The main components of my motorized time lapse slider are:

- 20RPM 12V DC Motor

- Threaded Rod with a fitting nut

- 2x Microswitch

- Voltage Regulator

- 6 Pin Toggle Switch

- 3x 3.7V Drones Battery (to achieve together nearly 12V)

- Ball Head

- Aluminum Angle

 

I decided to make my slider just about 0.7 meters long that it's not to heavy and also small enough to transport it in my backpack. Anyway I prefer slower motions in a time lapse. It creates a better contrast between the fast moving objects in the video and the motion of the camera itself.
Another advantage is that the leverage effect of the short slider is weak enough to only attach one connection in the middle of the slider to a tripod to hold it in place. 

I used a M5 treaded rod with a fitting nut to which the camera dolly was attached to. The motor is spinning the threaded rod which is held in place. With the threaded rod spinning, the nut moves along the rod and pulls the camera dolly with it.

At both ends of the slider I attached the two Microswitches which are pressed when the camera dolly reaches the end of the slider to cut the connection between the batteries and the motor and so to stop it from spinning and so pulling the camera dolly too far. Each of the Microswitches are only blocking one direction, that the camera dolly can still move in the other direction when reaching the end of the slider. 

I wired the Toggle Switch in a correctly way to manually change the direction of the motor spin and so to change the direction of movement of the camera dolly.

I connected the three 3.7V drone batteries with each 500mAh in series to achieve a 11.1V battery with 500mAh. (Sidefact: luckily each of the batteries I linked above had a voltage of 4V instead of 3.7V and so I could achieve the exact 12V the motor needs to spin at its highest speed of 20RPM) The simple reason why I used 3x 3.7V instead of just a normal 12V battery is the ability to charge each of the batteries with a standard 5V powerbank per USB and afterwards connect them together again.