There are a whole bunch of camera sliders to find on thingiverse.

But none fitted my needs. I had some parts here, a motor, an arduino, switches, aluminium rods, screws, bearings … and wanted to print all the rest - including the sled itself.
The legs I designed have threads so you can mount the thing onto a tripod.

See it in action: https://youtu.be/kDJ_6ikYeX0

The delivered arduino sketch is really simple. It just manages the speed of the sled by turning the knob (poti) and reverses the direction, whenever an endstop is reached.
You can define the range, the sled goes, just by moving the endstops - it's so simple :)

Upgrade:
I you want a really good sketch with an touchscreen and many possibilities, especially for timelapse than have a look at this thing: https://www.thingiverse.com/thing:2166008

UPDATE: I made a case for the aruino mega with display:
https://www.thingiverse.com/thing:3080693

Here a video of the latest version:
https://youtu.be/y6CyFwhTeEA

Instruction:

• Use epoxy to glue the two gliders to the plate. Have the rods sticking in while doing this, to be sure, everything is straight
• mount the toothed belt by clipping it to the plate
• mount the motor and the pulley to the right foot
• mount the roll (or bearing) to the left foot (5 mm screw) with the toothed belt around it
• mount the left foot to the rods
• mount the right foot.
• tension the toothed belt by pulling the feet apart and fixing them with the screws

Partlist:

2 x 12 mm Alu Pipes, up to 100 cm long
4 x Screws 3x10 mm, with nuts and washers
4 x Srews 4x40 mm, with nut
1 x Screw 5x50 mm (approximately) for the roll
1 x Toothed belt, about 2m long
1 x Pulley (or print it: https://www.thingiverse.com/thing:133918)
some glue (epoxy)

Electronics:

1 Arduino
1 Stepper Motor Nema17
1 Stepper Driver
1 Shield and/or grid-style PC board
2 Switches as Endstops
1 Potentiometer (I use a 3k poti - but better will be up to 10k)
1 Resistor 1k
some wires
As a battery I use a 2S-Lipo. 3S will be even better.
But I ran into an issue after welding everything together. The arduino now needs some extra 5V to start up reliable. The simplest way is to use a powerbank and an USB-cable as second battery. Another possibility is a step-down module that delivers 5V.