
Re: Dolly for milky way timelapse
You've got the procedure exactly. Trigger camera, wait until exposure is finished, move, wait, repeat. Some advanced controllers monitor the flash synch port to know when the shutter opens and closes, but most just do it with timing.
If you use timing to keep the dolly still while the shutter is open, consider having it move first, then wait, then shoot. There will be less conflict. My first controller used an external intervalometer which I already had for regular timelapse. When the intervalometer said go, it moved the motor, then triggered the camera after the move. As long as the interval was long enough, it worked great. More advanced units have their own intervalometer and have you enter an amount of time it should wait after triggering the shutter before it begins a move. A good controller will save this value so you don't have to enter it every time.
Dynamic still has some kits for making a copy of their MX-2 dolly controller. It can control two motors, and allows you to ramp up the speed going into the move and ramp down at the end if desired. It can do continuous movement if you want some motion blur for artistic reasons, and lots of other advanced features. If you don't mind soldering the components and downloading the software into an Arduino, its a bargain for $55. You'll probably spend more if you build your own from scratch. I just got one to assemble for a friend who is getting a dolly for Christmas. Last one I put together took about an hour or two. Here's a link to it in their online store.
http://dynamicperception.com/products/d ... ld-diy-kitCoding for a simple controller can be pretty easy. My first one used BCD thumbwheel switches because they served as both input device and display. There was no need to drive an LCD or have a menu system and buttons. I set the number of steps the motor should move on the thumbwheels. Whenever the intervalometer said go, it read the thumbwheels, moved that number of steps, then triggered the shutter. Direction was controlled by a toggle switch wired directly into the direction input on the motor driver.