Attach a portable hard drive to my phone and transfer files?

[Helen Barber]

I use my phone to download movies etc. I always have to get my laptop out and attach HD and my Android phone.

With a otg cable, is it possible to transfer the files directly?

Thanks

 

[Helen Barber]

I have a small 500gb drive that is self powered by USB... Happy to buy a power adapter or even a new HD if needed

Ideas?