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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/XMMSEH5MPI6CAKEIUSDRSXXUDY4HYLFB/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "XMMSEH5MPI6CAKEIUSDRSXXUDY4HYLFB",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/CLOQYBU3FX2QD32ZMTRJOW3ZPNOG7XYE/",
    "sender": {
        "address": "8p6sm (a) anjo.com",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Gus",
    "subject": "[amsat-bb] Re: inquiry about homebrew az-el systems",
    "date": "2013-03-02T22:10:03Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/CLOQYBU3FX2QD32ZMTRJOW3ZPNOG7XYE/",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/E6H3VXIV3ACZPY3IZZKPBYBRRFURFKYH/"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On 03/02/2013 06:55 AM, Robert C. Campbell wrote:\n> My thought would be to count the pulses instead of a pot. I think we \n> will be stuck with gear motors if the goal is to go small and have \n> lots of torque.\n\nCounting pulses will only be practical if there is a direct correlation \nbetween pulse count and angular displacement.  That means you are \npulsing a stepper and counting those pulses, or you are activating an \nordinary motor and the pulse train is coming back from some sort of \nshaft encoder.  But I prefer this approach (digital) to reading the \nvoltage on a pot (linear/analog).  I am mentally working on a \nstraightforward, easy-to-build shaft-encoder. But how accurate do we \nneed to be, if we're building a system for small antennas with \nreasonable wide beam-widths?\n\nI am coming to the conclusion that for a globally ubiquitous supply of \nsecond hand motors, we will have to turn to the automobile junk yard.  \nWindshield wiper motors and window wider motors spring instantly to \nmind.   Newer cars have motors everywhere. Repositioning seats, \nadjusting rear view mirrors, opening and closing tailgates.  Perhaps \ncentral locking mechanisms can be adopted to lock the rotors in position \nbetween moves to prevent weather-cocking.  I'm fairly sure that \nvirtually anywhere in the world you could get your hands on two wiper \nmotors from a junk yard without breaking the bank.\n>\n> I would like to move away from stops and find another way to establish \n> 0~360az and 0~90/180ex indication so as to enable continuous rotation \n> to do  continuous sky scan or search and rescue with out having to \n> wind up and damage my coax.\n\nContinuous rotation probably requires some sort of coaxial slip-ring \nsystem.  Google \"coax rotary joint.\"  They look expensive, and I can't \nhelp worrying about insertion loss.  But perhaps limit switch is the \nwrong word.  But with a cam on your shaft and a micro-switch, you have \nhard position-detection of two places on the circle:  when the switch \ngoes ON and when the switch goes OFF.  (In theory, enough switches and \ncams and you could detect any number of places on the circle.)  I think \nit's useful, e3specially with a pulse counting system, to be able to \nconfirm your position at least a couple points around your circle.  This \nwould allow your controller to calibrate itself when ever it needed to, \nand possibly to double-check itself during normal operation.  Whether or \nnot you choose to wire a hard-shutoff based on the output of these \nswitches depends on whether you have a continuous-rotation coax joint or \nnot.\n\n> I am not sure what battle ship radar uses for constant rotation but \n> that would be the ticket.\n>\n>\n> Bob Campbell\n> KB3PMR\n\n-- \n73, de Gus 8P6SM\nBarbados, the easternmost isle.\n\n",
    "attachments": []
}