• How it's going

    RobG • an hour ago • 0 comments

    I've been working on this a few weeks, so the design is already quite advanced. Here's what I've got so far:

    The mechanism is quite different: a nut is driven along a straight, linear leadscrew which in turn opens the two halves via a linkage. Since the opening angle must increase at a constant rate, but the position of the nut along the screw is not proportional to the angle, the screw cannot be driven at a constant rate. Instead a microcontroller (Arduino Nano) is used to calculate the precise moment to step the motor each time (20-30 times per second) in order to compensate for the changing relationship between nut position and opening angle.

  • Where it all started

    RobG • an hour ago • 0 comments

    Here's a pic of the original wooden tracker with my DSLR attached:

    It uses a stepper motor driven at a fixed 32-steps-per-second rate, courtesy of a 32kHz quartz crystal clock and frequency divider. The motor drives a nut along a curved, threaded rod, which opens the two halves at the required 15degrees-per-hour rate. The down-side is that the curved rod tends to waggle (the thread isn't very accurate) so very long exposure images are a little blurry. Overall accuracy is also limited by poor dimensional tolerance when drilling the holes for the bearings - the whole thing has to be large to minimise the tolerance effects.

    Nevertheless, here's a pic I managed to take by stacking dozens of short(ish) exposures:

    This is the benchmark to try and beat!