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Thread: I'm planning building an EQ platform

  1. #11
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    Default Re: I'm planning building an EQ platform



    Quote Originally Posted by Aero787 View Post
    Well thanks guys !
    I think before building the platform i will try making a small one (barn door) for my canon 1200d, i'll see what mistakes i can make and i will later try to not do them on the telescope's platform
    Hardly anyone has built an EQ platform that was used successfully for AP. One thing to keep in mind is that it needs to be dual axis because an autoguider is needed badly to compensate for the crappy mechanics, and it needs to work in both axes. Also keep in mind that pointing a Dob away from the meridian, your RA and DEC actions will not be perpendicular so whatever controlling action you get will somewhat fight the orthogonal controller by PHD2. Mostly, people get away with it.

    The most often successfully used EQ platforms are those by Tom Osypowski - high quality, dual axis but pricey. Well, pricey as the aperture goes up it actually becomes cheap if you look at EQ mounts that can achieve the same.

    It is good to build a simple camera barndoor first. If you use an Arduino it will produce the code that you can use for the real thing later. I have personally built a dual axis barndoor tracker for my 10" and used successfully for AP. I also built a dual axis EQ platform intended for AP that I never gave the final test (I won a telescope lottery, bought an AVX mount and never looked back, sorry). For both builds, check my threads and albums.

    Go for it!
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    Clear skies, Henk. Telescopes: Carbon fiber ES ED127CF, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: AVX, LXD55, Tiltall, Cameras: Canon (SX40, 450D, 350D, ELPH 100HS), Samsung NX100, DIY: Dob and camera barndoor trackers, afocal adapter, foldable Dob base with leveling feet, Az/Alt setting circles, Accessories: Counterweight bar attachment, Plossls, Barlows, Telrad, SSAG, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK

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  3. #12
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    Default Re: I'm planning building an EQ platform

    Quote Originally Posted by CamelHat View Post
    Hardly anyone has built an EQ platform that was used successfully for AP. One thing to keep in mind is that it needs to be dual axis because an autoguider is needed badly to compensate for the crappy mechanics, and it needs to work in both axes. Also keep in mind that pointing a Dob away from the meridian, your RA and DEC actions will not be perpendicular so whatever controlling action you get will somewhat fight the orthogonal controller by PHD2. Mostly, people get away with it.

    The most often successfully used EQ platforms are those by Tom Osypowski - high quality, dual axis but pricey. Well, pricey as the aperture goes up it actually becomes cheap if you look at EQ mounts that can achieve the same.

    It is good to build a simple camera barndoor first. If you use an Arduino it will produce the code that you can use for the real thing later. I have personally built a dual axis barndoor tracker for my 10" and used successfully for AP. I also built a dual axis EQ platform intended for AP that I never gave the final test (I won a telescope lottery, bought an AVX mount and never looked back, sorry). For both builds, check my threads and albums.

    Go for it!
    Thank you for the advices !
    I think making a 2 axis motorised EQ platform with tracker will be to difficult for me Also i don't understand all you said with perpendicular actions


    I've seen this : A Tracking Platform for Astrophotography – Gary Seronik
    I would like to build it but i don't understand what "10-32" refers to, for the threaded rod. I assume it's about the pitch of the rod.
    I live in France, so when i'll buy one the pitch will be written in centimeters, somebody could maybe show me an equivalent rod with metric units ?

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    Default Re: I'm planning building an EQ platform

    Quote Originally Posted by Aero787 View Post
    I've seen this : A Tracking Platform for Astrophotography – Gary Seronik
    I would like to build it but i don't understand what "10-32" refers to, for the threaded rod. I assume it's about the pitch of the rod.
    I live in France, so when i'll buy one the pitch will be written in centimeters, somebody could maybe show me an equivalent rod with metric units ?
    10-32 is a ANSI bolt size // see ANSI External Screw Threads Size Tolerances Chart - Engineers Edge

    There are various classes of bolt sizes.

