VR2 appears to control something to do with the head stepper motor, as it gets loud or quiet depending on what position the pot is in. As far as I can tell, it doesn't effect the functionality of the drive. VR1 controls how the data is read in some way, but it doesn't affect the speed whatsoever. 

https://forum.vcfed.org/index.php?threads/cant-figure-out-360k-floppy-drive.1243247/page-4