Sunday, September 10, 2006

Weighing Video Cameras

I had wanted to use a Panasonic DVC30 camera onboard the helicopter. This camera is quite similar to the DVX100, a good camera that I use rather often. The DVC30 can shoot 30P (30 progressive frames per second), which is close enough to the 24P mode commonly used on the DVX100. The DVC30 has the advantage of weighing about half as much as the DVX100.

Unfortunately, in the context of this project, the DVC30 still weighs a lot: around 1100g with a battery and tape. In order to lift that much, along with motor batteries, servos, and structural components, my recent electrical designs have required four motors and weighed nearly 10 pounds. Keeping 10 pounds in the air for 10 minutes requires an unreasonable amount of battery power.

So, I decided to look for a lighter camera. One option is the Panasonic SDR-S100, which records to SD memory cards and has reasonably good image quality. (It has 3 CCDs and a Leica lens, like most good Panasonic models.) It weighs just 282g, including the memory card and battery.

After building a spreadsheet of the weights of all the Panasonic consumer 3 CCD cameras and reading a number of reviews, I'm going to aim for the GS300. It has better image quality than the S100 and costs half as much, but weighs twice as much: 550g. Running through the numbers, I think I may be able to fly a 550g camera using a minimalist 2 motor design.

Because of the trouble and expense of renting helium tanks, I'm designing the new version without balloons.

Monday, September 04, 2006

Wireless Video

A couple weeks ago I tested my 1.7 GHz transmitter/receiver and found that they did not work well enough to be usable. The problem appeared to be interference (which isn't surprising in New York), but could have also been some kind of device failure or mis-configuration.

I had selected 1.7 GHz specifically to avoid interference. Most wireless video transmitters operate at 2.4 GHz, but using that frequency in an urban environment would be foolish (given the proliferation of wireless ethernet, microwave ovens, and other devices at that frequency).

Other common wireless video frequencies include 5.8 GHz, 1.2 GHz, and 900 MHz. I would choose 5.8 GHz (since it's not a very crowded frequency), but that frequency is obstructed by many materials and is not good for non-stationary transmitters. (This table provides a useful summary.) So, I'm left with 1.2 GHz and 900 MHz.

After looking at various websites offering 1.2 GHz and 900 MHz wireless video systems, I've settled on this transmitter and receiver.

If that doesn't work, I suppose I'll try 1.2 GHz or a more powerful 900 MHz transmitter. (or a tether!)

Saturday, September 02, 2006

User Interface

The original plan was to use a laptop for the helicopter control console. The laptop would run a program that sends commands to a wireless serial link and displays video from a wireless video link (via a pcmcia video input device).

After some further thought, I've decide it would be better to use an R/C controller. This would be easier to hold while walking and less conspicuous (which may be a big deal when filming in difficult or shady locations). The R/C controller provides finer control than a keyboard and has built-in trim controls (for making extra-fine adjustments).

Also, the R/C controller provides simple, reliable, long-range radio transmission (which would be questionable using an inexpensive wireless serial link).

In order to do this, the airborne microcontroller will need to decode the signals from the R/C receiver and translate them into commands to send to the motors and servos. (The mapping between the controls and the motors/servos is simple but not direct.) Preliminary research suggests that this will be fairly easy.

(It's amazing how complicated and expensive R/C controllers can get. This one costs $2200.)

For the video display, I've ordered a small 12V LCD TV that I'll attach to the transmitter. This will be more reliable than feeding the video signal through a laptop.

The only disadvantage of not using a laptop for the control console is that the laptop would have been able to display status info coming down from the wireless serial link. Perhaps I'll still use a wireless serial link for debugging.