Camera Tracker

I was interested in building myself a barn door style camera tracker to allow a camera to track the stars accurately for a reasonably long exposure time of 10 minutes. After doing a bit of research I realised that a barn door style tracker was not going to work for me. I used to piggyback my camera to my Meade SCT 8″ telescope and that can track quite well. The only problem with this is that I have to lug the telescope along and only use it for a fancy tripod that can track. I was looking for a simple and light solution that will track well enough to allow for relatively long exposures on wide field views.

I realised that my Meade tripod and wedge can provide a solid foundation for a camera tracker. The tripod folds up reasonable small and can go with on weekends and trips to the outback. I needed a camera mount that will sit on a clock drive that can be aligned to the south celestial pole on the wedge.

 Meade SCT tripod and wedge

A small stepper motor is used with a gearbox (worm gear and belt drive with combined gear ratio of ~227). The stepper is a 400 step motor and the electronic driver (Big Easy Driver) allows for a 16th step micro stepping mode. This allows me to run the stepper at 400*16 = 6400 steps per revolution. A single step of the stepper motor will turn a 10mm stainless steel shaft approximately 0.892 arc seconds. The rotation of earth is 23 hours, 59 minutes and 4.09 seconds. I have calculated the delay period between individual steps to be 0.059238 seconds. This may sound difficult to achieve but with an Arduino processor it is quite simple.

I currently drive the Big Easy Driver with the Arduino microprocessor but will replace it later with an accurate crystal oscillator to get rid of the microprocessor.

Here is the latest code. Note the delay time of 59 milliseconds plus 238microseconds. This will have to be calibrated once I get it working.

—————————————————————————————–

//
// Stepper Motor sketch for use with the Big Easy Driver
//
// Based on original code from Dan Thompson 2008
// Use this code at your own risk.

int dirpin = 2;
int steppin = 3;

void setup() {
Serial.begin(9600);

pinMode(dirpin, OUTPUT);
pinMode(steppin, OUTPUT);
}
void loop()
{

int i;

digitalWrite(dirpin, LOW);     // Set the direction.
delayMicroseconds(0);

Serial.println(“>>”);
for (i = 0; i<6400; i++)      // Iterate for 6400 microsteps.
{
digitalWrite(steppin, LOW);     // This LOW to HIGH change is what creates the
digitalWrite(steppin, HIGH);    // “Rising Edge” so the easydriver knows to when to step.
delay(59);
delayMicroseconds(238);     // A delay time of 50us is close to top speed for this
}                                            // particular motor. Any faster the motor stalls.

}

—————————————————————————————–

The back plate is mounted on the wedge and can be aligned accurately to the south celestial pole.

 Design and Components of the camera tracker
Camera tracker assembled
Big Easy Driver

I fitted a camera mount on the 10mm stainless steel shaft. I will use a Canon EOS 600D with the tracker.

Complete system.   Note the box containing the microprocessor and stepper driver. A USB port is available to change the programming if required. A small regulated 12V, 1A supply plugs into the box. This makes remote use easy as a car battery will run the system without any issues.

Watch this space for some sample photos….

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4 thoughts on “Camera Tracker

  1. Pingback: DIY Autoguider for Long Exposure Astrophotography (Part 3) | stars*in*photos

  2. Pingback: DIY Autoguider for Long Exposure Astrophotography | stars*in*photos

  3. Dasphys

    Will that tensioner being effectively octhagonal or hexagonal produce slight variation on rotational distance ?

    Reply
    1. Theo Post author

      Hi, yes it was probably not very clever of me to use it but it would onlu havr impacted on the tension on the belt. The belt was pulling on the other side which means that the tension would probably not have a big effect. But, the tensioner should have been a plain cylindrical type….. 😕

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