smooth rods and a bunch of bearing , but all the threaded rod is 3/8 and too fat
08:13 Triffid_Hunter RifRaf: I have a bit of wood with a single cutout, is missing drill holes etc though and I'm not entirely sure I can drill them straight with the parts I have available
11:55 rue_shop3 whats a good cut depth for a 6mm ream
11:55 moriarty about twenty
11:55 theBear err, 6mm, what ?
11:55 rue_shop3 6mm ream
11:55 theBear what
11:55 theBear what's a ream, some kinda bit ?
11:56 rue_shop3 straight fluted ream
11:56 rue_shop3 want to make valves
11:56 rue_shop3 http://www.practicalmachinist.com/vb/general/how-much-should-left-reaming-137847/
11:56 theBear hmmm, is there a different/foreign name for them ? surely there isn't a bit i've never heard of
11:57 Tom_itx .005" or so
11:57 theBear OH ! tapered reamer ! i got one of them
11:57 rue_shop3 http://www.ebay.com/itm/0-2385-CARBIDE-STRAIGHT-FLUTE-CHUCKING-REAMER-USA-MADE-/190705613226
11:57 rue_shop3 no, mines straight
11:57 rue_shop3 5 thou dia or radius?
11:57 Tom_itx .005" or so D
11:58 theBear yeah, i just never heard a straight one named, and for some reason i didn't think of half the term tapered-reamer :)
11:58 Tom_itx depends how good your drills are
11:58 theBear i remember them, my dad got a handful with his taps
11:58 Tom_itx you can go up to around .010"
11:58 Tom_itx more than that and you may risk wrecking the reamer
12:01 Tom_itx why did you ask if you had the answer?
14:28 MrCurious yay! robot stereo amplifiers came
14:28 MrCurious yay! robot stereo amplifiers came
21:00 rue_shop3 <rue_shop3> I got a pneumatic solinoid from ebay today
21:00 rue_shop3 <rue_shop3> saw an interesting trick
21:00 rue_shop3 <rue_shop3> they took excess port holes in the plastic block and jammed small bb's in them to plug them up
21:08 GargantuaSauce sounds like a recipe for an eventual projectile
21:50 MrCurious got my stereo amp board for my robot working. its swearing like a sailor-bot now.
21:51 GargantuaSauce noice