How feasible would such a thing be? I'm brainstorming an Apple //e portable. I'd like to use half-height drives, but the few that were made for the Apple II are a bit pricey, and I would feel bad gutting them for this project.
Shugart interface drives are laying around the place, and I'm wondering if an interposer could be built to translate Shugart commands to Disk ][ commands and vice versa.
There are two different approaches I used:
The first approach is a true Shugart Bus to Apple II Disk II flat band cable converter. It used a small PLD to look at the four DISK II stepper motor phases and then translated that to direction/step pulses for the Shugart bus. All other signals such as Motor on, write gate, write protect sense, RDDATA and WRDATA only need an inverter or can be connected directly.
The drawback of this approach is that some Apple II copy protection schemes which need half track and quarter track head positioning won't work.
The second approach is to cut the four input signals to the stepper motor driver IC of a 40 track floppy disk drive and to connect them to uncommitted signal lines on the Shugart Bus (such as the drive selects, none of which are needed). These four signals may need inversion or not.
The drawback of this approach is that the floppy drive electronics are modified, and it's a bit of hit-and-miss because the success with said copy protection schemes depends on the exact nature of the stepper motor involved. Most should work, though.
Note that some floppy drives had a linear motor for head positioning, and these can't be modified with the 2nd approach and might choke on the first approach if the step pulses get too fast. Using a microcontroller instead of a PLD state machine could help, but I never tried that.
I've used both approaches with success, except for the copy protection issue of the 1st approach. There is a nasty copy protection called "Spiradisk" which never worked with it.
And before you ask, sorry, all the schematics etc. have long been lost over the many decades since I did that. But I think I have one of these modified drives somewhere in my basement.
- Uncle Bernie