Not being overly chuffed with the battery mount on the 3DR and wanting somewhere to mount a camera, I decided to make another layer to the quad. A third plate below the quad seemed idea.
I fished out a scrap of unused fibreglass PCB I had in my goodie box. I took the quad apart to get at the bottom plate to copy as a template.
The normal plates have a series of 3 holes in the middle of each edge which seemed a perfect option to mount stuff. I drilled the same hole patter in the new plate.
Using M3 * 30mm screws built up my new platform. it is suspended under the quad and allows for a snug fit ot my 2200mAh 3S lipo. It simply slides in and is held there by itself. I might look at putting a strap in for safety to stop it sliding out.
The underside of the board is the copper clad which I was going to etch off but decided against it. It would make a perfect solution to adding more stuff like a camera gimbal because you can solder it :D
I did not take any pics during the build but it was pretty straight forward. The copper clad board is very easy to work with and rather strong.
The only think I am concerned about and will be changing is the screw length. I think the battery is a very tight fit and apparently lipos expand as they (dis?)charge so this might be an issue. 35mm will be ample.
The battery in place (above)