On Thursday, December 22, 2011 04:33:44 PM Anders Wallin did opine: > > I have been given a quote for electrochemical machining of an encoder > > for my project. > > http://www.photofab.co.uk/index.php/services/chemical-etch-photo-etch/ > > There is a £95 setup charge, then another £100 for a sheet of parts. I > > get 25 of my design (75mm dia) on a sheet, but only need 6 or so. > > The material I want to use is 0.3mm 304 stainless. I can add different > > designs to the sheet for no extra charge. > > Does anyone have anything intricate that they need making from > > stainless shim like this? > > What resolution can they produce? > How do you read the encoder, transmission/reflection of IR-LED or ? > Would the pattern produce a square wave-signal, or a sine-wave (which > can be 'interpolated' to yield higher resolution) > > a dream project of mine would be a telescope mount. To minimize > tracking error one should measure the rotation directly on the geared > axis (not the motor) and one wants maybe 4 million pulses (22 bits) > per rev for that.
The resolution needed would likely be best measured on the worm gears axis in order to do the multiplication needed. This could lead to an error due to backlash in the worm/gear fitting, and of course the cyclic errors as the two gears turn but it seems to me much of that could be reduced to near vanishing by either spring loading a dual bull gear, lots of $ for that, or gently spring loading the worm axis into a bull gear it doesn't quite bottom in. But that does (to me at least) seem allow one to pick a star out of the star atlas, plug its name into the co-ordinates table, massage that against ntpd derived time, and slew the scope to where that star was awfully close to centered in the FOV. FWIW, I have an elderly Meade DS-10 that I wouldn't mind being able to put in its own little roll off roof shed, with a decent camera fixed to the eyepiece piping video stills into a nice comfy house. That thing is a decent light bucket, we once took the eyepiece out and fired a wooden kitchen match at its focal point by light of the full moon on a warm summer evening nearly 20 years ago. The secondary mirror had to be replaced as the alu surface corroded from condensation, but the primary, if after 25 years, it still has its figure, is still in decent shape it should be good to go. Because here, the only clear air is in the dead of winter, I haven't had it out recently. > From what I've understood it's done by A/D converting a sine-wave > encoder, so if you get e.g. 8 to 10-bits of reliable interpolated data > then you > want an encoder with 12 to 14 bits of sine-shaped counts, i.e. up to > 16k-counts/rev. How big a circle would that require? > > Anders > > ------------------------------------------------------------------------ > ------ Write once. Port to many. > Get the SDK and tools to simplify cross-platform app development. Create > new or port existing apps to sell to consumers worldwide. Explore the > Intel AppUpSM program developer opportunity. appdeveloper.intel.com/join > http://p.sf.net/sfu/intel-appdev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> <aj> come on <aj> it's a pico clone <aj> it's *meant* to be annoying ------------------------------------------------------------------------------ Write once. Port to many. Get the SDK and tools to simplify cross-platform app development. Create new or port existing apps to sell to consumers worldwide. Explore the Intel AppUpSM program developer opportunity. appdeveloper.intel.com/join http://p.sf.net/sfu/intel-appdev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
