I began my research into KAP by reading all the back issues of The Aerial Eye. This was an amazing experience as the torential flow of creative ideas and solutions is somewhat overwhelming. By the end of my reading, however, some key design guidelines had formed in my mind.
First, I would use a Picavet suspension. This seemed to emerge as the clear winner after all was said and done. Even some vociferous pendulum fans had been won over by Issue 5.2 of The Aerial Eye. In addition the Picavet looks highly portable, and I knew that would be important to my long term usage.
Secondly, I determined that I would not use R/C controls on my first project. I am still not convinced that guessing the aim with radio control from the ground is much of an improvement over guessing your aim before launch, but regardless of that it's clear that R/C brings much complexity and cost to the rig. My first rig would be manual.
Of course, I would use a digital camera. I hate film cameras anyhow, but how you could ever hone your flying skills if you had to wait until an entire roll of film was finished to see your results? Plus I expected to trigger my digital camera with an electronic timer. That way each flight would bring me enough photos to improve my chances of getting at least one good image.
The other two traits I desired in my rig were low wind resistance, so it wouldn't bounce around in the air; and low weight, so I could fly more often and with a smaller kite. My digital camera was a lot lighter than the SLR's the other people were flying, plus I thought using a wire frame rather than aluminum bar would make it lighter and less likely to catch the wind.
The first step was to braze (or solder) up seven lengths of wire and 2 washers, as shown below.
Based on Harald Prinzler's web pages I decided that a 12" square rig would be adequate, yet still portable. Harald's point is that rigs much smaller than that are tricky to balance with a camera mounted.
Once the two major components were brazed up, I bent them using a pair of pliers. The "X" part merely needs loops bent at each end to recieve the pulleys. Note that for Picavet, the pulleys will all be parallel on one axis of the rig. So at the end of the four legs, two bends are in-line with their legs, two are perpendicular. (Note: a variation on Picavet called the Rendsburg requires a different pulley orientation. If you wish to use Rendsburg you have to decide at this point, not later. See The Aerial Eye Vol. 1, No. 4)
The two straight pieces are bent to form a frame around the camera. Notice that the placement of the washer in the lower element depends will vary depending upon the center of gravity of the camera. The camera's CG must be in the middle of the "U".
Lastly some scrap metal pieces are bent and attached to the lower "U" to provide protection for the camera (shown in green) and a bolt is attached to the top "U". All that remains is painting and inserting two small bolts to join the upper and lower "U" elements.
(Click to enlarge.)
After lengthy trial and error I was able to construct a timer circuit that would fire the camera at 30 second intervals and draw power from the camera's batteries. The timer design can be found in Forrest Mims' basic electronic books at Radio Shack (such as Timer, Op Amp & Optoelectronic Circuits, RS# 62-5032) or in The Aerial Eye (Vol. 5, No. 1, "Camera Conversion" by Scott McCann). Everyone has the same basic 555 timer design, but some use two 555's to give greater control over the timing. With a single 555 it took me quite a while to get "5 second ON / 25 second OFF" timing.
|V+ is 3 volts (2 x AA batteries)|
K1: 5V, 250 ohm relay, RS #275-232
D1: 2mA LED, RS #276-044
D1 glows in "Ready" mode, winks off when shutter fires
I used "Project Box" RS #270-288 to hold everything.
NOTE: I use a TLC555 (CMOS) because it will operate at low voltages. With the more common 555 chip as the batteries run down the timer will quit before the camera.
All of the components are available from Radio Shack. The last step is to velcro it to the back of camera. That way it can be removed and the camera returned to normal usage when desired. Note that one useful side effect of this approach is that the camera's desire to turn itself off after a period of inactivity is defeated by the steady clicks of the shutter every 30 seconds!
The last decision is how to attach to the kite line. The Aerial Eye has a wide variety of complex gadgets for this purpose. Most of them seemed impossible to attach one-handed and heavy as well. The best option I saw came from Christian Becot. He designed a U-shaped wire thing you could wind the line into. But none of these seemed simple enough to me.
I searched hardware stores and fishing rod dealers for solutions. I was tending toward alligator clips or spring loaded clips based on fishing floats when I discovered the solution in my own kitchen. One type of potato chip bag clip had sufficient flex to grab a kite line, but a secure enough latch not to let go. It's light, can be handled with one hand, and attaches with a satisfying "click".
For the suspension itself, I ordered six "jewel-like" Pekabe pulleys and used pink "Mason's Twine" to rig it. This turned out to be a fortuitous choice since the bright pink string makes it easy to find the rig laying on the ground or in the bushes. It's much more visible than the camera rig itself, even though I painted it bright colors too.