Change your UI's background color to black and then render.  Save to a JPG. If you save to PNG then your going to save it out with a transparent background, which can work as well since you can then take your finished render into a image editing program and add in a layer, fill it with black and there you go (make sure your droid layer is the top most layer and the background layer is the bottom layer  )

HTH's

---Wolff On The Prowl---

My Store is HERE

My Freebies are HERE