    Personally, I would look for a simpler barn door tracker. The one you're looking at could be a bit difficult to do.

    I just built one myself and decided to avoid the curved rod design. I prefer the TROT type 4 double arm.

    Double Arm Barn Door Drive - DaveTrott.com

    PLUS, you can avoid all the need for calculations based on matching angles & lengths of the arms to the motor speed. If you use an Arduino with a stepper motor, you don't have to worry about all those calculations. The Arduino lets you control the rpm of the motor and you can find the right speed for the motor by trial and error.

    Joe
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    Default Re: I'm planning building an EQ platform

    Thanks ! Arduino + stepper motor seems a great idea, plus, i've learned how all of this works not so long ago in my high school "Engineer's science" lessons

    I've seen this :
    https://fstop138.berrange.com/2014/0...motor-control/
    He's using a 12v stepper motor, with an arduino uno and a Easydriver, because arduino outputs 5v and the motor need 12v.

    Do I need a lot of torque just for my dslr?
    Would this one do it ? https://arduino-info.wikispaces.com/SmallSteppers
    Seems great, and cheap, it has 4 phases 64 steps per revolution with a 1/64 gear ratio

    Is it better to turn the nut or the bolt ?

    I've also seen people doing their trackers with a normal rod, not bended Build a Motorized Barn Door Tracker...
    Is that precise ?

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    Default Re: I'm planning building an EQ platform

    Quote Originally Posted by Aero787 View Post
    Do I need a lot of torque just for my dslr?
    Would this one do it ? https://arduino-info.wikispaces.com/SmallSteppers
    Yes for a camera that's plenty of power. I used it for both the camera barndoor tracker but also to move my 60 lbs. 10" Dob on a barndoor. And the dual axis EQ platform as well. For the big ones it's all a matter of careful balancing.

    Quote Originally Posted by Aero787 View Post
    Is it better to turn the nut or the bolt ?
    Personally I turned the bolt but turning the nut is fine too, depends on what design you go with. It is easier to make a bolt turn than a nut, I think.

    Quote Originally Posted by Aero787 View Post
    I've also seen people doing their trackers with a normal rod, not bended Build a Motorized Barn Door Tracker...
    Is that precise ?
    It can be made precise if you know how to do the math. I built mine with a straight bolt compensating the rotation speed programmatically with a cosine term, and it is very precise. Saves me the trouble of using a curved bolt and having to turn the nut. Here's the mechanical design: Rainy day project - camera barndoor

    The Arduino code is attached in some other thread. Honestly it's best to figure the math and code out yourself so you know how to make it work. It's really elementary but has a lot of details that need to be done right, and someone else telling how to do it won't work well IMHO.
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    Clear skies, Henk. Telescopes: Carbon fiber ES ED127CF, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: AVX, LXD55, Tiltall, Cameras: Canon (SX40, 450D, 350D, ELPH 100HS), Samsung NX100, DIY: Dob and camera barndoor trackers, afocal adapter, foldable Dob base with leveling feet, Az/Alt setting circles, Accessories: Counterweight bar attachment, Plossls, Barlows, Telrad, SSAG, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK

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    Default Re: I'm planning building an EQ platform

    Thanks ! I think i'm gonna build one similar to yours

    Quote Originally Posted by CamelHat View Post
    The Arduino code is attached in some other thread. Honestly it's best to figure the math and code out yourself so you know how to make it work. It's really elementary but has a lot of details that need to be done right, and someone else telling how to do it won't work well IMHO.
    I agree with you, plus, i'm not that bad at math
    I just saw some of your threads, (nice work !) I couldn't figure how do you deal with the tangential problem, can you tell more about that cosine term please?
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    Default Re: I'm planning building an EQ platform

    It has been a while, the code below was saved somehow after my Win10 transition was kind enough to wipe out all my files. There is a cos call that implements the straight screw logic. It is based on the half angle between the arms. I can manage to recall the logic exactly but don't want to right now, see if you can figure it out. The BARNDOOR configuration determines camera or Dob barndoor, if Dob DEC or RA.

