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#apertus IRC Channel Logs

2013/07/16

Timezone: UTC


01:38
intracube
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03:11
dmj_nova
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07:58
ApertusWeb0
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ApertusWeb0
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08:57
dmj_nova
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09:12
dmj_nova
Bertl: hmm...if you were interfacing with a sensor, what would you want that interface to be?
09:53
FergusL
dmj_nova: if I can allow myself to answer, the direct interface to the sensor varies
09:53
FergusL
it might be analog values to read directly or sometimes I2C
09:55
dmj_nova
FergusL: yeah, first time designing an interface for a sensor if you can't tell
09:56
FergusL
hehe
09:57
FergusL
I've been using Arduino for about a year, it was a great first step
09:57
FergusL
(though I already had learned quite a lot about electronics at school)
09:58
dmj_nova
I've had a fair bit of experience with other sorts of electronic stuff
09:58
dmj_nova
but it can be interesting when one realizes a gap in experience
10:10
dmj_nova
FergusL: probably a serial interface would be less of a pain to work with if you have many sensors
10:11
dmj_nova
and each sensor communicated a 10-12 bit code
10:12
FergusL
yes, definitely, but sensors don't generally have directly serial outputs, most of the time they're connected to a microcontroller which in turn process the signal and sends serial messages
10:15
dmj_nova
I suppose it's the same here
10:15
dmj_nova
10 "digital" lines per sensor
10:16
dmj_nova
(okay the number is rather arbitrary and based on how long and how precise the encoder is)
10:16
FergusL
what is the sensor you're looking it ?
10:16
dmj_nova
Basically trying to figure out how best to make that useful
10:17
dmj_nova
FergusL: I'm building a new kind of linear encoder with absolute positioning via graycode
10:18
FergusL
okay, I see
10:23
FergusL
is it for something apertus-related or ?
10:23
dmj_nova
motion control camera rig related :)
10:25
FergusL
oh nice !
10:26
dmj_nova
I found that linear encoders are stupid expensive
10:26
dmj_nova
and most of them can't do absolute positioning so you've got to recalibrate every time you start it up
10:29
FergusL
yes, but that's what gray code fixes iirc
10:29
dmj_nova
yep
10:29
dmj_nova
which is why the graycode in my design is built into the physical nature of the sensor
10:30
FergusL
hm, some encoders do that
10:30
dmj_nova
yep, but totally not cheap
10:31
dmj_nova
(well, cheap by industrial robot standards, yes)
10:31
dmj_nova
but still like ZedBoard expensive
10:35
FergusL
ha yes...
10:35
FergusL
though the Zedboard isn't that expensive for what it is
10:35
FergusL
FPGA programming is *always* expensive anyway
10:35
dmj_nova
quite true
10:35
dmj_nova
but it's still a big chunk of change for an individual
10:36
dmj_nova
and when your design needs at least 3 of them, it adds up
10:36
dmj_nova
BTW, I'm trying to design a moco rig for indie film
10:39
dmj_nova
so cost is a big deal when you have lots of parts added together, and it would be rather silly for the encoders to double your rig cost
10:40
dmj_nova
heck, my stepper controllers are $35 bucks
10:41
FergusL
is it a 3 axis controlled head ?
11:09
dmj_nova
Well, at the moment the only thing that's been built is an arm
11:10
dmj_nova
but the intent is for something like a 6-axis rig
11:10
dmj_nova
so rotation and translation
11:28
FergusL
I see
11:28
FergusL
what range to you plan to achieve ?
11:30
dmj_nova
about a 6 foot cubed area?
11:30
dmj_nova
ish
11:30
dmj_nova
meaning about 6ft on each dimension
11:30
dmj_nova
perhaps more on one translation axis
11:31
dmj_nova
I'm hoping to be able to get repeatable "handheld" or "steadicam" type shots
11:32
dmj_nova
which should be good for having actual ground truth 3D coordinates for each frame (rather than having to spend hours and hours matchmoving in blender)
11:34
FergusL
that and more importantly the ability to shoot multiple passes
11:38
dmj_nova
FergusL: and potentially be able to film the same scene simultaneously in multiple locations
11:39
dmj_nova
(assuming one had the software to do real-time sync...which is really trivial)
11:40
FergusL
the usual technique is to shoot one or two passes at a location
11:40
FergusL
and then doing others on green screen for example
11:41
dmj_nova
yep, though for example you could film a location and two actors in separate locations and have the rig respond to both
11:42
dmj_nova
so you can play the actor's timing off each other
11:42
dmj_nova
but the bigger deal is enabling multiple passes and allowing freer use of vfx in smaller productions
11:43
dmj_nova
also getting background plates for compositing with
11:44
dmj_nova
often you can get away without much masking by diffing against the background plate, but that only works for tripod shots
11:47
FergusL
ToS has proven 3D tracking are okay, also it might have been on tripod and/or travelling rails only
11:48
dmj_nova
FergusL: ToS enabled us to do good tracking at all
11:49
dmj_nova
But, keep in mind that tracking still takes significant human effort and requires that the shot have good references to track in the first place
11:49
dmj_nova
