Actobotics is a solid building platform with many great features. One thing it's missing is a rack and pinion linear slide mechanism that operates internal to a channel allowing one full-sized channel to slide past another one, like the mechanism offered for the Tetrix platform. This design provides such a mechanism.
Actobotics offers many good 32 pitch pinion gears, so this is a 3D printable rack to mate to a chosen Actobotics pinion gear plus sliders to hold the channel on. The rack width depends on the width of the pinion gear selected, so make sure you print the rack that corresponds to the pinion gear you'll use. STL files are provided for racks that mate with 20 tooth and 24 tooth pinion gears.
Each rack is 3" long. The racks can be used in series to provide 6", 9", 12", etc. racks.
Tested with 20T pinion gear at 9" and works smoothly.
Actobotics does provide a fixed length linear slide gear rack for beams, so it might be easier to use that rack and its associated parts if that is sufficient for your needs. But if you need full-sized channels sliding, this 3D-printable option might be useful to you. Happy building!