    One important thing, calculate the time line and do not depend on incremental changes only because errors in time will accumulate.

    HTH

    Henk




    //////////////////////////////////////////////////////////////////////////////
    // This Arduino example demonstrates bidirectional operation of a
    // 28BYJ-48, which is readily available on eBay, using a ULN2003
    // interface board to drive the stepper. The 28BYJ-48 motor is a 4-
    // phase, 8-beat motor, geared down by a factor of 64. One bipolar
    // winding is on motor pins 1 & 3 and the other on motor pins 2 & 4.
    // Refer to the manufacturer's documentation of Changzhou Fulling
    // Motor Co., Ltd., among others. The step angle is 5.625/64 and the
    // operating Frequency is 100pps. Current draw is 92mA.
    //////////////////////////////////////////////////////////////////////////////
    // Motor step angle = 5.625 degrees ==> 64 pulses per internal rev
    // Gear reduction = 1/64 ==> 4096 pulses per external rev
    //////////////////////////////////////////////////////////////////////////////

    // Configuration:
    // DEBUG
    // 0: No debug output
    // 1: Print debug output in the serial console
    // BARNDOOR
    // 1: Dobsonian barndoor (RA/autoguiding)
    // 2: Old camera barndoor
    // 3: New camera barndoor
    // 4: Dobsonian barndoor (DEC/autoguiding)
    int DEBUG = 0;
    int BARNDOOR = 3;

    // Motor pins: blue=1, pink=2, yellow=3, orange=4
    int motorPin[4] = {8, 9, 10, 11};
    // One counter-clockwise internal revolution going down the rows
    int ccw[8][4] =
    {
    {HIGH, LOW, LOW , LOW },
    {HIGH, HIGH, LOW , LOW },
    {LOW , HIGH, LOW , LOW },
    {LOW , HIGH, HIGH, LOW },
    {LOW , LOW, HIGH, LOW },
    {LOW , LOW, HIGH, HIGH},
    {LOW , LOW, LOW, HIGH},
    {HIGH, LOW, LOW, HIGH}
    };

    // Global variables used by the stepper algorithm
    long ip, np, npMin;
    double phi0, t, t0, dtpp;


    //////////////////////////////////////////////////////////////////////////////
    // Simple character bar plot that shows x on a scale of xmin to xmax from
    // left to right using a marker character and a | to indicate xmax.
    //////////////////////////////////////////////////////////////////////////////
    void plotData(double xmin, double xmax, double x, char marker)
    {
    char buf[80];
    int i;
    if ((x >= xmin) && (x <= xmax)) {
    for (i = 0; i < 78; i++) {
    if (double(i)/78 >= (x - xmin)/(xmax - xmin))
    buf[i] = ' ';
    else
    buf[i] = marker;
    }
    buf[78] = '|';
    buf[79] = char(0);
    Serial.println(buf);
    } else {
    Serial.print(marker);
    Serial.print(" is out of range, value = ");
    Serial.println(x);
    }
    }


    //////////////////////////////////////////////////////////////////////////////
    void setup() {

    if (DEBUG == 1) {
    // Initialize the serial device
    Serial.begin(9600);
    Serial.println("Entering setup...");
    }

    // Basic constants
    double pi = 4*atan(1.0); // Pi = 3.1415927
    double inch2cm = 2.54; // One inch is 2.54 cm
    double secSidDay = 86164.1; // Seconds in a siderial year
    double eRot = 2*pi/secSidDay; // Earth's rotation in radians per sec

    // Motor characteristics
    int ppir = 64; // Pulses per internal rev (360/5.625)
    int ppr = 64*ppir; // Pulses per revolution (gear reduction factor = 64)

