How to remotely Transfer Files directly (from my Android phone) to an external hard drive without using cloud service like Dropbox

Solution 1:

A NAS might be the way you want to go. Network Attached Storage is basically a harddisk with a small computer attached. I have personally used both Synology and Western digital disks (Go for Synology), and they are basically linux machines, which means you can mod them.

I did exactly what you are trying to do by enabling SFTP on my Synology NAS, and installing an SFTP client on my phone. This has the further benefit of being able to use public-private key validation instead of passwords, giving a major boost to security.

OpenSSH SFTP server: http://www.openssh.org/

Android SFTP client: https://play.google.com/store/apps/details?id=lysesoft.andftp&hl=en

SFTP is simply an extension of SSH. For more on logging on to SSH with keys see here: http://sshkeychain.sourceforge.net/mirrors/SSH-with-Keys-HOWTO/SSH-with-Keys-HOWTO-4.html

Solution 2:

In theory, if its a powered hard drive formatted with FAT32, you could simply get a USB OTG cable and plug it in. I've tried it with my tablet and it works with external hard drives with their own PSU and some USB thumb drives.

Solution 3:

You can use AirDroid [for free]. Its a web-based app that runs on your android device and allows you control the device and also copy files.