Most A/V equipment repairers have heaps of dead CD players, VCR's and tape decks in their junk pile out the back. These are units that were written-off because they were not economical to repair or perhaps the parts are no longer available. Often, if you ask nicely & tell them that you want the parts for playing around with robotics, they will quite happily give you (yes, for free !) some bits to muck about with. Just be honest with them and don't bug them every 2nd day for stuff! Remember, they are at work to make a living, so don't take up too much of their time. A lot of motors that are replaced in CD players for example are just worn & out-of-spec but will do fine for what you need them for. You might be able to get the technician to put some aside for you if you ask politely.
Computer repair centres may also be willing to give you some old floppy disk drives
(3.5" or 5.25") that you can pull stepper motors out of. Most 3.5" floppy drives are
replaced because it's cheaper than trying to fix them. CDROM drives are just the same.
There's not much useful stuff in hard disk drives apart from the platter motor but the
technician may be reluctant to part with them intact as they may contain the previous
owners data. Stick to CDROM & floppy drives and they should be helpful enough.

CD Player Parts