    // Barndoor geometry - initialized in setup
    double tpi; // Threads per inch of the screw
    double beam; // Hinge to T-nut/cap nut in cm
    double y0; // Initial vertical T-nut position in cm
    double y1; // Final vertical T-nut position in cm

    if ((BARNDOOR == 1) || (BARNDOOR == 4)) {
    // 1: RA controller, 4: DEC controller
    // For some odd reason we use RA settings for DEC see below
    tpi = 20;
    beam = 65.7;
    y0 = 9.0;
    y1 = 1.0;
    } else if (BARNDOOR == 2) {
    tpi = 20;
    beam = 18.8;
    y0 = 3.0;
    y1 = 1.0;
    } else if (BARNDOOR == 3) {
    tpi = 20;
    beam = 19.6;
    y0 = 3.0;
    y1 = 1.0;
    }

    double cmpr = inch2cm/tpi; // cm per revolution (1 thread of the screw)
    double phipr = cmpr/beam; // Angle (phi) difference per revolution (in radians)
    double dtpr = phipr/eRot; // The time it takes the sky to rotate that much
    dtpp = dtpr/ppr; // Pulse time in sec, nominal value = 6471.8 mu

    phi0 = y0/beam; // Initial angle between the beams (approximate)
    np = (y0/inch2cm)*tpi*ppr; // Number of pulses needed from y0 down to 0
    npMin = (y1/inch2cm)*tpi*ppr; // Turn off at the last y1 cm
    ip = 0; // Pulse counter

    // Declare the motor pins as outputs
    for (int j = 0; j < 4; j++)
    pinMode(motorPin[j], OUTPUT);
    analogReference(DEFAULT);

    t = micros(); // Time in micorseconds. Note, the math above is in seconds.
    t0 = t;
    ip = 0;

    if (DEBUG == 1) {
    Serial.print("np = "); Serial.println(np);
    Serial.print("npMin = "); Serial.println(npMin);
    Serial.println("Setup complete...");
    Serial.println("I = Revolution number counting down from nRev to nMin");
    Serial.println("A = Actual time per revolution");
    Serial.println("R = Requested time per revolution");
    }
    }

    //////////////////////////////////////////////////////////////////////////////
    void loop(){
    // We don't need this outer loop, let's write our own for better control
    // so this only gets called once

    while (ip + npMin <= np) {
    int ic = ip % 8; // Internal cycle index
    int inc = 0; // 1 = up/faster, -1 = down/slower
    double dt, dt1;

    // Autoguider configurations - get the signal and determine inc
    if ((BARNDOOR == 1) || (BARNDOOR == 4)) {
    int a0 = analogRead(0); // up
    int a1 = analogRead(1); // down
    if (a0 < 400) // up
    inc = 1;
    if (a1 < 400) // down
    inc = -1;
    if (DEBUG == 1) {
    Serial.print("inc="); Serial.print(inc); Serial.print(' ');
    Serial.print("ic="); Serial.print(ic); Serial.print(' ');
    Serial.print("a0="); Serial.print(a0); Serial.print(' ');
    Serial.print("a1="); Serial.println(a1);
    }
    }

    // Depending on the configuration, determine dt
    if ( BARNDOOR == 4) {
    dt = 2*dtpp; // speed delta = 2 times nominal RA speed
    } else if (BARNDOOR == 1) {
    // v = c/dt, vNew = c/dtNew, dtNew = fac*dt ==>
    // dv = vNew - v = c/(fac*dt) - c/dt = v*(1/fac - 1)
    if (inc == 1) // faster
    dt = 0.727272*dtpp; // dv/v = (1/0.727272) - 1 = 0.375
    if (inc == -1) // slower
    dt = 1.6*dtpp; // dv/v = 1 - (1/1.6) = 0.375
    } else if ((BARNDOOR == 2) || (BARNDOOR == 3))
    dt = dtpp;

    // Compensate for the fact that we are using a straight screw
    double fac = cos((phi0*(np - ip))/(2*np));
    dt = dt/fac;

