Time-lapse Dolly
As one of my hobbies is photography I always wanted to play around with a time-lapse dolly. Unfortunately they are quite pricey. When I salvaged an step motor from some old scanner, I knew immediately that this is going to be a nice time-lapse dolly project. The first Idea was to use the motor as an engine for a small “wagon” where the camera is placed on. However, as I did not have much time to build some proper wagon I decided for an easier approach. In this approach the stepper is on a fixed position and is attached to a wagon with a string. The string is coiled up by the stepper and therefore shortens the string which pulls the wagon to the stepper.
To control the stepper I used the Teensy 2.0 micro controller and the L298N dual full-bridge motor driver. I added two potentiometer to the micro controller with whom I can set the interval and the distance the stepper should pull the wagon. The strip-board can be seen below:
The eight diodes (Schottky Barrier Rectifier) protect the micro-controller from counter-electromotive force produced by the stepper. Unfortunately there are some flaws with this circuit. For instance should the micro-controller be powered by an independent power supply from the power supply who powers the stepper. This circuit as it is now could harm the micro-controller. Of course I tried the circuit first on a breadboard before soldering everything together.
Then I put everything on a piece of wood and the system was ready to go:
For testing I used a GoPro Hero2 camera which is perfect for testing as it is really lightweight and has also a built-in time-lapse mode. In the first test I just attached the GoPro to an skateboard, which was pulled by the stepper over the terrace. 
It turned out that the joints between the tiles were rather deep for the skateboard wheels, which resulted in a really shaky inconstant video. So in the next test I built a LEGO wagon for the GoPro. I placed the LEGO wagon in some kind of guide rail, which kept the wagon on track.
Here is the Video, without any post-processing (Image Stabilization):
We can see that the footage is still rather shaky and the speed is not really constant. This is mainly because the wheels of the wagon were not perfectly round. Furthermore was the used string a little bit elastic, which caused that through some intervals the string just built up some tension and did not move the wagon. In the next step this tension was released and the wagon was pulled further than supposed.
Marcel Schmidt 