• Camera
• Balloon
• Crash Box
• Radio Link
• Bugs and Possible Fixes

The camera is a Nikon FE2, a vintage piece of rugged machinery from the late 70's. I used a 50mm lens, to provide about the same perspective as would have been seen by a human eye at the camera position. The film was 100 ASA Kodak Royal Gold. I metered on automatic, adjusted for one more stop of exposure (assuming that most of the viewfinder would be filled with light-colored playa).

The "8' diameter weather balloon" turned out to be a fragile aging balloon made of thick latex. These balloons are designed to lift radiosondes high into the atmosphere where metereological measurements are taken, and then to burst, I suppose so that they don't drift too far from their release point. The latex material is less stretchy than ordinary balloon rubber; the pressure inside the full balloon was not much higher than atmospheric. I estimated that I would be lifting around 10 pounds of equipment; assuming an 8' diameter sphere (which was a little optimistic; see this picture), I calculated an expected lift of about 24 pounds.

I rented a "T"-size tank (294 cubic feet of helium) from Gerin Welding Supply in Santa Clara. The rental was about $7 per month, and filling the tank cost about $90.

The crash box was made out of light-weight pine 1x1, held together with nuts and bolts. A 1/4" bolt held the motor drive (Nikon MD-12) to the box, and the camera screwed into the motor drive. Some horizontal wooden pieces provided additional support for the camera. The electronics attached to the box with tie-wraps.

The receiver and transmitter were both CB radios. A push button triggered a cheap 8-bit microcontroller (MicroChip 16C58) to generate a 1 kHz square wave which capacitively coupled into the mic input of the transmitter CB radio. The receiver fed its audio output to an LM567 tone decoder, whose output went to another micro, which rejected too-short pulses. When a suitable signal was detected, the micro triggered a MOSFET which activated the motor drive. The range of this setup was measured at about 500 feet on the ground.

Obviously, the biggest problem is that the balloon burst. This photo, taken during a test run, shows a possibly over-filled balloon which ascended to 1000 feet, was retrieved, and lasted about an hour before bursting. (This didn't inspire complete confidence, but it worked better than the balloon used at Burning Man.) I had brought along a balloon of a different type, a large balloon made of ordinary rubber. I emptied the the helium tank into this balloon the Monday after the Man burned, and I found that this ordinary rubber balloon was much tougher than the weather balloon was. I sent the balloon up to 1000 feet where it hung for a while, until it was destroyed by a passing small airplane (I'm still puzzled about this: was it accidental or intentional?). If I were to do more aerial photography, I'd use two of these rubber balloons.

The radio link was not perfect - I think I was getting less than 1000 feet of range, and the simplicity of the design made it susceptible to noise and double triggering. Recently I've been looking into radio tranceiver modules made by RFM (http://www.rfm.com). These are designed to transmit serial data over a radio link, which could lead to some interesting possibilities. For example, instead of just triggering the shutter whenever the signal was detected, it could be triggered in response to the arrival of a sequence of bytes, which would reduce the likelihood of spurious triggers.