Im planning on building something called a barn-door sky tracker. fundamentally its a camera mount that will rotate with the axis of the earths rotation to take longer exposures with a DSLR of the night sky. Its a simple design that has 2 platforms hinged together at one end and on the other end there is a curved bolt. i want to use a high torque motor to push a DSLR and maybe a heavy lens 6lbs or so. So now there issue I am having is the fact that I need to get the drive down to a 1 rpm. I plan on using either a 4 or a 6 rpm motor with a gear mounted on it and a second gear mounted to a nut that will thread on a curved bolt. I also plan on controlling the motor by a dc-dc buck converter to adjust the output speed to match that 1rpm I need. the issue I am having is if I say I get a 3-12v 4rpm motor with a 16 tooth gear and a 64 tooth gear mounted on the bolt I equal 1rpm however how much will load effect that rotation speed and if I used 9v to power it how will it preform as far as speed goes. Im leaning on giving myself a safe zone on using a 6rpm gear and using the same gear ratio and adjust the voltage down to 1rpm. As far as power source im thinking of using either a 11.1 3 cell lipo or a 4 cell lipo or even run off 12v car power source. There are a few tutorials that explain the project but none of them have been good at sourcing drive train or well covering the electronics of it. Thanks much in advance.