    // Step the motor
    for (int j = 0; j < 4; j++) {
    if (BARNDOOR == 1)
    digitalWrite(motorPin[j], ccw[ic][j]);
    else if ((BARNDOOR == 2) || (BARNDOOR == 3))
    digitalWrite(motorPin[3-j], ccw[ic][j]);
    else if (BARNDOOR == 4) {
    if (inc == 1)
    digitalWrite(motorPin[j], ccw[ic][j]);
    if (inc == -1)
    digitalWrite(motorPin[3-j], ccw[ic][j]);
    }
    }

    // Update the timeline
    t = t + 1000000*dt;

    // Delay to regulate the speed.
    // delayMicroseconds() is accurate up to a few milliseonds so delay
    // in 1 ms chunks. Note also that micros() cycles in 70 minutes.
    while (t > micros() + 1000)
    delayMicroseconds(1000);
    dt1 = t - micros();
    if (dt1 > 0)
    delayMicroseconds(dt1);

    // Increase or decrease the pulse count
    if (BARNDOOR == 4)
    ip = ip + inc;
    else
    ip = ip + 1;

    if (DEBUG == 1) {
    if (ip % 512 == 0) { // Each revolution has 8*64 pulses
    double tmp = micros();
    int nRev = (np - npMin)/512;
    int iRev = ip/512;
    plotData(0, nRev, nRev-iRev, 'I');
    plotData(27400000, 27600000, tmp - t0, 'A');
    plotData(27400000, 27600000, t - t0, 'R');
    }
    }
    }
    }
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    Clear skies, Henk. Telescopes: Carbon fiber ES ED127CF, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: AVX, LXD55, Tiltall, Cameras: Canon (SX40, 450D, 350D, ELPH 100HS), Samsung NX100, DIY: Dob and camera barndoor trackers, afocal adapter, foldable Dob base with leveling feet, Az/Alt setting circles, Accessories: Counterweight bar attachment, Plossls, Barlows, Telrad, SSAG, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK

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    Default Re: I'm planning building an EQ platform

    Huge thanks for the code! It seems very well done and well explained
    I'm gonna try to understand how it works

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    Default Re: I'm planning building an EQ platform

    I forgot to mention, some of that code is for autoguiding. It reads the voltage over a resistor that is connected to the SSAG's optocoupler IIRC (the analogRead portions). You can ignore that part of the code, for a regular unguided camera barndoor. Also, for a regular barndoor you won't need DEC control.
    Clear skies, Henk. Telescopes: Carbon fiber ES ED127CF, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: AVX, LXD55, Tiltall, Cameras: Canon (SX40, 450D, 350D, ELPH 100HS), Samsung NX100, DIY: Dob and camera barndoor trackers, afocal adapter, foldable Dob base with leveling feet, Az/Alt setting circles, Accessories: Counterweight bar attachment, Plossls, Barlows, Telrad, SSAG, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK

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    Default Re: I'm planning building an EQ platform

    Hi, it has been a while ! I managed to build a prototype of the barndoor tracker, and I have new questions for you guys

    first of all here's the tracker (crappy, but that was just for doing some tests)
    (Direct website uploader still don't work for me, whtvr)
    http://image.noelshack.com/fichiers/...325-150654.jpg

    The rod is directly attached to the motor shaft, and goes straight through a nut, a square one, so it can't rotate, only slide as the rod turns
    http://image.noelshack.com/fichiers/...325-150715.jpg

    I don't understand how yours is working Camel, nothing seems to slide, rotate or anything, stress must build in the rod and the motor shouldn't turn passed a certain angle

    Closed :
    http://image.noelshack.com/fichiers/...325-150816.jpg
    Opened:
    http://image.noelshack.com/fichiers/...325-150842.jpg

    I also modified your code, big parts were useless for me :
    [C] Barndoor - Pastebin.com
    I still have one question, what exactly is y0 and y1 ?

    More time passes, the more difficult it gets

 

 
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