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#apertus IRC Channel Logs

2013/07/16

Timezone: UTC


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