Floppy disk drives of the late ’70s and early ’80 are typical of standards in computing of that era. In theory, they are standard, in practice there is enough variation that you can’t just plug bits together and expect them to work.
TANDOS was designed to work with 5.25 inch disks, the 3.5 inch disk drive standard was created in 1983, right at the end of the Microtan era. In making a system work today their reduced size, reduced power needs and greater reliability makes them very attractive, but to use them the variations in the standard need to be allowed for.
TANDOS records in Modified Frequency Modulation encoding (MFM). The easiest drives to source are from the time when 1.44MB floppies were used in PCs. The 1.44MB standard does not use MFM encoding but all of these drives should support the older 720K format which was an 80 Track double sided double density MFM format. TANDOS only records in single density but this is identical to double density from a hardware point of view. The other twist to the standards introduced by IBM was in the cabling of the interface, and particularly the handling of the drive select connections. This requires a special cable to connect IBM standard drives to TANDOS.
On my system I have 2 drives working reliably. Full technical details can be downloaded below.