You can simplify this if you replace the resolvers with magnetic encoders. They cost $4 each and come mounted to PCBs and with a magnet. What you do is super-glue the magnet to the shaft end and then face the chip at the magnet with an about 1mm air gap. The chip tells you the shaft angle to within 1/4000 of a revolution. It is easy because it is an absolute encoder so you don't have to track the shaft you can query the angle whenever you need it. There is both an analog and digital output
It is a 4mm diameter magnet and you mount it by first making a small hole in the shaft with a drill if the shaft is not already center drilled. Then the magnet is very powerful and you really don't need glue. They work better if you get larger 6mm dia. magnets but still I get reading good to about 0.1 degree. With resolvers and quadrature encoders you have to track the encoders continuously but these are "query on demand." With more money, for $10 you get a better sensor that does 16,000 "ticks" per revolution, absolute. These are cheap enough to place them on the motor and the driven structure https://www.amazon.com/HiLetgo-Magnetic-Encoder-Measurement-Precision/ <https://www.amazon.com/HiLetgo-Magnetic-Encoder-Measurement-Precision/dp/B09KGWC1PT/ref=sr_1_2_sspa?keywords=as5600&qid=1674349813&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzOThLWTdPUkkyWlpCJmVuY3J5cHRlZElkPUEwMjg2NTczMjVSOVNEOU1aTDFEUCZlbmNyeXB0ZWRBZElkPUEwMzE1MDEwMk5UUjVRNlJINkhRQiZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=> On Sat, Jan 21, 2023 at 4:59 PM gene heskett <ghesk...@shentel.net> wrote: > On 1/21/23 06:25, Robin Szemeti via Emc-users wrote: > > So, in a vaguely CNC related folly I have purchased a 2 axis military > dish > > mount for radio stuff (moonbounce, if you must know) > > > > My plan is to control it from EMC, with a Mesa anything io card and the > > resolver interface, I already have various Mesa cards under EMC, so thats > > not an issue and I have a spare 5i23 PCI card and the isolated IO > duaghter > > card, so with the resolver card I should be able to uses the resolvers, > and > > pick up the limit switches on the IO card. I can just use some Python > > script to work out the moon position and generate "G1 X285.4, Y23.8" or > > whatever MDI motion commands every 15 seconds or so to track the moon, > not > > a problem. > > > > Now, the question is driving the two phase AC servos. Generating vast > > quantities of 50 or 400Hz or whatever AC for the drives is simple > enough, I > > can just use a couple of large Class D amplifiers, no worries. Generating > > the AC low level signals to drive these .... basically, it needs a > constant > > 50Hz signal on one coil of a fixed level, and a variable level sine wave > on > > the other coil, at either +90 or -90 degrees depending on which way it > > needs to go. > > > > Is it possible to use HAL or something to generate the variable level > 50Hz > > servo drive signals and output them from the PWM outputs on the resolver > > card? > > > I've not used it in that context, but take a look at man 9 siggen. > There are several mux's available that could be used to switch motor > directions. Its main use is in 1 kilohertz loop stuff for linuxcnc, but > if you need finer time resolution, should be happy in a 3 to 5 kilohertz > threads Use a halmeter to see how much time the individual module takes. > > Hal can do a lot, look the logic choices over in /usr/share/man/man9 of > an linuxcnc install and let your imagination out to play w/o a > chaperone. You can use float vars at a 1 or even 4 kilohertz loop > thread, so updating a motor drive at 50HZ ought to be doable. > > For motor amps, take a look at class D audio amps, the 400 watt modules > are rather commonplace these days, running at ultrasonic carrier > frequencies. Use chokes to keep the carrier out of the motor wires, and > good single point(one bolt) grounds. > > Use mux's for analog switches. > > Using modern stepper drives that have current limits built in, you can > creep steppers along at .01 hz a second, and if you spend the sheckels > for the closed loop stepper/servo's suitably geared down, you ought to > be able to track the moons motion within an arcsecond in real time and > do it on 40 watts of power or less since they use the error to determine > how hard to drive the motor. The recovery time when it goes below the > horizon and has to pre-aim at the other horizon for when the moon comes > back in sight at next moonrise is a problem since the active times match > the dead times pretty closely. > > I've not paid that much attention but from satellite experience, you > likely need just a little azimuth, even for polar mounts, your latitude > above or below the equator determines that, and a large longitude. > > I have an old friend from back in the 70's that at that time was > building a 12 bay steerable 2 meter get up. 16 element yagi's in a > broadside array. But another job opening took me to NM from NE so I lost > track of him. Employment brought me to WV 38 years ago, and I'm now 21 > years retired, and still here. > > And tell us how you did it when it working. > > Cheers, Gene Heskett. > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author, 1940) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > Genes Web page <http://geneslinuxbox.net:6309/> > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
