I read that an mp3 player is a hard drive to music. Can i reprogram it to make a hard drive?

Solution
the old ipods were a spinning hdd. would not be too hard to pop it out and format it. the newer ones are all flash memory. may as well go with a flash drive if you're gonna use flash memory anyway. probably cheaper than an mp3 player as well.

rasperry pi would be a solid option as well. pretty small and there are a ton or resources for how to use them in many different projects.
the old ipods were a spinning hdd. would not be too hard to pop it out and format it. the newer ones are all flash memory. may as well go with a flash drive if you're gonna use flash memory anyway. probably cheaper than an mp3 player as well.

rasperry pi would be a solid option as well. pretty small and there are a ton or resources for how to use them in many different projects.
 
Solution
Most non apple mp3 players already have the option for simple data storage. Whether they be spinning drives or flash drives, you still need the controller card circuitry. A better bet would be a simple raspberry pi with a $14 SD card. Or just tear into an old laptop for a hdd. Robots generally don't need GBs of storage.