Due to the sustained 15g load on the vehicle during launch, we decided that a hard disk for flight computer would be a bad idea. Instead, we took the obvious route and went with CompactFlash.
CompactFlash looks exactly like an IDE drive, so for our purposes it was plug and play. In fact, we formatted and loaded Linux on it by simply connecting it to a Linux-based desktop PC's IDE connector and formatting it as another drive.
We used Tucson Area Packet Radio's CompactFlash Type II adapter board to connect the CompactFlash to a standard IDE cable. For $49.00 they're a good deal, although finding a PC104 form factor would have been better for us.
To mount it to the FC's PC104 stack, we used PCB material (FR-4 sandwiched by copper) and drilled 8 holes (4 for the PC104 stack, 4 for the CF adapter). We aligned the CF card such that during launch the CF card would be pushed down into it's socket. Here's a drawing of the adapter board, although note there's a PDF file available:
Since the FC board has a 2mm 44pin connector (the kind used for 2.5" drives on laptops) which includes power, we modified the CF adapter board by:
- Removing the standard 0.1" 40pin IDE pin header and adding the 2mm 44pin pin header,
- Removing the "PC" power connector,
- Replacing the Master Select 0.1" jumper with a hardwired (soldered) jumper,
- Replacing the electrolytic power supply filter cap with a smaller Tantalum one.
Although this is a workable solution, we'll probably want to roll our own CompactFlash carrier to PC104 adapter in the future: we could use a locking CF connector, save weight in fasteners and PCB material, and possibly mount the 2mm cable directly to the PCB (thus removing one connector, which seems to be a good thing for aerospace applications).