I was having the same problem you describe with a newly configured OSPi. Then I remembered that an older setup that was more reliable was set to a static IP address.
I set a static IP address on the Raspi itself as well as on the router and it has not dropped the connection since.
You can set a static address on the Pi by editing the file /etc/network/interfaces to look like:
#iface eth0 inet dhcp #this line commented out
iface eth0 inet static
address 192.168.x.x #where x = your chosen IP address
Hope this helps.
Nope. That didn’t fix the problem. I did discover that the image on the SD card was damaged. I re-formatted and re-imaged the SD card. So far it seems to be OK. Time will tell if this actually fixed the problem.