--- But you must have some ceiling, no?
I'm only asking because I'm interested, and if your ceiling is high enough, that's what I'd use to determine whether the investment of resources, on my part, to do a paper design of the system in order to generate a responsible bid would be worthwhile.
---
--- By when will you need quotes?
-- JF
Michael Brown hath wroth:
Sanity check. Methinks the number of steps is a bit excessive. Assuming a 30 degree viewing angle (my guess), 0.0036 degrees per step equals a: 30 / 0.0036 = 8,333 pixel wide display. Assuming a square image area, that's: 8K * 8K = 70 MegaPixels I don't think that's very reasonable and well beyond the state of the art in imaging resolution.
Working backwards, and again assuming a 30 degree viewing angle, a good B&W 8 MegaPixel imager will be about 3000 pixels across, which works out to: 30 / 3000 = 0.01 degrees/pixel which methinks is more reasonable.
Of course, a narrow viewing angle, as in a telescope will work, but I don't know of any 1 lb telescopes.
Continuing to brainstorming with insufficient information...
Perhaps do the positioning in two stages. Stepper motors, motor-encoders, or selsyn:
drives to do the coarse positioning. The fine positioning is done electronically using one of the various image stabilization methods found in todays digital cameras and telescopes:
I recently saw a vehicle mounted camera that could generate perfectly stabilized images while literally bouncing down a dirt road. (It could also detect motion and center the image on the motion). Sorry, but I can't seem to find the manufactory.
Not me. I'm buried, lazy, obsolete, burned out, etc.
Methinks this be somewhat more complexicated for the average hacker.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
$1000 to $2000 per unit for 13 arc-seconds of accuracy? Or when you said "resolution" did you really mean resolution, but the accuracy could be less?
I assume that when you specified repeatability as being "exactly" where it was before, you really meant "within the accuracy of the unit".
You'll find if you really need that kind of accuracy that you'll learn all sorts of things about how apparently rigid materials are really quite flexible in the presence of such things as light breezes and sunlight. You'll also learn a lot about backlash, friction, possibly anti-backlash gears, and other things you may never have wanted to know.
Expect that this will probably take at least a small team, and that you won't get the price down to that level until you're building hundreds of units per month.
Send me mail off list if I haven't discouraged you yet -- tim at wescott design dot com (take out spaces as appropriate, replace phonetic punctuation, etc.).
-- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
drive
zoom
[...] Add: Have no general solutions :)Idea seems reasonable though. Being bloody minded I've just opened up a JVC PTZ domecam, thinking there might be a bit of room to fineagle in some mechanical contrivance such as a linear mass compensator. Not a sausage of space. 'Tis engineered to perfection.
Nope, the sagebrush unit uses servos. From your other replies it is clear you are still underestimating the difficulty of what you are trying to achieve. Sagebrush does custom designs. It won't hurt to ask if they can build a unit in large quantities for a price you feel comfortable with.
A fish-eye lense and software to un-warp the image may be more cost effective and you'll be a apple to pan & tilt at infinite speed without any mechanical wear. There are very nice high resolution 'machine vision' cameras on the market that can be used for such purposes.
-- Reply to nico@nctdevpuntnl (punt=.) Bedrijven en winkels vindt U op www.adresboekje.nl
Just curious: why is absolute pointing accuracy important? Why not just slew it to within, say, 1 degree of the ideal direction, clamp the drive, and take pictures? Does the exact center of some object have to hit the exact center pixel of the sensor?
You could still use a good encoder to tell you the actual az/el if needed. But the drive could be something soft and sloppy, toothed belts maybe.
John
Jeff,
The reason for the extended accuracy (and again, we're talking roughly
13-18 arcseconds) is because we often work at the far extents of the zoom lens, we're not imaging the whole wide shot at once in high res as that wouldn't call for such accuracy.
Just to add a little more info:
Sony EVI-D70: 0.075 degrees resolution (270 arcseconds) Sony BRC-300: 0.0048 degrees resolution (17 arcseconds)
They both have an impressive resolution but relatively the same accuracy (much less than the resolution, probably 360 arcseconds or thereabouts). It seems doable in small form factor but I'm not sure the encoding methods they use, notably both cameras have the same accuracy.
I'm definately interested in pursuing ideas regarding a software based system but the biggest factor is image resolution. I don't know whether or not I can achieve similar quality using a high rez machine vision camera using software panning versus a normal res camera zooming and moving and such. Certainly it's benefits are directly financial, but quality is of big importance as well. If there are any programmers out there that have some experience doing this and want to give it a shot, hit me up.
As noted by many, it would be difficult to satisfy those requirements because of the mechanical constraints.
It could be possible to use several fixed cameras pointed at the different angles and synthesise the rotated image by means of the digital video processing.
Hackery doen't seem to be an option in this case.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
Michael Brown snipped-for-privacy@360replays.com posted to sci.electronics.design:
You can barely get 1 degree accuracy at that price point. (us$1000). I am actually surprised that you can even get that accuracy in a standard product at all.
Michael Brown snipped-for-privacy@360replays.com posted to sci.electronics.design:
Actually i expect that you will have more problems dealing with inconsistent zoom of the zoom lens that the camera positioning error. Small errors in the zoom lens are much harder to deal with than mere lateral / vertical image shifts.
john jardine snipped-for-privacy@idnet.co.uk posted to sci.electronics.design:
Even if you could readily stuff high resolution position sensors into that enclosure, it may not be enough. The expected zoom lens kills everything.
Michael Brown snipped-for-privacy@360replays.com posted to sci.electronics.design:
You should try thinking about different solutions when you mix in that zoom lens. Zoom lenses are not all that repeatable. That part of the solution needs to be pressed into the software. Not that is easy there either.
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