Hi Chris, An interesting device, but you are making a fundamental mistake in confusing resolution with accuracy. If you read the datasheet, they make no claims whatsoever about accuracy, if it was good, I am sure they would mention it. That said, I would reasonably expect them to achieve +- 5 degrees of accuracy, maybe better, and yes, I appreciate they have a much higher resolution.
A good 2 pole resolver will achieve 5' of accuracy (that's 1/12th of a degree), resolution will be limited to the resolution of the ADC's reading the signals. Being an AC device it is relatively immune to the earths magnetic field. The devices I have are fully waterproof high quality resolvers costing probably thousands of dollars each ... I think I'll stick with them. On Sun, 22 Jan 2023 at 01:35, Chris Albertson <albertson.ch...@gmail.com> wrote: > 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 > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
