If you need to fly a camera that's heavier than a point-and-shoot, like an SLR, you may need a camera rig that's a little larger than the PET Bottle Rig. Here's a sturdy design developed for kite aerial photography that makes use of a small plastic waste bin and some aluminum bars, which are available at most hardware stores. It includes a picavet, which can help keep the camera from swinging.
Cross-section diagram of the rig. Use lock nuts on the ends of the bolts and a lock washer on the camera screw.
The camera attaches to the metal bar on the inside of the trash can with a tripod screw through the bar into the tripod mount in the bottom of the camera. The camera should be mounted high enough inside the can so that the lens doesn't touch the ground, but low enough that the edge of the can is not visible in the photos. The black rectangle is a piece of hook-and-loop tape that holds camera timing device.
Keep in mind that flying a heavy camera means you'll need a large kite and higher wind speeds.