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GET /hyperkitty/api/list/[email protected]/email/SSQFHHX4AQ2XE6OAWDMEJY2EV7LL525M/?format=api
{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/SSQFHHX4AQ2XE6OAWDMEJY2EV7LL525M/?format=api", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api", "message_id": "[email protected]", "message_id_hash": "SSQFHHX4AQ2XE6OAWDMEJY2EV7LL525M", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/GOPLREH6KKWJ3FABQJRT5MZKECIDYLNV/?format=api", "sender": { "address": "gary_mayfield (a) hotmail.com", "mailman_id": "fe442cdc520e4857a9168b9182091295", "emails": "https://mailman.amsat.org/hyperkitty/api/sender/fe442cdc520e4857a9168b9182091295/emails/?format=api" }, "sender_name": "Gary \"Joe\" Mayfield", "subject": "[amsat-bb] Re: Non-mechanical Azimuth/Elevation Feedback Advice", "date": "2013-08-08T04:15:01Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/GOPLREH6KKWJ3FABQJRT5MZKECIDYLNV/?format=api", "children": [], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "Maybe someone can dig the archives better than me, but I remember there was\nan elegant solution years ago.\n\nPart of a thread can be found here:\n\nhttp://www.amsat.org/amsat/archive/amsat-bb/200101/msg00697.html\n\n73,\nJoe kk0sd\n\n\n-----Original Message-----\nFrom: [email protected] [mailto:[email protected]] On\nBehalf Of Zach Leffke\nSent: Wednesday, August 07, 2013 8:58 AM\nTo: 'AMSAT BB'\nSubject: [amsat-bb] Non-mechanical Azimuth/Elevation Feedback Advice\n\nHello Everyone,\n\n I recently came into possession of a Pelco PT170-24P\ntracking pan tilt pedestal designed to support large security cameras. My\nintent with this new acquisition is to repurpose it as a \"low cost\" (got it\non Ebay for ~$75 + S&H) alternative for an antenna tracking pedestal for\namateur satellites. It uses 24VAC induction motors to move the azimuth and\nelevation assemblies, pretty much just like the G5500s that I'm sure so many\nof us are familiar with. It definitely cannot support the same amount of\nweight as the G5500, but I'm looking to construct a small, portable\nsatellite ground station node and this thing is plenty beefy enough to\nhandle a couple of Arrow style antennas. Here is the problem, it provides\nabsolutely no feedback.\n\n \n\nMy question to the group is does anyone know of a non-mechanical method for\ngetting relatively accurate feedback for azimuth and elevation. I'm looking\nfor an all electronic means that I can mount somewhere outside of the actual\npedestal assembly (like perhaps on the cross-boom) that will be able to\nprovide measurement of the az/el (or pan/tilt, or yaw/pitch, whatever you\nwant to call it) position. I'm using an arduino microcontroller for the\ntracking controller. Originally I intended to find a way to mount\npotentiometers in inside the unit and simply use the ADCs on the arduino to\nread the position feedback voltage from the pots, however, there is barely\nenough space to mount an elevation feedback pot inside the unit, and there\nis virtually no space for an azimuth feedback pot. Hence I'm looking for a\nnon-mechanical method.\n\n \n\nMy first thoughts for the elevation feedback was to use the old\npotentiometer plus nice heavy weight method mounted out on the boom. This\nidea doesn't appeal to me very much as other factors can now affect the\nposition feedback (such as high winds). I then thought of something along\nthe lines of an accelerometer. I also tossed around the idea of a 2-axis\ngyro for both Az/El. My issue is I have limited experience working with\nthese types of sensors, and was hoping to get advice from everyone in this\ngroup. I know for example that the gyro will provide rate of motion around\nan axis and thus I have to integrate over time to get the actual position.\nThis becomes cumbersome because now I have to keep track of time in the\nArduino while executing movement commands (certainly do-able, just more\ncomplicated than reading an ADC voltage). Additionally, I believe these\ndevices suffer from drift and require frequent calibration (although there\nmay be a scheme of starting from a known position, say at one of the limit\nswitch contact points, for each pass that might work). I also toyed with\nthe idea of an electric compass for azimuth feedback, but I'm worried about\ndistortion of the magnetic field near the pedestal due to the AC induction\nmotors or when the antennas are radiating. In theory the motors are housed\ninside the metal pedestal enclosure and thus are shielded from the outside\nworld, but I can just see it now, nice steady feedback when the pedestal is\nstopped and as soon as I execute a motion command the azimuth feedback\nstarts dancing all over the place. Since the motion stop command is based\non achieving the target position, system instability is sure to occur. Even\nif I solve the AC motor EMI problem, I still worry that when transmitting\nthe fields could potentially be distorted if near the antenna (remember my\ngoal is a compact design) and taint the position feedback.\n\n \n\nAny ideas from the group would be greatly appreciated. I'm looking for a\n\"sparkfun\" type solution here and if anyone has experience working with\naccelerometers, gyros, electric compasses, etc. I would love your advice on\nwhich might be the way to go for the position feedback. If you think I've\nhit on a good idea above and should go with it please let me know. Again\nI'm using an Arduino, so analog voltage feedback, I2C, SPI, and UART serial\nare all on the table for communicating with the sensors to get the feedback\ninfo.\n\n \n\nThanks in advance!\n\n \n\nSincerely,\n\nZach, KJ4QLP\n\n \n\n_______________________________________________\nSent via [email protected]. Opinions expressed are those of the author.\nNot an AMSAT-NA member? Join now to support the amateur satellite program!\nSubscription settings: http://amsat.org/mailman/listinfo/amsat-bb\n\n", "attachments": [] }