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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/PDPZV6AL6LUP3LDLS5P5CBTRQXVYYEOK/", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/", "message_id": "[email protected]", "message_id_hash": "PDPZV6AL6LUP3LDLS5P5CBTRQXVYYEOK", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/GOPLREH6KKWJ3FABQJRT5MZKECIDYLNV/", "sender": { "address": "co7wt (a) frcuba.co.cu", "mailman_id": "e0c3935155ca4fb78cafec35cf64d7f2", "emails": "https://mailman.amsat.org/hyperkitty/api/sender/e0c3935155ca4fb78cafec35cf64d7f2/emails/" }, "sender_name": "Ing. Pavel Milanes Costa", "subject": "[amsat-bb] Re: Non-mechanical Azimuth/Elevation Feedback Advice", "date": "2013-08-08T22:58:12Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/MBC3O75MCKNNMX6MWH5ZRYXLR5W4IBDL/", "children": [ "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/PED5YMXXMGRIL235IBPJ4SVKPAQQJJRJ/" ], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "This is the link to the system I described in the earlier email\n\nhttp://www.cbk.waw.pl/~mstolars/projekty/rotor/index_en.html\n\n73\n\nEl 07/08/13 19:01, Ing. Pavel Milanes Costa escribió:\n> Yes, me to...\n>\n> I do have a old Japanese tracking camera mounting also with 24 AC motors\n> here... 360 degrees azimuth with stop switch on 0 and 360 degrees and\n> about 0 to 120 degrees of elevation (0 ~ horizon, 90 ~cenit)\n>\n> Pretty good construction, a ham here in Havana have one the uses to move\n> 2 phased yaguis of 5 elements for 2m... the brake system is primitive\n> but works fine...\n>\n> Pointing is by eye and as in your case no means of feedback... recently\n> after completing some TODO-IN-THE-FUTURE projects with Jal/JalLib (Just\n> Another Language and libs for PIC devices) and pics I get hands on this\n> project\n>\n> A couple o months or so (maybe more) there was a thread on the list\n> about this...\n>\n> I find the arduino project from K3NG, but no arduino here, only\n> Microchip PIC (PIC18F4520) so I have to re-invent the wheel...\n>\n> I was thinking on gray encoding the position with 7 bits, but this is A\n> LOT of cables to run..\n>\n> Then I see on the specs of the arduino a feedback mechanism of pulse\n> counting... and find on the internet a project from a polish? ham that\n> uses this mechanism wit a ATMEGA MCU but with a trick... (I have the\n> link on my work place... link will be tomorrow)\n>\n> I explain, he uses several magnets glued on the edge of an intermediate\n> gear in the reduction mechanism... then get a magnetic switch (or a hal\n> sensing device if you like) close to the edge where the magnets are...\n>\n> This mechanism do about 500+ pulses for each 360 degrees... pretty neat\n> an simple... with only 2 cables...\n>\n> The only thing is you have to reset the mechanical position of the\n> antennas at each power-on to reset the internal count in the\n> pic/arduino/atmega MCU...\n>\n> I'm on the ideas-on-the-boad part of this project for making it 450\n> degrees instead of only 360 and how to deal in software with the 0 to 90\n> degrees restriction on the elevation part...\n>\n> Just another idea to the brain storm...\n>\n> 73 de CO7WT.\n>\n> PS: control will be serial emulating a RS232B protocol from Yaesu...\n>\n> El 07/08/13 09:58, Zach Leffke escribió:\n>> Hello Everyone,\n>>\n>> I recently came into possession of a Pelco PT170-24P\n>> tracking pan tilt pedestal designed to support large security\n>> cameras. My\n>> intent with this new acquisition is to repurpose it as a \"low cost\"\n>> (got it\n>> on Ebay for ~$75 + S&H) alternative for an antenna tracking pedestal for\n>> amateur satellites. It uses 24VAC induction motors to move the\n>> azimuth and\n>> elevation assemblies, pretty much just like the G5500s that I'm sure\n>> so many\n>> of us are familiar with. It definitely cannot support the same amount of\n>> weight as the G5500, but I'm looking to construct a small, portable\n>> satellite ground station node and this thing is plenty beefy enough to\n>> handle a couple of Arrow style antennas. Here is the problem, it\n>> provides\n>> absolutely no feedback.