I could give you plenty of shots that are untrackable
11:51
dmj_nova
and the tracking has to be done separately for every shot
11:51
dmj_nova
one tracking shot is fine, and entire scene...takes a lot of work
11:52
dmj_nova
whereas setting up a moco rig and tracking that way gets more efficient the more shots you need
11:54
FergusL
absolutely yes, that's what is used on bigger setups
11:55
dmj_nova
moco rigs are really expensive though
11:55
dmj_nova
not something an indie production could use for half their film
11:55
FergusL
yes
11:55
FergusL
and I think you can't avoid expensive sensors which are a crucial point
11:56
FergusL
or rather shouldn't !
11:57
dmj_nova
well, as long as you stay within the stepping capacity of the motors you don't need hardly any sensors for moving the rig accurately
11:57
dmj_nova
(ie, as long as you aren't skipping steps)
11:57
dmj_nova
the sensors are just an input mechanism
11:58
dmj_nova
so your operator can follow the actors rather than planning the shot out ahead of time in the computer
11:58
Bertl
morning everyone!
11:59
dmj_nova
morning Bertl
11:59
Bertl
dmj_nova: well, the sensor interface largely depends on what kind of data (amount, interval) you need to transport over what distance and how reliably
12:00
Bertl
there are quite a number of standartized bus systems for transferring data digitally (which usually is preferable over analog)
12:01
dmj_nova
yeah, and the sensor is pretty much inherently digital
12:01
Bertl
simple/cheap systems include IIC, one wire and SPI
12:02
dmj_nova
IIC == I2C?
12:02
Bertl
more expensive but also more reliable ones include rs-232, rs-485 and CAN
12:02
Bertl
yes I²C = I2C = IIC
12:03
dmj_nova
hmm...I wonder if mocobus would be a good idea
12:03
dmj_nova
seeing as how the sensor will necessarily be used with mocobus steppers
12:05
Bertl
it seems to be a modified rs-485+ttl system (never heard of mocobus before_
12:05
Bertl
s/_/)
12:05
dmj_nova
mocobus is what's used by the nanomoco stepper controllers made by dynamic perception
12:06
dmj_nova
The Axiom is supposed to eventually have a mocobus interface.
12:07
Bertl
yeah, well, I do not see a problem with that interface per se, no idea why I would want a mixed bus though
12:08
dmj_nova
you mean mixed with both sensors and motors?
12:09
Bertl
no, I mean rs-485 and ttl (for whatever purpose)
12:09
dmj_nova
ah
12:09
Bertl
because that will severely limit the usability IMHO
12:10
dmj_nova
how so?
12:11
Bertl
rs-485 is a standard defining the electrical characteristics of a serial connection
12:12
Bertl
termination, voltages, etc, but not the actual protocol
12:12
Bertl
(so you can do whatever you like with it)
12:12
Bertl
and rs-485 can be used over quite a distance
12:13
Bertl
35MBit/s over 10m, 100kBit/s over 1km
12:13
Bertl
now TTL levels on the other hand will not be reliable over more than a few meters at most
12:14
Bertl
(their level will fall below anything which can be recognized on the other end)
12:14
Bertl
they also suffer from EMI and offset voltage issues
12:14
Bertl
(they are not differential signals)
12:16
Bertl
so, at first glance that looks to me like you are building a high security transport vehicle but you decide to send half of the data via pigeons
12:17
Bertl
but maybe I'm just misinterpreting the design, haven't found a conclusive documentation
12:18
dmj_nova
could be, I haven't tested mocobus with anything longer than a couple meters
12:20
dmj_nova
seems to used twisted cat5 cable for all the connections
12:21
dmj_nova
I could ask Chris about the TTL thing though
12:26
dmj_nova1
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12:26
dmj_nova1
hooray, I just had a power failure
12:26
dmj_nova
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12:26
dmj_nova1
changed nick to: dmj_nova
12:27
FergusL
hu
12:48
dmj_nova
I suppose I'm rather limited to the constraints of mocobus anyway :/
12:49
dmj_nova
well, unless I also build my own motor controllers
12:49
dmj_nova
which would be a huge waste of effort and a giant fuck you to dynamic perception
12:53
dmj_nova
might be able to design it so it can be used as regular RS-485 except when interfacing multiple devices on a single bus
12:57
christiankrupa
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christiankrupa
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13:35
Bertl
rs-485 is not limited to 2 endpoints
15:09
jucar2
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16:36
intracube
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jucar1
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jucar1
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jucar1
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19:22
dmj_nova
Bertl: there must've been some good reason for the TTL logic
19:23
Bertl
maybe, if you feel like, you might ask the developers :)
19:24
dmj_nova
I might do that when he gets back to me with my last set of questions
19:24
Bertl
no doubt there has been a reason for adding it, not sure it was a good one though :)
19:25
dmj_nova
so far their engineering has seemed sound to me (though everyone makes mistakes)
19:26
dmj_nova
the stepper controller is quite good, and the software for it is also well-done (though it didn't work on Linux until I got my hands on it)
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