To make splitted .rar archive files within Linux, you must install rar command first. After that, if you want to compress your 300 MB projects/ folder and split it to files, each of 50 MB, you must use following command:
rar a -m3 -v50M -R projects.rar projects/
-m switch selects the compression level (0:fast, 5:low)
-v switch selects the max size of each part. You can use K for Kb like -v50K