\n>>\n>>\n>>\n>> My question to the group is does anyone know of a non-mechanical\n>> method for\n>> getting relatively accurate feedback for azimuth and elevation. I'm\n>> looking\n>> for an all electronic means that I can mount somewhere outside of the\n>> actual\n>> pedestal assembly (like perhaps on the cross-boom) that will be able to\n>> provide measurement of the az/el (or pan/tilt, or yaw/pitch, whatever you\n>> want to call it) position. I'm using an arduino microcontroller for the\n>> tracking controller. Originally I intended to find a way to mount\n>> potentiometers in inside the unit and simply use the ADCs on the\n>> arduino to\n>> read the position feedback voltage from the pots, however, there is\n>> barely\n>> enough space to mount an elevation feedback pot inside the unit, and\n>> there\n>> is virtually no space for an azimuth feedback pot. Hence I'm looking\n>> for a\n>> non-mechanical method.\n>>\n>>\n>>\n>> My first thoughts for the elevation feedback was to use the old\n>> potentiometer plus nice heavy weight method mounted out on the boom.\n>> This\n>> idea doesn't appeal to me very much as other factors can now affect the\n>> position feedback (such as high winds). I then thought of something\n>> along\n>> the lines of an accelerometer. I also tossed around the idea of a 2-axis\n>> gyro for both Az/El. My issue is I have limited experience working with\n>> these types of sensors, and was hoping to get advice from everyone in\n>> this\n>> group. I know for example that the gyro will provide rate of motion\n>> around\n>> an axis and thus I have to integrate over time to get the actual\n>> position.\n>> This becomes cumbersome because now I have to keep track of time in the\n>> Arduino while executing movement commands (certainly do-able, just more\n>> complicated than reading an ADC voltage). Additionally, I believe these\n>> devices suffer from drift and require frequent calibration (although\n>> there\n>> may be a scheme of starting from a known position, say at one of the\n>> limit\n>> switch contact points, for each pass that might work). I also toyed with\n>> the idea of an electric compass for azimuth feedback, but I'm worried\n>> about\n>> distortion of the magnetic field near the pedestal due to the AC\n>> induction\n>> motors or when the antennas are radiating. In theory the motors are\n>> housed\n>> inside the metal pedestal enclosure and thus are shielded from the\n>> outside\n>> world, but I can just see it now, nice steady feedback when the\n>> pedestal is\n>> stopped and as soon as I execute a motion command the azimuth feedback\n>> starts dancing all over the place. Since the motion stop command is\n>> based\n>> on achieving the target position, system instability is sure to\n>> occur. Even\n>> if I solve the AC motor EMI problem, I still worry that when transmitting\n>> the fields could potentially be distorted if near the antenna\n>> (remember my\n>> goal is a compact design) and taint the position feedback.\n>>\n>>\n>>\n>> Any 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\n>> accelerometers, gyros, electric compasses, etc. I would love your\n>> advice on\n>> which might be the way to go for the position feedback. If you think\n>> I've\n>> hit on a good idea above and should go with it please let me know. Again\n>> I'm using an Arduino, so analog voltage feedback, I2C, SPI, and UART\n>> serial\n>> are all on the table for communicating with the sensors to get the\n>> feedback\n>> info.\n>>\n>>\n>>\n>> Thanks in advance!\n>>\n>>\n>>\n>> Sincerely,\n>>\n>> Zach, KJ4QLP\n>>\n>>\n>>\n>> _______________________________________________\n>> Sent via [email protected]. Opinions expressed are those of the author.\n>> Not an AMSAT-NA member? Join now to support the amateur satellite\n>> program!\n>> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb\n>>\n> _______________________________________________\n> Sent via [email protected]. Opinions expressed are those of the author.\n> Not an AMSAT-NA member? Join now to support the amateur satellite program!\n> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb\n>\n", "attachments": [] }